In vivo expression of inducible nitric oxide synthase in supraventricular amoeboid microglial cells in neonatal BALB/c and athymic mice.

The present study investigated whether the supraventricular amoeboid microglial cells (SAMC) in neonatal BALB/c and athymic nude mice were able to express inducible nitric oxide synthase (iNOS) after intraperitoneal injections of lipopolysaccharide (LPS) or interferon-gamma (IFN-gamma). The results showed that iNOS, undetectable in these cells in vehicle injected mice, could clearly be demonstrated immunohistochemically in a large number of them in LPS treated normal and mutant mice. Only a few iNOS-positive SAMC were observed in IFN-gamma injected mice. Immunoelectron microscopy confirmed the microglial nature of the labelled cells and that the immunoprecipitate of iNOS was cytosolic, being diffusely present throughout the cytoplasm of the cells. It is suggested that iNOS in the SAMC of neonatal BALB/c and athymic mice may be involved in the synthesis of nitric oxide which is necessitated more for host defence mechanism against bacterial endotoxin than against immunological stimuli.