Induction of a beta-1,3-D-glucan receptor in P388D1 cells treated with retinoic acid or 1,25-dihydroxyvitamin D3

Abstract

Retinoic acid (RA) and 1,25-dihydroxyvitamin D3 (1,25(OH)2D3) induce the capability to phagocytose heat-killed yeast (Y) (Saccharomyces cerevisiae) in P388D1 cells. Y phagocytosis is specifically inhibited (100%) by particulate and soluble beta-1,3-D-glucan. Other polysaccharides, such as agarose, dextran and dextran sulphate, are not inhibitory. The inhibitory capacity of mannan was totally abrogated by treatment with beta-glucanase, suggesting that its activity is derived from a residual beta-glucan structure. Partial hydrolysis of glucan particles with formic acid yielded soluble glucan that was fractionated according to size. Glucan1, glucan2 and glucan3 had an average chain length of 34, 23.5 and 15.5 glucose units, respectively. Fifty percent inhibition of Y phagocytosis by RA-P388D1 cells was attained at less than 0.02 microgram/ml (approximately 2 nM) glucan1 and at 1.1 micrograms/ml glucan3. A further decrease in chain length (less than or equal to 12.6) resulted in oligomers of marginal inhibitory activity. Preincubation of RA- and 1,25(OH)2D3-P388D1 cells with glucan1 for 30 seconds to 5 min, at 4 degrees or 37 degrees, followed by washes with buffer, sufficed to bring about 85-95% inhibition of Y phagocytosis. Recovery of the phagocytic capability was time dependent and required protein synthesis, suggesting a glucan1-induced removal of membrane receptors. The results suggest that recognition and ingestion of Y by RA- or 1,25(OH)2D3-treated P388D1 cells depends almost exclusively on a beta-glucan-specific receptor.