Bacterial LPS inhibits the expression of la by macrophages stimulated by IFN-ã. We now present the following observations that suggest a causal relationship between nitric oxide (NO) and this inhibition of la expression: 1) NO production precedes inhibition of la, 2) the ability of LPS to inhibit la expression by IFN-γ stimulated macrophages is correlated in a dose-dependent fashion with NO production, 3) la expression is restored if NO production is inhibited by NG-monomethyl-L-arginine or culturing the macrophages in L-arginine-free medium, and 4) exogenous NO inhibits IFN-γ-stimulated la expression. Taken together these experiments indicate that NO inhibits macrophage expression of la. Furthermore, the following studies showed that inhibition of la by NO was not due to macrophage death: trypan blue exclusion, macrophage adhesion, conversion of the tetrazolium dye (MTT) to its formazan by a functioning electron transport system, and phagocytosis of IgG opsonized SRBCs. By inhibiting la expression, NO may inhibit Ag-presentation to T cells, secretion of IFN-γ by these T cells, and ultimately inhibit the IFNγ-dependent production of NO synthetase. This inhibitory mechanism may prevent excessive NO formation and tissue injury.
|Original language||English (US)|
|Number of pages||8|
|Journal||Journal of Immunology|
|State||Published - Aug 1 1994|
ASJC Scopus subject areas
- Immunology and Allergy