Multiple Mycobacterium microti Derived Lipids Stimulate iNOS Gene Expression in the J774 Murine Macrophage Cell Line

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Abstract
The inducible nitrogen oxygen synthase (iNOS) and nitric oxide (NO) system acting in concert with superoxide radicals is recognized as a powerful macrophage microbicidal mechanism. However, experimentation with iNOS knockout mice has rendered contradictory results on the protective role of iNOS/NO in the course of mycobacterial infections. On the other hand, NO also plays an immunoregulatory role. Knowing the nature of the mycobacterial constituents that induce iNOS gene expression would help to better understand the host–parasite relationship.Lipoarabinomannan (LAM) and a 19 KDa lipoprotein are the two known mycobacterial constituents that have shown to induce iNOS. By screening a set of methanol extracted lipids from Mycobacterium microti, here we provide evidence that multiple mycobacterial molecules of lipidic nature both of intermediate and of high polarity, with free amino groups or carbohydrates but no phosphate groups as part of their structure are capable of inducing iNOS gene expression in J774 cells, thus implying a complex relationship between mycobacteria and their host immune system in regard to iNOS gene expression.