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Characteristics of the beta-glucan receptor of murine macrophages
1Department of Membrane Research, Weizmann Institute of Science, Rehovot, Israel.
Abstract:
Phagocytosis of heat-killed yeast (HK-yeast), zymosan, and glucan particles by thioglycollate-elicited mouse peritoneal macrophages (Tg-macrophages) was inhibited by soluble glucan polymers/oligomers. The inhibitory capacity of soluble glucans decreased steeply with the decrease in the degree of polymerization (DPn); i.e., the concentration at which 50% inhibition of phagocytosis was attained was 0.23 microgram/ml for glucan 1 (DPn 24.8), 0.8 microgram/ml for glucan 2 (DPn 21.9), and greater than 40 micrograms/ml for glucan 3 (DPn 13.8). The glucan polymers were obtained by partial hydrolysis of glucan particles with formic acid (90%, 95 degrees C, 20 min) and fractionation according to solubility in ethanol water mixtures. A short preincubation (5 min, 4 or 37 degrees C) of Tg-macrophages with glucan 1 led to a subsequent inhibition of HK-yeast phagocytosis. Recovery of the phagocytic function was slow (27% in 3 h; 68% in 5 h) and required protein synthesis. beta-Glucan receptor expression was also suppressed by dexamethasone treatment. Mannan exerted at high concentrations (5 mg/ml) a partial inhibitory activity which was totally abrogated by beta-glucanase treatment. Treatment of macrophages with glucan together with mannan did not enhance the inhibitory capacity of glucan beyond the component abrogated by enzyme treatment. Contribution of local opsonization of HK-yeast to the phagocytic response (involvement of complement receptors) was indirectly negated; (a) glucan 1 which inhibits HK-yeast phagocytosis by up to 95% is not an activator of complement and therefore could not compete for the opsonizing proteins; (b) cycloheximide treatment in itself inhibited only partially HK-yeast phagocytosis whereas it inhibited the reexpression of the glucan receptors; (c) glucan 1 did not affect the phagocytosis of serum opsonized HK-yeast. Thus under the experimental conditions described, phagocytosis of HK-yeast by murine macrophages is mediated by and large by the beta-glucan receptors, while the mannose receptors and complement receptors do not contribute to the process.
Insights
Soluble beta-glucan polymers inhibit yeast phagocytosis by mouse macrophages, with efficacy dependent on polymer size. This process primarily involves beta-glucan receptors, not mannose or complement receptors.
Area of Science:
- Immunology
- Cell Biology
Background:
- Phagocytosis is a key immune mechanism by which macrophages engulf pathogens.
- Beta-glucans are fungal cell wall components recognized by specific macrophage receptors.
Purpose of the Study:
- To investigate the role of soluble beta-glucan polymers in inhibiting yeast phagocytosis by macrophages.
- To elucidate the specific macrophage receptors involved in yeast particle uptake.
Main Methods:
- Thioglycollate-elicited mouse peritoneal macrophages were used.
- Phagocytosis of heat-killed yeast, zymosan, and glucan particles was measured.
- Soluble glucan polymers of varying degrees of polymerization (DPn) were synthesized and tested for inhibitory effects.
- Receptor expression and function were assessed using specific inhibitors and enzyme treatments.
Main Results:
- Soluble glucan polymers significantly inhibited yeast phagocytosis in a dose-dependent manner.
- The inhibitory capacity of glucans correlated strongly with their degree of polymerization (DPn).
- Beta-glucan receptors were identified as the primary mediators of yeast phagocytosis, with mannose and complement receptors playing minimal roles.
Conclusions:
- Soluble beta-glucans, particularly those with higher DPn, effectively inhibit macrophage phagocytosis of yeast.
- Macrophage phagocytosis of yeast particles is predominantly mediated by beta-glucan receptors.
- The findings highlight the specificity of immune receptor recognition in phagocytosis.