To determine whether IL-10 was upregulated following FMDV infection in mice and then explore its association with the lymphopenia observed, we examined the concentrations of IL-10 and other potential cytokines/chemokines, including IL-10, IL-6, IL-2, IL-17, IL-18, IL-1β, TNF-α, IFN-α, IFN-β, TGF-β, CXCL13, and CXCL1, in the serum from the mice infected with FMDV. The gene discussed is TGFB1; the disease is lymphopenia.