NITRIC-OXIDE PRODUCTION AND EXPRESSION OF INDUCIBLE NITRIC-OXIDE SYNTHASE BY BOVINE ALVEOLAR MACROPHAGES

Alveolar macrophages play a central role in host defense in the lower respiratory tract. Production of the reactive intermediate nitric oxid e (NO), via expression of inducible nitric oxide synthase (iNOS) is an important microbicidal effector mechanism possessed by macrophages. I n this study, cytokine regulation of NO production by bovine alveolar macrophages (bAM) was evaluated. Bovine alveolar macrophages were expo sed to one or more of the following: recombinant human (rh) and recomb inant bovine (rb) IFN gamma, rh- and rbIL-1 beta, rbGM-CSF, rhTNF alph a, rhIL-4 endotoxin (LPS), fetal bovine serum (FBS), mitogen-stimulate d bovine splenic supernatant (SS), and purified human TGF beta-1. LPS alone, or in combination with SS, rbIFN gamma, or rbIL-1 beta stimulat ed production of NO in a time and dose dependent fashion. Recombinant bovine IFN gamma, rbIL-1 beta, and rhTNF alpha in combination produced maximal stimulation which was not further enhanced by LPS. Recombinan t human IFN gamma, rhIL-1 beta, and rbGM-CSF had minimal effect either as single stimuli, or in combination with LPS, rbIFN gamma, rbIL-1 be ta, or rhTNF alpha. Nitric oxide production was inhibited by rhIL-4, a nd the L-arginine analogue antagonists of iNOS, N-(G)-monomethyl-L-arg inine (N(G)MMA) and aminoguanidine (AG). Purified human TGF beta-1 did not inhibit NO production. Messenger RNA for iNOS was maximally expre ssed by 8 h and remained detectable for at least 48 h. Expression of i NOS mRNA induced by cytokines and LPS varied with strength of the stim ulus as determined by nitrite production in culture supernatant.