ROLE OF CONSERVED REGIONS OF CLASS-I MHC MOLECULES IN THE ACTIVATION OF CD8-LYMPHOCYTES BY PEPTIDE AND PURIFIED CELL-FREE CLASS-I MOLECULES( CYTOTOXIC T)

To analyze the molecular interactions involved in CD8+ cytotoxic T lym phocyte (CTL) recognition quantitatively, we developed a cell-free ant igen presenting system. Genetically engineered soluble H-2D(d) molecul es coated on plastic microtiter plates could present HIV envelope pept ide to an antigen-specific CTL clone, inducing it to produce IFN-gamma in the absence of accessory cells and their accessory or co-stimulato ry molecules. The peptide - MHC complexes were functionally stable for over 24 h. The magnitude of T cell activation was dependent on the co ncentrations of both class I MHC molecule and the peptide, but was mor e sensitive to the concentration of the MHC molecule than to that of p eptide. This result suggests that one MHC molecule can play more than one role in activating the CTL. One such role is the interaction betwe en CD8 and a conserved region of class I MHC, as suggested by the find ing that holding the total MHC concentration constant with an irreleva nt class I MHC molecule (H-2K(b) engineered to have the same alpha3 do main as H-2D(d)) made the T cell response less sensitive to the change in concentration of the relevant MHC molecule (H-2D(d)). The irreleva nt class I MHC molecule (H-2K(b)), unable to present this peptide by i tself, augmented the T cell response at lower concentrations of peptid e. These results suggest that the conserved a3 domain of the class I M HC heavy chain as well as polymorphic regions play an important role i n T cell activation and that T cell interaction with MHC molecules not presenting peptide can still augment the response.