C4d Deposits in Renal Allografts Are Associated With Inferior Graft Outcome G.A. Bo ¨ hmig, M. Exner, B. Watschinger, C. Wenter, M. Wahrmann, C. O ¨ sterreicher, M.D. Sa ¨ emann, N. Mersich, W.H. Ho ¨ rl, G.J. Zlabinger, and H. Regele T HERE IS INCREASING evidence for a pathogenetic role of humoral immunity in acute kidney allograft rejection. The complement split product C4d represents an attractive marker for antibody-mediated graft injury. Cap- illary C4d deposits in kidney allograft biopsies were found to be associated with the appearance of posttransplant anti-donor antibodies 1 and with poor graft outcome. 2 The objective of this retrospective study was to analyze the incidence and clinical relevance of C4d deposition in biop- sies not selected for a specific type of allograft dysfunction with special emphasis on correlations between C4d staining patterns and histopathologic features of acute rejection. PATIENTS AND METHODS One hundred two biopsies (1 to 532 days posttransplantation; median, 14 days; 81 biopsies performed during the first 3 months) obtained in 61 renal allograft recipients (transplantation between January 1998 and December 1998; 18 months follow-up) were analyzed. For immunohistochemistry a polyclonal anti-C4d anti- body (C4dpAb) applicable on paraffin sections was generated by immunization of a rabbit with a 15-mer peptide corresponding to aa 1242-1256 of C4. All patients had a negative pretransplant cytotoxic crossmatch. Thirteen recipients at high immunologic risk (PRA 50% or previous immunologic graft loss) received prophy- lactic therapy with antithymocyte globulin (ATG). According to a local protocol, six of these patients received prophylactic immuno- adsorption (staphylococcal protein A). Rejection treatment con- sisted of initial steroid bolus therapy. Steroid-resistant rejection was treated with antilymphocyte antibody (ATG or OKT3). RESULTS C4d Deposition and Histopathology In 42 of 102 (41.2%) renal allograft biopsies peritubular C4d deposition was detected (Table 1). In biopsies with C4d deposits in peritubular capillaries (PTC), acute rejection according to the Banff classification was significantly less common than in biopsies without such deposits (P = .0035). The majority of C4d-positive biopsies (33 of 42, 78.6%) showed no signs of rejection (Table 1). However, all three biopsies graded Banff III showed peritubular C4d deposits. C4d Deposition and Clinical Outcome For clinical evaluation two patient subgroups were defined, recipients with one or more posttransplant biopsies showing C4d deposits in PTC (C4d PTC positive, n = 31) and recipients without such deposits in any of their biopsies (C4d PTC negative, n = 30). All eight highly immunized patients (PRA levels 50%) were classified C4d PTC posi- tive. Mean serum creatinine in functioning kidney grafts was significantly higher in C4d PTC positive than in C4d PTC negative recipients (Table 2). Even after exclusion of pa- tients with morphologic evidence for rejection, differences in serum creatinine levels between the two subgroups were significant (6 months: 2.01  0.75 vs 1.41  0.27 mg/dL; 12 months: 1.95  0.60 vs 1.36  0.34 mg/dL; 18 months: 1.98  0.50 vs 1.47  0.31 mg/dL; P  .05). Evaluating patients with acute rejection, we found no significant dif- ferences (Table 2). All four recipients with antibody-resis- tant rejection (two classified grade III, one grade II, and one borderline) belonged to the C4d PTC -positive subgroup (P = .042). In one case, antibody-resistant humoral rejec- tion was successfully treated with immunoadsorption. 3 Four From the Department of Internal Medicine III, the Department of Laboratory Medicine, the Institute of Clinical Pathology, and the Institute of Immunology, University of Vienna, Vienna, Aus- tria. Address reprint requests to Dr Heinz Regele, Institute of Clinical Pathology, University of Vienna, Wa ¨ hringer Gu ¨ rtel 18-20, A-1090 Vienna, Austria. Table 1. C4d Deposition and Histopathology Histopathology All Biopsies (n = 102) C4d Deposition in Peritubular Capillaries Yes (n = 42) No (n = 60) Rejection (Banff I, II or III), (%) 39/102 (38.2%) 9/42 (21.4%)* 30/60 (50%) No Rejection, (%) 63/102 (61.8%) 33/42 (78.6%) 30/60 (50%) *P  .01, C4d positive vs C4d negative subgroup (Pearson’s  2 test). © 2001 by Elsevier Science Inc. 0041-1345/01/$–see front matter 655 Avenue of the Americas, New York, NY 10010 PII S0041-1345(00)02467-2 Transplantation Proceedings, 33, 1151–1152 (2001) 1151