Toll-Like Receptors and Their Potential Roles in Kidney Disease

J Am Soc Nephrol 15: 854–867, 2004 Signaling Danger: Toll-Like Receptors and their Potential Roles in Kidney Disease

HANS-JOACHIM ANDERS,* BERNHARD BANAS,† and DETLEF SCHLO¨ NDORFF* *Nephrological Center, Medizinische Poliklinik, Klinikum der Universität München-Junenstadt, Germany; and †Klinik u. Poliklinik f. Innere Medizin II, Universität Regensburg, Germany.

Abstract. Toll-like receptors (TLR) are an emerging family of cells are among the non-immune cells that express TLR1, -2, receptors that recognize pathogen-associated molecular pat- -3, -4, and -6, suggesting that these TLR might contribute to terns and promote the activation of leukocytes and intrinsic the activation of immune responses in tubulointerstitial injury renal cells. Ligands of the TLR include exogenous microbial (e.g., bacterial pyelonephritis, sepsis, and transplant nephrop- components such as LPS (TLR4), lipoproteins and peptidogly- athy). In addition, TLR9 has been shown to be involved in cans (TLR1, -2, -6), viral RNA (TLR3), bacterial and viral antigen-induced immune complex glomerulonephritis and lu- unmethylated cytosin-guanosin dinucleotide (CpG)-DNA pus nephritis by regulating humoral and cellular immune re- (TLR9), and endogenous molecules including heat-shock pro- sponses. TLR are evolutionary conserved regulators of innnate teins and extracellular matrix molecules. Upon stimulation, and adaptive immune reponses. It is likely that TLR are in- TLR induce expression of inflammatory cytokines or costimu- volved in many if not all types of renal inflammation. Here the latory molecules via the MyD88-dependent and MyD88-inde- authors provide an overview on the biology of TLR, summa- pendent signaling pathways shared with the interleukin-1 re- rize the present data on their expression in the kidney, and ceptors. TLR are differentially expressed on leukocyte subsets provide an outlook for the potential roles of TLR in kidney and non-immune cells and appear to regulate important aspects disease. of innate and adaptive immune responses. Tubular epithelial

Infection is commonly associated with a decline of renal tial roles of TLR in infection- and injury-associated deteriora- function. Infections can trigger the onset of immune complex tion of renal function and kidney diseases in general. glomerulonephritis (GN), transplant rejection, or a worsening of underlying GN and renal vasculitis. As most of these kidney Danger Recognition by Pattern Recognition diseases lack direct pathogen invasion, it is thought that the Receptors: An Ancient Concept of Defense activation of systemic and local immune responses contributes Our general understanding of the immune system is based on to renal dysfunction, but the mechanisms of this activation are the assumption that self and foreign must be distinguished to poorly understood. preserve tolerance to self and to defend against foreign. This The recent discovery of the toll-like receptor (TLR) family model has been questioned because it fails to integrate several has focused attention on the disease processes as TLR mediate observations. Certain “foreign” tissues or organisms in the pathogen recognition and immune activation (1,2). Both im- body do not induce defense reactions as one would expect from mune and non-immune cells express inflammatory cytokines this model such as the fetus during pregnancy or most bacteria and chemokines upon stimulation of the TLR with their spe- and fungi in the intestine. For the nephrologist, it is surprising cific ligands. These ligands include LPS or other pathogen- that kidney transplants from MHC-mismatched living donors associated molecular patterns (PAMP). Although it is likely show a better outcome than kidneys from matched cadavers that TLR are involved in the pathogenesis of many diseases, a even though the degree of the “foreigness” is comparable (3). paucity of data exists on their expression in the kidney and Furthermore, systemic autoimmunity involves activation of their role in renal disease. Stimulated by these new concepts of humoral and cellular immune responses as in systemic lupus immune activation and first studies on the role of TLR in (SLE), although this is not caused by foreign antigens, an kidney disease, we have summarized an outlook on the poten- unknown process triggers a loss of self-tolerance. Triggering immune responses relies on the specific recognition of a pathogen, or foreign antigen, or as it has been proposed in a more general sense, a danger signal (4–6). In Correspondence to PD Dr. Hans-Joachim Anders, Medizinische Poliklinik der LMU, Pettenkoferstr. 8a, 80336 Munich, Germany. Phone: 49-89-5996856; any case, the trigger mechanisms for innate and adaptive Fax: 49-89-5996860; E-mail: [email protected] immune responses are different (Table 1). Innate immunity 1046-6673/1504-0854 involves binding of the pathogen by so-called pattern recogni- Journal of the American Society of Nephrology tion receptors (PRR) to enable danger signaling. Macrophages Copyright © 2004 by the American Society of Nephrology and dendritic cells use families of non-clonal PRR, including DOI: 10.1097/01.ASN.0000121781.89599.16 TLR that are genetically defined in their molecular and peptide J Am Soc Nephrol 15: 854–867, 2004 TLR and Kidney Disease 855

Table 1. Differences between activation of innate and adaptive immune responses

Innate Immunity Adaptive Immunity

Recognition receptors type of receptors Pattern recognition receptors (complement, T cell receptors, B cell receptors mannose, immunoglobulins, TLR) clonality of receptors Non-clonal Clonal genetical structure Single gene Encoded in gene segments receptor rearrangement Not required Required recognition patterns Conserved molecular patterns Details of (secondary) structure Self-foreign discrimination Selected by evolution Selected individually Time to effector activation Immediate activation Delayed activation Effector response Opsonization, activation of complement and Clonal expansion or anergy of coagulation cascades, phagocytosis, antigen-specific B and T cells proinflammatory cytokines and chemokines

structure and provide the best distinction between the self and the non-self that has been selected by evolution (Table 1 [7–9]). Within the PRR, the TLR family is specifically involved in immune cell activation because they all can activate NF␬B-dependent gene expression on the basis of the recognition of their specific ligands (2,10). Interestingly, TLR also recognize endogenous ligands (11). Endogenous danger signal can be provided by injured cells or tissue fragments representing a second level for monitoring tissue homeostasis in addition to the distinction between self and foreign based on T cells (1,12,13). In this context, apoptotic cell death is important to avoid danger signaling (e.g.,by necrotic cell debris during tissue injury) (14). Therefore, the tissues themselves appear to be critical components of tolerance since normal tissue homeostasis, including the appropri- ate apoptotic cell removal avoids danger signaling and stimulation of the innate immune system (1,12). In contrast, tissue injury provides endogenous and exogenous ligands that activate TLR on immune and non-immune cells (1,15). For example, cadaver kidneys may experience ischemic or septic injury Figure 1. Structural homology of human TLR1 to TLR10 to Toll and which might provide danger signals to the host‘s innate im- IL-1R1. mune system and result in an exaggerated immune response (16). In contrast, the lack of significant ischemia or other injury in living unrelated renal transplants could translate into less (18). MyD88 seem to be the only adaptor molecule for TLR9, danger signaling and avoid this additional immune activation but TLR1, -2, -4, and -6 can use Mal or MyD88, and TLR3 and via TLR, a hypothesis that remains to be proven. TLR4 activation can involve MyD88 or TICAM-1 (23,25,26).

The TLR Family Ligand Interactions of TLR To date, 10 human and 9 murine proteins related to the TLR2, TLR1, and TLR6 Drosophila Toll gene have been characterized (Figure 1 TLR2 is essential for the signaling of a variety of ligands [1,17]). The specificity of TLR signaling within the family of (Table 2 [27–34]). For example, TLR2 responds to peptidogly- TLR depends on heterodimerization of certain TLR and on a can, a main wall component of Gram-positive bacteria (27), group of cytoplasmatic adaptor molecules (17,18). The first lipopeptides, and lipoproteins. TLR2 cooperates with other recognized adaptor molecule was myeloid differentiation fac- TLR family members, in particular, TLR1 and TLR6, which tor MyD88 (19–22). Studies with MyD88-deficient mice re- contributes to the discrimination among different microbial vealed other MyD88-independent signaling pathways involv- components. TLR1 interacts with TLR2, and coexpression of ing MyD88-adapter-like (Mal) protein (23,24) or the TIR TLR1 and TLR2 enhance NF␬B activation in response to domain-containing adaptor molecules TRIF (24) and TRAM triacetylated lipopeptides (35,36) on human monocytes (33). 856 Journal of the American Society of Nephrology J Am Soc Nephrol 15: 854–867, 2004

Table 2. Toll-like receptors, their expression on human leukocytes, and their exogenous ligandsa

TLR TLRϩ Immune Cells Ligand Source of the Ligand Reference

TLR1 M, DC, B, MC, NK Soluble factors Neisseria meningitides (33) Triacetylated lipoproteins Mycobacteria (151) TLR2 M, B, NK, DC Lipoproteins, peptidoglycan, Gram-positive bacteria (152, 153) Modulin Staphylococcus (28) Glycolipids, lipoproteins Spirochetes (154, 155) LPS Spirochetes, H. pylori (34, 155) Lipoara binomannan Mycobacteria (156, 157) Lipoproteins/peptides Other bacteria (152) Zymosan Yeast (10, 158) GPI anchors Trypanosoma cruzi (31) Outer membrane protein A Klebsiella (32, 47) Soluble factors Neisseria meningitides (33) Mannuronic acid polymers Pseudomonas aerug. (30) TLR3 DC dsRNA, ssRNA Viruses (15, 44) TLR4 M, N LPS Gram negative bacteria (52) Lipoteichoic acids Gram positive bacteria (27) Taxol Plants (57) F protein RS Virus (58) Mannuronic acid polymers Pseudomonas aerug. (30) TLR5 M, DC Flagellin Bacteria with flagella (65, 67) TLR6 M Modulin Staphylococcus (28) Zymosan Yeast (10) Outer surface protein A Borrelia burgdorferi (154) Diacetylated lipopeptides Mycobacteria (36) TLR7 M, DC Imidazoquinolines Antiviral compounds (70, 71) Guanosin analogs TLR8 TLR8 Imidazoquinolines Antiviral compounds (70) TLR9 DC, B Unmethylated CpG DNA Bacteria, viruses (73) TLR10 B ? ? (78)

a M, monocytes; NK, NK cells; B, B cells; T, T cells; MC, mast cells; DC, dendritic cells; N, neutrophils.

