There are several lines of evidence, deriving from the HIV-1 infection model, suggesting that T-cells contribute to the development of cavitary tuberculosis: 1) HIV-1 infected subjects less frequently have cavitary tuberculosis; 2) HIV-1 infected patients less frequently transmit mycobacteria as compared to HIV-1 uninfected people; 3) in HIV-1 infected patients more the CD4+ T-cells and more the frequency of cavitary tuberculosis. The gene discussed is CD4; the disease is tuberculosis.