RESEARCH ARTICLE Oral Administration of Lactococcus lactis Subsp. lactis JCM5805 Enhances Lung Immune Response Resulting in Protection fromMurine Parainfluenza Virus Infection

When activated by viral infection, plasmacytoid dendritic cells (pDCs) play a primary role in the immune response through secretion of IFN-α. Lactococcus lactis subsp. lactis JCM5805 (JCM5805) is a strain of lactic acid bacteria (LAB) that activates murine and human pDCs to express type I and type III interferons (IFNs). JCM5805 has also been shown to activate pDCs via a Toll-like receptor 9 (TLR9) dependent pathway. In this study, we investigated the anti-viral effects of oral administration of JCM5805 using a mouse model of murine parainfluenza virus (mPIV1) infection. JCM5805-fed mice showed a drastic improvement in survival rate, prevention of weight loss, and reduction in lung histopathology scores compared to control mice. We further examined the mechanism of anti-viral effects elicited by JCM5805 administration using naive mice. Microscopic observations showed that JCM5805 was incorporated into CD11c+ immune cells in Peyer’s patches (PP) and PP pDCs were significantly activated and the expression levels of IFNs were significantly in-creased. Interestingly, nevertheless resident pDCs at lung were not activated and expres-sions levels of IFNs at whole lung tissue were not influenced, the expressions of anti-vira