Nocardia brasiliensis Modulates IFN-gamma, IL-10, and IL-12 cytokine production by macrophages from BALB/c Mice

Interferon-gamma (IFN-gamma) is a critical cytokine involved in control of different infections. Actinomycetoma is a chronic infectious disease mainly caused by the bacterium Nocardia brasiliensis, which destroys subcutaneous tissue, including bone. Currently, the mechanism of pathogenesis in N. brasiliensis infection is not known. Here, we demonstrate that N. brasiliensis induced an IFN-gamma response in serum after 24 h of infection, while, in infected tissue, positive cells to IFN-gamma appeared in 2 early peaks: the first was present only 3 h after infection, then transiently decreased; and the second peak appeared 12 h after infection and was independent of interleukin-10. Resident macrophages produced an immediate IFN-gamma response 1 h after in vitro infection, and spleen-positive cells began later. The phase of growth of N. brasiliensis affected cytokine production, and exposure of macrophages to Nocardia opsonized with either polyclonal anti-Nocardia antibodies or anti-P61 monoclonal antibody led to a suppression of cytokine production. Our report provides evidence that N. brasiliensis as an intracellular bacterium modulates macrophage cytokine production, which helps survival of the pathogen. Modulation of these cytokines may contribute to pathogenesis once this bacterium is inside the macrophage.