Background: In-vitro reduction of lymphocyte proliferation by human plasma has been previously reported.  Reduced activation of lymphocytes of patients on immunosuppressive drugs is well documented.
Aim: To analyse the effect of transplant recipients’ plasma and healthy controls’ plasma on lymphocyte activation according to immunosuppressive drugs.
Methods: Peripheral blood mononuclear cells (PBMC) were separated from the blood samples of healthy controls and kidney transplant patients on cyclosporine, tacrolimus and sirolimus, based regimens by density gradient centrifugation. Cells were counted and incubated overnight with and without phytohemagglutinin (PHA) ± plasma. The luciferin-luciferase enzyme reaction that induces bioluminescence and the Turner Biosystem luminometer were used to measure intracellular ATP levels in relative light units (RLU) and converted to ng/ml using an ATP standard curve. According to normality test results, parametric or non-parametric tests from Instat 3 program (GraphpadR) were performed to compare various group results.
Results: PHA stimulation of PBMC from healthy individuals produced a 47% increase ATP production. The ATP increase is reduced to 14% when normal plasma was added (p<0.05). However, when normal plasma was replaced by patient plasma, the ATP increase was reduced only to 31%. While lymphocyte from all transplants patients were supressed by control plasma, those from patients on tracrolimus were even more supressed (ATP level: 1252.30±64.07ng/ml) than those on cyclosporine or sirolimus (ATP level: 1915.29±149.94 ng/ml, and 1834.10±151.39 ng/ml respectively) (p=0.0388, ANOVA).
Conclusion: Plasma isolated from patients on immunosuppressant drugs and more so, plasma from healthy controls contain factors that suppress the response of lymphocytes to PHA stimulation. Resulting from this study, we propose that selected plasma with the greatest potency be evaluated for immunosuppression in transplantation such as part of anti-rejection treatment especially in combination with tacrolimus. Furthermore, factors responsible for the overall inhibitory role of plasma on T cells, need to be determined.