Monocyte derived macrophage cytokine responses induced by M-bovis BCG

Setting: One important aspect of macrophage function is the production of i nflammatory and antiinflammatory cytokines, which in turn affect the surviv al of intracellular organisms such as mycobacteria. Objective: To determine the relationship between phagocytosis of mycobacter ia and expression of intracellular cytokines. Design: Phagocytosis and cytokine production were studied simultaneously wi thin human monocyte-derived macrophages (MDMs) from healthy donors using fl uorescent labelling of M. bovis BCG and flow cytometry. Results. At a range of infection ratios (5:1, 1:1, 0.2:1) TNF-alpha, IL-10, IL-6 and IL-12 were all produced in a dose-dependent manner. At an infecti on ratio representative of the in vivo situation (1:1), cytokine production was induced in both MDMs containing intracellular M. bovis BCG and in unin fected bystander MDMs. Phagocytosis increased over time, but there was cons iderable donor variation: the proportions of cells containing one or more m ycobacterium were 15.4 +/- 14.8% (mean +/- SD) at 4 h and 32.7 +/- 21.1% at 24 h (n = 19). Analysis of cytokine production by MDMs not containing myco bacteria (bystander cells) at 4 h revealed that these uninfected cells prod uced 79 +/- 6.6% of the TNF-alpha, 53.9 +/- 40.0% of the IL-10 and 64.2 +/- 12.4% of the IL-12. By 20 h these proportions had decreased to 57 +/- 13.5 %, 30.9 +/- 7.4% and 45.5 +/- 13.3% respectively. Conclusion: Both infected and bystander MDMs can be stimulated to produce c ytokines in response to IM. bovis BCG, indicating that the ability of MDMs to produce cytokines is not necessarily dependent on the ability to phagocy tose mycobacteria. (C) 2000 Harcourt Publishers Ltd.