Activated alveolar macrophages: IgG and complement receptors.

Receptors for IgG and C on PM populations can be modulated by activation. AM populations constantly exposed to environmental particulates may not be subject to changes of IgG and C receptors after activation. We compared normal and activated rabbit AMs and PMs. Activation was accomplished by treatment with intravenous BCG or intratracheal Micropolyspora faeni. We examined the ability of these AM populations to attach to (form rosettes) and phagocytize SRBC coated with varying concentration of IgG or C. Compared to normal AMs, activated AM populations formed more rosettes with SRBC coated with IgG or C and phagocytized more via the IgG receptor. PMs from BCG-treated rabbits did not form more rosettes with IgG- or C-coated SRBC but demonstrated more IgG-mediated phagocytosis than did normal PMs. C-mediated phagocytosis occurred in AM populations from only five of 25 BCG-treated rabbits and two of 20 normal rabbits. The TG broth-induced rabbit PM also exhibited a low level of C and IgG-mediated phagocytosis compared to the mouse TG broth-induced PM. We conclude that rabbit AM IgG and C receptors can be altered by events that activate AMs. C-mediated phagocytosis is much lower in rabbit macrophages (both AMs and PMs) than in activated mouse PM populations. IgG-mediated phagocytosis can be used as an index of rabbit AM activation.