CD8(+) T-CELLS SPECIFIC TO THE EXOGENOUS ANTIGEN - MODE OF ANTIGEN RECOGNITION AND POSSIBLE IMPLICATION IN IMMUNOSUPPRESSION

This study demonstrates and characterizes CD8(+) T cells specific to the exogenous Ag, bovine alpha s1-casein. Purified CD8(+) T cells from alpha s1-casein-primed lymph node cells proliferated well in response to an asl-casein derivative, trypsin-digested alpha s1 -casein. CD8(+) T cell repertoire for the exogenous Ag was directly demonstrated in the primary culture condition. The intact asl -casein primed the responding CD8(+) T cells in vivo more efficiently than the tryptic alpha s1-casein; however, the in vitro proliferative response by the intact alpha s1-casein was weaker than that of the tryptic alpha s1-casein. CD8(+) T cells recognized the exogenous Ag in association with MHC class I molecules as revealed by an Ab-blocking study. The major immunodominant region for the CD8(+) T cells was mapped to region 136-151 of alpha s1-casein, and peptide 136-151 primed the responding CD8(+) T cells but not any CD4(+) T cells. Peptide 136-151 is the CD8(+) T cell-specific determinant. Upon antigenic stimulation, the exogenous Ag-specific CD8(+) T cells produced a significant level of IFN-gamma, which has immune suppressive activity for IgE synthesis. Our study strongly implies that CD8(+) T cells that proliferate and produce IFN-gamma in response to the exogenous Ag would play a vital role in Ag-specific immunosuppression.