Prostaglandin synthesis in different phases of phagocytosis in lung macrophages.

Macrophages have a central role in bodily defence and inflammatory responses. Prostaglandins (PGs), mediators of inflammation, are secreted by macrophages during phagocytosis. PGE-like activity was first demonstrated in macrophage-rich peritoneal exudate cell preparations from guinea pigs; later, other kinds of PGs were also found to be released by mouse peritoneal macrophages in response to inflammatory stimuli. We have shown that rabbit alveolar macrophages also produce various PGs in response to phagocytic stimuli like zymosan and heat-killed bacteria; however, it was not known precisely which cellular event is associated with PG production. Traditionally, the phagocytic process is considered in three stages: (1) attachment of the particle to the cell membrane; (2) interiorisation (phagocytosis); and (3) fusion of the phagocytic vesicle with intracellular lysosomes (digestion). We show here that PG secretion in response to phagocytic stimuli by macrophages is independent of the first stage, but dependent on engulfment of the particle. Moreover, PG production does not appear to be associated with the process of engulfment per se, but with some event following internalisation.