Abstract
A new fraction, Fr. 8-A, which consists of a phosphatidylethanolamine with C14 : 0-C18 : 0 isofatty acids was obtained from Bacillus stearothermophilus UBT8038. The fraction inhibited major histocompatibility complex class II (Ia) antigen expression and antigen presentation on mouse macrophages. The effect of Fr. 8-A on macrophage functions related to antigen presentation was investigated. Fr. 8-A increased arachidonate release, prostaglandin (PG) E2 release and nitrite production from peritoneal macrophages. It increased further the levels of PGE2, nitrite and tumor necrosis factor in the culture supernatant of the macrophages induced by the supernatant from concanavalin A-stimulated spleen cell cultures. Fr. 8-A augmented the activity of peritoneal macrophages to suppress Con A-stimulated T cell proliferation. Addition of either indomethacin or NG-methyl-L-arginine had no effect on the augmentation of suppressor macrophage activity or the inhibition of antigen presentation by Fr. 8-A, while simultaneous addition of both inhibitors abrogated the effect of the fraction. These results indicate that Fr. 8-A inhibits Ia expression and antigen presentation, and augments suppressor macrophage activity at least partly via the activation of both cyclooxygenase and nitric oxide synthase pathways.
