Interferon gamma fails to activate human monocyte-derived macrophages to kill or inhibit the replication of a non-pathogenic mycobacterial species.

The ability of interferon gamma (gamma) to activate human macrophages to kill mycobacteria was investigated using a mycobacterial species that does not cause disease in man. Although interferon activated human macrophage activity against other intracellular parasites, Toxoplasma gondii and Listeria monocytogenes, it failed to activate human monocyte-derived macrophages to kill not only Mycobacterium tuberculosis but also the non-pathogenic species, Mycobacterium phlei.