DEFECT IN THE INDUCTION OF NITRIC-OXIDE SYNTHASE BY LIPOPOLYSACCHARIDE (LPS) IN AN LPS-RESISTANT MUTANT OF A MURINE MACROPHAGE-LIKE CELL-LINE, J774.1

Nitric oxide (. NO)-generating activity was examined in a lipopolysacc haride (LPS)-resistant mutant of a murine macrophage-like cell line, J 774.1, treated with LPS or LPS and interferon-gamma (IFN-gamma). This mutant, an LPS1916 cell line, showed no NO2- accumulation in the cultu re medium, and no expression of NOS activity in the cell extract, . NO synthase (NOS(II)) protein or NOS(II) mRNA on treatment with up to 10 (4) ng/ml LPS, although the parental cell line, JA-4, showed significa nt . NO production. The addition of 10 U/ml IFN-gamma, together with m ore than 1 ng/ml LPS to JA-4 cells, increased NO production remarkably , while IFN-gamma did not reverse the defect of NO production in LPS19 16 cells when they were treated with less than 10 ng/ml LPS; however, it induced NO production by the mutant cells with more than 100 ng/ml LPS, Analysis of NOS activity, NOS(II) protein and NOS(II) mRNA reveal ed that LPS1916 cells are not devoid of the NOS(II) gene, but are rath er defective in transcription of the gene in response to LPS, and this defect is partly reversed by lFN-gamma with higher LPS doses at more than 100 ng/ml. In addition, the delay of NOS(II) mRNA induction in LP S1916 cells, compared to that in JA-4 cells, treated with LPS+IFN-gamm a seems to suggest some additional inducer(s) of NOS(II) transcription , followed by LPS signaling.