Serum factors required for arginase induction in macrophages

Two nondialyzable factors in the sera of several species were required for the induction of arginase in resident peritoneal macrophages in vitro. One factor stimulated PGE₂ production by macrophages, was inhibited by indomethacin, and could be replaced by the addition of PGE₂ or DBcAMP. Thirty percent serum was required for maximal activity of this factor. DBcAMP reduced the requirement for serum by 10-fold, suggesting the requirement of a second factor which required less than 3% serum for maximal activity. A factor with similar activity was found in the supernatant of tumor cells grown in vitro.