Induction of macrophage lysosomal hydrolase synthesis and secretion by β-1,3-glucan

Abstract

Studies were undertaken to elucidate the active component in zymosan necessary to induce the delayed-onset synthesis and secretion of representative lysosomal hydrolases, hexosaminidase, and β-glucuronidase in macrophages. Resident mouse peritoneal macrophages were challenged with zymosan particles and particulate β-1,3-glucan, the major subcomponent of zymosan. Zymosan was found to induce a rapid secretion of preformed hexosaminidase with maximal release (75%) occurring 6 hr after the addition of zymosan. By contrast, β-1,3-glucan was totally inactive in this respect. However, both zymosan and β-1,3-glucan were found to induce the delayed-onset synthesis and secretion of hexosaminidase and β-glucuronidase while maintaining constant cellular enzyme levels over a 5-day period following the addition of stimulus. These late responses were almost totally blocked by a noncytolytic concentration of cycloheximide, indicating their dependence on de novo protein synthesis. Mannan, the second major subcomponent of zymosan, had no effect on either immediate secretion or delayed-onset synthesis and secretion of hexosaminidase. These results suggest that the induction of the delayed-onset synthesis and secretion of the lysosomal hydrolases by zymosan may be dependent on the glucan subcomponent of zymosan. Moreover, it would also appear that the release of preformed lysosomal enzymes is not the trigger for the delayed-onset synthesis and secretion of hexosaminidase.