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-2Kb alloantigen and originated from H-2k mice. The results indicate that the property of the Tg+CD8+ cells from H-2k 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-2Kb-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-2k/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-2Kb-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-2k/b Tg+CD4-CD8- cells was sufficient to induced CTL activity in the "CD8-independent" model, whereas stimulation with cells which overexpressed H-2Kb 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-2Kb can still be triggered by H-2Kb with a sensitivity correlated with the degree of CD8 dependence.