CD16+ Cells and Costimulatory Molecules of Lymphocyte Activation Present inside Human Kidney Grafts and in Blood Circulation

Background: We studied the expression of important costimulatory molecules of lymphocyte activation and the presence of CD16+ cells on aspiration biopsies of kidney transplants, measured three soluble factors and when indicated tested their robustness in diagnosing acute rejection. Methods: Fine-needle aspiration biopsies were performed either on days seven or 14 - 30 post-transplantation among stable kidney transplants and on the day of acute rejection diagnosis, while a sample of peripheral blood was collected simultaneously. The cyto preparations were studied by the enzymatic avidin biotin complex staining. The immunocytochemistry was directed to CD16, CD28, CD152, ICOS, CD40, CD154, CD26 and CD27. We performed the analysis in the peripheral blood by ELISA for soluble(s) CD16, CD26, and CD154. Results: The group of acute rejection cases showed a significant up-regulated expression of CD16, CD26, ICOS and CD40 as compared to the group of stable cases. Both sCD16 and sCD154 were significantly higher in the blood samples of the group with acute rejection. Thymoglobulin down-regulated CD154 and sCD16. CD16, CD26 and ICOS exhibited very high sensitivity and specificity for acute rejection diagnosis. Conclusions: The presence of CD16+ cells inside the graft emerged as a distinct player in acute rejection, confirming other previous reports whereas we first document that in human kidney transplants, ICOS and CD26 are significantly up-regulated and both reached positive predictive values for acute rejection ≥ 80%. The other costimulatory molecules, with the exception of CD40, though widely known, did not show robust association with immune events.