Enhanced phagocytic activity of blood leukocytes in athymic nude mice.

After 30-min incubation, blood leukocytes of adult athymic BALB/c nude mice (nu/nu) have a distinctly higher methacrylate or yeast particle uptake than leukocytes of euthymic nu/+ or +/+ mice. This permanent enhancement is not due to humoral factors, since the percentage of phagocytosing nu/nu leukocytes increases further in nu/+ littermate's plasma. Also, chronic infection or intraperitoneal immunization causes an additional transitory increase of the percentage of phagocytosing leukocytes and numbers of particles ingested; the phagocytic performance of leukocytes of euthymic mice is raised under these conditions by a greater factor. In fetuses enhanced phagocytosis of nu/nu mice is found only in monocytes. The bulk of ingestion of methacrylate particles is mediated by Fc receptors and significantly more receptors for IgG2B, IgG1, and IgG2A are demonstrable on nu/nu neutrophils; ingestion of particles via these receptors is again higher in nu/nu neutrophils, whereas nu/nu monocytes display a higher uptake via Fc(IgG1) receptors.