Effect of Probiotic Bifidobacterium lactis Bl-04 on Innate Antiviral Responses in vitro

Consumption of certain probiotic strains may be beneficial for reducing the risk of acute upper respiratory tract infections (URTIs), however, underlying immunological mechanisms are elusive. Bifidobacterium lactis Bl-04 has been reported in humans to significantly reduce the risk of URTIs, affect the innate immunity in the nasal mucosa, and reduce nasal lavage virus titer after a rhinovirus (RV) challenge. To study the immunological mechanisms, we investigated the effect of Bl-04 on cytokine production and transcriptomes of human monocyte-derived macrophages and dendritic cells, and further on RV replication and cytokine production in MRC-5 fibroblasts. The results showed that Bl-04 modulates antiviral immune responses and potentiates cytokine production during viral challenge mimic in immune cells. In fibroblasts, Bl-04 inhibited rhinovirus replication and modulated fibroblast cytokine production. Overall, the findings suggest that Bl-04 mildly stimulates antiviral immunity that may be the immunomodulatory mechanisms behind reduced URTIs and viral replication observed in clinical studies.