Reduced CD40L Expression on ex vivo Activated CD4+ T-Lymphocytes from Patients with Excellent Renal Allograft Function Measured with a Rapid Whole Blood Flow Cytometry Procedure

Abstract

Background: The CD40-CD40L (CD154) costimulatory pathway plays a critical role in the pathogenesis of kidney allograft rejection. In renal transplant biopsies, CD4+CD40L+ graft-infiltrating cells were detected during chronic rejection in contrast to acute rejection episodes. Using a rapid noninvasive FACS procedure, we were able to demonstrate CD40L upregulation in peripheral blood of patients with chronic renal allograft dysfunction. Materials and Methods: Whole blood from recipients of renal allografts was stimulated with PMA and ionomycin and measured by flow cytometry. Patients were assigned to three groups based on transplant function. Group 1: 26 patients with excellent renal transplant function; group 2: 28 patients with impaired transplant function; group 3: 14 patients with chronic allograft dysfunction and group 4: 8 healthy controls. Results: The median percentage ±SEM of CD4+/CD40L+cells stimulated ex vivo at 10 ng/ml PMA was as follows: group 1: 28.3 ± 4.1%; group 2: 18.4 ± 2.4%; group 3: 50.1 ± 5.0% and group 4: 40.4 ± 3.4%. Subdivisions of groups 2 and 3 resulted in different CD40L expression patterns. Patients with increased serum creatinine since the initial phase after transplantation (groups 2a and 3a) revealed a higher percentage of CD4+CD40L+ cells than patients showing a gradual increase over time (groups 2b and 3b). Consequently, patients of group 3a exhibited a significantly reduced transplant function compared with those of group 3b. Conclusion: After PMA + ionomycin stimulation, patients with excellent kidney graft function displayed significantly reduced expression of CD40L surface molecules on CD4+ cells early after transplantation. Those with a chronic dysfunction of the renal graft showed significantly more CD4+ cells expressing CD40L compared to the other transplanted groups. These results demonstrate that the percentage of CD4+CD40L+ cells stimulated ex vivo in peripheral blood may be a valuable marker for chronic allograft nephropathy.