CD8β increases CD8 coreceptor function and participation in TCR-ligand binding

Abstract

To study the role of CD8β in T cell function, we derived a CD8α/β- (CD8(-/-)) T cell hybridoma of the H-2K(d)-restricted N9 cytotoxic T lymphocyte clone specific for a photoreactive derivative of the Plasmodium berghei circumsporozoite peptide PbCS 252-260. This hybridoma was transfected either with CD8α alone or together with CD8β. All three hybridomas released interleukin 2 upon incubation with L cells expressing K(d)-peptide derivative complexes, though CD8α/β cells diet so more efficiently than CD8α/α and especially CD8(-/-) cells. More strikingly, only CD8α/β cells were able to recognize a weak agonist peptide derivative variant. This recognition was abolished by Fab' fragments of the anti-K(d) α3 monoclonal antibody SF1- 1.1.1 or substitution of K(d) D-227 with K, both conditions known to impair CD8 coreceptor function. T cell receptor (TCR) photoaffinity labeling indicated that TCR-ligand binding on CD8α/β cells was ~5- and 20-fold more avid than on CD8α/α and CD8(-/-) cells, respectively, SF1-1.1.1 Fab' or K(d) mutation D227K reduced the TCR photoaffinity labeling on CD8α/β cells to approximately the same low levels observed on CD8(-/-) cells. These results indicate that CD8α/β is a more efficient coreceptor than CD8α/α, because it more avidly strengthens TCR-ligand binding.