Gasim Arthritis Research & Therapy 2014, 16:105 http://arthritis-research.com/content/16/1/105 EDITORIAL Cathelicidin antimicrobial peptide as a serologic marker and potential pathogenic factor in antineutrophil cytoplasmic antibody-associated vasculitis Adil Gasim See related research by Zhang et al., http://arthritis-research.com/content/15/5/R161 Abstract is found within the lysosomes of macrophages and the secondary granules of neutrophils, and can be produced Antineutrophil cytoplasmic antibodies are associated by epithelial cells [1,2]. Cathelicidin LL37 is an effector with pauci-immune small-vessel vasculitis and molecule of the innate immune system that is important crescentic glomerulonephritis. Cathelicidin LL37 is the in defense against microbial pathogens. Cathelicidins have human member of a family of antimicrobial peptides also been proposed to play a role in the nonspecific that are released from activated neutrophils and defense against tumors [2], angiogenesis, and wound heal- monocytes at sites of acute inflammation. Zhang and ing [3]. IFNα is a type I interferon that functions in anti- colleagues evaluated serum levels of cathelicidin LL37 viral, antiproliferative, and immunomodulatory activities. and interferon-alpha in patients with antineutrophil Antineutrophil cytoplasmic antibody-associated vascu- cytoplasmic antibody-associated vasculitis (AAV) and litis (AAV) is necrotizing vasculitis with few or no im- glomerulonephritis. Increased levels of cathelicidin mune deposits that predominantly affects small vessels LL37 and interferon-alpha were associated with AAV and is associated with antineutrophil cytoplasmic anti- patients, particularly those with glomerular crescent bodies (ANCA) specific for myeloperoxidase (MPO- formation. Cathelicidin LL37 may also be involved in ANCA) or proteinase 3 (PR3-ANCA) [4]. MPO and PR3 the pathogenesis of AAV and thus could be a target are in the lysosomes of monocytes and the primary gran- for novel therapy. Cathelicidin LL37 is a promising ules of neutrophils, and are released when neutrophils new biomarker for active AAV, including aggressive and monocytes are activated by ANCA [5,6]. crescentic glomerulonephritis, and may prove to be The role of cathelicidin LL37 in pathogenesis of differ- both a prognostic marker and a guide for treatment. ent human diseases has been investigated by several re- search groups, mostly in the field of autoimmune and autoinflammatory diseases. Cathelicidin LL37 is overex- Zhang and colleagues have reported a potential role for pressed in inflamed skin in patients with psoriasis [7]. the endogenous antimicrobial peptide cathelicidin LL37 Human cathelicidin LL37 and its fragments inhibit HIV- α and interferon-alpha (IFN ) as serum markers for sys- 1 replication and the enzymes essential to the lifecycle of temic and local inflammation in patients with antineu- HIV, including HIV reverse transcriptase, HIV protease, trophil cytoplasmic antibody-associated pauci-immune and HIV integrase [8]. Plasma concentrations of catheli- vasculitis and crescentic glomerulonephritis [1]. cidin LL37 are significantly higher in active hepatitis C Cathelicidins are one family of antimicrobial peptides, virus infection and inactive hepatitis B virus infection, with various immune functions. Cathelicidin LL37 (also implicating cathelicidin LL37 in certain forms of hepa- known as human cationic antimicrobial protein, hCAP18) titis caused by hepatitis C virus and hepatitis B virus in- fections [9]. Human cathelicidins are involved in Correspondence: [email protected] mucosal immunity of the respiratory tract, gastrointes- Department of Pathology & Laboratory Medicine, University of North tinal tract, genitourinary tract, and eye [10]. Human Carolina at Chapel Hill, Chapel Hill, NC 27599-7525, USA ©2014 BioMed Central Ltd. Gasim Arthritis Research & Therapy 2014, 16:105 Page 2 of 3 http://arthritis-research.com/content/16/1/105 cathelicidin is overexpressed in head and neck squamous development of more sophisticated assays for ANCA cell carcinoma, and is strongly correlated with radiother- epitope specificity, but this has not been definitively doc- apy effectiveness [11]. umented in a clinical setting [19]. Pathologic evaluation Zhang and colleagues are the first to