This antibody blockade data suggested that the PD-1 pathway was the major player in the increased and sustained maintenance of Selplg-/-Pdcd1-/- P14 CD8+ T cells and that PSGL-1 antibody blockade at late stages of infection has less impact on the numbers of virus-specific T cells than PSGL-1 genetic deletion. The gene discussed is PDCD1; the disease is infection.