Arginine metabolism during macrophage autocrine activation and infection with mouse hepatitis virus 3

In contrast to BALB/c mouse macrophages (M Φ), M Φ from the A/J mouse strain, upon activation by exogenous interferon gamma (IFN γ), develop an anti-mouse hepatitis virus 3 (MHV3) state which correlates with resistance to virus infection. To investigate the autocrine activation of BALB/c and A/J M Φ, we activated them with interleukin-12 (IL-12) and/or IL-18, and quantified IFN γ production, the anti-MHV3 state and arginine metabolism. Synergistic activation by IL-12/IL-18 induced the expression of the IFNγ gene in M Φ from both mouse strains. In bone marrow (BM) or peritoneal (P) M Φ of specific pathogen-free ( spf) mice of both strains, IFN γ synthesis occurred only with a synergistic IL-12/IL-18 activation and showed increasing levels from 24 to 72 h of activation. In contrast, when non- spf mice were used in the assay, their PM Φ synthesized higher IFNγ levels upon activation with only IL-12 or only IL-18 or both. The BALB/c M Φ were always capable of synthesizing higher amounts of IFN γ than the A/J M Φ. An anti-MHV3 state was observed only in A/J M Φ upon activation with IL-12/IL-18 or IFN γ regardless of their origin from the peritoneum or bone marrow. Arginine metabolism in activated and/or virus infected BMM Φ was investigated through nitric oxide (NO) and arginase induction as well as the consumption of arginine and synthesis of citrulline, ornithine and spermine. The results showed that both BALB/c and A/J BMM Φ populations released NO only after activation with IL-12/IL-18 or IFN γ. Arginase was not induced in BMM Φ from both strains by IL-12/IL-18 or IFN γ but only by IL-4/IL-10. Higher arginine consumption was observed in BMM Φ from both strains upon activation with IL-4 or IFN γ which further increased, in this case, when the cells were infected with MHV3. As a consequence of nitric oxide synthase synthesis and arginine consumption in IFN γ activated BMM Φ, we observed a higher synthesis of citrulline. High levels of ornithine were induced only upon IL-4 activation. Polyamine synthesis was higher in A/J BMM Φ than in BALB/c ones, which correlated with the slightly lower levels of ornithine observed. Upon infection with MHV3, we observed a higher synthesis of spermine. IL-12/IL-18 or IFN γ activation, mainly in MHV3 infected cells, led to a decreased synthesis of polyamines, notably spermine, only in A/J BMM Φ. Difluoromethylornithine treatment, which leads to inhibition of polyamine synthesis, induced a decreased MHV3 multiplication in both