Inhibitory effects of nitric oxide and gamma interferon on in vitro and invivo replication of Marek's disease virus

The replication of Marek's disease herpesvirus (MDV) and herpesvirus of tur keys (HVT) in chicken embryo fibroblast (CEF) cultures was inhibited by the addition of S-nitroso-N-acetylpenicillamine, a nitric oxide (NO)-generatin g compound, in a dose-dependent manner, Treatment of CEF culture, prepared from 11-day-old embryos, with recombinant chicken gamma interferon (rChIFN- gamma) and lipopolysaccharide (LPS) resulted in production of NO which was suppressed by the addition of N-G-monomethyl L-arginine (NMMA), an inhibito r of inducible NO synthase (iNOS), Incubation of CEF cultures for 72 h prio r to treatment with rChIFN-gamma plus LPS was required for optimal NO produ ction. Significant differences in NO production were observed in CEF derive d from MDV-resistant N2a (major histocompatibility complex [MHC], (BB21)-B- 21) and MDV-susceptible S-13 (MHC, (BB13)-B-13) and P2a (MHC, (BB19)-B-19) chickens. N2a-derived CEF produced NO earlier and at higher levels than CEF from the other two lines. The lowest production of NO was detected in P2a- derived CEF, NO production in chicken splenocyte cultures followed a simila r pattern, with the highest levels of NO produced in cultures from N2a chic kens and the fewest levels produced in cultures from P2a chickens, Replicat ion of MDV and HVT was significantly inhibited in CEF cultures treated with rChIFN-gamma plus LPS and producing NO. The addition of NMMA to CEF treate d with rChIFN-gamma plus LPS reduced the inhibition. MDV infection of chick ens treated with S-methylisothiourea, an inhibitor of iNOS, resulted in inc reased virus load compared to nontreated chickens, These results suggest th at NO may play an important role in control of MDV replication in vivo.