Difference in neutrophil cytokine production induced by pathogenic and non‐pathogenic mycobacteria

This study shows differences between Mycobacterium tuberculosis and Mycobacterium avium (opportunistic) and Mycobacterium smegmatis (non-pathogenic), with respect to their abilities to induce cytokine/chemokine release from human neutrophils. Neutrophils incubated with live cells of M. tuberculosis, M. avium, or M. smegmatis produced and released TNF-alpha, IL-6, and IL-8. No or very small amounts of these cytokines/chemokines were found in resting neutrophils, suggesting that they were newly synthesised. The levels of TNF-alpha, IL-6, and IL-8 produced/released from neutrophils incubated with M. tuberculosis were markedly lower than those of the opportunistic or non-pathogenic bacterial species. The production of TNF-alpha reached a maximum level at a time (4 h) when the production of IL-8 had only just started, and this was true for all three mycobacteria tested. However, the time course for IL-6 production differed between the species, reaching a peak value after 8 h for M. tuberculosis not seen with the other bacteria. It is likely that the relatively high levels of cytokines induced by opportunistic/non-pathogenic mycobacteria are of importance for the induction of an innate immune response through which these organisms are eliminated, while the low levels of cytokines released by neutrophils interfering with M. tuberculosis might help the bacteria to persist.