In contrast, on day 14 of infection, CD25, IL-12Rβ1, IFN-γR, IL-18R, IL-15R, cytotoxic T lymphocyte antigen-4 (CTLA-4), Lymphocyte activation gene-3 (LAG-3), T cell immunoglobulin and musin domain containing protein-3 (Tim-3) and CD226, were all expressed at higher levels by effector CD4+ T-bet+ T cells derived from WSX-1−/− mice compared to cells from WT mice, whereas Programmed cell death protein 1 (PD-1) and BTLA were both expressed at lower levels by cells from WSX-1−/− mice (Figure 3A–D). Here, PDCD1 is linked to infection.