Influence of FK506 on certain aspects of lymphocyte activation and lymphocyte-endothelial cell interactions in vitro

Abstract: In the present thesis, the influence of the immunosuppressive drug FK506 on mitogen-induced changes in the expression of subunits a and ß of the IL-2 receptor by isolated human peripheral blood mononuclear cells has been studied. Up-regulation and release of the a-chain were potently depressed by FK506, even in the presence of exogenous IL-2. In contrast, up-regulation of the ß-chain on these same cells was not affected by FK506. Binding studies using 125I-IL-2 demonstrated that binding and uptake were, however, reduced on these cells, indicating that FK506 decrease the sensitivity of lymphocytes to IL-2. In order to further characterize the effects of FK506 on lymphocyte metabolism, we employed a calorimetric technique to monitor lymphocyte proliferation. FK506 and cyclosporin A were found to dramatically attenuate the increase in heat output by lymphocytes associated with mitogen stimulation. Both of these drugs also decreased heat output by quiescent lymphocytes. Further metabolic studies revealed that the major effect of both compounds was on the induction of the glycolytic pathway during mitogen stimulation and the consequent production of lactate. Their effect on heat production by quiescent cells probably also reflects inhibition of glycolysis. The influence of FK506 on the endothelial response to inflammatory mediators such as IL-1ß, TNF-a and LPS was also studied. The release of IL-6 and IL-8, up-regulation of ICAM-1 and induction of ELAM-1 in response to these stimuli were found to be unaffected by FK506. Adhesion of resting or mitogen-activated lymphocytes to these cells, as determined using a functional static assay, was also insensitive to FK506. Treatment of lymphocytes with FK506 was, on the other hand, found to reduce their capacity to adhere to both resting and TNF-activated endothelial cells.