Phagocytosis of heat-killed blastospores of Candida albicans by human monocyte beta-glucan receptors.

Candida albicans is an opportunistic human pathogen with a cell wall that is qualitatively similar in carbohydrate composition to zymosan. Monolayers of human peripheral blood monocytes ingested 2.5 x 10(6)-2.5 x 10(7) heat-killed C. albicans blastospores in a dose-related manner. The percentage of monocytes ingesting at least one C. albicans reached a near plateau level of 68 +/- 6% (mean +/- SD, n = 3) when 2.5 x 10(7) particles per ml were incubated with monocytes for 30 min. Pretreatment of monocytes with 10 ng/ml to 100 micrograms/ml of soluble yeast beta-glucan inhibited C. albicans ingestion in a dose-dependent manner without affecting Fc-mediated ingestion of IgG-coated sheep erythrocytes (EsIgG). Pretreatment of monocytes with 100 micrograms/ml of soluble yeast beta-glucan inhibited the ingestion of 1 or more C. albicans by 80 +/- 11% (mean +/- SD, n = 4), with 50% inhibition occurring with approximately 7 micrograms/ml of soluble beta-glucan. Incubation of monocytes with 100 micrograms/ml to 1000 micrograms/ml of soluble yeast mannan resulted in no significant inhibition of C. albicans ingestion. The pretreatment of monolayers of monocytes for 30 min with 1 microgram/ml to 50 micrograms/ml of affinity-purified trypsin resulted in a dose-dependent inhibition of C. albicans ingestion with 10 micrograms/ml of trypsin inhibiting the percentage of monocytes ingesting 1 or more organisms by 71 +/- 6%. The inhibitory effects of soluble yeast beta-glucan and trypsin pretreatment on the ingestion of heat-killed C. albicans are comparable to the inhibitory effect of these agents on monocyte phagocytosis of zymosan and glucan particles. This relationship indicates that C. albicans contain a ligand that is recognized by the monocyte beta-glucan receptor of human monocytes.