CD1d-mediated interaction between activated T cells and B cells is essential to B-cell proliferation and anti-alpha-Gal antibody production.

Antibody-mediated rejection is central to ABO-incompatible transplantation as well as to xenotransplantation. The carbohydrate structure of xenoantigen alpha-Gal is highly analogous to the human blood group antigens. Both require memory B-cell activation for antibody production. We hypothesized that B cells, reactive to the alpha-Gal xenoantigen, required the presence of fully activated T cells to survive and proliferate in vitro. This hypothesis was contrary to the traditional theory that the response of B cells to carbohydrate antigens is T cell independent (Wong and Arsequell: Immunobiology of Carbohydrates. New York: Kluwer; 2003). When we compared the capacity of B cells to proliferate, we observed that activated T cells were necessary for B-cell proliferation. However, this proliferation was independent of the presence of antigen. A relevant question was also to investigate the role of the specific class of T cells: the CD1d-restricted iNKT (iNKT) cells in the activation of alpha-Gal-reactive B cells. The iNKT cells are reactive to glycolipids and capable of producing both Th1 and Th2 cytokine responses. We therefore wanted to determine the role of the iNKT cells as mediators of a Th2-type response when B cells were exposed to a glycolipid antigen extracted from pig red blood cells, which express blockade of the alpha-Gal epitope. We observed that the interaction between B cells and iNKT cells prevents B-cell proliferation and anti-alpha-Gal antibody production.