Compared with mice receiving no adjuvant or antigen only, the PCP-immunized group demonstrated markedly increased antibody production of IgG2a (indicative of a Th1-type response) and IgG1 (indicative of a Th2-type response), significantly enhanced proliferation of CD4+ T cells, elevated numbers of CD8+ central memory T cells, and heightened secretion of the cytokines IFN-γ, IL-2, IL-4, IL-6, and IL-10. This evidence concerns the gene CD4 and pneumocystosis.