Immunomodulatory and prophylactic effects of Bifidobacterium bifidum probiotic strain on influenza infection in mice

The limited efficacy of available influenza vaccines against rapidly emerging new viral strains stresses the need for the development of new antigen-independent prophylactic treatment for enhancing immunity against influenza infection. Recent studies suggest that probiotics possess immunomodulatory properties and can reduce the severity of respiratory infections. Here, we investigated the potential of prophylactic Bifidobacterium bifidum in improving anti-influenza immune responses in an experimental lethal mouse-adapted influenza A (H1N1) infection in a BALB/c mouse model. One week after viral challenge, splenocyte proliferation assay (MTT), IFN-gamma, IL-12, and IL-4 in spleen and IL-6 in the lung homogenates were conducted using ELISA assays. Sera samples were collected to measure IgG1 and IgG2a levels. Furthermore, the mice challenged with lethal influenza virus were assessed for survival rate. The findings demonstrated a strong induction of both humoral and cellular immunities, as well as decreased level of IL-6 production in the lung and an increase in survival rate in the mice receiving Bifidobacterium than those of the control group were observed. Taken together, the results indicate a robust potential for Bifidobacterium to modulate humoral and cellular immune responses and induce balanced Th1/Th2 immune responses against influenza infection.