THE DEGREE OF CD8 DEPENDENCE OF CYTOLYTIC T-CELL PRECURSORS IS DETERMINED BY THE NATURE OF THE T-CELL RECEPTOR (TCR) AND INFLUENCES NEGATIVE SELECTION IN TCR-TRANSGENIC MICE

Although much has been learned about CD8 structure-function properties, it has so far not been tested whether the nature of the TCR is sufficient to transfer the property of CD8 dependence versus non-dependence to CD8(+) cytotoxic T lymphocytes (CTL) and their precursors differentiating in T cell receptor (TCR)-transgenic (Tg) mice. In the present study, we compared the characteristics of dependence on CD8 for stimulation of CTL precursors and antigen-specific cytolysis by CD8(+) T cells from two TCR-Tg mice expressing respectively the TCR (Tg) from a ''CD8-dependent'' and from a ''CD8-independent'' CTL clone, which were both reactive against the H-2K(b) alloantigen and originated from H-2(k) mice. The results indicate that the property of the Tg(+)CD8(+) cells from H-2(k) TCR-Tg mice corresponds to that of the CTL clone of origin, demonstrating that it is linked to the nature of the TCR. Consistent with this property, Tg(+)CD4(+) cells could also differentiate into H-2K(b)-specific CTL when originating from the ''CD8-independent'', but not from the ''CD8-dependent'' Tg-TCR. The influence of the property of ''CD8 dependence'' on negative selection occurring in TCR-Tg H-2(k/b) mice was apparent at two levels: (i) in the thymus, the extent of deletion was much more pronounced for the ''CD8-independent'' TCR-Tg mice; (ii) in the periphery, Tg(+(hi)) cells with low to negative CD8 expression were present for the ''CD8-dependent'' Tg-TCR, whereas only Tg(+)CD4(-)CD8(-) cells with low surface Tg-TCR and CD3 expression were found for the ''CD8-independent'' Tg-TCR, indicating that Tg(+)CD4(-)CD8(-) cells are susceptible to tolerance induction involving TCR/CD3 surface down-modulation, Furthermore, different in vitro conditions led to H-2K(b)-induced stimulation of Tg(+)CD4(-)CD8(-) cells to differentiate into CTL detected in an anti-TCR clonotypic monoclonal antibody redirected cytolysis assay. Culture in interleukin-2 of H-2(k/b) Tg(+)CD4(-)CD8(-) cells was sufficient to induce CTL activity in the ''CD8-independent'' model, whereas stimulation with cells which overexpressed H-2K(b) was required in addition to interleukin-2 to induce CTL differentiation in the ''CD8-dependent'' model. These data suggest that peripheral Tg(+)CD4(-)CD8(-) cells present in a situation of in vivo tolerance to H-2K(b) can still be triggered by H-2K(b) with a sensitivity correlated with the degree of CD8 dependence.