TLR1 and TLR2 heterodimerization activates dendritic cells, B induction of antiviral and proinflammatory cytokines and den- cells, NK cells (37), mast cells (38), and keratinocytes (39), but dritic cell maturation. The effects of TLR3 activation are also not T cells (40). Macrophages from TLR1-deficient mice modulated by the specific RNA sequences, as polyA:polyU showed impaired proinflammatory cytokine production in re- RNA tends to induce predominately IgG2a antibody produc- sponse to a 19-kD mycobaterial lipoprotein and other synthetic tion, whereas polyI:polyC RNA induce predominately IgG1 triacylated lipopeptides. In contrast, heterodimerization of TLR2 with TLR6 seems to be required for the detection of yeast zymosan and diacylated mycoplasmal lipopeptides Table 3. Toll-like receptors and their endogenous ligands (10,41). Recently, endogenous TLR2 ligands have been identified TLR Ligand Reference (Table 3 [11]). Necrotic but not apoptotic cells activate fibro- TLR2 Oxygen radicals (126) blasts and macrophages via TLR2 (42). This could be mediated Necrotic cells (42) by uptake of intracellular proteins such as heat shock protein TLR4 HSP60 (?), HSP70; GP96 (43, 59, 60, 130) (HSP) 70 shown to induce IL-12 expression through TLR2 Fibronectin EDA domain (62) (43). Therefore the recognition of molecules that are expressed Fibrinogen (63) during cellular injury may modulate the function of non-im- Heparan sulfate (61) mune cells. Hyaluronan (64) Lung surfactant protein A (159) TLR3 ␤-defensin 2 (51) TLR3 has shown to mediate the response to single- and TLR9 CpG chromatin-IgG complexes (75) double-stranded viral RNA (44). TLR3 activation leads to an J Am Soc Nephrol 15: 854–867, 2004 TLR and Kidney Disease 857 antibodies (15). It appears that viral RNA can act as a natural commensally Escherichia coli, can activate epithelial proin- adjuvant that may promote the loss of tolerance against endog- flammatory gene expression (68). In contrast, murine renal enous or exogenous antigens and modulates the Th1/Th2 bal- tubular epithelial cells seem not to express TLR5 in culture ance of the specific immune response (15). There seem to be (49). considerable differences in TLR3 expression on leukocyte subsets between humans and rodents as TLR3 is expressed on TLR7 and TLR8 murine macrophages; whereas, in humans TLR3 is exclusively In contrast to other TLR, TLR7, -8, and -9 are thought to act expressed on myeloid dendritic cells (44–46). Recently TLR3 intracellularly in endosomes and bind to their ligands after has been shown to be expressed on mouse and human kidney phagocytosis and lysis of a surrounding envelope (50,69). tissues (47,48). One source of renal TLR3 expression could be TLR7 and TLR8 are highly homologous to TLR9, although tubular epithelial cells. These cells appear to express TLR3 their natural ligands are still unclear (17). Several guanosin constitutively at low levels and upregulate TLR3 upon chal- analogs induce proinflammatory cytokines and activate den- lenge with LPS in vitro (49). dritic cells via TLR7 (70). As TLR7-deficient mice do not respond to imidazoquinoline compounds, synthetic antiviral TLR4 compounds with nucleic acid–like structure, it has been pro- TLR4 is considered to be the critical component of the LPS posed that TLR7, similar to TLR9, participates in the discrim- receptor complex. But this receptor can also bind a variety of ination of nucleic acid-like structures (71). other ligands (50). In vivo LPS can cause endotoxic shock by inducing the release of proinflammatory cytokines and chemo- TLR9 kines from immune and non-immune cells. This may be ex- TLR9 binds unmethylated cytosin-guanosin dinucleotide clusively mediated by TLR4. ␤-defensin 2 is produced in (CpG)-DNA, a dinucleotide sequence that has been identified response to microbial infection of mucosal tissue or skin and as a stimulatory motif of bacterial and viral DNA (72). CpG activates dendritic cells via TLR4 (51). In 1998, a point mu- motifs are common in DNA of bacteria and viruses, but they tation in the TLR4 gene was found to be the molecular basis of are underrepresented in vertebrate DNA, which is usually LPS hyporesponsiveness in C3H/HeJ mice (52). The same methylated. CpG rich DNA and oligodeoxynucletides carrying phenotype is seen in C57BL/10ScCr mice, which have a chro- the CpG motif induce immunostimulatory activities on B cells mosomal defect that leads to a loss of the whole TLR4 gene and antigen-presenting cells (APC) exclusively via TLR9, as (53). These mice show a similar phenotype as mice with a TLR9-deficient mice lack these responses (73). TLR9 signal- targeted disruption of the TLR4 gene (54). In humans, TLR4 ing on B cells or dendritic cells may be enhanced by CpG- mutations are also associated with impaired responsiveness to DNA–conjugated proteins such as IgG or ovalbumin, thereby LPS (55), but lack of TLR4 in humans does not affect the enhancing an antigen-specific humoral or cellular immune outcome of bacterial sepsis (56). TLR4 recognizes not only response of the Th1 type (74,75). LPS but also PAMP distantly related to LPS (Table 2, [57,58]). It was recently suggested that endogenous ligands may act through TLR4 (Table 3 [11]). HSP60 and HSP70 have shown TLR10 to activate NF␬B mobilization and mitogen-activated protein TLR10 is expressed on human B cells after activation of the kinases (MAPK) pathways through their direct binding to B cell receptor. However, ligands for human TLR10 as well as TLR4 (43,59,60). Extracellular matrix breakdown products the effects of TLR10 activation remain to be identified (76,77). such as hyaluronan, heparan sulfate, fibrinogen, or the fi- TLR10 seems not to be expressed in the healthy kidney bronectin EDA domain can also activate TLR4 (61–64). How- (48,78). ever, whether these data relate to LPS contamination of ligand preparation remains controversial (65). Nevertheless, it is hy- Biologic Effects Induced by TLR Activation on pothesized that TLR4 recognizes endogenous molecules that Immune Cells are exposed during cellular injury and extracellular matrix Activation of APC remodeling. This suggests that TLR4 signaling may also be APC that express various TLR, including TLR1, -2, -4, and involved in signaling during tissue injury that is independent of -6, include murine dendritic cells and microglia (79–81). TLR pathogen invasion. activation may therefore play a major role during septic shock, systemic inflammatory response syndromes, and local immune TLR5 responses (8,82–90). In macrophages, the expression of CC- TLR5 has been shown to bind bacterial flagellin from both chemokines and CC-chemokine receptors by TLR9 activation Gram-positive and Gram-negative bacteria (66). To date, this is may contribute to additional leukocyte infiltration to the site of the only ligand for this receptor that has been identified. TLR5 injury as it has been observed in several disease models, induces maturation of human but not murine dendritic cells including GN (87–90). (67). In addition to immune cells, TLR5 is also expressed on TLR are also involved in dendritic cell maturation induced the basolateral but not on the apical membrane of human by exogenous pathogens. Interestingly, dendritic cell subpopu- intestinal epithelial cells. This could explain why pathogenic lations show different TLR expression profiles (91,92). Human Salmonella, that translocate flagellin across epithelia, but not plasmocytoid dendritic cells express TLR1, -6, -7, and -9, the 858 Journal of the American Society of Nephrology J Am Soc Nephrol 15: 854–867, 2004

latter being most prominent (37). In contrast, myeloid dendritic cells express TLR4, -7, and -3 but not TLR9 (46). Stimulation of TLR4 or TLR9 on dendritic cells induces IL-12 and IFN-␥ secretion as well as surface expression of costimulatory molecules, including CD40, CD80, and CD86 (64,79,81,93–95). TLR activation with their specific TLR ligands induces dendritic cell maturation, CCR7 expression (95) and cytokine secretion increase antigen-presenting capacity and migration from peripheral tissues to lymphnodes, where the dendritic cells interact with and specifically stimulate T cells (95,96). Thus, activation of TLR such as TLR4 and TLR9 induce maturation of both dendritic cells and tissue macrophages, but this process leads to different functional activation that relates to the specific function of these cells (Figure 2). Macrophage stimulation supports local cytokine and chemokine secretion that contributes to local inflammation and leukocyte accumulation. In contrast, maturation of dendritic cells leads to emi- gration from the site of injury to the regional lymphnodes to convey antigens and proinflammatory signals to T cells, which is a prerequisite for the adaptive immune response.

Activation of B Cells Human B cells express high amounts of TLR7, -9, and -10, but they lack or show variable expression of the other TLR (37,48,71). In 1995, Krieg et al. (72) described the stimulatory effects of CpG-DNA on B cells, which was later found to be exclusively mediated via TLR9 (73). TLR9 activation induces proliferation of B cells, which is associated with the inhibition Figure 3. Possible ligand interactions with TLR expressed on intrinsic of B cell receptor–induced apoptosis (97–99). Furthermore, cells and infiltrating cells in glomeruli and renal interstitium. Potential ␬ TLR9 stimulates NF B-dependent expression of IL-6, IL-10, TLR ligands may be exposed via the blood stream to the glomerulus. IL-12 and costimulatory molecules such as MHC class II, Interstitial cells may be exposed to TLR ligands by local production CD80, and CD86 (Figure 3 [72,100,101]). Crosslinking of the (ligands listed on the lower left) or via ascending infection (ligands surface B cell receptors with TLR9 by immuncomplexes that listed on the lower right). MC, mesangial cells; MØ, monocytes/ contain chromatin triggers T cell-independent proliferation of macrophages; DC, dendritic cells; TEC, tubular epithelial cells. B cells and secretion of IgG and IgM autoantibodies (75,102).

