Indication for prophylaxis in pneumocystis carinii pneumonia include

Defects in cellular and/or humoral immunity predispose to development of PCP. CD4+ T cells are critical in host defense against Pneumocystis. For HIV-infected patients, the incidence is inversely related to the CD4+ T cell count: at least 80% of cases occur at counts of <200 cells/mL, and most of these cases develop at counts of <100 cells/mL. Ref Harrison 19th edition pg 1017