Reperfusion Injury of Ischemic Skeletal Muscle Is Mediated by Natural Antibody and Complement by Martin R.Weiser,% Julian Rwilliams,*~ Francis D

Brief Definitive Report

Reperfusion Injury of Ischemic Skeletal Muscle Is Mediated by Natural Antibody and Complement By Martin R.Weiser,% Julian RWilliams,*~ Francis D. Moore, Jr.,*~ Lester Kobzik,*~ Minghe Ma,~: Herbert B. Hechtman,*~ and Michael C. Carroll*

From the *Departments of Surgery and *Pathology, Harvard Medical School and ~Brigham and Women's Hospital, Boston, Massachusetts 02115

Summary Reperfusion ofischemic tissue induces an acute inflammatory response that can result in necrosis and irreversible cell injury to both local vascular endothelium and parenchyma. To examine the pathogenesis of ischemia/reperfusion injury, we have used mice deficient in complement components C3, C4, or serum immunoglobulin in a hindlimb model of ischemia. We found that mice homozygous deficient in C3 or C4 were equally protected against reperfusion injury based on a significant reduction in leakage of radiolabeled albumin out of the vasculature. This demonstrates that classical pathway complement is an important factor in the initiation ofinflam- marion following reperfusion. Furthermore, mice deficient in serum immunoglobulin were equally protected and this protection could be reversed by reconstitution with serum from nor- real mice. Thus, this report describes a novel mechanism for reperfusion injury that involves antibody deposition and activation of complement leading to inflammation permeability.

hile the pathogenesis of reperfnsion injury is not deficient (RAG-2-/-) (8), were equally protected and W completely understood, the complement system is protection could be abrogated by reconstitution with fresh thought to be involved since there is clear evidence of dep- mouse serum. These results support the hypothesis that is- osition of complement components C5-9 after repeffusion chemia/reperfusion injury is initiated by natural antibody of hypoxic tissue (1, 2) and injury can be inhibited in part binding to hypoxic endothelium and activation of the by pretreatment with soluble complement receptor type 1 complement system. (sCR1) (3-6). Weisman et al. found that pretreatment with sCR1 substantially reduced influx of neutrophils, deposition of C5-9 and myocardial infarct size in a rat model of Materials and Methods myocardial ischemia (3). Similar studies have used sCR1 to block or reduce inflammation after reperfusion ofischemic Reconstitution of Antibody-d!ficient Mice. RAG2-/- mice were rat hindlimb or intestine and of mouse skeletal muscle (cre- reconstituted by i.v. administration of 0.5 ml of pooled serum from control mice 15 h before ischemia. Strain FVB mice were master) (4-6). Complement receptor type 1 (CR1; CD35), used as controls since the RA G2-/- allele had been backcrossed which is normally expressed by human erythrocytes, B onto that background. Circulating Ig levels were confirmed as lymphocytes, granulocytes, and macrophages, binds acti- "50% normal by ELISA. Briefly, 96-well plates were coated with vated C3 (C3b) and C4 (C4b) leading both to dissociation rabbit anti-mouse Fc (diluted in carbonate buffer, pH 9.5) and of the complement system's C3 and C5 activating enzymes following blocking with 5% milk protein, dilutions of serum from and to proteolytic degradation of C3b and C4b by serum control mice or reconstituted RAG2-/- mice were added for factor I. When administered in a soluble form, recombi- 2 h at room temperature. After wash, a detection antibody (alka- nant sCR,1 functions as a highly effective inhibitor of se- line-phosphatase conjugated goat anti-mouse IgG or IgM) was rum complement activation (7). added for 1 h followed by color substrate (Sigma 105; Sigma To clarify the role of complement and gain insight into Chem. Co., St. Louis, MO). Serum samples and detection antibodies were diluted with 5% milk protein in phosphate-buffered the pathogenesis of ischemia/reperfusion injury, we have saline, pH 7.5. Following addition of substrate, O.D. 540 was examined novel strains of mice deficient in either comple- measured in a Micro-titer plate reader. ment components C3 or C4 in a mouse model ofhindlimb Hindlimb Model of lschemia/repegCusion Injury. Mice underwent ischemia reperfusion. Both strains of mice were equally 2 h of hindlimb ischemia and 3 h of reperfusion as described (4). protected from vascular injury demonstrating that injury is Bilateral tourniquets were placed above the greater trochanter of mediated by the classical pathway. Moreover, mice totally pentobarbital anesthetized mice (20-35 g). Sham controls did not deficient in antibody, i.e., recombination-activation gene 2 undergo ischemia. 5 rain before tourniquet release animals re-