report elevated of the diagnostic renal biopsy specimen provides some levels of cathelicidin LL37 in AAV, especially in patients prognostic value [20], but is most effective for demon- with crescentic glomerulonephritis [1]. In this study, strating advanced chronic disease that will not respond serum levels of cathelicidin LL37 and IFNα correlated well to therapy [21]. One or more effective clinical la- with crescent formation and also with serum creatinine. boratory tests for biomarkers that can predict outcome This observation is important because the correlation at the time of diagnosis, detect induction of remission, with cellular crescents would indicate a correlation with and identify relapses are badly needed to improve the disease activity, which could be an important prognostic management of ANCA disease. Cathelicidin LL37 and factor and may even suggest novel strategies for treat- IFNα should be investigated further to determine ment if the association results from a pathogenic role for whether they can serve this purpose. cathelicidin LL37. This hypothesis would be further sub- In summary, the report by Ying Zhang and colleagues stantiated if the correlation is with active cellular cres- supports the possibility that cathelicidin LL37 and IFNα cents accompanied by necrosis rather than with fibrotic are useful serologic markers for active AAV, including crescents accompanied by glomerular scarring. The aggressive crescentic glomerulonephritis. This study also presence of crescents, especially cellular crescents, is an raises the possibility that cathelicidin LL37 and IFNα important histological marker of active glomeruloneph- could be involved in the pathogenesis of AAV and thus ritis, which can be diagnosed only through renal biopsy, could be a target for novel therapy. an expensive, time-consuming, and invasive technique. Abbreviations Cathelicidin LL37 is a serological marker, and is non- AAV: Antineutrophil cytoplasmic antibody-associated vasculitis; invasive and cost-effective compared with renal biopsy. ANCA: Antineutrophil cytoplasmic antibodies; IFNα: Interferon-alpha; Cathelicidin LL37 is stored as an inactive pro-form in MPO: Myeloperoxidase; PR3: Proteinase 3. secondary granules of neutrophils and is activated by Competing interests PR3 (the autoantigen target of PR3-ANCA) when re- The author declares that he has no competing interests. leased at sites of inflammation [12]. Neutrophils and monocytes are activated by ANCA and release their Published: 28 Feb 2014 lysosome and granule proteins, including MPO and PR3 References [5,6]. Activated neutrophils also release cathelicidin 1. Zhang Y, Shi W, Tang S, Li J, Yin S, Gao X, Wang L, Zou L, Zhao J, Huang Y, LL37 [12,13]. Cathelicidin LL37 is found in neutrophil Shan L, Gounni AS, Wu Y, Yuan F, Zhang J: The influence of cathelicidin LL37 in human anti-neutrophils cytoplasmic antibody (ANCA)-associated extracellular traps that are released by activated neutro- vasculitis. Arthritis Res Ther 2013, 15:R161. phils [13]. These neutrophil extracellular traps have been 2. Heilborn JD, Nilsson MF, Chamorro Jimenez CI, Sandstedt B, Borregaard N, implicated in the induction of autoimmunity and the Tham E, Sørensen OE, Weber G, Ståhle M: Antimicrobial protein hCAP18/ LL-37 is highly expressed in breast cancer and is a putative growth mediation of inflammation in AAV [14]. factor for epithelial cells. Int J Cancer 2005, 114:713–719. To validate its value as a prognostic and predictive 3. Kittaka M, Shiba H, Kajiya M, Ouhara K, Takeda K, Kanbara K, Fujita T, biomarker, future studies should investigate the levels of Kawaguchi H, Komatsuzawa H, Kurihara H: Antimicrobial peptide LL37 promotes vascular endothelial growth factor-a expression in human cathelicidin LL37 in patients with different severities of periodontal ligament cells. J Periodontal Res 2013, 48:228–234. and different clinicopathologic phenotypes of AAV in 4. Jennette JC, Falk RJ, Bacon PA, Basu N, Cid MC, Ferrario F, Flores-Suarez LF, large cohorts of patients with different levels of disease Gross WL, Guillevin L, Hagen EC, Hoffman GS, Jayne DR, Kallenberg CGM, Lamprecht P, Langford CA, Luqmani RA, Mahr AD, Matteson EL, Merkel PA, activity, remission, and relapse. 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