Interferon‐γ‐activated human granulocytes kill ingested Mycobacterium fortuitum more efficiently than normal granulocytes

Abstract

Although shortly after the onset of a mycobacterial infection granulocytes are present at the site of inflammation, the role of granulocytes in the elimination of mycobacteria is not well understood. In vitro studies with, for example Mycobacterium tuberculosis or M. bovis, are hampered by the slow proliferation and clumping of the bacteria. To avoid these disadvantages, we developed a model using the atypical mycobacterium M. fortuitum. The present study concerned two questions: whether human granulocytes are able to phagocytose and intracellularly kill opsonized M. fortuitum and whether intracellular killing of these bacteria can be enhanced by treatment of the granulocytes with recombinant human interferon-gamma (rIFN-gamma). The results showed that normal granulocytes phagocytosed opsonized M. fortuitum rapidly, but did not kill these bacteria effectively. The intracellular killing of M. fortuitum was significantly enhanced by incubation of the granulocytes with rIFN-gamma for 18 h before the start of the killing assay. Since these rIFN-gamma-pretreated granulocytes did not release more O2- and H2O2 upon stimulation with phorbol 12-myristate 13-acetate or opsonized M. fortuitum than control granulocytes, non-oxidative killing mechanisms are probably involved in the enhanced killing of M. fortuitum.

Human phagocytes lack the ability to kill Mycobacterium gordonae, a non-pathogenic mycobacteria

“…another non-pathogenic mycobacteria, although non adherent cells killed the bacteria [17]. M. fortuitum, a third non-pathogenic mycobacteria was, however, elimitaded by monocytes [16], and by INF-γ activated neutrophils [7]. In our experiments neutrophils did not kill M. tuberculosis, although it has been claimed that TNF-α succesfully activate them [8].…”

“…There has been several reports that indicate variable activities of phagocytes against non-pathogenic mycobacteria [6,7,15,16] . The bacteria usually analysed, We also wondered whether neutrophils, isolated from the same donors, exhibited any anti-microbial activity (Fig.1, panel B).…”

“…An unexpected finding was the discovery that M. phlei, a non-pathogenic mycobacteria, is not eliminated by human monocytes even when they are activated with IFN-γ [6]. This cytokine has also been described to activate neutrophils against another non-pathogenic mycobacteria, M. fortuitum [7]. It fails, however, to induce the killing of M. tuberculosis, which may be instead accomplished by Tumor Necrosis Factor α (TNF-α) [8].…”

“…The activities of both human monocytes and neutrophils against nonpathogenic mycobacteria have already been addressed [6,7,15,16] . The comparison of results between reports is, however, very difficult because of the application of various methods of purification of cells, protocols of infections, and models of bacteria.…”

katGI and katGII encode two different catalases-peroxidases in Mycobacterium fortuitum

“…M. fortuitum in particular has been described as a human pathogen (26). It has often been chosen as a model for studying the intracellular killing of mycobacteria (13,26), and its gene encoding superoxide dismutase (sodA) has also been studied (22). It is relatively resistant to INH (MIC of Ͼ1 g/ml) and shows both (M-and T-catalase activities.…”