IMMUNOHISTOCHEMICAL EXPRESSION OF INDUCIBLE NITRIC-OXIDE SYNTHASE (INOS) IN REVERSIBLE ENDOTOXIC-SHOCK STUDIED BY A NOVEL MONOCLONAL-ANTIBODY AGAINST RAT INOS

An antirat monoclonal antibody (mAb) against inducible nitric oxide sy nthase (iNOS), ANOS11, was used for immunohistochemistry to examine th e expression of iNOS in various organs and tissues of adult rats in ex perimental endotoxic shock induced by lipopolysaccharide (LPS) injecti on. The phenotype of iNOS-expressed cells was also examined immunohist ochemically using various mAbs. In control rats, very few cells were p ositive for ANOS11 except in the thymus. After intravenous injection o f LPS, the number of iNOS-positive cells increased rapidly in almost a ll organs, except the thymus and brain, peaked 6 h after the injection , and decreased slowly. Of the numerous inflammatory cells that infilt rated the lungs, liver, and spleen after LPS injection, many were posi tive for ANOS11. Besides inflammatory cells, hepatocytes and endotheli al cells of the aorta were also positive for ANOS11 but only around 6 h after injection. The cellular composition of iNOS-positive infiltrat ed cells changed along with the progression of endotoxic shock. At 4 t o 6 h after injection, most iNOS-positive cells were considered polymo rphonuclear leukocytes judging by their positive reactivity to OX42 an d their nuclear morpholopy. The population of iNOS-positive macrophage s positive for ED1 or ED2 increased with time. After 24 h, many iNOS-p ositive macrophages were found around the focal necrosis in the liver and spleen. These results indicate that the expression of iNOS in neut rophils, endothelial cells, and hepatocytes precedes that of macrophag es in experimental endotoxic shock. The expression of iNOS in various cells and organs is closely associated with the progress and pathologi cal changes of endotoxic shock.