2343 J. Exp. Med. The Rockefeller University Press 0022-1007/96/05/2343/06 $2.00 Volume 183 May 1996 2343-2348 0 Wildtype C3-/- C4-/- sCR1 Sham FVB RAG2-/- RAG2-/- Sham + Serum Figure 1. Ischemia/reperfusion injury is mediated by classicalpathway of complement. Mice underwent 2 h of hindlimb ischemia and 3 h of Figure 2. Antibody is important in ischemia/reperfusion injury. Ische- repeffusion. Hindlimb PT was reduced significantly(P <0.05) in C3-/-, mia/reperfusion injury was induced in RAG2-/- or control mice as de- C4-/- and sCR.1 treated compared to complement sufficient litter- scribed in Fig. 1. RAG2-/- mice (strain FVB background) were recon- mates. The group treated with sCR1 received 20 mg/kg before tourni- stituted by i.v. administration of 0.5 ml of pooled serum from control quet release. The hindlimb permeability index (P.I.) was determined by mice (strain FVB) 15 h before ischemia. RAG2-/- mice had a signifi- the ratio (CPM/g dry muscle)/(CPM/g blood). Error bars represent the cant reduction in P.I. (P <0.05) (indicated by asterisk) which was re- standard error of the mean and significance at P <0.05 is indicated by an versed by addition of normal serum (P <0.05). asterisk.

combination in embryonic stem cells (ES) and both strains ceived 1 p~Ci 12SI-labeled albumin intravenously. The group had undetectable levels of serum C3 (10) or C4 (Fischer, treated with sCR.1 received 20 mg/kg at the same time as radio- M.B., M. Ma, S. Goerg, X. Zhou, J. Xia, O. Finco, S. labeled albumin. Tourniquets were removed and limb reperfusion was confirmed by return of pink color. Animals received 0.1 ml of Hans, G. Kelsoe, P,.G. Howard, T.L.R.othstein et al., 0.9% saline intraperitoneal during each hour or repeffusion. Fol- manuscript submitted for publication), respectively. lowing euthanasia hindlimb muscle was harvested bilaterally, its The extent of complement-mediated damage in the radioactivity measured, and dried to a constant weight at 90~ for hindlimb model of ischemia/reperfusion injury was exam- 3 d. The hindlimb permeability index (P.I.) was determined by ined by comparing the complement-deficient mice, i.e., the ratio (CPM/g dry muscle)/(CPM/g blood). C3-/- and C4-/-, with normal littermates. Hindlimbs Statistics. Groups were subjected to analysis of variance fol- of treated animals were made ischemic for 2 h followed by lowed by Student's t-test with the Bonferroni correction for mul- 3 h of repeffusion. Subsequently, both right and left hind- tiple comparisons. limbs were harvested for analysis. Injury, i.e., vascular leak- Immunohistological Analysis. Immunoperoxidase labeling of IgM, age, was evaluated by administering radiolabeled albumin IgG and C3 was performed on paraformaldehyde-fixed cryostat serial sections of hindlimb muscle using goat anti-mouse IgM immediately before repeffusion and comparing the level of (Sigma), goat anti-mouse IgG (Sigma) or goat anti-mouse C3 radioactivity in dry muscle to that of blood. (5 ~g/rnl) (Organon Teknia, Durham, NC) and a standard avi- Reperfusion of ischemic skeletal muscle resulted in en- din-biotin protocol (9). dothelial cell injury characterized by vascular leakage with permeability edema. The muscle permeability index (P.I.) of normal complement-sufficient mice (n = 19) was 2.47 + Results and Discussion 0.19 (mean + standard error) compared to sham animals, Mice deficient in either C3 (C3-/-) or C4 (C4-/-) 0.15 + 0.01. In contrast, C3-/- (n = 13) animals had a were constructed using the techmque of homologous re- significant (P <0.05) reduction in vascular leakage, i.e., P.I.

