DISASSOCIATION BETWEEN THE IN-VITRO AND IN-VIVO EFFECTS OF NITRIC-OXIDE ON A NEUROTROPIC MURINE CORONAVIRUS

Intranasal inoculation of the neuroattenuated OBLV60 strain of mouse h epatitis virus results in infection of mitral neurons in the olfactory bulb, followed by spread along olfactory and limbic pathways to the b rain. Immunocompetent BALB/c mice were able to clear virus by 11 days postinfection (p.i.). Gamma interferon (IFN-gamma) may play a role in clearance of OBLV60 from infected immunocompetent BALB/c mice through a nonlytic mechanism. Among the variety of immunomodulatory activities of IFN-gamma is the induction of expression of inducible nitric oxide synthase (iNOS), an enzyme responsible for the production of nitric o xide (NO), Studies were undertaken to investigate the role of IFN-gamm a and NO in host defense and clearance of OBLV60 from the central nerv ous system (CNS), Exposure of OBLV60-infected OBL21a cells, a mouse ne uronal cell line, to the NO-generating compound S-nitroso-L-acetyl pen icillamine resulted in a significant decrease in viral replication, in dicating that NO interfered with viral replication, Furthermore, infec tion of IFN-gamma knockout (GKO) mice and athymic nude mice with OBLV6 0 resulted in low-level expression of iNOS mRNA and protein in the bra ins compared to that of OBLV60-infected BALB/c mice. Nude mice were un able to clear virus and eventually died between days 11 and 14 p.i. (B . D. Pearce, M. V. Hobbs, T. S. McGraw, and M. J. Buchmeier, J. Virol. 68:5 183-5495, 1994); however, GKO mice survived infection and cleare d virus by day 18 p.i. These data suggest that IFN-gamma production in the olfactory bulb contributed to but may not be essential for cleara nce of OBLV60 from the brain. In addition, treatment of OBLV60-infecte d BALB/c mice with aminoguanidine, a selective inhibitor of iNOS activ ity, did not result in any increase in mortality, and the mice cleared the virus by 11 days p.i. These data suggest that although NO was abl e to block replication of virus in vitro, expression of iNOS with NO r elease in vivo did not appear to be the determinant factor in clearanc e of OBLV60 from CNS neurons.