Modulation of macrophage mannosyl-specific receptors by cultivation on immobilized zymosan. Effects on superoxide-anion release and phagocytosis

Unopsonized zymosan effectively induces a respiratory burst (O₂^- release, hexose monophosphate (HMP) shunt stimulation) in thioglycollate-elicited and BCG-activated macrophages (Mφ). These Mφ are known to express lectin-like receptors specific for mannose or fucose-terminated glycoconjugates (MFR). A role for the MFR in phagocytosis of zymosan was demonstrated by cultivating Mφ on a glutaraldehyde-fixed layer of zymosan, a procedure which depleted Mφ of MFR-mediated pinocytic activity, but not other surface antigens (F4/80, Mac-1) or receptors (FcR, C3R). After modulation of MFR, Mφ lost the ability to phagocytose zymosan, but ingested antibody or complement-coated zymosan vigorously via alternative receptors. Challenge with free zymosan failed to enhance respiratory burst activity in Mφ which had been cultivated on zymosan. Such Mφ were also refractory to zymosan taken up by alternative receptors or other ingested particles (EIgG), but responded to a non-particulate challenge, PMA. These studies show that the MFR, like other receptors, can mediate phagocytosis and elicit a respiratory burst in suitably primed Mφ, but indicate that phagocytosis via specific receptors (FcR, C3R) need to trigger a respiratory burst.