CD4 and Pneumocystis infectious disease: Effector CD4+ T cells accounted for only 7.5% of the T cells in the uninfected mice; however, the proportion of effector CD4+ T cells significantly increased to 36.8% in the fourth week after Pneumocystis infection, supporting previous reports that the role of CD4+ T cells in Pneumocystis infection was fundamental (Otieno-Odhiambo et al., 2019).