Increased expression of the lymphocyte early activation marker CD69 in peripheral blood correlates with histologic evidence of cardiac allograft rejection

Background The human leukocyte membrane protein CD69 is an early activation marker induced in T lymphocytes, B cells, and natural killer cells in resp onse to inflammatory stimuli. Cardiac catheterization and endomyocardial bi opsy remain the "gold standard" for diagnosis of rejection after transplant ation, and noninvasive methods of rejection surveillance have long been sou ght. We studied CD69 membrane protein expression in peripheral blood T lymp hocytes obtained from pediatric cardiac transplant recipients at the time o f biopsy and correlated the results with histologic rejection scores. Methods. Heparinized whole blood samples were obtained from pediatric cardi ac transplant recipients at the time of cardiac biopsy, as well as from con trol subjects. Lymphocytes were labeled with antibodies for CD3, CD4, CD8, and CD69 and analysis performed using flow cytometric methods. Results. Resting CD69 expression (measured as a percentage of gated events) was significantly increased in patients with concurrent histologic evidenc e of rejection (International Society for Heart and Lung Transplantation gr ade greater than or equal to 3A) when compared to those with minimal or no rejection and controls. Although statistically significant for both lymphoc yte subsets, this relationship was more pronounced for CD8+ T cells (P<0.00 1) than for CD4+ T cells (P=0.001). When data were analyzed by rejection sc ore, a percentage activation of the CD8+ subset (CD69+/CD8+ cells as a perc entage of total gated events) exceeding 15% correlated with significant rej ection. Conclusions. Measurement of the expression of the early activation marker C D69 in peripheral blood lymphocytes by flow cytometry may provide a noninva sive means of assessing immune activation and possible rejection in cardiac transplant recipients.