Efficient presentation of endogenous superantigen by H-2A(q)

Endogenous superantigens encoded by mouse mammary tumor viruses associate with MHC class II and interact with T cells bearing particular Vβ gene segments. H-2E is more efficient at presentation than H-2A, indeed A(q) has not been shown to be capable of presenting endogenous superantigens. Atypically, the superantigen vSAG-3 encoded by Mtv-3 is presented efficiently in non-obese diabetic (H-2(g7)) mice by H-2A; we have examined the independent contributions of VSAG-3 and A(g7) to this process. A(g7) was not found to have a more general ability to efficiently present endogenous superantigens other than Mtv-3. Examination of Mtv-3-mediated thymic deletion of Vβ3⁺ thymocytes in the presence of H-2(q) additionally demonstrated the efficient presentation of vSAG-3 by A(q). Interaction of vSAG-3 with A(q) and A(g7) is likely to reflect the unique sequence of Mtv-3 within the second polymorphic region previously implicated in MHC class II binding. The demonstration that mouse endogenous superantigens can be presented by a wider range of MHC haplotypes than previously thought is further evidence for their immunological impact on the mouse population.