The non-MHC transplantation antigens: neither weak nor minor

Strain differences in the expression of the Epa-1-restricting element

Epa-1-specific cytotoxic T lymphocytes (CTL) lyse epidermal cells (EC) of different Epa-1+ H-2k strains, such a AKR, CBA, C58, and RF, at different levels. We used an H-2Kk-specific monoclonal antibody (mAb) to test the hypothesis that this phenomenon is due to differences in the H-2-restricting element. Initially, we established the specificity of this mAb for the Epa-1-restricting element by demonstrating its capacity to inhibit the lysis of CBA EC by Epa-1-specific CTL. We then used it as the probe in a cellular radioimmunoassay to quantify the expression of the restricting element by EC of different H-2k strains. We found that C58 and RF EC bound significantly less of the mAb than did CBA EC. Although AKR also bound less of the mAb than did CBA EC, the difference was not statistically significant. To examine the generality of this phenomenon, we quantified the expression of Kk antigens on spleen cells (SC) of the same four strains. We found that RF SC, but not AKR or C58 SC, bound significantly less of the Kk mAb than did CBA SC. Thus, the differential CTL lysis of Epa-1+ EC of different strains probably reflects differences in expression of the H-2-restricting element rather than of the nominal antigen.

Mouse fibroblasts that express a cloned gene for the human transferrin receptor induce a specific cytolytic T cell response

From CBA mice immunized with mouse L cells that express a cloned gene for the human transferrin receptor (hTR) we have isolated cytolytic T cells (CTL). The CTL were Lyt-2+/L3T4- and lysed L cell transfectant clones that expressed the hTR gene but not control untransfected L cells or transfectants selected for the expression of an unrelated human cell surface antigen, 4F2. Lysis of independent hTR transfectant clones correlated with the relative level of receptor expression. The availability of CTL directed against a non-major histocompatibility complex-controlled cellular protein-like hTR may provide an interesting model system for studying antigen processing and recognition.

All in the superfamily: presentation of antigen receptors in the context of the major histocompatibility complex

I propose that the antigen-induced internalization of antigen receptors of B or T lymphocytes serves to assure the interaction of those receptors, in intracellular compartments, with the major histocompatibility complex (MHC)-encoded molecules of the cells, which are themselves internalized constitutively. Antibody and T-cell receptors have conserved regions which promote the association of their unique amino acid sequences ("idiotypes") with MHC molecules as a consequence of exposure to the acidic environment of endocytic vesicles. If the antigen is internalized with the antigen receptor, it may associate with MHC molecules which it encounters after internalization if it has sequences permitting this association. Thus, these cells may express either "idiotype"-MHC or antigen-MHC complexes, or both, after the re-expression at the cell surface of the complexes which form intracellularly, permitting the recognition of these cells by T cells specific for these structures. This mechanism permits the organism to respond to antigens for which it has affinity, in a manner which does not depend on the structure of the antigen, by the use of its own receptors. These molecules co-evolve with the MHC molecules of the species in a way that preserves the possibility of their interaction.