In contrast to the cell-intrinsic IL-27R regulation of LCMV-specific CD4 T cell numbers late after LCMV Cl13 infection (43), we observed that there were similar frequencies of both virus-specific CD8+ T cells and their PD-1 expression in the WT and Il27ra−/− compartments of CD45.1:Il27ra−/− mixed BM chimeras at both days 9 and 30 after LCMV Cl13 infection (Fig. 8A). This evidence concerns the gene CD4 and infection.