Fig. 6.

Effect of exogenous IFN-γ on (a) mycobacterial growth, (b) cytopathic effect and (c) NO production in I/St and A/Sn lung macrophages following in vitro infection. Lung macrophages were recovered from control and infected mice and plated at 4 × 10⁴ macrophages/well. Live M. tuberculosis H37Rv were added at MOIs between 10 and 1 in triplicates, and infected macrophages were incubated in the absence (▪) or presence (hatched bars) of 100 u/ml rIFN-γ. Results for MOI = 10 are displayed. Mycobacterial growth was assessed (a) by [³H]-uracil uptake and (b) by its cytopathic effect on macrophages by specific LDH release into culture supernatants after 72 h of culture. (c) After 36 h of culture, 50 µl samples of each supernatant were removed to evaluate nitrite content. Results of one out of three (mycobacterial growth) or two (LDH release and NO production) similar independent experiments are depicted as mean ± SD for triplicate determinations. As assessed by Mann–Whitney U-test, addition of IFN-γ significantly increased NO production by all macrophages (P < 0·001) and inhibited mycobacterial growth in macrophages recovered from infected mice (P < 0·01).