Differing mechanisms of early and late B cell hyporesponsiveness induced by mixed chimerism

Abstract

Mixed hematopoietic chimerism induced via nonmyeloablative bone marrow transplantation (BMT) leads to unresponsiveness of anti-Galα1,3Galβ1, 4G1cNAc (Gal) natural antibody (NAb)-producing cells in α1,3- galactosyltransferase deficient (GalT-/-) mice. We analyzed the mechanisms of anti-Gal-producing B cell unresponsiveness induced by Gal +/+ BMT. C57BL/6 (B6) GalT-/- mice received 3Gy whole-body irradiation and BMT from B6-CD45 congenic mice. BMT led to marked reductions in serum anti-Gal IgM levels and in the numbers of splenic anti-Gal-producing cells by 2 weeks post-BMT. B cells with anti-Gal Ig receptors were present in the spleens of 2-week but not 12-week chimeras. In vitro studies and adoptive transfer studies using B6 GalT-/-B cell-deficient recipients showed that B cell hyporesponsiveness to Gal at 2 weeks, but not 12 weeks, depended on persistent Gal antigen. Thus, pre-existing B-1 cells are anergic when there is continuous exposure to Gal, whereas long-term unresponsiveness does not require persistent antigen, implicating clonal deletion and/or receptor editing. These results have implications for the potential use of mixed hematopioetic chimerism as an approach to performing organ transplantation in recipients with pre-existing anti-donor IgM antibodies. Copyright © Blackwell Munksgaard 2005.