This mechanism may play an important role in systemic autoimmunity (103). B cells require two different signals to regulate the isotype of secreted IgG (104). In the presence of the Th2 cytokine, IL-4 CpG-DNA promotes IgG1 and IgE secretion, whereas in the presence of the Th1 cytokine IFN-␥ B cells secrete IgG2a (100). However, in vivo the activation of TLR9 appears to induce a Th1-like response due to the predominant secretion of IFN-␥, IL12, and other Th1 cytokines by macrophages and dendritic cells (Figure 3 [105]).

Polarization of Adaptive Immune Responses by TLR Activation TLR stimulation has been shown to induce different cytokine patterns that are associated with either predominant Th1 or Th2-like immune responses (93). This may also depend on the mouse strain studied (92). While in isolated dendritic cells from mouse spleens, TLR2 activation favors a predominat Th2-like response and TLR4 activation a Th1-like response, Figure 2. Cell-specific maturation of phagocytes and the impact on considerable overlap exists (106). For example, TLR4 appears innate and adaptive immune responses. CCR, chemokine receptors; to be required for Th2 responses, suggesting a complex inter- DC, dendritic cell. play of stimulatory signals (107). In vivo, the overall immune J Am Soc Nephrol 15: 854–867, 2004 TLR and Kidney Disease 859 response will be further modulated by a large number of phil infiltration in a model of bacterial pyelonephritis (121). molecules. To date, in vivo studies are only available for Furthermore, bacterial infections of the kidney induce the CpG-DNA-TLR9 interaction (97), which appears to be most secretion of defensins, small antimicrobial peptides, in tubular relevant for costimulatory cytotoxic T cell responses (108). epithelial cells (122–123). Interestingly, ␤-defensin 2 has been TLR9 activation is followed by a robust Th1 humoral and shown to be an endogenous ligand for TLR4 and to induce cellular immune response in vivo (105,108–112), which iden- dendritic cell activation (51). Ingested bacteria also release tified synthetic oligodeoxynucleotides containing stimulatory CpG-DNA in endosomes, which activate phagocytes via TLR9 CpG motifs as a potential tool for the development of novel in the kidney. Whether these mechanisms also play a role in the immunomodulatory treatment strategies (113,114). These in- pathogenesis of renal diseases that are associated with viral clude CpG-DNA as vaccine adjuvants (108,115,116), as im- infection such as HIV, CMV, HCV, EBV, or BK virus is mune modulators of atopy (117), as inductors of T cell re- unknown to date. However, viral surface proteins as well as sponses against malignancy (109,118), and as modulators of viral RNA and DNA bind to TLR in vitro and may therefore the immune response during infection with intracellular mi- also be involved in virus-related kidney disease. crobes (119). Acute Renal Failure Implications of TLR Activation for the Acute renal failure (ARF) is caused by ischemic (50%) or Pathogenesis of Kidney Disease nephrotoxic (35%) injury to the kidney. However, in 50% of the cases of hospital-acquired ARF, the cause is multifactorial The basic mechanims of danger recognition via TLR signal- or associated with sepsis (124). Nevertheless, irrespective of ing in response to infectious and non-infectious cellular dam- the initial triggers that lead to tubular cell injury, the activation age may also be involved in renal disease. To date, however, mechanisms that induce the inflammatory response in the only limited studies have addressed this issue. Nevertheless, kidney may share a common pathway (124,125). Necrotic initial data point toward a contribution of TLR to the patho- tubular cells release potential TLR ligands such as HSP, which genesis of a number of renal diseases (Table 4). could activate other tubular cells or resident immune cells in the kidney (Figure 3). Activation of TLR2 and TLR4 on Sepsis and Renal Infection tubular epithelial cells has been shown to specifically stimulate Mouse renal tubular cells in culture constitutively express the NF␬B pathway in response to oxidative stress TLR1, -2, -3, -4, and -6 in vitro (49). Upon stimulation with (49,126,127). Furthermore, TLR2 and TLR4 activation on LPS, they upregulate TLR2, -3, and -4 and secrete CC-chemo- tubular epithelial cells leads to secretion of CC-chemokines kines such as CCL2/MCP-1 and CCL5/RANTES (49). These (49), indicating a role for these TLR in the initiation of phago- data suggest that tubular TLR expression might be involved in cyte influx and immune activation during acute tubular necro- mediating interstitial leukocyte infiltration and tubular injury sis. Thus TLR activation may be a link between mechanical, during bacterial sepsis (Figure 3). Furthermore, TLR-depen- toxic, or ischemic tubular cell injury and the onset of an dent activation of circulating immune cells could lead to cy- inflammatory “innate” immune response in the pathogenesis of tokine production that either directly or indirectly contribute to ARF. renal injury. The latter hypothesis is supported by a study with LPS-induced acute renal failure in TLR4-deficient mice. These Interstitial Fibrosis mice were completely resistant to endotoxin-induced acute During progressive renal fibrosis, increased matrix turnover renal failure, which was associated with a lack of a systemic exposes endogenous TLR ligands such as fibrinogen, heparan TNF-␣ response (120). Cross transplantation studies showed sulfate, hyaloran, and fibronectin EDA domain to TLR4 on that TLR4-deficient recipients of wild-type kidneys developed macrophages (Figure 3 [61–64,128,129]). Other endogenous minimal LPS-induced acute renal failure, whereas wild-type ligands for TLR2 and TLR4 that may be exposed by necrotic recipients of a TLR4-deficient kidney had severe acute renal tubular cells during chronic tubulointerstitial injury include injury after exposure to endotoxin (120). These data strongly HSP and GP96 (59,60,130). Immune cells and intrinsic renal indicate a role for TLR4 activation in acute renal failure of cells that respond to TLR activation could get activated by sepsis. However, they do not support the hypothesis that renal these extracellular matrix molecules promoting the secretion of TLR4 expression (e.g., on tubular epithelial cells) plays a inflammatory cytokines and chemokines. This in turn will be major role in sepsis-induced acute renal failure. In contrast, followed by additional leukocyte recruitment to the kidney they rather implicate a systemic response to sepsis, involving supporting sustained interstitial inflammation and interstitial TLR4 and TNF␣ in the development of acute renal failure fibrosis. during sepsis. Direct activation of renal cells via TLR, however, occurs by Renal Involvement in Systemic Immune Disorders recognition of invading pathogens during renal infection (e.g., TLR-mediated immune activation may well play a role in during bacterial pyelonephritis). Tubular epithelial cells as well immune complex diseases of the kidney triggered by infections as resident interstitial macrophages or dendritic cells get acti- (Table 4). Preliminary data suggest that TLR9 activation by vated by binding bacterial wall components via TLR as studies exogenous CpG-DNA does affect the course of immune com- with TLR4-deficient mice show decreased interstitial neutro- plex disease. These observations come from recent studies 6 ora fteAeia oit fNephrology of Society American the of Journal 860

Table 4. Possible roles of TLRs in renal disease

TLR Known Ligands Renal Disease Possible Ligands Pathophysiological Consequences

TLR2 Pathogen wall components, (e.g., lipoproteins) Sepsis-induced ATN, renal infection, Lipoproteins, peptidoglycans, lipoteichoic acids, Local activation of tubular cells and APC leading to components of necrotic cells CAPD peritonitis zymosan, and other pathogen wall components chemokine expression and leukocyte infiltration Ischemia-reperfusion ATN Yet undefined necrotic cell components Local activation of tubular cells and APC leading to chemokine expression and leukocyte infiltration Toxic or immune injury Yet undefined necrotic cell components Local activation of tubular cells, and APC leading to chemokine expression and leukocyte infiltration TLR3 dsRNA, ssRNA Hepatitis-associated HCV RNA, other viral RNA Intrarenal macrophage and dendritic cell activation glomerulonephritis leading to renal cytokine and chemokine expression ssRNA HIV nephropathy HIV RNA Immune cell activation and local injury TLR2/4 Pathogen wall components (e.g., LPS), Immune complex GN or renal Infection-triggered disease flares by release of LPS or Stimulation of the underlying local immune response, lipoteichoic acids vasculitis other pathogen wall components into the local macrophage activation, cytokine and chemokine circulation expression, and leukocyte infiltration TLR4 Pathogen wall components (e.g., LPS), Sepsis-induced tubular necrosis LPS, lipoteichoic acids, and other pathogen wall Local activation of tubular cells and APC leading to lipoteichoic acids components chemokine expression and leukocyte infiltration ␤-defensin 2 Renal infection CAPD peritonitis Bacterial wall components, ␤-defensin 2 Local activation of tubular cells and APC leading to chemokine expression and leukocyte infiltration HSP, fibronectin, fibrinogen hyaloran heparan Interstitial fibrosis, ischemic, toxic, or HSP60, HSP70, GP96 breakdown products of Local activation of tubular cells and APC leading to sulfate obstruction-related tubular injury extracellular matrix molecules chemokine expression and leukocyte infiltration TLR9 Unmethylated CpG-DNA Immune complex GN or renal Pathogen-derived DNA Stimulation of specific antibodies, predominant IgG2a, vasculitis antigen-specific Th1 T cells, local APC activation, chemokine expression, and leukocyte infiltration Lupus nephritis Pathogen-derived DNA, Hypomethylated self DNA Stimulation of DNA autoantibody secretion (IgG2a (UV light-related reduction of DNA isotype, DNA-specific Th1 T cells), local APC methyltransferase enzyme activity) activation, chemokine expression, and leukocyte infiltration Drug-induced SLE Hypomethylated self DNA (drug-related reduction of Stimulation of DNA autoantibody secretion (IgG2a DNA methyltransferase enzyme activity) isotype, DNA-specific Th1 T cells), local APC activation, chemokine expression, and leukocyte infiltration HBV-associated vasculitis, GN or HBV DNA Stimulation of B cell proliferation and HBV antibody lymphoma secretion (IgG2a, isotype, EBV-specific Th1 T cells) Local APC activation and chemokine expression BK virus-induced allograft BK virus DNA Stimulation of BK antibody secretion (IgG2a isotype,

