Cellular immune response in HIV-infected patients with histoplasmosis

The relationship of immunity to Histoplasma capsulatum and CD4 count in HIV-1-infected patients is unknown. Samples of blood from people with HIV infection and from HIV-negative volunteers were assessed for immune responsiveness to the histoplasmin antigen using proliferation and interferon-gamma production as indicators of immunity. Results of histoplasmin skin tests, lymphoproliferative responses (LPR), and interferon-gamma production were positive in 9 of 20 (45%) HIV-negative controls, and in vitro measurements agreed highly with skin test reactivity. Among HIV-1-infected patients with recent histoplasmosis, skin test results were positive in none, LPR results were positive in 14%, and interferon-gamma production in 18%. Among HIV-1-infected patients with CD4 counts between 200 and 500 cells/mm(3), LPR was positive in 8% and interferon-gamma production in 33%, and among those with CD4 counts >500 cells/mm(3), LPR was positive in 31% and interferon-gamma production in 46%. In conclusion, immune responsiveness to H. capsulatum was depressed in HIV-1-infected persons with CD4 counts between 200 and 500 cells/mm(3), but approached normal in those with CD4 counts >500 cells/mm(3).