Ly-6C is a marker of memory CD8⁺ T cells

This study examined long-term phenotypic and functional effects of TCR ligation in vivo. Flow cytometric analysis of T cells from mice treated with anti-CD3 revealed an increase in CD44 expression in both the CD4⁺ and CD8⁺ populations. The phenotypic changes were a result of TCR engagement, because treatment with staphylococcal enterotoxin B (SEB) resulted in a preferential increase in CD44 expression on the SEB-reactive Vβ8 T cells. In addition, the percentage of cells expressing Ly-6C increased among the CD8⁺ subset after anti-CD3 treatment and in the Vβ8⁺ CD8⁺ subset after treatment with SEB. Finally, the TCR transgenic (Tg) mouse strain 2C was used to confirm that the phenotypic changes can be induced by exposure to a physiologic ligand (H-2L(d)). Before treatment, nearly all of the Tg⁺CD8⁺ cells were CD44(low)/Ly-6C^-. Tg⁺ peritoneal exudate T cells isolated from mice challenged with P815 cells (H-2L(d)) up-regulated Ly-6C and secreted higher levels of IFN-γ on a per Tg⁺ CD8⁺ T cell basis after treatment. Taken together, these data indicate that in vivo TCR/CD3 engagement results in phenotypic and functional changes in T cells. Furthermore, Ly-6C expression correlates with an increase in IFN-γ, production after antigenic stimulation of CD8⁺ T cells, suggesting that it is a 'memory' marker that correlates with Ag-specific functional changes in CD8⁺ T cells.