I-J revisited: is the I-J genetic restriction in downregulation due to an endogenous superantigen analogous to mammary tumour virus (Mtv)-encoded endogenous superantigen?

This article puts forward the hypothesis that the I-J genetic restriction observed between certain downregulatory (suppressor) T cells and antigen presenting cells is due to an endogenous superantigen analogous to the mouse mammary tumour virus (Mtv) products encoded by the open reading frames in the 3' long terminal repeat (LTR) of mtv's. In its weak form this hypothesis asserts that the I-J genetic restriction is due to an endogenous superantigen ligand on antigen presenting cells, which crosslinks the V beta and/or V alpha chains of certain T cell receptors (TCR) with major histocompatibility complex (MHC) class II, and that MHC together with this superantigen ligand causes positive selection of T cells bearing the appropriate I-J+ TCR in the thymus. In the periphery these T cells recognize peptide/MHC complex in the presence of the superantigen. In its strong form the hypothesis states that this superantigen ligand for TCR and MHC is encoded by integrated virus genome, e.g. Mtv. These possibilities can now be approached experimentally and their exploration may uncover one of the ways in which T cells are assigned to different functions, including downregulation.