PAF is involved in the Mycoplasma arthritidis superantigen-triggering pathway for iNOS and COX-2 expression in murine peritoneal cells

Abstract

We investigated the capacity of Mycoplasma arthritidis mitogen (MAM) to induce (a) expression of the inducible enzymes cyclo-oxygenase (COX-2) and nitric oxide synthase (iNOS), (b) production of prostaglandin E 2 (PGE 2) and nitric oxide (NO), and (c) involvement of platelet-activating factor (PAF) in the MAM-induced activation pathway. Resident peritoneal cells from C3H/HePas mice were incubated with MAM in the presence or absence of a PAF-antagonist (WEB2170) or COX-2 inhibitors (nimesulide or NS398). Enzyme expression was evaluated by immunoblotting, PGE 2 by EIA, and NO by Griess reaction. Following MAM-stimulation of peritoneal cells, expression of COX-2 was detected at 3 h (peak levels at 12 h) and of iNOS at 6 h (peak levels at 20 h). PGE 2 increased till 20 h, decreasing thereafter, whereas NO increased with time. WEB2170 (5 × 10 −5 M) treatment caused 44% inhibition of NO output and reduced iNOS expression (48% at the peak of expression). Concomitant treatment with WEB2170 and nimesulide (10 −5 M) reversed these inhibitory effects. WEB2170 reduced COX-2 expression (43% at the peak of expression) and prevented the decline in PGE 2 levels after 20 h. These results suggest the involvement of PAF in the signaling pathway triggered by MAM that leads to expression of iNOS and COX-2, and show that PAF regulates the production of NO, possibly by controlling levels of PGE 2.