Can Double-Negative B Cells and Marginal Zone B Cells Have a Potential Impact on the Outcome of Kidney Transplantation?

B lymphocytes are involved in both graft function and rejection. The role of double-negative (DN) and marginal zone B (MZB) lymphocytes in transplantation remains unclear. This study aims to investigate their role one year after transplant. The frequency and absolute numbers of DN and MZB cells were determined by flow cytometry before transplantation and at 3, 6 and 12 months after transplant. They were correlated with graft function and rejection. Both the frequency and absolute number of MZB and DN cells increased 12 months after transplantation. Variations were observed in the populations studied at different time points. The observed decrease in the frequency of MZB lymphocytes in kidney recipients with rejection at 12 months, the end of follow-up, was associated with rejection episodes. On ROC curve analysis, a cut-off value of <20.6% could be a predictor of rejection risk in the first 12 months after transplantation (sensitivity 72.7%, specificity 69.6%). No relationship was found between the frequencies and absolute numbers of cell populations and graft function at any time point. The kinetics of B cells (DN and MZB) were determined over the course of 12 months after kidney transplantation. The frequency of MZ B cells was associated with rejection episodes.