dysfunction BKV-specific Th1 T cells), local APC activation, 2004 854–867, 15: Nephrol Soc Am J chemokine expression 3 transplant rejection CMV-induced allograft dysfunction CMV DNA Stimulation of CMV antibody secretion (IgG2a isotype, CMV-specific Th1 T cells), local APC activation, chemokine expression 3 transplant rejection All TLR Multiple pathogen wall components, including Renal infection Lipoproteins, peptidoglycans, LPS, lipoteichoic acids, Stimulation of innate and adaptive immune responses LPS, pathogen-derived DNA/RNA zymosan, and other pathogen wall components, modulating the systemic immune response and and DNA/RNA binding to respective TLR aggravating local inflammation J Am Soc Nephrol 15: 854–867, 2004 TLR and Kidney Disease 861 from our laboratory. We used horse apoferritin (HAF)-induced DNA autoantibody titers, predominantely of the IgG2a type GN as a model of immune complex GN that is characterized by (139a). However, stimulation of DNA autoantibody secretion circulating HAF-specific antibodies, mesangioproliferative by exogenous DNA does not necessarily lead to aggravation of GN, glomerular macrophage accumulation, and proteinuria lupus nephritis, as E. coli DNA improved proteinuria, renal (131). At 14 d, when a marked macrophage infiltrate and damage, and survival in autoimmune NZB/NZW mice (140). proteinuria is present, the early expression of the CC-chemo- In contrast, in lupus nephritis of MRL lpr/lpr mice, injected E. kines CCL2/MCP-1 and CCL5/RANTES chemokine signal is coli DNA and synthetic CpG-DNA had different effects. In already downregulated (131). The latter was not the case when MRL lpr/lpr mice, injected DNA bound to macrophages and single doses of 40 ␮g of CpG-DNA were administered intra- CD11cϩ dendritic cells in glomeruli and tubulointerstital areas peritoneally on days 7 and 8. The sustained glomerular che- in nephritic kidneys, which markedly induced CCL2/MCP-1 mokine expression was associated with a marked increase of and CCL5/RANTES expression in those areas (unpublished the number of glomerular macrophages, the extent of glomer- observation). This was associated with an increase of macro- ular damage, and proteinuria (88). Exogenous CpG-DNA ac- phage and T cell infiltrates compared with control DNA or cumulated in glomerular macrophages in mice with GN and saline-injected mice. CpG-DNA and E. coli DNA severely TLR9 expression was exclusively found in infiltrating macro- aggravated glomerular and tubulointerstitial damage in MRL phages in nephritic but not mesangial cells or glomeruli of lpr/lpr mice, which was associated with nephrotic range pro- healthy mice. Furthermore, analysis of serum anti-HAF anti- teinuria compared with respective controls. These data dem- body isotypes, mesangial immune deposits, and splenocyte onstrate that in experimental SLE of MRL lpr/lpr mice bacte- IFN-␥ secretion indicated that CpG-DNA induced a Th1 re- rial CpG-DNA can activate the adaptive immune response sponse in mice with HAF GN. Thus bacterial DNA or anti- against self DNA. Furthermore, circulating bacterial CpG- genic wall components such as lipoteichoic acid, endotoxin, or DNA may then bind to TLR9 on macrophages and dendritic peptidoglycans may aggravate underlying local or systemic cells in the nephritic kidney, leading to aggravation of renal immune reactions. This could also involve activation of tissue inflammation, proteinuria, and tissue damage. Whether the macrophages that are present irrespective of the defense to a discrepancy of the data obtained in MRL lpr/lpr mice and specific pathogen. For example, systemic immune activation NZB/NZW mice to different pathomechanisms of the SLE in could reactivate local, intrarenal “resting” inflammatory re- different mouse models remains to be determined. However, in sponses and cause flares (e.g., in IgA nephropathy, renal vas- human SLE the release of unmethylated CpG motifs during culitis, or lupus nephritis) (132). bacterial infection may act as a costimulus for adaptive immu- In lupus nephritis, the CpG-DNA receptor TLR9 may have nity against dsDNA but may also directly activate immune an additional role. It has been suggested that in SLE TLR9 cells in the nephritic kidney and thereby aggravate renal in- activation by chromatin particles could be involved in directing flammation (93,141,142). an adaptive immune response against dsDNA (103,133,134). In the case of infection with RNA viruses (e.g., hepatitis C In SLE, both potential sources of circulating CpG-DNA may virus during cryoglobulinemic GN) activation of TLR3 by the be relevant: exogenous microbial DNA and endogenous hy- specific recognition of viral ssRNA and dsRNA might mediate pomethylated genomic DNA (72,135). SLE patients have similar mechanisms, but experimental evidence for this hy- higher serum levels of hypomethylated CpG-DNA that may pothesis is not available at present (15,44,143–145). also relate to reduced methyltransferase activity during disease flares (136,137). Interestingly, known triggers of SLE or lupus- Renal Transplant Rejection like syndromes such as procainamide, hydralazine, and ultra- Activation of innate immune responses has long been sus- violet light are potent inhibitors of DNA methyltransferase pected to be involved in renal transplant rejection (146–148). activity (138). Thus hypomethylated CpG-DNA may provide For example, ischemia-reperfusion injury is an important trig- an endogenous stimulus for activation of innate and adaptive ger of acute rejection, and mitigating free radical-mediated immune responses that bypass tolerance to self in systemic reperfusion injury reduced the incidence of rejection episodes autoimmune diseases (103). Recent data have shown that co- (149). It may turn out that endogenous TLR ligands, such as activation of TLR9 and the IgG receptors on B cells has been HSP derived from necrotic cells signal danger and act as described with immune complexes from lupus mice containing endogenous immune adjuvants and trigger acute rejection of also chromatin particles (75). Most interestingly the coactiva- the allograft. The latter hypothesis is supported by a recent tion of both receptors by the IgG-chromatin immune com- study with MyD88-deficient mice that were unable to reject plexes provides a T cell–independent signal for proliferation of minor antigen-mismatched (HY-mismatched) skin allografts autoreactive B cells and secretion of autoantibodies (75). Fur- compared with wild-type controls (150). This was associated thermore, DNA autoantibodies induced by bacterial DNA with a reduced number of mature dendritic cells in draining crossreact with methylated vertebrate DNA, and thereby ag- lymph nodes, leading to impaired generation of anti-graft re- gravate the humoral disease activity in SLE (139). A role of active T cells and impaired Th1 immunity. These data argue bacterial CpG-DNA for the pathogenesis of SLE is supported for a role of TLR activation in the transplant setting just like by in vivo studies with CpG-DNA and E. coli DNA in a murine during infections. model of lupus nephritis. In MRL lpr/lpr mice, both E. coli Similar mechanisms might be involved in rejection episodes DNA and synthetic CpG-DNA induced a marked rise of serum triggered by systemic infections or by infectious organisms that 862 Journal of the American Society of Nephrology J Am Soc Nephrol 15: 854–867, 2004 reside in the kidney, such as cytomegalovirus or polyomavirus. 7. Hoffmann JA, Kafatos FC, Janeway CA, Ezekowitz RA: Phylo- If these speculations turn out to be relevant during renal trans- genetic perspectives in innate immunity. Science 284: 1313– plant rejection, one may feel that blocking inappropriate im- 1318, 1999 mune activation with specific TLR antagonists could represent 8. Stoy N: Macrophage biology and pathobiology in the evolution a new approach for the treatment or prevention of renal allo- of immune responses: A functional analysis. Pathobiology 69: 179–211, 2001 graft rejection. 9. Underhill DM, Ozinsky A: Phagocytosis of microbes: Complex- ity in action. Annu Rev Immunol 20: 825–852, 2002 Summary 10. Ozinsky A, Underhill DM, Fontenot JD, Hajjar AM, Smith KD, Among the PPR, the TLR activate multiple effectors of Wilson CB, Schroeder L, Aderem A: The repertoire for pattern innate and adaptive immunity upon stimulation with endoge- recognition of pathogens by the innate immune system is defined nous and exogenous ligands that relate to microbial pathogens by cooperation between toll-like receptors. Proc Natl Acad Sci or cellular injury. Initial studies suggest that TLR2 and TLR4 USA 97: 13766–13771, 2000 can induce chemokine expression by tubular epithelial cells 11. Beg AA: Endogenous ligands of Toll-like receptors: Implications and that TLR9 is expressed on infiltrating APC during immune for regulating inflammatory and immune responses. Trends Im- injury. TLR-mediated immune activation may occur during munol 23: 509–513, 2002 12. Matzinger P: The danger model: A renewed sense of self. Sci- any type of renal injury by exposure to an increasing number of ence 296: 301–305, 2002 exogenous or endogenous molecules. 13. Medzhitov R, Janeway CA Jr: Decoding the patterns of self and nonself by the innate immune system. Science 296: 298–300, Note Added in Proof 2002. Recently, mRNA has been identified as an endogenous ligand 14. Stuart LM, Lucas M, Simpson C, Lamb J, Savill J, Lacy-Hulbert for TLR3 on dendritic cells (Kariko K, Ni H, Capodici J, Lam- A: Inhibitory effects of apoptotic cell ingestion upon endotoxin- phier M, Weissman D: mRNA is an endogenous ligand for driven myeloid dendritic cell maturation. J Immunol 168: 1627– toll-like receptor 3. J Biol Chem 2004; Jan 16 [Epub ahead of 1635, 2002 print]). TLR9 was shown to be localized in the endoplasmic 15. Wang L, Smith D, Bot S, Dellamary L, Bloom A, Bot A: reticulum before translocating to the lysosome, where it can bind Noncoding RNA danger motifs bridge innate and adaptive immunity and are potent adjuvants for vaccination. J Clin Invest to CpG-DNA (Latz E, Schoenemeyer A, Visintin A, Fitzgerald 110: 1175–1184, 2002 KA, Monks BG, Knetter CF, Lien E, Nilsen NJ, Espevik T, 16. Lu CY, Penfield JG, Kielar ML, Vazquez MA, Jeyarajah DR: Golenbock DT: TLR9 signals after translocating from the ER to Hypothesis: Is renal allograft rejection initiated by the response CpG DNA in the lysosome. Nat Immunol 5: 190–198, 2004). to injury sustained during the transplant process? Kidney Int 55: TLR-mediated activation of dendritic cells was shown to trigger 2157–2168, 1999 autoimmune disease in vivo (Eriksson U, Ricci R, Hunziker L, 17. Takeda K, Kaisho T, Akira S: Toll-like receptors. Annu Rev Kurrer MO, Oudit GY, Watts TH, Sonderegger I, Bachmaier K, Immunol 21: 335–376, 2003 Kopf M, Penninger JM: Dendritic cell-induced autoimmune heart 18. O’Neill LA, Fitzgerald KA, Bowie AG: The Toll-IL-1 receptor failure requires cooperation between adaptive and innate immu- adaptor family grows to five members. Trends Immunol 24: nity. Nat Med 9: 1484–1490, 2003). 286–289, 2003 19. Barton GM, Medzhitov R: Toll-like receptor signaling pathways. Science 300: 1524–1525, 2003 Acknowledgments 20. Cao Z, Xiong J, Takeuchi M, Kurama T, Goeddel DV: TRAF6 We thank Peter J. Nelson for carfully reading the manuscript. The is a signal transducer for interleukin-1. Nature 383: 443–446, work was supported by grants from the Deutsche Forschungsgemein- 1996 schaft (AN 372/4–1) to HJA and BA 2137/1–1 to BB and DS. 21. Muzio M, Ni J, Feng P, Dixit VM: IRAK (Pelle) family member IRAK-2 and MyD88 as proximal mediators of IL-1 signaling. References Science 278: 1612–1615, 1997 1. Janeway CA Jr, Medzhitov R: Innate immune recognition. Annu 22. Fitzgerald KA, Palsson-McDermott EM, Bowie AG, Jefferies Rev Immunol 20: 197–216, 2002 CA, Mansell AS, Brady G, Brint E, Dunne A, Gray P, Harte MT, 2. Akira S, Takeda K, Kaisho T: Toll-like receptors: Critical pro- McMurray D, Smith DE, Sims JE, Bird TA, O’Neill LA: Mal teins linking innate and acquired immunity. Nat Immunol 2: (MyD88-adapter-like) is required for Toll-like receptor-4 signal 675–680, 2001 transduction. Nature 413: 78–83, 2000 3. D’Alessandro AM, Pirsch JD, Knechtle SJ, Odorico JS, Van der 23. Horng T, Barton GM, Medzhitov R: TIRAP: an adapter molecule Werf WJ, Collins BH, Becker YT, Kalayoglu M, Armbrust MJ, in the Toll signaling pathway. Nat Immunol 2: 835–841, 2001 Sollinger HW: Living unrelated renal donation: the University of 24. Yamamoto M, Sato S, Mori K, Hoshino K, Takeuchi O, Takeda Wisconsin experience. Surgery 124: 604–610, 1998 K, Akira S: Cutting edge: a novel Toll/IL-1 receptor domain- 4. Gallucci S, Matzinger P: Danger signals: SOS to the immune containing adapter that preferentially activates the IFN-beta pro- system. Curr Opin Immunol 13: 114–119, 2001 moter in the Toll-like receptor signaling. J Immunol 169: 6668– 5. Guermonprez P, Valladeau J, Zitvogel L, Thery C, Amigorena S: 6672, 2002 Antigen presentation and T cell stimulation by dendritic cells. 25. Oshiumi H, Matsumoto M, Funami K, Akazawa T, Seya T: Annu Rev Immunol 20: 621–667, 2002 TICAM-1, an adaptor molecule that participates in Toll-like 6. Sprent J, Surh CD: T cell memory. Annu Rev Immunol 20: receptor 3-mediated interferon-beta induction. Nat Immunol 4: 551–579, 2002 161–167, 2003 J Am Soc Nephrol 15: 854–867, 2004 TLR and Kidney Disease 863

