Glucan receptor and zymosan-induced lysosomal enzyme secretion in macrophages

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Abstract
A receptor for beta-glucan was in the present study shown to mediate binding of zymosan particles to resident mouse peritoneal macrophages. Lysosomal enzyme secretion in response to zymosan was maximal at a low particle/cell ratio, continuous for at least 3 h after particle/cell contact and inhibitable by soluble glucan. Latex particles of various size caused no selective secretory response, but at high particle/cell ratios were toxic. By use of a fluorescent ligand, the macrophage beta-glucan receptor was shown to be trypsin-sensitive, Ca2+/Mg(2+)-independent, recirculating and also present in an intracellular mobilizable pool. Binding of ligand to the beta-glucan receptor and inhibition of the lysosomal secretory response to zymosan were both more efficient with glucans of larger size, indicating that clustering of glucan receptors at the cell surface occurs. Such clustering could stabilize ligand binding by multiple interactions and possibly trigger intracellular signaling events on binding of zymosan particles.