Although the association between HIV and overall TB (including pulmonary TB) is well-characterized (29), the relationship between extrapulmonary TB and HIV is less clear; the mechanisms related to the escape of Mtb to TB sites out of the lungs are not yet fully clarified, although extrapulmonary TB is very likely due to the reduction of CD4+ T cell counts in HIV-infected patients, since CD4+ T-helper cells are important for controlling of Mtb infection (30–34). The gene discussed is CD4; the disease is tuberculosis.