CD4 and pneumocystosis: In recent years, studies have down to explore the immune function of specific T helper (Th) subsets during the pathogenesis of PCP, such as IFN-γ-producing CD4+ T (Th1) cells, IL-4-producing CD4+ T (Th2) cells (7) and CD4+CD25+FoxP3+ regulatory T cells (8, 9).