Serological evidence of pneumonia virus of mouse (PVM) infection in laboratory rats

The chemokine macrophage-inflammatory protein-1 alpha and its receptor CCR1 control pulmonary inflammation and antiviral host defense in paramyxovirus infection

In this work, we explore the responses of specific gene-deleted mice to infection with the paramyxovirus pneumonia virus of mice (PVM). We have shown previously that infection of wild type mice with PVM results in pulmonary neutrophilia and eosinophilia accompanied by local production of macrophage-inflammatory protein-1 alpha (MIP-1 alpha). Here we examine the role of MIP-1 alpha in the pathogenesis of this disease using mice deficient in MIP-1 alpha or its receptor, CCR1. The inflammatory response to PVM in MIP-1 alpha-deficient mice was minimal, with approximately 10-60 neutrophils/ml and no eosinophils detected in bronchoalveolar lavage fluid. Higher levels of infectious virus were recovered from lung tissue excised from MIP-1 alpha-deficient than from fully competent mice, suggesting that the inflammatory response limits the rate of virus replication in vivo. PVM infection of CCR1-deficient mice was also associated with attenuated inflammation, with enhanced recovery of infectious virus, and with accelerated mortality. These results suggest that the MIP-1 alpha/CCR1-mediated acute inflammatory response protects mice by delaying the lethal sequelae of infection.

Pulmonary eosinophilia and production of MIP-1alpha are prominent responses to infection with pneumonia virus of mice

Human eosinophils secrete two distinct ribonucleases that have antiviral activity against pathogens of the family Paramyxoviridae. To examine the role of eosinophils and their ribonucleases in host defense against paramyxovirus pathogens in vivo, we have developed a mouse model involving a viral pathogen that naturally targets a rodent host. In this work we describe infection of Balb/c mice with pneumonia virus of mice (PVM, strain J3666), a paramyxovirus pathogen found frequently among rodent populations. We show here that pulmonary eosinophilia is an immediate response to infection with PVM, with bronchoalveolar lavage fluid containing 12-14% eosinophils obtained as early as day 3 postinoculation. Infection is accompanied by the production of macrophage inflammatory protein-1-alpha (MIP-1alpha), a chemokine that has been associated with the pulmonary eosinophilia observed in response to respiratory syncytial virus infection in humans and with enhanced clearance of influenza virus in mice. Interestingly, we observed no changes in expression of the chemoattractants eotaxin and RANTES in response to PVM infection, and interleukin-5 remained undetectable throughout. These responses-clinical pathology, viral recovery, pulmonary eosinophilia, and production of MIP-1alpha-will provide a means for exploring the role of eosinophils, eosinophil secretory ribonucleases, and eosinophil chemoattractants in host defense against PVM and related paramyxovirus pathogens in vivo.

New isolates of pneumonia virus of mice (PVM) from Japanese rat colonies and their characterization

Two virus strains were isolated from the lungs of athymic rats and mice used as sentinel animals in 2 colonies of laboratory rats in Japan in which antibodies to the pneumonia virus of mice (PVM) had been detected. The new isolates were identified as PVM by the following characteristics: RNA virus, susceptibility to ether treatment, long filamentous viral structure in the cytoplasm of infected cells, and hemagglutinating activity in various erythrocytes, including those of mice and rats. In addition, cross neutralization with the prototype of PVM (No. 15 strain) was observed. This is the first report of the isolation of PVM from laboratory animals in Japan.