T helper cell-dependent, microbial superantigen-mediated B cell activation in vivo

We have utilized a severe combined immune-deficient (SCID) mouse adoptive transfer model to explore the in vivo immunostimulatory effects of bacterial superantigens (SAg). B cell reconstituted SCID recipients were treated with the Staphylococcus aureus-derived toxic shock syndrome toxin (TSST-1) alone or in conjunction with syngeneic L3T4(+) TSST-1-reactive T-h cells. Over several months of study, the repetitive administration of TSST-1 resulted in a prompt, transient increase in serum Ige levels, This response required both biologically active TSST-1 and T-h cells, These findings demonstrate that certain bacterial SAgs can promote T-h cell-dependent B cell activation and differentiation in vivo. These studies strengthen the analogy between SAg-mediated and allospecific T-h-B cell interactions responsible for the autoimmune sequelae of graft-versus-host disease.