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Superantigen-like properties of an antibody bispecific for MHC class II molecules and the V beta domain of the T cell antigen receptor.

A working model for the action of superantigens (SAg) is that they are simple proteins having binding sites for both MHC class II molecules and the V beta domain of the TCR. Binding of a SAg to both molecules cross-links the TCR, inducing a biologic response. In this study, we have tested this working model using a SAg mimic consisting of a hybrid Ab bispecific for the murine MHC class II molecule I-E and the V beta 8 domain of the murine TCR. The bispecific Ab activates V beta 8-bearing T cells only in the presence of I-E molecules on APC when tested in vitro. The effect of the bispecific Ab in vivo revealed both clonal deletion and a reduction in the responsiveness of V beta 8-bearing T cells. Thus, the results suggest that molecules distinct from SAg that can bind to both MHC class II molecules and the V beta domain of the TCR can mimic the biologic actions of a SAg.