Induction of C3b-mediated phagocytosis in macrophages by distinct populations of lipopolysaccharide-stimulated lymphocytes

Abstract

Unelicited resident peritoneal macrophages do not significantly ingest erythrocytes coated with C3b. However, these resident macrophages can be induced to ingest via the C3b receptor when cocultured with peritoneal or splenic nonadherent cells obtained from mice previously injected with lipopolysaccharide. In this study, the extent of ingestion induced in resident macrophages was dependent on the number of stimulated nonadherent cells cocultured with the macrophages as well as on the amount of lipopolysaccharide injected in the mice from which the nonadherent cells were obtained. The ability of the stimulated nonadherent cells to convert resident macrophages to a state of C3b receptor-mediated ingestion was not abrogated by the inclusion of polymyxin B in the cocultivation medium. To further characterize these nonadherent cells, different lipopolysaccharide-stimulated cells were obtained by either nylon-wool filtration, depletion of C3b receptor-bearing cells, or depletion of Thy 1.2-positive cells. None of these populations by themselves were capable of inducing resident macrophages to ingest via the C3b receptor, whereas unfractionated cells were. However, coculture of resident macrophages with recombinations of splenic nylon-wool effluent (T cell-enriched) or bound (B cell-enriched) nonadherent cells from lipopolysaccharide-injected mice reconstituted the ability to induce ingestion via the C3b receptor. Taken together, these results suggest that one means by which lipopolysaccharide can induce C3b receptor-mediated ingestion by macrophages is through the cooperative effects of stimulated T and B lymphocytes.