Defining the role of graft-infiltrating B cells in the acute rejection of kidney allografts in mice

Abstract B-cell infiltrates has been observed in kidney biopsies undergoing clinical cellular or mixed rejection. Some studies suggest poorer graft survival is associated with the presence of B cell infiltrates in biopsies diagnosed with cellular rejection, whereas others have not. We have developed a mouse kidney transplant model to study the role of donor-specific B cells infiltrate kidney allografts undergoing acute rejection. To this end, C57BL/6 female mice were subjected to left nephrectomy and were transplanted with kidneys from BALB/c mice expressing 2W-OVA, transgene. Donor-specific B and T cells were identified with donor MHC Class I & II tetramers. All graft were rejected by D28 post-transplant and showed an average 36-fold increase in donor specific antibodies (DSA). At D14, ~5% of the donor specific B cells had a Fas+GL7+ germinal center phenotype in both SLO’s (pooled spleen and peripheral lymphnodes) and kidney allografts. In addition, about 47% of donor-specific T cells in both the SLO and allograft had a CD4+ICOS+ expression, suggesting Tfh phenotype. ~4000 and ~900 Anti Kd-IgG secreting B cells (ASC’s) were detected in both SLO’s and in kidney allografts, respectively. Our data raise the possibility that in situ donor-specific T and B cell interactions are occurring in SLOs and also in the rejecting allografts. We plan to use this transplant model to further investigate whether graft infiltrating B cells serve as antigen-presenting cells to alloreactive T cells mediating acute rejection, whether these B cells differentiate into ASC in situ, and to define the relationship between the intrarenal B cells and ASCs in the allograft and those expanded in the SLO.