Stimulation of macrophages by Bacillus firmus: production of nitric oxide and cytokines.

Immunostimulatory properties of gram-positive Bacillus firmus were investigated under in vitro conditions using murine peritoneal macrophages. B. firmus stimulated in a concentration and time dependent manner the secretion of tumour necrosis factor-alpha (TNF-alpha) and interleukin-10 (IL-10), but it had no influence upon interferon-gamma (IFN-gamma) and interleukin-2 (IL-2) production. It also substantially augmented production of nitric oxide (NO) induced by exogenous IFN-gamma. Inhibitory experiments using neutralizing antibodies against TNF-alpha and/or IL-10 have demonstrated that these cytokines are responsible for triggering the underlying mechanism(s) leading to enhanced NO production. The cytokine-stimulatory and NO-costimulatory properties could participate in the antiinfectious and anticancer effects of B. firmus, detected previously in the in vivo experiments.