26. Hoebe K, Du X, Georgel P, Janssen E, Tabeta K, Kim SO, 40. Ochoa MT, Legaspi AJ, Hatziris Z, Godowski PJ, Modlin RL, Goode J, Lin P, Mann N, Mudd S, Crozat K, Sovath S, Han J, Sieling PA: Distribution of Toll-like receptor 1 and Toll-like Beutler B: Identification of Lps2 as a key transducer of MyD88- receptor 2 in human lymphoid tissue. Immunology 108: 10–15, independent TIR signalling. Nature 424: 743–748, 2003 2003 27. Takeuchi O, Kawai T, Sanjo H, Copeland NG, Gilbert DJ, 41. Takeuchi O, Kawai T, Muhlradt PF, Morr M, Radolf JD, Zych- Jenkins NA, Takeda K, Akira S: TLR6: A novel member of an linsky A, Takeda K, Akira S: Discrimination of bacterial lipopro- expanding toll-like receptor family. Gene 231: 59–65, 1999 teins by Toll-like receptor 6. Int Immunol 13: 933–940, 2001 28. Hajjar AM, O’Mahony DS, Ozinsky A, Underhill DM, Aderem 42. Li M, Carpio DF, Zheng Y, Bruzzo P, Singh V, Ouaaz F, A, Klebanoff SJ, Wilson CB: Functional interactions between Medzhitov RM, Beg AA: An essential role of the NF-kappa toll-like receptor (TLR) 2 and TLR1 or TLR6 in response to B/Toll-like receptor pathway in induction of inflammatory and phenol-soluble modulin. J Immunol 166: 15–19, 2001 tissue-repair gene expression by necrotic cells. J Immunol 166: 29. Opitz B, Schroder NW, Spreitzer I, Michelsen KS, Kirschning 7128–7135, 2001 CJ, Hallatschek W, Zahringer U, Hartung T, Gobel UB, Schu- 43. Vabulas RM, Ahmad-Nejad P, Ghose S, Kirschning CJ, Issels mann RR: Toll-like receptor-2 mediates Treponema glycolipid RD, Wagner H: HSP70 as endogenous stimulus of the Toll/ and lipoteichoic acid-induced NF-kappaB translocation. J Biol interleukin-1 receptor signal pathway. J Biol Chem 277: 15107– Chem 276: 22041–22047, 2001 15112, 2002 30. Flo TH, Halaas O, Lien E, Ryan L, Teti G, Golenbock DT, 44. Alexopoulou L, Holt AC, Medzhitov R, Flavell RA: Recognition Sundan A, Espevik T: Human toll-like receptor 2 mediates of double-stranded RNA and activation of NF-kappaB by Toll- monocyte activation by Listeria monocytogenes, but not by like receptor 3. Nature 413: 732–738, 2001 group B streptococci or ipopolysaccharide. J Immunol 164: 45. Heinz S, Haehnel V, Karaghiosoff M, Schwarzfischer L, Muller 2064–2069, 2000 M, Krause SW, Rehli M: Species-specific regulation of toll-like 31. Campos MA, Almeida IC, Takeuchi O, Akira S, Valente EP, receptor 3 genes in men and mice. J Biol Chem 278: 21502– Procopio DO, Travassos LR, Smith JA, Golenbock DT, 21509, 2003 Gazzinelli RT: Activation of Toll-like receptor-2 by glyco- 46. Muzio M, Bosisio D, Polentarutti N, D’amico G, Stoppacciaro A, sylphosphatidylinositol anchors from a protozoan parasite. J Im- Mancinelli R, van’t Veer C, Penton-Rol G, Ruco LP, Allavena P, munol 167: 416–423, 2001 Mantovani A: Differential expression and regulation of toll-like 32. Jeannin P, Renno T, Goetsch L, Miconnet I, Aubry JP, Delneste receptors (TLR) in human leukocytes: selective expression of Y, Herbault N, Baussant T, Magistrelli G, Soulas C, Romero P, TLR3 in dendritic cells. J Immunol 164: 5998–6004, 2000 Cerottini JC, Bonnefoy JY: OmpA targets dendritic cells, in- 47. Alexopoulou L, Thomas V, Schnare M, Lobet Y, Anguita J, duces their maturation and delivers antigen into the MHC class I Schoen RT, Medzhitov R, Fikrig E, Flavell RA: Hyporespon- presentation pathway. Nat Immunol 1: 502–509, 2000 siveness to vaccination with Borrelia burgdorferi OspA in hu- 33. Wyllie DH, Kiss-Toth E, Visintin A, Smith SC, Boussouf S, mans and in TLR1- and TLR2-deficient mice. Nat Med 8: 878– Segal DM, Duff GW, Dower SK: Evidence for an accessory 884, 2002 protein function for Toll-like receptor 1 in anti-bacterial re- 48. Zarember KA, Godowski PJ: Tissue expression of human Toll- sponses. J Immunol 165: 7125–7132, 2000 like receptors and differential regulation of Toll-like receptor 34. Smith MF Jr, Mitchell A, Li G, Ding S, Fitzmaurice AM, Ryan mRNAs in leukocytes in response to microbes, their products, K, Crowe SE, Goldberg JB: TLR2 and TLR5, but not TLR4, are required for helicobacter pylori-induced NF-kappa B activation and cytokines. J Immunol 168: 554–561, 2002 and chemokine expression by epithelial cells. J Biol Chem 278: 49. Tsuboi N, Yoshikai Y, Matsuo S, Kikuchi T, Iwami K, Nagai Y, 32552–32560, 2003 Takeuchi O, Akira S, Matsuguchi T: Roles of toll-like receptors 35. Krutzik SR, Ochoa MT, Sieling PA, Uematsu S, Ng YW, Le- in C-C chemokine production by renal tubular epithelial cells. gaspi A, Liu PT, Cole ST, Godowski PJ, Maeda Y, Sarno EN, J Immunol 169: 2026–2033, 2002 Norgard MV, Brennan PJ, Akira S, Rea TH, Modlin RL: Acti- 50. Ahmad-Nejad P, Hacker H, Rutz M, Bauer S, Vabulas RM, vation and regulation of Toll-like receptors 2 and 1 in human Wagner H: Bacterial CpG-DNA and lipopolysaccharides activate leprosy. Nat Med 9: 525–532, 2003 Toll-like receptors at distinct cellular compartments. Eur J Im- 36. Takeuchi O, Sato S, Horiuchi T, Hoshino K, Takeda K, Dong Z, munol 32: 1958–1968, 2002 Modlin RL, Akira S: A role of toll-like receptor 1 in mediating 51. Biragyn A, Ruffini PA, Leifer CA, Klyushnenkova E, Shakhov immune response to microbial lipoproteins. J Immunol 169: A, Chertov O, Shirakawa AK, Farber JM, Segal DM, Oppenheim 10–14, 2002 JJ, Kwak LW: Toll-like receptor 4-dependent activation of den- 37. Hornung V, Rothenfusser S, Britsch S, Krug A, Jahrsdorfer B, dritic cells by beta-defensin 2. Science 298: 1025–1029, 2002 Giese T, Endres S, Hartmann G: Quantitative expression of 52. Poltorak A, He X, Smirnova I, Liu MY, Huffel CV, Du X, toll-like receptor 1–10 mRNA in cellular subsets of human Birdwell D, Alejos E, Silva M, Galanos C, Freudenberg M, peripheral blood mononuclear cells and sensitivity to CpG oli- Ricciardi-Castagnoli P, Layton B, Beutler B: Defective LPS godeoxynucleotides. J Immunol 168: 4531–4537, 2002 signaling in C3H/HeJ and C57BL/10ScCr mice: Mutations in 38. McCurdy JD, Olynych TJ, Maher LH, Marshall JS: Cutting edge: Tlr4 gene. Science 282: 2085–2088, 1998 distinct Toll-like receptor 2 activators selectively induce differ- 53. Qureshi ST, Lariviere L, Leveque G, Clermont S, Moore KJ, ent classes of mediator production from human mast cells. J Im- Gros P, Malo D: Endotoxin-tolerant mice have mutations in munol 170: 1625–1629, 2003 Toll-like receptor 4 (Tlr4). J Exp Med 189: 615–625, 1999 39. Baker BS, Ovigne JM, Powles AV, Corcoran S, Fry L: Normal 54. Hoshino K, Takeuchi O, Kawai T, Sanjo H, Ogawa T, Takeda Y, keratinocytes express Toll-like receptors (TLRs) 1, 2 and 5: Takeda K, Akira S: Toll-like receptor 4 (TLR4)-deficient mice Modulation of TLR expression in chronic plaque psoriasis. Br J are hyporesponsive to lipopolysaccharide: evidence for TLR4 as Dermatol 148: 670–679, 2003 the Lps gene product. J Immunol 162: 3749–3752, 1999 864 Journal of the American Society of Nephrology J Am Soc Nephrol 15: 854–867, 2004

