Allotype-dependent binding of HLA class I to CD8 influences natural killer cell (NK) inhibitory signaling.

Human leukocyte antigen (HLA) class I molecules are key players in immune responses mediated by T cells and natural killer (NK) cells. CD8 fine-tunes the activation and inhibition mediated by receptors of CD8⁺ T cells and NK cells, following their engagement of HLA class I molecules. Our previous study showed that empty conformers of HLA class I molecules bind CD8 with higher affinity than the peptide-loaded forms. Here we demonstrate allotype-dependent variations in the affinities of soluble CD8 for soluble HLA-B molecules, despite identical CD8 binding site residues. In addition, using a reporter assay designed to probe interactions between membrane-bound CD8 and cell surface HLA-B, we find considerable HLA-B allotype-dependent binding variations in CD8 engagement. CD8 binding of HLA-B is correlated with the tapasin dependency of cell surface expression, which reflects conformational plasticity variations of cell surface HLA-B. Moreover, the extent of cellular HLA-B/CD8 binding influences the magnitude of CD8-dependent inhibitory signals delivered to NK cells via HLA-B. Taken together, these findings suggest global cell surface conformational variations between HLA class I allotypes that drive weaker or stronger CD8 engagement, with functional consequences for immunity.