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The mononuclear cell infiltrate in a total of 279 human renal allograft biopsies was determined by a panel of monoclonal antibodies using an indirect immunoperoxidase technique. Two hundred and seventy-two biopsies were obtained from 83 patients randomly allocated to receive short-term cyclosporine (CsA) or conventional azathioprine and low-dose prednisolone (AP). Biopsies were obtained routinely at days 0 (control biopsies), 7, 21, 90, and 365, as well as at other times when clinically indicated. A further 7 patients on AP therapy were biopsied several years after transplantation (median: 6 years 1 month). Morphometric analysis of cryostat tissue sections using a point-counting technique has shown that the infiltration in rejecting grafts is significantly greater than in grafts with stable function. However, significant infiltration also occurs within the first week after transplantation in grafts with stable function. While this infiltrate diminishes with time, it remains significant even in grafts biopsied several years after transplantation. The infiltration with CsA treatment is significantly less than with AP therapy. The magnitude of the infiltrate therefore varies with time, graft status, and immunosuppression. In contrast the phenotypic composition of the infiltrate remains relatively constant in all biopsies after transplantation with T lymphocytes (CD3+), accounting for approximately 35% of infiltrating cells and CD8+ cells more common than CD4+. Monocytes and macrophages account for most of the remainder of the infiltrate.

Platelets, expressing only class I antigens on their surface, have been shown to improve renal allograft survival in some experimental models but do not lead to humoral sensitization. In this pilot study, 24 previously untransfused patients were given 3 platelet transfusions at 2-week intervals before renal transplantation. Twelve patients (group 1) received 200 X 10(8) platelets contaminated by 15 X 10(6) leukocytes in each transfusion, and 42% developed cytotoxic antibodies; 12 further patients (group 2) received a purified preparation containing 200 X 10(8) platelets and less than 5 X 10(6) leukocytes, and no cytotoxic antibodies were detected. Using a more sensitive flow cytometry technique, 83% of group 1 but only 17% of group 2 (P less than 0.004) responded to their platelet donors. From each group 9 patients have been transplanted. Four grafts in group 1 and 6 in group 2 have failed, yielding a 1-year graft survival rate of 44%, compared with 69% in blood-transfused patients (P = 0.03). Pure platelet transfusions, using our protocol, do not appear to improve renal allograft survival, and minimal contamination by leukocytes can lead to humoral sensitization.

These results show that image analysis is an accurate alternative to point counting in the assessment of infiltration in renal allograft biopsies and can provide an efficient and rapid diagnosis of cellular rejection in the transplanted patient.