Interactions between lactobacilli and chicken macrophages induce antiviral responses against avian influenza virus

Macrophages are an important cell type of the innate immune system that upon activation, can exert antiviral functions and also can induce virus-specific adaptive immune responses. Macrophage interaction with certain probiotic bacteria such as lactobacilli can enhance antiviral functions of these cells. We have previously shown that administration of lactobacilli to chickens can effectively augment immune response to vaccine antigens. Here, we investigated the effects of representative strains of three Lactobacillus species, L. acidophilus, L. reuteri and L. salivarius used alone or in combination, in enhancing antiviral activity of chicken macrophages against avian influenza virus in an in vitro model using MQ-NCSU cells. Treatment of macrophages with probiotic lactobacilli significantly enhanced the antiviral functions, as determined by the virus titration assay. We also found that lactobacilli stimulation of macrophages induced significantly higher expression of interleukin (IL)-1β, interferon (IFN)- γ and IFN-α cytokine genes as well as interferon regulatory factor-7 (IRF7), 2',5'-oligoadenylate synthetase (OAS) and interferon-inducible transmembrane protein M3 (IFITM3) genes. Furthermore, macrophages that were treated with lactobacilli had significantly enhanced production of nitric oxide (NO) and IFN-γ protein as well as surface expression of the costimulatory molecule CD40. However, the antiviral and immunostimulatory effects of probiotic lactobacilli largely depended on the Lactobacillus species studied. Collectively, the results from our study using an in vitro model showed that certain Lactobacillus species can effectively augment antiviral responses in chicken macrophages.