Nitric oxide increases the amount of murine cytomegalovirus-DNA in mice latently infected with the virus

Therapeutic effect of a traditional Chinese medicine, ren-shen-yang-rong-tang (Japanese name: Ninjin'yoeito) on nitric oxide-mediated lung injury in a mouse infected with murine cytomegalovirus

The therapeutic effect of a traditional Chinese medicine ren-shen-yang-rong-tang (Japanese name: Ninjin'yoeito, NYT) on murine cytomegalovirus (MCMV)-associated pneumonitis was examined. In MCMV-pneumonitis, IFN-gamma-induced nitric oxide (NO) mediates its pathogenesis. When mice, which had been infected with 0.2LD(50) of MCMV at 28 days previously, were intraperitoneally injected with anti-CD3 monoclonal antibody (mAb), MCMV-pneumonitis was induced in the lung, where high amounts of IFN-gamma-producing cells thereafter accumulated, accompanied by an elevation in the NO level in the serum and abundant expression of inducible NO synthase (iNOS) mRNA, thus resulting in all mice eventually dying. When the mice were orally treated with NYT (1000 mg/kg/day) once on the day of mAb injection and once the day after, the expression level of iNOS-mRNA was suppressed and NO level in the serum decreased. The survival rate improved from 0% to 57.1%. The pathological findings of the lungs in the NYT-treated mice were comparable to those of the uninfected controls. In contrast, NYT itself did not affect either the ratio of IFN-gamma-producing cells or MCMV titer. As a result, NYT had a therapeutic effect on MCMV-pneumonitis by decreasing the degree of inflammation mediated by the IFN-gamma-induced NO. It is also interesting to note that only two oral administrations of NYT had a therapeutic effect on viral disease.

Role of nitric oxide synthase type 2 in acute infection with murine cytomegalovirus

Whether or not NO plays a critical role in murine CMV (MCMV) infection has yet to be elucidated. In this study, we examined the role of NO in acute infection with MCMV using NO synthase type 2 (NOS2)-deficient mice. NOS2(-/-) mice were more susceptible to lethal infection with MCMV than NOS2(+/+) mice and generated a much higher peak virus titer in the salivary gland after acute infection. A moderate increase in the MCMV titer was also observed in other organs of NOS2(-/-) mice such as the spleen, lung, and liver. The immune responses to MCMV infection including NK cell cytotoxicity and CTL response in NOS2(-/-) mice were comparable with those of NOS2(+/+) mice. Moreover, the ability to produce IFN-gamma is not impaired in NOS2(-/-) mice after MCMV infection. The peritoneal macrophages from NOS2(-/-) mice, however, exhibited a lower antiviral activity than those from NOS2(+/+) mice, resulting in an enhanced viral replication in macrophages themselves. Treatment of these cells from NOS2(+/+) mice with a selective NOS2 inhibitor decreased the antiviral activity to a level below that obtained with NOS2(-/-) mice. In addition, the absence of NOS2 and NOS2-mediated antiviral activity of macrophages resulted in not only an enhanced MCMV replication and a high mortality but also a consequent risk of the latency. It was thus concluded that the NOS2-mediated antiviral activity of macrophages via NO plays a protective role against MCMV infection at an early and late stage of the infection.