55. Arbour NC, Lorenz E, Schutte BC, Zabner J, Kline JN, Jones M, activity of guanine nucleoside analogs: Activation of Toll-like Frees K, Watt JL, Schwartz DA: TLR4 mutations are associated receptor 7. Proc Natl Acad SciUSA100: 6646–6651, 2003 with endotoxin hyporesponsiveness in humans. Nat Genet 25: 71. Hemmi H, Kaisho T, Takeuchi O, Sato S, Sanjo H, Hoshino K, 187–191, 2000 Horiuchi T, Tomizawa H, Takeda K, Akira S: Small anti-viral 56. Feterowski C, Emmanuilidis K, Miethke T, Gerauer K, Rump M, compounds activate immune cells via the TLR7 MyD88-depen- Ulm K, Holzmann B, Weighardt H: Effects of functional Toll- dent signaling pathway. Nat Immunol 3: 196–200, 2002 like receptor-4 mutations on the immune response to human and 72. Krieg AM, Yi AK, Matson S, Waldschmidt TJ, Bishop GA, experimental sepsis. Immunology 109: 426–431, 2003 Teasdale R, Koretzky GA, Klinman DM: CpG motifs in bacterial 57. Kawasaki K, Akashi S, Shimazu R, Yoshida T, Miyake K, DNA trigger direct B-cell activation. Nature 374: 546–549, 1995 Nishijima M: Mouse toll-like receptor 4. MD-2 complex medi- 73. Hemmi H, Takeuchi O, Kawai T, Kaisho T, Sato S, Sanjo H, ates lipopolysaccharide-mimetic signal transduction by Taxol. Matsumoto M, Hoshino K, Wagner H, Takeda K, Akira S: A J Biol Chem 275: 2251–2254, 2000 Toll-like receptor recognizes bacterial DNA. Nature 408: 740– 58. Kurt-Jones EA, Popova L, Kwinn L, Haynes LM, Jones LP, 745, 2000 Tripp RA, Walsh EE, Freeman MW, Golenbock DT, Anderson 74. Shirota H, Sano K, Hirasawa N, Terui T, Ohuchi K, Hattori T, LJ, Finberg RW: Pattern recognition receptors TLR4 and CD14 Shirato K, Tamura G: Novel roles of CpG oligodeoxynucleotides mediate response to respiratory syncytial virus. Nat Immunol 1: as a leader for the sampling and presentation of CpG-tagged 398–401, 2000 antigen by dendritic cells. J Immunol 167: 66–74, 2001 59. Ohashi K, Burkart V, Flohe S, Kolb H: Heat shock protein 60 is 75. Leadbetter EA, Rifkin IR, Hohlbaum AM, Beaudette BC, a putative endogenous ligand of the toll-like receptor-4 complex. Shlomchik MJ, Marshak-Rothstein A: Chromatin-IgG com- J Immunol 164: 558–561, 2000 plexes activate B cells by dual engagement of IgM and toll-like 60. Vabulas RM, Braedel S, Hilf N, Singh-Jasuja H, Herter S, receptors. Nature 416: 603–607, 2002 Ahmad-Nejad P, Kirschning CJ, Da Costa C, Rammensee HG, 76. Bernasconi NL, Onai N, Lanzavecchia A: A role for toll-like Wagner H, Schild H: The endoplasmic reticulum-resident heat receptors in acquired immunity: Up-regulation of TLR9 by BCR shock protein Gp96 activates dendritic cells via the Toll-like triggering in naive B cells and constitutive expression in memory receptor 2/4 pathway. J Biol Chem 277: 20847–20853, 2002 B cells. Blood 101: 4500–4504, 2003 61. Johnson GB, Brunn GJ, Kodaira Y, Platt JL: Receptor-mediated 77. Bourke E, Bosisio D, Golay J, Polentarutti N, Mantovani A: The monitoring of tissue well-being via detection of soluble heparan Toll-like receptor repertoire of human B lymphocytes: inducible sulfate by Toll-like receptor 4. J Immunol 168: 5233–5239, 2002 and selective expression of TLR9 and TLR10 in normal and 62. Okamura Y, Watari M, Jerud ES, Young DW, Ishizaka ST, Rose transformed cells. Blood 102: 956–963, 2003 J, Chow JC, Strauss JF 3rd: The extra domain A of fibronectin 78. Chuang T, Ulevitch RJ: Identification of hTLR10: A novel activates Toll-like receptor 4. J Biol Chem 276: 10229–10233, human Toll-like receptor preferentially expressed in immune 2001 cells. Biochim Biophys Acta 1518: 157–161, 2001 63. Smiley ST, King JA, Hancock WW: Fibrinogen stimulates mac- 79. Bauer M, Redecke V, Ellwart JW, Scherer B, Kremer JP, Wag- rophage chemokine secretion through toll-like receptor 4. J Im- ner H, Lipford GB: Bacterial CpG-DNA triggers activation and munol 167: 2887–2894, 2001 maturation of human CD11c-, CD123ϩ dendritic cells. J Immu- 64. Termeer C, Benedix F, Sleeman J, Fieber C, Voith U, Ahrens T, nol 166: 5000–5007, 2001 Miyake K, Freudenberg M, Galanos C, Simon JC: Oligosaccha- 80. Dalpke AH, Schafer MK, Frey M, Zimmermann S, Tebbe J, rides of Hyaluronan activate dendritic cells via toll-like receptor Weihe E, Heeg K: Immunostimulatory CpG-DNA activates mu- 4. J Exp Med 195: 99–111, 2002 rine microglia. J Immunol 168: 4854–4863, 2002 65. Gao B, Tsan MF: Recombinant human heat shock protein 60 81. Kaisho T, Akira S: Dendritic-cell function in Toll-like receptor- does not induce the release of tumor necrosis factor alpha from and MyD88-knockout mice. Trends Immunol 22: 78–83, 2001 murine macrophages. J Biol Chem 278: 22523–22529, 2003 82. Brightbill HD, Libraty DH, Krutzik SR, Yang RB, Belisle JT, 66. Hayashi F, Smith KD, Ozinsky A, Hawn TR, Yi EC, Goodlett Bleharski JR, Maitland M, Norgard MV, Plevy SE, Smale ST, DR, Eng JK, Akira S, Underhill DM, Aderem A: The innate Brennan PJ, Bloom BR, Godowski PJ, Modlin RL: Host defense immune response to bacterial flagellin is mediated by Toll-like mechanisms triggered by microbial lipoproteins through toll-like receptor 5. Nature 410: 1099–1103, 2001 receptors. Science 285: 732–736, 1999 67. Means TK, Hayashi F, Smith KD, Aderem A, Luster AD: The 83. Deng GM, Verdrengh M, Liu ZQ, Tarkowski A: The major role Toll-like receptor 5 stimulus bacterial flagellin induces matura- of macrophages and their product tumor necrosis factor alpha in tion and chemokine production in human dendritic cells. J Im- the induction of arthritis triggered by bacterial DNA containing munol 170: 5165–5175, 2003 CpG motifs. Arthritis Rheum 43: 2283–2289, 2000 68. Gewirtz AT, Navas TA, Lyons S, Godowski PJ, Madara JL: 84. Jones BW, Heldwein KA, Means TK, Saukkonen JJ, Fenton MJ: Cutting edge: bacterial flagellin activates basolaterally expressed Differential roles of Toll-like receptors in the elicitation of proin- TLR5 to induce epithelial proinflammatory gene expression. flammatory responses by macrophages. Ann Rheum Dis J Immunol 167: 1882–1885, 2001 60[Suppl 3]: iii6–iii12, 2001 69. Hacker H, Mischak H, Miethke T, Liptay S, Schmid R, Spar- 85. Sparwasser T, Miethke T, Lipford G, Borschert K, Hacker H, wasser T, Heeg K, Lipford GB, Wagner H: CpG-DNA-specific Heeg K, Wagner H: Bacterial DNA causes septic shock. Nature activation of antigen-presenting cells requires stress kinase ac- 386: 336–337, 1997 tivity and is preceded by non-specific endocytosis and endoso- 86. Aliprantis AO, Yang RB, Mark MR, Suggett S, Devaux B, mal maturation. EMBO J 17: 6230–6240, 1998 Radolf JD, Klimpel GR, Godowski P, Zychlinsky A: Cell acti- 70. Lee J, Chuang TH, Redecke V, She L, Pitha PM, Carson DA, vation and apoptosis by bacterial lipoproteins through toll-like Raz E, Cottam HB: Molecular basis for the immunostimulatory receptor-2. Science 285: 736–739, 1999 J Am Soc Nephrol 15: 854–867, 2004 TLR and Kidney Disease 865

