TNF and infection: To determine whether the observed differences in susceptibility following infection with different M. tuberculosis strains might reflect differences in the production of TNF-α or IL-10, we measured the amount of TNF-α or IL-10 that was secreted into the supernatant of each type of BMDM at 24 h after the cells were infected with the virulent M. tuberculosis strain H37Rv or the attenuated H37Ra strain at an MOI of 0.1 or 1.