CD62L (L-Selectin) Down-Regulation Does Not Affect Memory T Cell Distribution but Failure to Shed Compromises Anti-Viral Immunity

The down-regulation of CD62L that accompanies T lymphocyte activation is thought to redirect cells away from lymph nodes to sites of infection. In this study, CD62L was maintained on Ag-activated T cells and their distribution, and ability to clear pathogen from peripheral sites determined. CD62L was down-regulated on Ag-specific CD8 T cells in lungs of C57BL/6 mice but maintained in CD62L transgenic mice at day 8 after influenza infection. However, the numbers of influenza-specific CD8 T cells recruited were similar in CD62L transgenic and C57BL/6 mice. Memory CD8 T cell numbers in the lungs and noninvolved organs 100 days after primary infection were similar in CD62L transgenic and C57BL/6 mice, despite differing CD62L expression. Transgenic mice expressing wild-type CD62L cleared a recombinant vaccinia virus expressing an influenza-derived CD8 T cell epitope as efficiently as C57BL/6 mice. However, transgenic mice expressing a protease resistant mutant of CD62L showed significantly delayed viral clearance, despite normal CTL generation and the presence of CD107a and IFN-γ expressing influenza-specific CD8 T cells. These results demonstrate that CD62L down-regulation is not required for CD8 memory cells to home to sites of infection. However, their ability to clear virus is significantly compromised if CD62L shedding is abrogated.