Rat T Cell Responses to Superantigens . II . Ailelic Differences in V 38 . 2 and V 38 . 5 3 Chains Determine Responsiveness to Staphylococcal Enterotoxin B and Mouse Mammary Tumor Virus - encoded Products

The previous paper in this series demonstrates that rat T cells developing de novo in the presence of mouse mammary tumor virus (Mtv) antigens in rat --* severe combined immunodeficiency (SCID) mouse xenochimeras display a distinct pattern of V3-restricted deletion; this deletion pattern is remarkably similar to that occurring during thymic development of mouse T cells in Mtv + strains. In addition, T cells developing in the absence of Mtv antigens in these rat --~ mouse xenochimeras are tolerant of host antigens, but show strong primary proliferative responses in cultures stimulated with Mtv-7 § (Mls a) mouse cells; like the mouse, these rat T cell responses are dominated by V36 and V38 T cells. Here, we continue analysis of rat T cell responses to superantigens; we show that T cells from Lewis and Fischer 344 rats expressing VB8.2 display an important all-or-nothing difference in their responses to Mtv-7 superantigens. This all-ornone strain difference in the response to Mtv-7 applies also to the response by V38.2 and V38.5 T cells to the soluble superantigen staphylococcal enterotoxin B. Because these two rat strains express different alleles of these two V38 family members, this finding identifies additional, hitherto unreported residues of the T cell receptor 3 chain important in T cell responses to superantigens.