Effector molecules of the host defence mechanism against Mycobacterium avium complex: the evidence showing that reactive oxygen intermediates, reactive nitrogen intermediates, and free fatty acids each alone are not decisive in expression of macrophage antimicrobial activity against the parasites

Abstract

SUMMARYIn this study, we evaluated the roles of reactive oxygen intermediates (ROI), reactive nitrogen intermediates (RNI), and free fatty acids (FFA) as effectors of the macrophage-mediated host defence mechanism against Mycobacterium avium complex (MAC). First, M. avium (three strains) and M. intracellulare (two strains) were treated with the H 2 O 2 -Fe 2þ -mediated halogenation system, acidified NaNO 2 -derived RNI, or FFA (linolenic acid) in sodium acetate buffer pH 5 . 5, and then counted for the number of residual colony-forming units (CFU) of organisms. Although these effectors exerted strong bactericidal activity against the MAC, the susceptibility of test organisms markedly varied from strain to strain. There was no significant relationship between the degree of resistance of a given MAC strain to these effectors and its virulence in mice, indicating that ROI, RNI, and FFA each alone are not decisive as the effector components of the host defence mechanism against the MAC. Second, the increase in ROI-producing ability in murine peritoneal macrophages due to tumour necrosis factor-alpha (TNF-a) treatment was not accompanied by parallel potentiation of anti-MAC activity of the same macrophage population. This excludes the possibility that ROI play a central role in macrophage-mediated killing and inhibition of MAC organisms. Third, anti-MAC activity of BAM3 macrophage cell line was not significantly attenuated by N G -monomethyl-L-arginine (NO synthaseinhibitor causing reduction of RNI production) or by quinacrine (phospholipase A 2 -inhibitor causing reduction of FFA release), indicating that RNI and FFA each alone do not play crucial roles in the expression of macrophage antimicrobial activity against the MAC. The present findings suggest important roles of collaborating actions of various antimicrobial effectors and/or the participation of other kinds of effectors in macrophage-mediated killing and inhibition of MAC organisms.

Comparative roles of free fatty acids with reactive nitrogen intermediates and reactive oxygen intermediates in expression of the anti-microbial activity of macrophages againstMycobacterium tuberculosis

“…5; other detailed data are not shown). The anti-microbial activity of the H 2 O 2 -halogenation system against M. tuberculosis was dependent on concentrations of Fe 21 ion. In addition, NaNO 2 at neutral pHs was incapable of exhibiting significant levels of activity against M. tuberculosis.…”

“…The anti-microbial activities of RNI, FFA, H 2 O 2 -halogenation system, and XOA-Fe 21 -EDTA system (XOA system) against M.…”

“…We previously found that there was no relationship between the degree of susceptibility of a given M. avium complex strain to RNI and ROI and its virulence in mice [21]. Thus, RNI and ROI each alone are not decisive as the effector components of the host defence mechanism against M. avium complex, and alternative effectors may be involved in the anti-mycobacterial activity of macrophages.…”

“…However, we recently found that a H 2 O 2 -mediated halogenation system (H 2 O 2 -halogenation system) was potently efficacious in killing M. avium complex [17]. It thus appears that the H 2 O 2 -halogenation system may be involved in the activity of macrophages against M. tuberculosis, when the phagosomes of macrophages are supplied with catalytic Fe 21 by the action of divalent-cation transporter proteins encoded by Nramp-1 gene [18]. However, this concept needs some consideration, since the divalent cation transporters are also involved in the export of divalent cations, especially Fe 21 ions, from phagosomes, thereby causing the deprivation of divalent cations from the intracellular pathogens [19].…”

“…It thus appears that the H 2 O 2 -halogenation system may be involved in the activity of macrophages against M. tuberculosis, when the phagosomes of macrophages are supplied with catalytic Fe 21 by the action of divalent-cation transporter proteins encoded by Nramp-1 gene [18]. However, this concept needs some consideration, since the divalent cation transporters are also involved in the export of divalent cations, especially Fe 21 ions, from phagosomes, thereby causing the deprivation of divalent cations from the intracellular pathogens [19]. Moreover, it has been reported that Nramp-1 affects intracellular mycobacterial replication by modulating phagosomal pH, suggesting that Nramp protein plays a central role in this process [20].…”