Evidence that increases in lymphocyte tyrosine phosphorylation precede cardiac allograft rejection: Effects of cyclosporine and potential use in clinical management

Tyrosine phosphorylation is an early, critical event in lymphocyte signal transduction. We measured tyrosine phosphorylation in a porcine experimental transplant model to evaluate its utility in monitoring the allograft immune response. Using flow cytometry, we demonstrate a biphasic increase in phosphoty-rosine (ptyr) levels in peripheral blood mononuclear cells (PBMC), and that increases are detectable as early as 1 day posttransplantation in untreated transplanted animals (n=4). This biphasic response is likely result from the sequestration of ptyr⁺ cells from the periphery into the graft as graft-infiltrating lymphocytic cells show increased ptyr levels. This suggests possible lymphocyte trafficking between the peripheral compartment and the allograft. A 5-day course of treatment with cyclosporine (CsA) at 20 mg/kg/day (n=4), but not at 10 mg/kg/day (n=4), prevents graft rejection in this allograft model. Strikingly, treatment with 20 mg/kg/day CsA, but not with 10 mg/kg/day, suppressed increases in ptyr levels in both PBMC and graft-infiltrating cells. Increases in ptyr levels in PBMC are detectable 2-5 days before histologic and electrocardiographic signs of graft rejection, suggesting a potential diagnostic utility for measuring tyrosine phosphorylation in monitoring and managing transplant rejection.