I–J epitopes are adaptively acquired by T cells differentiated in the chimaeric condition

Abstract

I–J has been defined as a locus mapped in the murine major histocompatibility complex (MHC) which encodes serological markers found primarily on the surface of suppressor T cells (Ts) and soluble suppressor factors (TsF)^1,2. Recent studies have, however, revealed that there is no such specialized locus within the MHC at the DNA level^3,4. As the existence of I–J determinants at the protein level on functional T cells, T-cell clones and hybridomas has been confirmed by several serological and biochemical studies^5–7, this contradiction has raised serious arguments in the immunological community concerning the nature, origin and expression of I–J determinants. We have raised a number of monoclonal antibodies against the polymorphic structure of I–J molecules, and have studied the expression of I–J epitopes on T cells derived from irradiated bone marrow chimaeras in which stem cells of different genotype differentiated into T cells under the foreign host MHC environment. The results, presented here, indicate that I–J epitopes are not primarily determined by the MHC genes of the stem cells themselves, but are adaptively acquired by T cells differentiated in the chimaeric condition according to the environmental MHC phenotype. Thus, the serologically detectable I–J epitopes are found to be associated with inducible T-cell receptors recognizing self class II MHC antigens.