Functional expression and recognition of nonclassical MHC class I T10b is not peptide-dependent

Studies of classical and nonclassical MHC class I molecules have shown that unique peptides are associated and functionally recognized by alloreactive T cells. We have recently shown that an alloreactive TCR-gamma delta cell recognizes a nonclassical MHC molecule, T10b. However, T cell recognition of this glycoprotein did not appear to require typical peptide recognition based on studies using transporter-defective mutant cell lines. In the current study, we have analyzed in detail, the role of peptide in T10b expression and recognition. The findings reveal that the recognition of the nonclassical MHC molecule by TCR-gamma delta cells is independent of species, tissue type, both the class I and class II Ag processing and presentation pathways, or the presence of peptides. In fact, biochemical analysis of the T10b chimeric molecule, T10b/Ld, transfected into CHO cells using radiolabeled [3H]leucine, HPLC, and mass spectrometry suggest that peptides are not associated with this nonclassical class I molecule. Therefore, some class I molecules, e.g., T10b, do not associate with polymorphic peptides typical of classical MHC class I molecules and can be expressed in the absence of peptides on the cell surface in a functionally active form.