T Cell-B Cell Interaction: Autoreactive T Cells Recognize B Cells through a Terminal Mannose-Containing Superantigen-like Glycoprotein

Rat autoreactive T cells (ATs) recognize a membrane component(s) on syngeneic B cells in association with class II MHC antigens resulting in proliferation of ATs as well activation and differentiation of B cells. Results presented herein indicate that ATs recognize a stimulating antigen(s) SA, in association with class II MHC antigens, on the B cell surface. Our studies using inhibitors of carbohydrate and protein synthesis suggest that SA is a glycoprotein(s) with a high turnover rate but is not an immunoglobulin. Treatment of B cells with mannosidase abrogates their ability to stimulate AT proliferation. Furthermore, pretreatment of B cells with GNA (a lectin from Galanthus nivalis that reacts with free terminal-mannose residues on glycoconjugates) also inhibits their ability to stimulate ATs. However, these treatments do not affect the competence of B cells to stimulate an allogeneic MLR or present a conventional antigen to T cells. The frequency of CD4+ T cells proliferating in response to syngeneic B cells is very high (0.2-0.5%) and is in line with frequencies seen in "superantigen"-type responses. Moreover, T cell receptors expressed on ATs use mainly V beta 6, V beta 11, and V beta 8 regions. Based on these data, SA appears to be a fast turnover, terminal mannose-containing, superantigen-like glycoprotein on the B cell surface.