At the 8th week post-infection, in undernutrition 65% + infection group, PD-1, PD-L1, Bax and ICOS were upregulated and CD3+CD4+ and CD3+CD8+ T cell proportions were decreased, while the level of serum IL-10 was increased and IL-12 p70 was decreased. The gene discussed is ICOS; the disease is infection.