Inhibition of nitric oxide enhances ovine lentivirus replication in monocyte-derived macrophages Kevin A. Keane 1 , Gary L. Mason, James C. DeMartini * Department of Microbiology, Immunology, and Pathology, Colorado State University, Fort Collins, CO 80523, USA Received 31 May 2002; received in revised form 17 September 2002; accepted 25 September 2002 Abstract 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 RTactivity 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. # 2002 Elsevier Science B.V. All rights reserved. Keywords: Monocyte-derived macrophage; Nitric oxide; Ovine lentivirus; Reverse transcriptase 1. Introduction Ovine lentivirus (OvLV) also known as maedi-visna virus is the etiologic agent of lymphoid interstitial pneumonia (LIP) in sheep (DeMartini et al., 1993; Sigurdsson et al., 1952). LIP is a significant cause of morbidity and mortality in sheep (Narayan et al., 1993; Brodie et al., 1992) and also occurs in human and simian immunodeficiency virus infections (Jeena et al., 1998; Mankowski et al., 1998). Because in vivo infection and replication of OvLV occurs primarily in activated macrophages, and because activated macro- phages are primary sources of nitric oxide, there may be a mechanistic link between lentivirus replication and nitric oxide. The purpose of this investigation was to examine the role of nitric oxide in early OvLV replication. Pulmonary nitric oxide is produced by alveolar macrophages and is an important molecule in the Veterinary Immunology and Immunopathology 90 (2002) 179–189 Abbreviations: Agu, aminoguanidine; HIV, human immunode- ficiency virus; iNOS, inducible nitric oxide synthase; LIP, lymphoid interstitial pneumonia; MDMs, monocyte-derived macrophages; OvLV, ovine lentivirus; PBMCs, peripheral blood mononuclear cells; RT, reverse transcriptase * Corresponding author. Tel.: þ1-970-491-5410; fax: þ1-970-491-0603. E-mail addresses: kkeane@icos.com (K.A. Keane), james.demartini@colostate.edu (J.C. DeMartini). 1 Present address: ICOS Corporation, 22021 20th AVE SE, Bothell, WA 98021, USA. Tel.: þ1-425-415-5109; fax: þ1-425-489-0356. 0165-2427/02/$ – see front matter # 2002 Elsevier Science B.V. All rights reserved. PII:S0165-2427(02)00245-3