87. Takeshita S, Takeshita F, Haddad DE, Ishii KJ, Klinman DM: 105. Heeg K, Zimmermann S: CpG DNA as a Th1 trigger. Int Arch CpG oligodeoxynucleotides induce murine macrophages to up- Allergy Immunol 121: 87–97, 2000 regulate chemokine mRNA expression. Cell Immunol 206: 101– 106. Re F, Strominger JL: Toll-like receptor 2 (TLR2) and TLR4 106, 2000 differentially activate human dendritic cells. J Biol Chem 276: 88. Anders HJ, Banas B, Linde Y, Weller L, Cohen CD, Martin S, 37692–37699, 2001 Vielhauer V, Schlöndorff D, Gröne HJ: CpG -DNA aggravates 107. Dabbagh K, Dahl ME, Stepick-Biek P, Lewis DB: Toll-like glomerulonephritis by TLR9-mediated expression of chemokines receptor 4 is required for optimal development of Th2 immune and chemokine Receptors. J Am Soc Nephrol 14: 317–326, 2003 responses: role of dendritic cells. J Immunol 168: 4524–4530, 89. Deng GM, Liu ZQ, Tarkowski A: Intracisternally localized bac- 2002 terial DNA containing CpG motifs induces meningitis. J Immu- 108. Schwarz K, Storni T, Manolova V, Didierlaurent A, Sirard JC, nol 167: 4616–4626, 2001 Rothlisberger P, Bachmann MF: Role of Toll-like receptors in 90. Deng GM, Nilsson IM, Verdrengh M, Collins LV, Tarkowski A: costimulating cytotoxic T cell responses. Eur J Immunol 33: Intra-articularly localized bacterial DNA containing CpG motifs 1465–1470, 2003 induces arthritis. Nat Med 5: 702–705, 1999 109. Brunner C, Seiderer J, Schlamp A, Bidlingmaier M, Eigler A, 91. Kadowaki N, Ho S, Antonenko S, Malefyt RW, Kastelein RA, Haimerl W, Lehr HA, Krieg AM, Hartmann G, Endres S: En- Bazan F, Liu YJ: Subsets of human dendritic cell precursors hanced dendritic cell maturation by TNF-alpha or cytidine-phos- express different toll-like receptors and respond to different phate-guanosine DNA drives T cell activation in vitro and ther- microbial antigens. J Exp Med 194: 863–869, 2001 apeutic anti-tumor immune responses in vivo. J Immunol 165: 92. Liu T, Matsuguchi T, Tsuboi N, Yajima T, Yoshikai Y.: Differ- 6278–6286, 2000 ences in expression of toll-like receptors and their reactivities in 110. Roman M, Martin-Orozco E, Goodman JS, Nguyen MD, Sato Y, dendritic cells in BALB/c and C57BL/6 mice. Infect Immun 70: Ronaghy A, Kornbluth RS, Richman DD, Carson DA, Raz E: 6638–6645, 2002 Immunostimulatory DNA sequences function as T helper-1-pro- 93. Kaisho T, Akira S: Toll-like receptors as adjuvant receptors. moting adjuvants. Nat Med 3: 849–854, 1997 Biochim Biophys Acta 13; 1589: 1–13, 2002 111. Lipford GB, Bauer M, Blank C, Reiter R, Wagner H, Heeg K: 94. Ito T, Amakawa R, Kaisho T, Hemmi H, Tajima K, Uehira K, CpG-containing synthetic oligonucleotides promote B and cyto- Ozaki Y, Tomizawa H, Akira S, Fukuhara S: Interferon-alpha toxic T cell responses to protein antigen: a new class of vaccine and interleukin-12 are induced differentially by Toll-like recep- adjuvants. Eur J Immunol 27: 2340–2344, 1997 tor 7 ligands in human blood dendritic cell subsets. J Exp Med 112. Warren TL, Bhatia SK, Acosta AM, Dahle CE, Ratliff TL, Krieg 195: 1507–1512, 2002 AM, Weiner GJ: APC stimulated by CpG oligodeoxynucleotide 95. Jarrossay D, Napolitani G, Colonna M, Sallusto F, Lanzavecchia enhance activation of MHC class I-restricted T cells. J Immunol A: Specialization and complementarity in microbial molecule 165: 6244–6251, 2000 recognition by human myeloid and plasmacytoid dendritic cells. 113. Hengge UR, Benninghoff B, Ruzicka T, Goos M: Topical im- Eur J Immunol 31: 3388–3393, 2001 munomodulators—Progress towards treating inflammation, in- 96. Pulendran B, Banchereau J, Maraskovsky E, Maliszewski C: fection, and cancer. Lancet Infect Dis 1: 189–198, 2001 Modulating the immune response with dendritic cells and their 114. Krieg AM: From bugs to drugs: Therapeutic immunomodulation growth factors. Trends Immunol 22: 41–47, 2001 with oligodeoxynucleotides containing CpG sequences from bac- 97. Krieg AM: CpG motifs in bacterial DNA and their immune effects. Annu Rev Immunol 20: 709–760, 2002 terial DNA. Antisense Nucleic Acid Drug Dev 11: 181–188, 2001 98. Yi AK, Chang M, Peckham DW, Krieg AM, Ashman RF: CpG 115. Dalpke A, Zimmermann S, Heeg K: CpG-oligonucleotides in oligodeoxyribonucleotides rescue mature spleen B cells from vaccination: signaling and mechanisms of action. Immunobiol- spontaneous apoptosis and promote cell cycle entry. J Immunol ogy 204: 667–676, 2001 160: 5898–5906, 1998 116. Krieg AM, Davis HL: Enhancing vaccines with immune stimu- 99. Yi AK, Krieg AM: CpG DNA rescue from anti-IgM-induced latory CpG DNA. Curr Opin Mol Ther 3: 15–24, 2001 WEHI-231 B lymphoma apoptosis via modulation of I kappa B 117. Horner AA, Van Uden JH, Zubeldia JM, Broide D, Raz E: alpha and I kappa B beta and sustained activation of nuclear DNA-based immunotherapeutics for the treatment of allergic factor-kappa B/c-Rel. J Immunol 160: 1240–1245, 1998 disease. Immunol Rev 179: 102–118, 2001 100. Davis HL, Weeratna R, Waldschmidt TJ, Tygrett L, Schorr J, 118. Dass CR: Immunostimulatory activity of cationic-lipid-nucleic- Krieg AM, Weeranta R: CpG DNA is a potent enhancer of acid complexes against cancer. J Cancer Res Clin Oncol 128: specific immunity in mice immunized with recombinant hepatitis 177–181, 2002 B surface antigen. J Immunol 160: 870–876, 1998 119. Wagner H, Hacker H, Lipford GB: Immunostimulatory DNA 101. Kobayashi H, Horner AA, Takabayashi K, Nguyen MD, Huang sequences help to eradicate intracellular pathogens. Springer E, Cinman N, Raz E: Immunostimulatory DNA pre-priming: a Semin Immunopathol 22: 147–152, 2000 novel approach for prolonged Th1-biased immunity. Cell Immu- 120. Cunningham PN, Wang Y, He G, Guo R, Quigg RJ: Role of nol 198: 69–75, 1999 toll-like receptor-4 in endotoxin-induced acute renal failure [Ab- 102. Vos Q, Lees A, Wu ZQ, Snapper CM, Mond JJ: B-cell activation stract]. J Immunol 172: 2629–2635, 2004 by T-cell-independent type 2 antigens as an integral part of the 121. Shahin RD, Engberg I, Hagberg L, Svanborg Eden C: Neutrophil humoral immune response to pathogenic microorganisms. Immu- recruitment and bacterial clearance correlated with LPS responsiveness nol Rev 176: 154–170, 2000 in local gram-negative infection. J Immunol 138: 3475–3480, 1987 103. Vinuesa CG, Goodnow CC: Immunology: DNA drives autoim- 122. Lehmann J, Retz M, Harder J, Krams M, Kellner U, Hartmann J, munity. Nature 416: 595–598, 2002 Hohgrawe K, Raffenberg U, Gerber M, Loch T, Weichert-Jacobsen 104. Stavnezer J: Antibody class switching. Adv Immunol 61: 79–146, K, Stockle M: Expression of human beta-defensins 1 and 2 in 1996 kidneys with chronic bacterial infection. BMC Infect Dis 2: 20, 2002 866 Journal of the American Society of Nephrology J Am Soc Nephrol 15: 854–867, 2004

