Priming of the Respiratory Tract with ImmunobioticLactobacillus plantarumLimits Infection of Alveolar Macrophages with Recombinant Pneumonia Virus of Mice (rK2-PVM)
Authors: Dyer Kimberly D. , Drummond Rebecca A. , Rice Tyler A. , Percopo Caroline M. , Brenner Todd A. , Barisas Derek A. G. , Karpe Kendal A. , Moore Martin L. , Rosenberg Helene F. 
Published: November 2015

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 infectionin 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 vivoand 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 immunobioticLactobacillus 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 fromL. plantarum-primed mice challenged with virusex vivoexhibited no differential susceptibility to rK2-PVM. Although the mechanisms underlyingLactobacillus-mediated viral suppression remain to be fully elucidated, this study provides insight into the cellular basis of this response.

IMPORTANCEPneumonia 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 cellsin 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 immunobioticLactobacillusdirectly 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 thatLactobacillusadministration also limits infection of leukocytesin vivoand 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 immunobioticL. plantarum.