CD8 EXPRESSION ALTERS THE FINE SPECIFICITY OF AN ALLOREACTIVE MHC CLASS-I-SPECIFIC T-HYBRIDOMA

The influence of CDB on the fine specificity of MHC class I-restricted T cell allorecognition was evaluated by comparing the reactivity of CD8- and CD8-transfected forms of an allospecific, H-2K(b)-restricted T hybridoma. The CD8- T hybridoma responded to cells expressing H-2K(b), H-2K(bm6), and the individual H-2K(b --> bm10) back mutations 165V --> M, 173K --> E, and 174N --> L. Under the same conditions the CD8- T hybridoma responded poorly or not at all to cells expressing H-2K(bm10), H-2K(bm8), the individual H-2K(b --> bm10) back mutants 163T --> A and 167W --> S, and the individual H-2K(b --> bm8) back mutations 22Y --> F and 24E --> S. In contrast, T hybridoma cells expressing high levels of CD8 reacted strongly with antigen presenting cells (APC) expressing H-2K(b) and H-2K(bm6) molecules, as well as APC expressing H-2K(bm10) (weakly), H-2K(bm8), and all five individual H-2K(b --> bm10) and the two H-2K(b --> bm8) back mutants 22Y --> F and 24E --> S. The mutations which distinguish the T cell recognition of both H-2K(bm10) and H-2K(bm8) from H-2K(b) are predicted to control the interaction of these class I molecules with antigenic peptides in the binding site, implying an important role for peptide antigen in T cell allorecognition. Nonetheless, CD8 expression by the H-2K(b)-restricted T cells conferred novel or enhanced alloreactivity with cells expressing H-2K(bm10), H-2K(bm8), and each of the individual H-2K(b -- >bm10) and H-2K(b --> bm8) back mutants. These findings reflect an important role for CD8 in influencing the fine specificity of MHC class I recognition by T cells and may indicate a limited structural role for peptide antigen in defining the ligand recognized by these alloreactive T cells.