2344 Reperfusion Injury Is Mediated by Natural Antibody and Complement Figure 3. Ischemia/reperfusioninjury results in deposition of IgM (A) and C3 (B) on vascular endothetium. Immunoperoxidaselabeling of IgM and C3 was performed on paraformaldehyde-fixedcryostat serial sections of hindlimb muscle using goat anti-mouse IgM and C3 (5 jzg/ml) and a standard avidin-biotin protocol (9). No staining was seen with irrelevant goat IgG (5/~g/ml) (C) or with muscle samples from sham mice (D-F, anti-IgM, anti-C3 and irrelevant goat IgG, respectively). Results were similar in three mice analyzedper group. Original magnification, 200X.

of 1.25 + 0.11 (Fig. 1). Thus, deficiency in C3, which im- treated mice, i.e., P.I. of 1.56 + 0.21 (Fig. 1). Thus, the pairs both pathways of complement, resulted in a 50% re- extent of vascular leakage due to complement injury is me- duction in injury. To correlate this result with earlier reports diated by activation of the classical and not the alternative that used sCR1 to block C3 activation, complement-suffi- pathway. cient mice (n = 12) were treated with sCR1 immediately A principal mechanism for activation of classical pathway before reperfusion. Treatment with sCR1 reduced vascular of complement is serum antibody. To determine if the injury, i.e., 1.25 + 0.06, to a level similar to that observed complement-mediated injury observed in the hindlimb in the C3-/- mice (Fig. 1). model was initiated by antibody, mice deficient in recom- The complement system can be activated by either the bination-activation gene 2 (RAG2-/-) (8) were ana- classical or the alternative pathways (11). While the classical lyzed. The antibody-deficient mice were protected to a pathway is generally activated by antibody, the alternative similar level as the C3-/- and C4-/- mice, i.e., 1.82 + pathway can activate spontaneously and is tightly regulated 0.25 (n = 8) vs. 3.45 + 0.17 (n = 11) for RAG2-/- and by "regulators of complement activation" (12, 13). There- FVB controls, respectively (Fig. 2). fore, as a first step towards defining the mechanism of com- Since RAG2-/- mice also lack mature B and T lym- plement-mediated ischemia/reperfusion injury, it was im- phocytes, it was important to demonstrate that the reduc- portant to determine which pathway was being activated tion in vascular permeability was not a cellular effect. To by hypoxic endothelium. To test the hypothesis that classi- distinguish serum from cellular effects, RAG2-/- mice cal pathway was involved, C4-/- mice, which have an were reconstituted (intravenously) with 0.5 ml of pooled intact alternative pathway but can not form classical path- normal mouse serum and treated as described above in the way C3 convertase (C2aC4b), were compared in the hind- hindlimb model. Analysis of the mice, demonstrated that limb model. Interestingly, the C4-/- mice (n = 12) were pooled serum restored the level of injury to that of normal protected to a similar degree as the C3-/-- and sCR1- FVB controls, i.e., 3.45 -4- 0.50 (n = 5) vs. 3.45 + 0.17 (n =

