The low proportion of positive responses to the EC-ELISPOT in HIV infected person with CD4 cell counts lower than 200/mm3, and particularly among those with less than 50/mm3, could either reflect a smaller proportion of patients being infected with M. tuberculosis in that group of subjects, or more likely, the suppression of the antigen-specific M. tuberculosis T cell response with the progression of HIV infection, as has been shown by Sutherland et al. in chronic HIV-1 infected persons [31]. Here, CD4 is linked to HIV infectious disease.