Ricin- and concanavalin A-binding sites on the surface of polymorphonuclear leukocytes have no receptor function in phagocytosis.

Human and rabbit polymorphonuclear leukocytes (PMN) were incubated at 0 degrees C with ferritin conjugates of ricin or concanavalin A,and subsequently brought to 37 degrees C in order to induce the formation of lectin caps. The PMN were then alllowed to phagocytose yeast cells or staphylococci for 15 min and were subsequently processed for electron microscopy. The micrographs were evaluated by morphometry. It was found that lectin-treated PMN phagocytose as efficiently as untreated cells. Capped cells always engulfed the particles with a lectin-free portion of their plasma membrane. This indicates that ricin- and concanavalin A-binding sites on the PMN surface are not involved in particle recognition and uptake. The virtual absence of lectin on the membrane of the phagocytic vacuoles suggests that capped PMN is functionally polarized and only able to phagocytose at the pole opposite the cap.