Peritoneal macrophages were obtained from untreated mice and from mice treated with thioglycollate medium (TA), proteose peptone medium (PP), or a suspension of streptococcus A cell wall material (SA). The biochemical and secretory properties of these cells in long term cultures (up to 2 wk) were compared. TA-elicited macrophages contained more protein, lactate dehydrogenase, lysosomal hydrolases, and in particular, more plasminogen activator than the other cells studied. All types of macrophages studied were found to release considerable amounts of lysosomal hydrolases (beta-glucuronidase, N-acetyl-beta-glucosaminidase, alpha-mannosidase, and acid phosphatase) into the medium. Release was independent of phagocytosis and must, therefore, be regarded as true secretion. In both elicited and nonelicited macrophages, the rates of lysosomal enzyme secretion were virtually identical in the presence and in the absence of serum, and they were not enhanced by increasing serum concentrations. Lysosomal enzyme secretion in macrophages appears to depend on protein synthesis, since it was blocked by low concentrations of cycloheximide which neither affected cell viability nor lowered the intracellular enzyme levels. The amounts of lysosomal hydrolases secreted were highest in TA-elicited macrophages. The rates of secretion of PP- or SA-elicited and of nonelicited macrophages were about one-fourth of that of the TA-elicited cells. This difference, although significant, is much smaller than that observed for the secretion of plasminogen activator which was 20-50 times higher in TA-elicited cells. Acid glycosidases were also found in the peritoneal lavage media used for cell harvesting from both treated and nontreated mice. This indicates that active secretion of lysosomal hydrolases may be an in vivo property of the macrophage.

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