MAJOR HISTOCOMPATIBILITY COMPLEX CLASS-I BINDING GLYCOPEPTIDES FOR THE ESTIMATION OF EMPTY CLASS-I MOLECULES

Different forms of major histocompatibility complex (MHC) class I heav y chains are known to be expressed on the cell surface, including mole cules which are functionally 'empty'. Direct peptide binding to cells is obvious during sensitization of target cells in vitro for cytotoxic T lymphocyte killing and 'empty' MHC-I molecules are comparatively ab undant on TAP-1/2 peptide transporter mutant cells, In the present wor k we have estimated the fraction of 'empty' MHC class I molecules usin g glycosylated peptides and cellular staining with carbohydrate specif ic monoclonal antibodies. Synthetic D-b and K-b binding peptides were coupled at different positions with different di- or trisaccharides, u sing different spacing between the carbohydrate and the peptide backbo ne. Binding of sugar specific mAbs was compared in ELISA and cellular assays. An optimal D-b binding glycopeptide was used for comparative s taining with anti-D-b and anti-carbohydrate monoclonal antibodies to e stimate fractions of 'empty' molecules on different T lymphoid cells. On activated normal T cells, a large fraction of D-b molecules were fo und to be 'empty'. The functional role of such 'empty' MHC class I mol ecules on T cells is presently unclear, However, on antigen presenting cells they might participate in the antigen presentation process.