In vitro activation of CD8 interphotoreceptor retinoid-binding protein-specific T cells requires not only antigenic stimulation but also exogenous growth factors

In a previous study, we demonstrated that immunization with the uveitogenic peptide interphotoreceptor retinoid-binding protein (IRBP) 1-20 induces both CD4 and CD8 uveitogenic T cells in the B6 mouse. In the current study, we determined the role of the CD8 IRBP-specific T cells in the pathogenesis of experimental autoimmune uveitis. We also determined the conditions that facilitated the activation of CD8 autoreactive T cells. Our results showed that the beta2-microglobulin(-/-) mouse had a greatly decreased susceptibility to induction of experimental autoimmune uveitis by adoptive transfer of IRBP-specific T cells from B6 mice. We also showed that unlike CD4 autoreactive T cells, activated CD8 autoreactive T cells produced only a limited number and amounts of growth factors. As a result, in the absence of exogenously supplied growth factor(s), CD8 T cell activation and expansion were aborted. However, the growth and expansion of triggered CD8 autoreactive T cells could be supported by various cytokines. In addition to factors produced by activated CD4 autoreactive T cells, factors produced by nonlymphoid cells, such as IL-7 and IL-15, and unidentified factors in the culture supernatants of astrocytes and retinal pigment epithelial cells support the CD8 autoreactive T cells as well. Finally, we showed that, although several cytokines augmented the CD8 T cell response in vitro, different cytokines appeared to act on different CD8 subsets or on different activation/differentiation phases of CD8 autoreactive T cells. As a result, cytokines, such as IL-7, supported the proliferation and survival of CD8 IRBP-specific T cells, while others had only a growth-promoting effect.