Differential ability of isolated H-2 Kb subsets to serve as TCR ligands for allo-specific CTL clones: potential role for N-linked glycosylation.

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Abstract
It is not known whether all forms of cell surface peptide-class I complexes, when bound with relevant peptide antigen, are recognized by T cells. We demonstrate herein that two distinct subsets of the murine H-2 Kb molecule can be separately isolated from H-2b-expressing cell lines using Y3 mAb immunoaffinity chromatography. Although both isolated Kb subsets were found to be strongly reactive with Y3 mAb by ELISA, one Kb subset is S19.8 mAb reactive (Ly-m11+Kb subset) and exhibits low reactivity with the M1/42 antibody, while the other subset is negative for the Ly-m11 epitope and highly reactive with the M1/42 antibody (M1/42high Kb subset). More importantly, whereas the M1/42high Kb subset is a very effective ligand for both TCR and CD8, the Ly-m11+ Kb subset could only function as a CD8 ligand, as determined in allo-specific CD8+ CTL clone adhesion and degranulation assays. Peptides acid-eluted from both Kb subsets sensitized Kb-transfected T2 cells expressing "peptide empty" Kb for lysis to a similar extent by allo-CTL clones, indicating that relevant endogenous peptide antigens are not limiting in the Ly-m11+ Kb subset. The major distinction identified between the two Kb subsets is that they differ substantially in their degree of N-linked glycosylation, with the Ly-m11+ subset containing Kb molecules with larger and more complex carbohydrate modifications than the M1/42high subset. The differences in glycosylation may explain the functional differences observed between the two Kb subsets. It is therefore possible that some forms of glycosylation on class I molecules interfere with TCR recognition and may limit CD8+ T cell responses, perhaps under circumstances where peptide antigen is limiting.