In kidney transplantation, B cell is increasingly identified as an important determinant for graft outcome. Chronic antibody mediated rejection (cABMR) represent today the major complication in clinic. Patients with cABMR display a unique B cell phenotype characterised by a disturbance in B cell distribution. Here, the aim of our study was to research if cABMR B cells present also impaired regulatories functions.
Experiments are realised in 12 stable patients (ST) (delay from graft >12 months, no rejection, proteinuria <0.5g/24h, PRA <10%, no DSA and a one year biopsy without allograft glomerulopathy or rejection), 14 patients with cABMR (positive DSA, allograft glomerulopathy and/or C4d staining) and 17 controls (blood donors). B-cell functions were analysed using coculture with B and T cells. Proliferation and Th1 cytokine secretion of isolated CFSE labelled T cells in presence of autologous B cells was compared between the 3 groups. T cells were stimulated with anti CD3 and anti CD28, and co-cultured with CpG-activated B cells. Suppressive cytokines like TGFβ and IL-10 and the regulatory enzyme indoleamine 2,3-dioxygenase (IDO) were evaluated during the course of the culture.
First, we have demonstrated that compared with situation of stable graft function and healthy volunteers, B cells from cABMR patients display an impaired regulatory function on T cell proliferation and Th1 production. Furthermore, B cells induce more T regulatory cells (Tregs) in coculture after 4 days in HV and ST groups compared to cABMR group (p<10-3). We also evidenced that TGFβ and IDO expressed by B cells are involved in inhibition of T cell proliferation and Treg cells generation in HV and ST patients. We additionally shown that B cells from cABMR patients present a failure of TGFβ and IL-10 secretion in co-culture associated with a significantly decrease of IDO production leading to a defect in the capacity of activated-B cells to induce Treg cells and control T cell responses.
Finally, B cells from cABMR patients display functional abnormalities as evidenced by the loss of B cell suppressive activity. This work represents interesting perspectives with the discovered of new cellular targets who can be might guide therapy in transplantation in the future.