CD4 and pneumocystosis: The key role of CD4 + T cells in resisting Pneumocystis infection has become a consensus.[13] The most convictive evident is the strong correlation between the declining number of peripheral blood CD4 + T cell in HIV-infected patients and the increased risk of development of PCP,[14] and a similar correlation also existed in non-HIV-infected patients who receiving immunosuppressive therapy.[15] Shellito et al[16] showed that T helper (Th) 1 and 2 LYM were recruited to the lung of mice with Pneumocystis infection.