CD4-CD8- splenic T cells from Lewis rats recovered from experimental autoimmune encephalomyelitis respond to encephalitogenic T cells that mediate this disorder.

We previously demonstrated that encephalitogenic CD4+ T lymphocytes from the long-term cultured line S1, specific for myelin basic protein, induce a CD8+ T cell population in vivo that protects naive Lewis rats against experimental autoimmune encephalomyelitis caused by S1 cells. In order to determine the contribution of individual T cell population in the development of induced resistance, we have analyzed the in vitro proliferative capacity of phenotypically distinct T cell populations isolated from S1-immunized rats. We found that both CD8+ and CD8-CD4- T cells show striking proliferative responses when stimulated with S1 cells, whereas CD4+ T cells show only minimal responses. In addition, a significant proportion of the CD8-CD4- cells, after stimulated by S1 cells, became CD8+ and had a strong cytolytic activity toward S1 cells. These results suggest a contribution of double-negative splenic T cells in the regulatory circuit associated with autoimmune encephalomyelitis.