Effects of viability or bacterial load on M. marinum-induced IL-8 secretion by human monocytes. (A) Secretion of IL-8 by human monocytes infected with either live or killed mycobacteria. Cell supernatants were obtained 24, 48, or 96 h after infection with each mycobacterium, and IL-8 protein production was measured by ELISA. (B) IL-8 production by M. marinum at progressively higher MOIs (1, 10, 25, and 50). The IL-8 production data were obtained 48 h after infection with each mycobacterium. The data are expressed as the mean ± SD of triplicate supernatant samples. The cells infected with M. tuberculosis (M. tbc) and M. marinum were compared statistically. *, P < 0.05; **, P < 0.01; ***, P < 0.001.