Relationships between anionic sites and lectin receptors in the plasma membrane of Dictyostelium discoideum and their role in phagocytosis.

The disappearance of Wheat Germ Agglutinin (WGA) receptors from the membrane of yeast-engulfing-phagocytic cups in Dictyostelium suggested that these receptors could play a role in yeast adsorption or ingestion. This problem was approached by comparing the fate of WGA, Concanavalin A (Con A) and cationized ferritin (CF) and their effects on the phagocytosis of yeast, bacteria and latex beads. It can be concluded that CF capped in about 30 min and inhibited phagocytosis of any kind of particles for about 15 min. Con A capped in 20--60 min and inhibited phagocytosis of all particles for 1 h 30 min. The time at which phagocytosis started to occur corresponded approximately to the moment at which large areas of plasma membrane were totally devoid of marker. WGA did not cap but induced the formation of large and tight aggregates. The surface of the peripheral cells progressively released WGA in 1 h 30 min. Afterwards, the cells were able to ingest latex beads and bacteria but did not phagocytoze yeast. The latter started to be adsorbed onto the cells and to be ingested only 1 h later. Double labelling experiments showed that CF and Con A receptors were still absent in the plasma membrane, when phagocytosis of any kind of particles started to occur. WGA-labelled cells ingested latex beads and bacteria when their plasma membrane was still devoid of WGA receptors but were able to ingest yeast only after their regeneration. These observations strongly suggest that WGA receptors may correspond to specific receptors for yeast phagocytosis.