MHC Class II Expression and Antigen Presentation Function of Mouse Developing-B Cells (36.12)

Abstract

Abstract Developing-B cells (d-BC) in bone marrow (including pro-, pre- and immature B-cells) express MHC class II (MHC-II) for reasons not yet understood. We have studied mouse d-BCs for their MHC-II expression and antigen presentation function. Similar to human d-BCs, mouse d-BCs express MHC-II in the absence of co-stimulatory molecules or CD40, and do not express H2-O. Surprisingly, however, no H2-M expression is identified using antibody specific for H2-Mb2, despite the presence of H2-M activity as indicated by lack of cell-surface CLIP that are identified on H2-M-deficient d-BCs. Real-time PCR reveals only H2-Mb1 but not Mb2 mRNA, suggesting that H2-M activity in the d-BCs is derived from H2-Mb1. In vitro, d-BCs can present both peptide and protein antigens. In mixed lymphocyte cultures, d-BCs only stimulate allogeneic CD8 but not CD4 T cells to proliferate, and the d-BC-exposed CD4 T cells loss their rigor to respond to subsequent stimulation by similar allogeneic dendritic cells. Our results indicate that mouse d-BC selectively express components of the MHC-II antigen processing pathway, can present antigens and appear to be tolerogenic to CD4 T cells.