Background: The incidence of endothelitis in cardiac transplants, and the relationship to clinical symptoms and humoral rejection, is unclear. Recently, the finding of intravascular macrophages has been found to represent antibody-mediated rejection. This study investigated the role of intravascular T lymphocytes in antibody-mediated rejection.

Methods: A total of 819 sequential biopsy specimens from 93 cardiac allograft recipients were prospectively studied. Rejection was graded according to International Society for Heart and Lung Transplantation (ISHLT) criteria and inflammatory infiltrates characterized by immunohistochemical staining for CD3, CD4, CD8, CD68, and CD20. Endothelitis was defined as lymphocyte and macrophage infiltrates within arteriolar, capillary, or venular walls, with endothelial swelling, in contrast to perivascular inflammation of cellular rejection. Complement C4d was identified in capillary walls by immunofluorescent staining and immunohistochemical staining on paraffin sections.

Results: Endothelitis was identified in 27 specimens (3%) from 14 patients (15%). ISHLT rejection grades were 0 in 6 specimens, 1R in 20 (1A in 8; 1B in 12), and 2R (3A) in 1. In all cases, there were admixtures of macrophages and T lymphocytes. Inflammation was most prominent in venules. C4d was localized in 12 of the 27 specimens (44%). C4d was localized in 31 of 796 specimens without endothelitis (p < 0.001). The endothelial infiltrates were CD3, CD4, CD8, and CD68+. Twelve of 14 patients had > 0 panel reactive antibodies (PRA), 9 were above 10%, and 8 were above 25%; 5 patients were treated for clinical antibody-mediated rejection, and 4 had possible cardiac allograft vasculopathy by ultrasound imaging (mean follow-up, 40 months).

Conclusion: Endothelitis is present in more than 10% of heart transplant recipients and is associated with complement deposition on biopsy samples. Approximately 33% of patients have clinical evidence of humoral rejection. The eventual risk for developing graft vascular disease remains undetermined.