Nonimmune-mediated phagocytosis by "premedullary" lung macrophages: effects of concanavalin A, tuftsin, and macrophage-inhibitory peptide.

Abstract

Free cells arising in organ-cultured embryonic rat and hamster lungs share ultrastructural, lysosomal enzyme, and cell membrane properties with typical alveolar macrophages, expressing the developmental potential of the earliest-macrophage precursors resident in the lungs. In the lung culture environment cell proliferation is supported and macrophage attributes are developed despite absence of lymphocytes from the system. We have shown previously that among these attributes, the cells respond with increased phagocytosis of erythrocytes if these are opsonized with immunoglobulin G. Attention has now been turned to the question of nonimmune-mediated phagocytosis by the same population. Living macrophages that emerged from lung cultures bound rhodamine-coupled soybean and wheat germ agglutinins to a greater degree than concanavalin A (Con A), which nevertheless promoted lateral translocation of occupied receptors in the cell membrane. Emerged cells also phagocytosed living bacteria and native yeast cells (Y). The percentage of macrophages ingesting 3 or more yeast cells increased 400 (hamsters) to 500% (rats) when yeast was preincubated with Con A (200 micrograms/ml). Pretreatment of macrophages with Tuftsin (100 microM) enhanced uptake of Y by 100 (hamster) to 200% (rat). Pretreatment of macrophages with macrophage-inhibitory peptide (500 microM) appeared to inhibit phagocytosis of Y by 60% in hamsters but had no significant effect on cells from rat lung cultures.