CTLA4 and infection: To determine whether the expression of coinhibitory molecules was upregulated during acute infection with FMDV in mice, the expression of all known seven coinhibitory molecules (PD-1, CTLA-4, Tim-3, LAG-3, 2B4, TIGIT, and CD160) was analyzed on peripheral blood T lymphocytes, which were harvested from the mock mice and infected mice at 48 hpi when the increased apoptosis of T lymphocytes occurred (Supplementary Figure S4).