Two-color immunofluorescence and flow cytometry analysis of lymphocytes in long-term renal allotransplant recipients: identification of a major Leu-7+/Leu-3+ subpopulation.

Using two-color immunofluorescence with fluorescein isothiocyanate (FITC)- and phycoerythrin (PE)-labeled monoclonal antibodies to human lymphocyte antigens and flow cytometry, we studied lymphocyte subsets in 16 long-term renal allotransplant recipients at risk for a mean of 78 +/- 15 mo. The absolute number of Leu-1+, Leu-2a+, and Leu-3a+ lymphocytes is significantly decreased compared with a control population, whereas Leu-7+ and Leu-15+ subsets remain unchanged despite standard chronic immunosuppression (azathioprine and prednisone). Within the Leu-7+ subset, we found various phenotypes. Doubly fluorescent lymphocytes Leu-7+/Leu-1+ and Leu-7+/Leu-2a+ are not significantly different in the transplant population compared with a normal control population. The Leu-7+/Leu-3a+ subpopulation is seen to be significantly elevated, and the Leu-7+/Leu-15+ subpopulation decreases significantly. The relationship between the modification of these two phenotypes within the Leu-7 subset may be an important correlate of decreased NK cell activity in long-term renal allotransplant recipients. These Leu-7+/Leu-3a+ cells, normally less than 1% of peripheral blood lymphocytes, have no known functional activity.