Mutational analysis of the gene start sequences of pneumonia virus of mice

Priming of the Respiratory Tract with Immunobiotic Lactobacillus plantarum Limits Infection of Alveolar Macrophages with Recombinant Pneumonia Virus of Mice (rK2-PVM)

Pneumonia virus of mice (PVM) is a natural rodent pathogen that replicates in bronchial epithelial cells and reproduces many clinical and pathological features of the more severe forms of disease associated with human respiratory syncytial virus. In order to track virus-target cell interactions during acute infection in vivo, we developed rK2-PVM, bacterial artificial chromosome-based recombinant PVM strain J3666 that incorporates the fluorescent tag monomeric Katushka 2 (mKATE2). The rK2-PVM pathogen promotes lethal infection in BALB/c mice and elicits characteristic cytokine production and leukocyte recruitment to the lung parenchyma. Using recombinant virus, we demonstrate for the first time PVM infection of both dendritic cells (DCs; CD11c(+) major histocompatibility complex class II(+)) and alveolar macrophages (AMs; CD11c(+) sialic acid-binding immunoglobulin-like lectin F(+)) in vivo and likewise detect mKATE2(+) DCs in mediastinal lymph nodes from infected mice. AMs support both active virus replication and production of infectious virions. Furthermore, we report that priming of the respiratory tract with immunobiotic Lactobacillus plantarum, a regimen that results in protection against the lethal inflammatory sequelae of acute respiratory virus infection, resulted in differential recruitment of neutrophils, DCs, and lymphocytes to the lungs in response to rK2-PVM and a reduction from ∼ 40% to <10% mKATE2(+) AMs in association with a 2-log drop in the release of infectious virions. In contrast, AMs from L. plantarum-primed mice challenged with virus ex vivo exhibited no differential susceptibility to rK2-PVM. Although the mechanisms underlying Lactobacillus-mediated viral suppression remain to be fully elucidated, this study provides insight into the cellular basis of this response.

IMPORTANCE

Pneumonia virus of mice (PVM) is a natural mouse pathogen that serves as a model for severe human respiratory syncytial virus disease. We have developed a fully functional recombinant PVM strain with a fluorescent reporter protein (rK2-PVM) that permits us to track infection of target cells in vivo. With rK2-PVM, we demonstrate infection of leukocytes in the lung, notably, dendritic cells and alveolar macrophages. Alveolar macrophages undergo productive infection and release infectious virions. We have shown previously that administration of immunobiotic Lactobacillus directly to the respiratory mucosa protects mice from the lethal sequelae of PVM infection in association with profound suppression of the virus-induced inflammatory response. We show here that Lactobacillus administration also limits infection of leukocytes in vivo and results in diminished release of infectious virions from alveolar macrophages. This is the first study to provide insight into the cellular basis of the antiviral impact of immunobiotic L. plantarum.

Full-genome analysis of a canine pneumovirus causing acute respiratory disease in dogs, Italy

An outbreak of canine infectious respiratory disease (CIRD) associated to canine pneumovirus (CnPnV) infection is reported. The outbreak occurred in a shelter of the Apulia region and involved 37 out of 350 dogs that displayed cough and/or nasal discharge with no evidence of fever. The full-genomic characterisation showed that the causative agent (strain Bari/100-12) was closely related to CnPnVs that have been recently isolated in the USA, as well as to murine pneumovirus, which is responsible for respiratory disease in mice. The present study represents a useful contribution to the knowledge of the pathogenic potential of CnPnV and its association with CIRD in dogs. Further studies will elucidate the pathogenicity and epidemiology of this novel pneumovirus, thus addressing the eventual need for specific vaccines.

Genomic analysis of a pneumovirus isolated from dogs with acute respiratory disease

A previously unrecognized virus belonging to the subfamily Pneumovirinae and most closely related to murine pneumovirus (MPV) was identified in domestic dogs in 2 related animal shelters. Additional diagnostic testing yielded 3 new viral isolates and identified 6 additional PCR positive dogs from other USA locations indicating that its distribution is not geographically limited. Nucleotide sequences encompassing 9 of the 10 genes were compared to the only 2 available MPV strains, 15 and J3666. Several features distinguished the canine pneumovirus (CnPnV) from the murine strains. Two regions of diversity were identified in the amino-proximal region of P and the overlapping P2 ORF was only 54 amino acids (aa) compared to 137aa in MPV. The G protein had an amino-terminal cytoplasmic tail 18aa longer than in the MPV strains. The CnPnV SH protein showed the highest divergence with only 90.2% aa identity when compared to MPV strain 15. Like strain 15, the CnPnV SH ORF coded for a protein of 92aa while J3666 has a 114aa variant. Comparison of CnPnV isolates at culture passages 4 and 17 revealed 7nt differences within the 8598nt sequenced. Of note was a substitution at nt 364 in G resulting in a termination codon that would produce a truncated G protein of 122aa. Analysis of early passage and ex vivo samples showed the termination codon in G to be predominant after 6 days in culture indicating rapid selection of the mutation in A72 cells.

Pneumonia virus of mice: severe respiratory infection in a natural host

Pneumonia virus of mice (PVM; family Paramyxoviridae, genus Pneumovirus) is a natural mouse pathogen that is closely related to human and bovine respiratory syncytial viruses. Among the prominent features of this infection, robust replication of PVM takes place in bronchial epithelial cells in response to a minimal virus inoculum. Virus replication in situ results in local production of proinflammatory cytokines (MIP-1alpha, MIP-2, MCP-1 and IFNgamma) and granulocyte recruitment to the lung. If left unchecked, PVM infection and the ensuing inflammatory response ultimately lead to pulmonary edema, respiratory compromise and death. In this review, we consider the recent studies using the PVM model that have provided important insights into the role of the inflammatory response in the pathogenesis of severe respiratory virus infection. We also highlight several works that have elucidated acquired immune responses to this pathogen, including T cell responses and the development of humoral immunity. Finally, we consider several immunomodulatory strategies that have been used successfully to reduce morbidity and mortality when administered to PVM-infected, symptomatic mice, and thus hold promise as realistic therapeutic strategies for severe respiratory virus infections in human subjects.