123. Nitschke M, Wiehl S, Baer PC, Kreft B: Bactericidal activity of gression of renal disease in MRL-Fas(lpr) mice. FASEB J 2004; renal tubular cells: The putative role of human beta-defensins. Jan 20 [Epub ahead of print] Exp Nephrol 10: 332–337, 2002 140. Gilkeson GS, Ruiz P, Pippen AM, Alexander AL, Lefkowith JB, 124. Lameire N, Vanholder R: Pathophysiologic features and preven- Pisetsky DS: Modulation of renal disease in autoimmune NZB/ tion of human and experimental acute tubular necrosis. JAmSoc NZW mice by immunization with bacterial DNA. J Exp Med Nephrol 12[Suppl 17]: S20–S32, 2001 183: 1389–1397, 1996 125. Okusa MD: The inflammatory cascade in acute ischemic renal 141. Krieg AM: A role for Toll in autoimmunity. Nat Immunol 3: failure. Nephron 90: 133–138, 2002 423–424, 2003 126. Frantz S, Kelly RA, Bourcier T: Role of TLR-2 in the activation 142. McCluskie MJ, Weeratna RD, Payette PJ, Davis HL: The poten- of nuclear factor kappaB by oxidative stress in cardiac myocytes. tial of CpG oligodeoxynucleotides as mucosal adjuvants. Crit J Biol Chem 276: 5197–5203, 2001 Rev Immunol 21: 103–120, 2001 127. Wolfs TG, Buurman WA, van Schadewijk A, de Vries B, Dae- 143. Matsumoto M, Kikkawa S, Kohase M, Miyake K, Seya T: men MA, Hiemstra PS, van’t Veer C: In vivo expression of Establishment of a monoclonal antibody against human Toll-like Toll-like receptor 2 and 4 by renal epithelial cells: IFN-gamma receptor 3 that blocks double-stranded RNA-mediated signaling. and TNF-alpha mediated up-regulation during inflammation. Biochem Biophys Res Commun 293: 1364–1369, 2002 J Immunol 168: 1286–1293, 2002 144. Manzin A, Solforosi L, Candela M, Cherubini G, Piccinini G, 128. Shihab FS, Yamamoto T, Nast CC, Cohen AH, Noble NA, Gold Brugia M, Gabrielli A, Clementi M: Hepatitis C virus infection LI, Border WA: Transforming growth factor-beta and matrix and mixed cryoglobulinaemia: assessment of HCV RNA copy protein expression in acute and chronic rejection of human renal numbers in supernatant, cryoprecipitate and non-liver cells. J allografts. J Am Soc Nephrol 6: 286–294, 1995 Viral Hepat 3: 285–292, 1996 129. Viedt C, Burger A, Hansch GM: Fibronectin synthesis in tubular 145. Sabry AA, Sobh MA, Irving WL, Grabowska A, Wagner BE, epithelial cells: up-regulation of the EDA splice variant by trans- Fox S, Kudesia G, El Nahas AM: A comprehensive study of the forming growth factor beta. Kidney Int 48: 1810–1817, 1995 association between hepatitis C virus and glomerulopathy. Neph- 130. Asea A, Rehli M, Kabingu E, Boch JA, Bare O, Auron PE, rol Dial Transplant 17: 239–245, 2002 Stevenson MA, Calderwood SK: Novel signal transduction path- 146. Donnelly P, Henderson R, Fletcher K, Stratton A, Lennard T, Wilson R, Proud G, Taylor R: Specific and nonspecific immu- way utilized by extracellular HSP70: Role of toll-like receptor noregulatory factors and renal transplantation. Transplantation (TLR) 2 and TLR4. J Biol Chem 277: 15028–15034, 2002 44: 523–528, 1987 131. Anders HJ, Vielhauer V, Kretzler M, Cohen CD, Segerer S, 147. Land W: The potential impact of the reperfusion injury on acute Luckow B, Weller L, Grone HJ, Schlondorff D: Chemokine and and chronic rejection events following organ transplantation. chemokine receptor expression during initiation and resolution of Transplant Proc 26: 3169–3171, 1994 immune complex glomerulonephritis. J Am Soc Nephrol 12: 919– 148. Pratt JR, Basheer SA, Sacks SH: Local synthesis of complement 931, 2001 component C3 regulates acute renal transplant rejection. Nat Med 132. Hume DA, Underhill DM, Sweet MJ, Ozinsky AO, Liew FY, 8: 582–587, 2002 Aderem A: Macrophages exposed continuously to lipopolysaccha- 149. Land W, Schneeberger H, Schleibner S, Illner WD, Abendroth ride and other agonists that act via toll-like receptors exhibit a D, Rutili G, Arfors KE, Messmer K: The beneficial effect of sustained and additive activation state. BMC Immunol 2: 11, 2001 human recombinant superoxide dismutase on acute and chronic 133. Pisetsky DS, Wenk KS, Reich CF 3rd: The role of cpg sequences rejection events in recipients of cadaveric renal transplants. in the induction of anti-DNA antibodies. Clin Immunol 100: Transplantation 57: 211–217, 1994 157–163, 2001 150. Goldstein DR, Tesar BM, Akira S, Lakkis FG: Critical role of the 134. Krieg AM: CpG DNA: A pathogenic factor in systemic lupus Toll-like receptor signal adaptor protein MyD88 in acute allo- erythematosus? J Clin Immunol 15: 284–292, 1995 graft rejection. J Clin Invest 111: 1571–1578, 2003 135. Huck S, Deveaud E, Namane A, Zouali M: Abnormal DNA 151. Takeuchi O, Sato S, Horiuchi T, Hoshino K, Takeda K, Dong Z, methylation and deoxycytosine-deoxyguanine content in nucleo- Modlin RL, Akira S: Cutting edge: Role of Toll-like receptor 1 somes from lymphocytes undergoing apoptosis. FASEB J 13: in mediating immune response to microbial lipoproteins. J Im- 1415–1422, 1999 munol 169: 10–14, 2002 136. Richardson B, Scheinbart L, Strahler J, Gross L, Hanash S, 152. Underhill DM, Ozinsky A, Hajjar AM, Stevens A, Wilson CB, Johnson M: Evidence for impaired T cell DNA methylation in Bassetti M, Aderem A: The Toll-like receptor 2 is recruited to systemic lupus erythematosus and rheumatoid arthritis. Arthritis macrophage phagosomes and discriminates between pathogens. Rheum 33: 1665–1673, 1990 Nature 401: 811–815, 1999 137. Sano H, Morimoto C: DNA isolated from DNA/anti-DNA anti- 153. Schwandner R, Dziarski R, Wesche H, Rothe M, Kirschning CJ: body immune complexes in systemic lupus erythematosus is rich Peptidoglycan- and lipoteichoic acid-induced cell activation is me- in guanine-cytosine content. J Immunol 128: 1341–1345, 1982 diated by toll-like receptor 2. J Biol Chem 274: 17406–17409, 1999 138. Yung RL, Richardson BC: Role of T cell DNA methylation in 154. Bulut Y, Faure E, Thomas L, Equils O, Arditi M: Cooperation of lupus syndromes. Lupus 3: 487–491, 1998 Toll-like receptor 2 and 6 for cellular activation by soluble 139. Gilkeson GS, Pippen AM, Pisetsky DS: Induction of cross- tuberculosis factor and Borrelia burgdorferi outer surface protein reactive anti-dsDNA antibodies in preautoimmune NZB/NZW A lipoprotein: Role of Toll-interacting protein and IL-1 receptor mice by immunization with bacterial DNA. J Clin Invest 95: signaling molecules in Toll-like receptor 2 signaling. J Immunol 1398–1402, 1995 167: 987–994, 2001 139a.Anders HJ, Vielhauer V, Eis V, Linde Y, Kretzler M, Perez De 155. Werts C, Tapping RI, Mathison JC, Chuang TH, Kravchenko V, Lema G, Strutz F, Bauer S, Rutz M, Wagner H, Grone HJ, Saint Girons I, Haake DA, Godowski PJ, Hayashi F, Ozinsky A, Schlondorff D: Activation of toll-like receptor-9 induces pro- Underhill DM, Kirschning CJ, Wagner H, Aderem A, Tobias PS, J Am Soc Nephrol 15: 854–867, 2004 TLR and Kidney Disease 867

Ulevitch RJ: Leptospiral lipopolysaccharide activates cells through 158. Sato M, Sano H, Iwaki D, Kudo K, Konishi M, Takahashi H, a TLR2-dependent mechanism. Nat Immunol 2: 346–352, 2001 Takahashi T, Imaizumi H, Asai Y, Kuroki Y: Direct binding of 156. Means TK, Wang S, Lien E, Yoshimura A, Golenbock DT, Fenton Toll-like receptor 2 to zymosan, and zymosan-induced NF-kappaB MJ: Human toll-like receptors mediate cellular activation by My- activation and TNF-alpha secretion are down-regulated by lung cobacterium tuberculosis. J Immunol 163: 3920–3927, 1999 collectin surfactant protein A. J Immunol 171: 417–425, 2003 157. Underhill DM, Ozinsky A, Smith KD, Aderem A: Toll-like 159. Guillot L, Balloy V, McCormack FX, Golenbock DT, Chignard receptor-2 mediates mycobacteria-induced proinflammatory sig- M, Si-Tahar M: Cutting edge: the immunostimulatory activity of naling in macrophages. Proc Natl Acad SciUSA96: 14459– the lung surfactant protein-A involves Toll-like receptor 4. J Im- 14463, 1999 munol 168: 5989–5992, 2002