Role of cytokines and nitric oxide in the induction of tuberculostatic macrophage functions

THE aim of th is study was to deter mine phenotypic differences when BCG in vades macrophages. Bacilli prepared from the same BCG primary seed, but pro duced in different culture media, were analysed with respect to the ability to stimulate macrophages and the susceptibility to treatment with cytokine s and nitric oxide (NO). Tumour necrosis factor (TNF) activity was assayed by measuring its cytotoxic activity on L-929 cells, interleukin-6 (IL-6) an d interferon-gamma (IFN-gamma) were assayed by enzyme-linked immunosorbent assay (ELISA), where as NO levels were detected by Griess colorimetric reac tions in the culture supernatant of macrophages incubated with IFN-gamma, T NF or NO and subsequently exposed to either BCG-I or BCG-S. We found th at BCG-I and BCG-S bacilli showed different ability to simulate peritoneal mac rophages. Similar levels of IL-6 were detected in stimulated macrophages wi th lysate from two BCG samples. The highest levels of TNF and IFN-gamma wer e observed in macrophages treated with BCG-S and BCG-I, respectively. The h ighest levels of NO were observed in cultures stimulated for 48 h with BCG- S. We also found a different susceptibility of the bacilli to exogenous tre atment with IFN-gamma and TNF which were capable of killing 60 and 70% of b oth bacilli, whereas NO was capable of killing about 98 and 47% of BCG-I an d BCG-S, respectively. The amount of bacilli proportionally decreased with IFN-gamma and TNF, suggesting a cytokine-related cytotoxic effect. Moreover , NO also decreased the viable number of bacilli. Interestingly, NO levels of peritoneal macrophages were significantly increased after cytokine treat ment. This indicates that the treatment of macrophages with cytokines marke dly reduced bacilli number and presented effects on NO production. The resu lts obtained here emphasize the importance of adequate stimulation for guar anteeing efficient killing of bacilli. In this particular case, the IFN-gam ma and TNF were involved in the activation of macrophage bactericidal activ ity.