Inhibition of nitric oxide enhances ovine lentivirus replication in monocyte-derived macrophages

Ovine lentivirus (OvLV) also known as maedi-visna virus, infects and replicates primarily in macrophages. This investigation examined the role of nitric oxide in the replication of OvLV in cultured macrophages. Peripheral blood mononuclear cells were collected from OvLV-free sheep and cultured in Teflon coated flasks at a high concentration of lamb serum. The cells were subsequently infected with OvLV strain 85/34. OvLV replication was assessed under different experimental treatments by comparison of reverse transcriptase (RT) activity in culture supernatant. Cultures that were treated with exogenous nitric oxide via S-nitroso-acetylpenicillamine did not have altered levels of RT activity compared to cultures treated with the inactive control compound, acetylpenicillamine. However, blockage of nitric oxide production by treatment with aminoguanidine, a competitive inhibitor of inducible nitric oxide synthase (iNOS), led to a significant rise in RT activity. This rise in RT activity was partially reversed in aminoguanidine treated cultures by L-arginine, the normal substrate for iNOS. Finally, the number of viral antigen producing cells was also quantified after aminoguanidine treatment and found to be significantly higher than untreated cultures. Collectively, these results indicate that nitric oxide is a negative regulator of OvLV replication in macrophages.