We have recently shown that recognition of the mouse mammary tumor virus 9-associated superantigen (vSAG-9) by murine V beta 17+ T cells is strongly influenced by the major histocompatibility complex (MHC) class II haplotype of the presenting cells, resulting in a form of MHC-restricted recognition. This finding was unexpected, because T cell recognition of another well-characterized retroviral superantigen, minor lymphocyte-stimulating antigen 1 (Mls-1), had been shown to be independent of the MHC haplotype of the presenting cell. To determine whether recognition of vSAG-9 and Mls-1 is fundamentally different, we undertook an extensive analysis of MHC haplotype influences on vSAG-9 and Mls-1 recognition by panels of T cell hybridomas. Our results show that, although most hybridomas recognized Mls-1 regardless of the MHC haplotype of the presenting cells, as previously described by others, some hybridomas exhibited unique patterns of MHC fine specificity. Thus, T cell recognition of vSAG-9 and Mls-1 is not fundamentally different, but the apparent differences can be explained in terms of frequency. The MHC fine specificity of individual Mls-1-reactive hybridomas was influenced by both V beta and non-V beta T cell receptor (TCR) elements. First, the influence of the V beta element was apparent from the observation that V beta 8.2+ hybridomas were significantly more MHC specific in their recognition of Mls-1 than V beta 8.1 hybridomas. Second, a role for the TCR alpha chain was implicated from the distinct patterns of fine specificity of Mls-1 reactivity among a panel of transgenic hybridomas that expressed an identical beta chain (V beta 8.1D beta 2J beta 2.3C beta 2). Sequence analysis revealed that junctional residues of the TCR alpha chain and/or V alpha/J alpha combinations influenced the MHC haplotype fine specificity for Mls-1. Third, D beta J beta influences were implicated, in that the transgenic hybridomas expressed distinctive patterns of Mls-1 fine specificity not represented among V beta 8.1+ nontransgenic hybridomas. The findings that T cell recognition of endogenous superantigen is MHC specific, and that this specificity correlates with non-V beta elements of the TCR, support the hypothesis that there is a direct interaction between the TCR and either polymorphic residues of the MHC class II molecule or haplotype-specific dominant peptides presented by class II.

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