Decreased circulating large granular lymphocytes associated with depressed natural killer cell activity in renal transplant recipients

Renal transplant recipients (RTR) receiving prednisone and azathioprine (AZ) frequently have depressed natural killer (NK) cell activity. In humans, NK activity is mediated by the large granular lymphocyte (LGL). To determine the mechanism of depressed NK activity among RTR, we quantitated the NK activity of peripheral blood lymphocytes (PBL) and the percentage of circulating LGL in Giemsa-stained cytocentrifuge preparations of PBL from 20 RTR and 6 healthy volunteers. In addition, the PBL were incubated with 1000 U/ml IFN beta to assess augmentation of NK activity. Finally, single-cell cytotoxicity assays in agarose using highly purified LGL from our study subjects were performed to assess the ability of the LGL to bind and to kill the K562 target cells. Mean (+/- 1SD) NK activity at a 50:1 effector-to-target ratio using K562 targets was 51.2 +/- 21.8% among normals and 12.9 +/- 10.3% in RTR, and it was augmented to 60.5 +/- 13.1% and 17.5 +/- 10.3%, respectively, following interferon (IFN) exposure. Mean percentage of LGL among PBL in normals was 13.2 +/- 1.2%, and 4.0 +/- 1.7% in RTR. A significant correlation existed (R = 0.90) between NK activity and the numbers of LGL (P less than .001). In two patients, NK activity following cessation of azathioprine and prednisone increased significantly (P less than .005), and an increase of LGL from 6%-30% among PBL accompanied the increase in NK activity in one patient. Incubation with IFN boosted this patient's NK activity from 22% to 62%, suggesting the presence of circulating pre-NK cells among the LGL. There was no significant difference in the binding or killing of K562 targets by LGL in single-cell assays comparing RTR with normal controls (P greater than 0.1), indicating normal functioning LGL in our study subjects. These results indicate that decreased circulating LGL among RTR receiving AZ and prednisone is associated with depressed NK activity. The ability of IFN to augment the NK activity of RTR significantly suggests the presence of circulating pre-NK cells. Finally, the rebound of both the circulating number of LGL and the NK activity after cessation of immunosuppressive drugs suggests a direct effect of those drugs in the inhibition of NK in RTR.