Induction of interleukin 1 and tumor necrosis factor by mycobacterial proteins: The monocyte Western blot

Infection with Mycobacterium tuberculosis involves mononuclear phagocytic cells as hosts to intracellular parasites, accessory cells in the induction of the immune response, effector cells for mycobacterial killing, and targets of cytotoxic lymphocytes. When stimulated by whole mycobacteria or various mycobacterial preparations, monocytes and macrophages produce the cytokines interleukin 1 and tumor necrosis factor, which possess multiple functions, including immune induction, and may be responsible for the fever and cachexia prominent in tuberculosis. To identify mycobacterial proteins that may directly activate production of these cytokines, culture filtrate of M. tuberculosis that had been subjected to gel electrophoresis and transferred to nitrocellulose paper was used to stimulate monocyte production of cytokines. Fractions representing molecular weights of 46,000 and 20,000 consistently induced both interleukin 1 and tumor necrosis factor. The magnitude of the monocyte responses to these fractions was similar to that to intact mycobacteria or optimal concentrations of lipopolysaccharide. This stimulatory effect was not due to contamination with either bacterial lipopolysaccharide or mycobacterial lipoarabinomannan, as it was abolished by digestion with Streptomyces griseus protease but was unaffected by ammonium sulfate precipitation, preincubation with polymyxin B, or depletion of lipoarabinomannan by immunoaffinity chromatography. Proteins identified by this system may have considerable potential as immunogens, as the capacity to directly stimulate mononuclear phagocyte production of cytokines is an essential property of adjuvants.