Lactococcus lactis JCM5805 activates anti-viral immunity and reduces symptoms of common cold and influenza in healthy adults in a randomized controlled trial

• This study was a randomized, double-blind controlled trial in 396 healthy subjects.
• Heat-killed JCM5805 mitigated the incidence of common cold and influenza symptoms.
• Heat-killed JCM5805 upregulated the expression levels of anti-viral genes.
• Heat-killed JCM5805 upregulated the cell surface expression of HLA-DR on pDCs.

The effects of heat-killed Lactococcus lactis JCM5805 (JCM5805) on the pathogenesis of common cold and influenza were evaluated. A randomized, placebo-controlled, double-blinded study was conducted and 396 healthy subjects (placebo group n = 205, JCM5805 group n = 191) completed the intervention. Subjects consumed placebo capsules or JCM5805 capsules containing approximately 100 billion cells of heat-killed JCM5805 per day for 12 wk. Significantly fewer incident days were observed in the JCM5805 group than in the placebo group for the symptoms of sore throat (p < 0.05) and cough (p < 0.001). Cell surface expression of HLA-DR on plasmacytoid dendritic cells (pDC) and the expression of VIPERIN in peripheral blood mononuclear cells (PBMCs) were higher post-intervention compared to baseline in the JCM5805 group only (p < 0.05). The expression of IFNA in PBMCs was significantly higher in the JCM5805 group (p < 0.05). These data suggest that the intake of heat-killed JCM5805 stimulated pDC-related anti-viral immunity to mitigate the incidence of common cold and influenza symptoms.