Detection of humoral rejection in human cardiac allografts by assessing the capillary deposition of complement fragment C4d in endomyocardial biopsies

Background: There are no well-established diagnostic criteria to detect hum oral rejection in organ transplantation The value of commonly used markers in immunohistochemistry, such as C1q, C3c, IgG, IgM and fibrinogen, is ques tioned by some groups. Complement fragment C4d is a more stable marker of c omplement activation as it is covalently bound to graft capillaries. C4d ha s been shown to identify clinically relevant, but otherwise undetectable hu moral anti-graft reactions in human kidney transplants. Methods: Immunohistochemical techniques were used to evaluate 155 endomyoca rdial biopsies from 56 heart transplant recipients less than 3 months post transplantation for the presence of capillary C4d staining. In a subset of patients, C4d staining was compared with C1q, C3c, IgM and fibrin staining and was correlated with clinical outcome. Results: Within 3 months 9 of 56 patients died. Five of these nonsurvivors had prominent C4d staining (p < .05), whereas C1q, C3c and IgM showed no co rrelation with clinical outcome. Presence of fibrin correlated with clinica l outcome and C4d staining (p < .05). Conclusions: The capillary deposition of complement split product C4d in hu man endomyocardial biopsies was significantly associated with graft loss. D etermination of fibrin deposition may yield additional information to estab lish a diagnosis of humoral rejection. The immunohistochemical assessment o f capillary deposition of C4d and fibrin appears to be an appropriate tool for the identification of patients, who may require additional or alternati ve immunosuppressive therapy targeted against the humoral immune system.