2345 Weiser et al. Brief Definitive Report 11), respectively (Fig. 2). Thus, expression of normal serum natural antibodies is not clear, it is generally held that they immunoglobulin is required for ischemia/reperfusion in- represent the prod(act of germ-line genes (16) and they are jury in the hindlimb model. often implicated in autoimmune vasculitis (17). Anti-endo- To further evaluate the nature of the antibody involved thelial cell (anti-phospholipid) antibodies have been found in injury to hypoxic endothelium, sections ofreperfused or in sera of normal individuals and it has been postulated that sham control hindlimb tissues were stained with antisera alteration in the membrane of endothelial cells whether by specific for mouse IgG or IgM. As shown in Fig. 3 A, IgM exposure of existing negatively charged phospholipids or was deposited on vascular endothelium of hindlimb har- by induction of new determinants results in specific bind- vested from repeffused mice but absent in sham controls ing (17-21). Thus, in the proposed model, reperfusion of (Fig. 3 D). Although staining for IgG did not appear spe- hypoxic vessels results in binding of natural antibody and cific in the reperfused hindlimb, a role for IgG can not be activation of the classical pathway of complement. excluded (data not shown). This result demonstrates that Previous studies examining activation of complement in IgM binds to local vascular endothelium following reperfu- various models of ischemia/reperfusion have found evi- sion of ischemic hindlimb and supports the finding above dence in support of both pathways. For example, Lindsay that reconstitution of RAG2-/- mice with normal serum et al. found that classical but not alternative pathway of restores their inflammatory response. complement was consumed in their model ofhindlimb ische- Further support for a role of antibody and complement mia in the rat (4). In contrast, studies using a mouse skeletal in mediating injury, comes from the results of immuno- model (cremaster) of ischemia/reperfusion concluded that staining sections of injured hindlimb with antibody to C3. alternative pathway was responsible for injury since serum C3 deposition colocalized with IgM on the local vascular from mice treated with sCR1 retained classical but not al- endothelium of reperfused complement-su~cient mice teruative pathway activity in an in vitro hemolytic assay (6). (Fig. 3 B) but was absent in sham controls (Fig. 3 E) and Similarly, in a pig myocardial infarct model of reperfusion treated C3-/- mice as expected (data not shown). In ad- injury, activated factor B (alternative pathway) was found dition, C3 deposition was seen on the skeletal muscle of in serum of ischemic but not sham controls within 15 rain reperfused hindlimbs of control mice but it is not clear if after reperfusion (22). While it is possible that the patho- this represents C3 activated by classical or alternative path- genesis of injury varies in each model, a unifying explana- way since deposition of IgM was not observed in this re- tion is that classical pathway complement is required for gion. initial activation, i.e., by formation of C3 convertase, and The most probable explanation for the observations that the alternative pathway is subsequently activated and com- deficiency in either classical pathway complement, i.e., ponents such as factor B are consumed. Other differences C3-/- or C4-/-, or serum antibody impairs ischemia/ such as blocking of classical pathway in vivo but not in reperfusion injury by a similar level (50%), is that inflam- vitro could be explained by the sensitivity of the different mation is initiated by deposition of antibody on hypoxic assays. endothelium. While the remaining 50% of vascular perme- Activation of complement has varied effects on initiation ability is not explained by these results, it seems highly un- of local injury. Integration of the terminal components of likely that the observed complement- and antibody-medi- complement C5-C9 in the membrane of vascular endothe- ated injuries are independent of each other. Two major lium disrupts cell function and leads to injury as discussed mechanisms by which antibody initiates inflammation are above (1, 2). In addition, release of anaphylatoxins C3a and activation of classical pathway complement, i.e., binding of C5a induce vascular leakage and enhance infiltration and Clq, or binding to Fc receptors (FcR) on leukocytes. The activation of neutrophils (11). Moreover, adhesion and ex- later effector mechanism has been described for the IgG travasation of neutrophils is enhanced by covalent deposi- and IgE isotypes but not for IgM (14). Thus, binding of tion ofiC3b at the site of activation (23). A role for neutro- IgM in the absence of complement would not be expected phils in ischemia/reperfusion injury has been demonstrated to induce inflammation and vascular leakage. as depletion or blocking of neutrophil adhesion with anti- A possible explanation for the binding of IgM antibody body to B2 integrins or L-selectin reduces inflammation in reperfused vessels is that novel antigenic determinants (24-27). It is likely that neutrophil-mediated injury is in may be exposed as a result of subtle alterations in the part independent of complement activation and this would plasma membrane following ischemia. Two possible mech- explain the residual vascular leakage in the complement- anisms for hypoxia-mediated membrane disruption that are and antibody-deficient mice. not mutually exclusive are: (a) a reduction in phospholipid To our knowledge this is the first demonstration that se- biosynthesis, or (b) activation of Ca+ +-dependent phos- rum antibody is directly involved in ischemia/reperfusion pholipase and proteases. Alternatively, hypoxia induces en- injury. Thus, the novel concept that is emerging is that se- dothelial cell release of preformed products or synthesis of rum antibody recognizes neo-determinants on damaged novel membrane-associated proteins (15). These novel de- endothelium (owing to hypoxia in our model) and on terminants could serve as targets for binding of circulating binding to the cell surface initiates inflammation by activat- natural (preexisting) antibody. Although the function of ing the classical pathway of complement.

2346 Reperfusion Injury Is Mediated by Natural Antibody and Complement The authors wish to thank Drs. Fred Alt and Ben Rich for the RAG2-/- mice; Dr. Morris Kamovsky for helpful review of the manuscript; D. Smith for valuable help with the surgical preparations, A.C. Imrich for performing the immunohistochemistry, E. Kremmer (Mmfich, Germany) for the rat monoclonal antibodies and R. Ogata (La Jolla, CA) for the rabbit anti-mouse C4 antisera.

Supported in part by National Institutes of Health grants GM 52585-01, GM07560-18, GM35141-09; AI32544-03 (M.C. Carroll); HD17461 (M.C. Carroll); Arthritis Foundation Biomedical Science Grant (M.C. Carroll); The Brigham Surgical Group, Inc.; and The Trauma Research Foundation.

Address correspondence to Michael C. Carroll, Department of Pathology, Harvard Medical School, 200 Longwood Ave., Boston, MA 02115 or Herbert Hechtman, Department of Surgery, Brigham and Women's Hospital, 75 Francis St., Boston, MA 02115.

Received for publication 26January 1996 and in revised form 13 March 1996.

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2348 Reperfusion Injury Is Mediated by Natural Antibody and Complement