ABSTRACT
We have previously demonstrated that the AIDS-associated Mycoplasma fermentans as well as Mycoplasma capricolum membranes activated bone marrow macrophages to secrete tumor necrosis factor alpha (TNF alpha) and induce blast transformation of splenic lymphocytes. Herein, we show that the membrane component of Mycoplasma capricolum capable of inducing TNF alpha secretion is a hydrophobic protein. This is supported by our findings that the TNF alpha inducing activity was eluted by a phenyl-Sepharose column in a peak distinct from bulk membrane lipids. The hydrophobic nature of the protein is indicated by the activity of the "hydrophobic protein" fraction of the membranes, and the pattern of elution obtained by the phenyl-Sepharose column. Fractionation of the M. capricolum membranes, solubilized by CHAPS (3-[(3-cholamidopropyl)-dimethylammoniol]1-propane sulfate) on a gel filtration column revealed a major peak of TNF alpha inducing activity of about 75,000 daltons, and a minor peak of about 55,000 daltons. The mitogenic activity, though spread throughout the column, peaked in the same fractions as the TNF alpha inducing activity. Both activities co-eluted by the phenyl-Sepharose column as well. However, the mitogenic activity of the membranes was much more resistant to elevated temperatures and extreme pH treatment.