Purification and partial biochemical characterization of a Mycoplasma fermentans-derived substance that activates macrophages to release nitric oxide, tumor necrosis factor, and interleukin-6

Abstract

Mycoplasmal products may exert a number of diverse in vitro effects on cells of the immune system. A macrophage-activating substance from Mycoplasma fermentans was described in this laboratory and named mycoplasma-derived high-molecular-weight material (MDHM). Using synthesis of nitric oxide by peritoneal cells from endotoxin low-responder mice as an assay system, MDHM was purified as follows. After freeze-thawing of M. fermentans, MDHM activity was sedimented with the membrane fraction. Membranes were delipidated with chloroform-methanol, and MDHM activity was extracted with octyl glucoside. Coextracted proteins were degraded by proteinase K. MDHM was further purified by reversed-phase high-pressure liquid chromatography and eluted in one major and one minor peak of activity. Neither carbohydrates nor amino acids were found as constituents. MDHM had the following properties: it partitioned into the phenol phase upon phenol-water extraction and into the Triton phase after extraction with Triton X-114. MDHM was not inactivated by either phospholipase A2 or triglyceride lipases. However, mild periodate treatment led to a >95% loss of activity. Also, alkaline hydrolysis at 25°C completely abolished MDHM activity with a half-life of 2 min. MDHM activity was spread out over a wide molecular weight range upon sodium dodecyl sulfate- polyacrylamide gel electrophoresis of membranes, whereas after proteinase treatment MDHM activity migrated close to the front. These features of MDHM, taken together, speak in favor of an amphiphilic molecule with a lipid moiety carrying fatty acids in ester linkage and a polyol moiety of unknown character. MDHM was active in the nanogram-per-milliliter range, activating macrophages to release nitric oxide, interleukin-6, and tumor necrosis factor.