Monocyte-mediated destruction in the presence of serum of red cells coated with antibody.

In order to determine the conditions under which monocytes are able to destroy red cells coated with antibody in vitro in the presence of fluid-phase IgG, human peripheral blood monocytes and red cells coated with IgG anti-D antibody were incubated in media containing lgG (neat serum or medium containing 1000 tg/ml of purified IgGI). Although phagocytosis was markedly inhibited in media containing IgG, significant amounts of erythrophagocytosis were seen in these media. In neat serum, erythrophagocytosis was proportional to the concentration of red cells to 20 vol % and was not further increased at higher red cell volume. Phagocytosis was proportional to the concentration of RBC-bound antibody and was observed with as little as 1000-2000 molecules of antibody/RBC. Ingestion was markedly augmented by concurrent coating of the red cell with complement components; complement coating alone induced very little ingestion. Statistically significant extracellular red cell lysis, quantitated by measuring radioactive chromium release from 61Crlabeled red cells, occurred in the presence of serum if the red-cell-monocyte mixture was centrifuged to a pellet prior to incubation. Lysis under these conditions was augmented by increasing red cell concentration. These studies demonstrate that destruction by monocytes of antibodycoated red cells can occur under conditions that obtain commonly in the body.