Role of the Choline‐Binding Protein A in the Ability of Porcine Ligilactobacillus salivarius FFIG58 to Modulate TLR3‐Mediated Intestinal Antiviral Immunity

The choline‐binding protein A (CbpA) was shown to mediate adhesion of probiotic Ligilactobacillus salivarius strains to the human intestinal mucosa, but studies of this protein in porcine strains were not performed before. Previously, we demonstrated that the pig‐derived L. salivarius FFIG58 beneficially modulates the Toll‐like receptor (TLR)‐3‐triggered immune responses in porcine intestinal epithelial cells (IECs) and in the gut of mice, improving antiviral immunity and reducing the intestinal inflammatory damage. In this work, we advanced in the characterization of the immunomodulatory properties of L. salivarius FFIG58 by developing a surface‐layer protein CbpA mutant (Δ cbpA ). Both wild‐type and Δ cbpA strains were evaluated in terms of their interactions with porcine IECs and macrophages in the context of TLR3‐mediated inflammation. Additionally, the immunomodulatory activities of FFIG58 and Δ cbpA strains were assessed in vivo using infant mice as a young host model considering the potential application of this bacterium to improve the resistance to postweaning viral diarrhea in piglets. The deletion of the CbpA protein reduced the ability of FFIG58 to modulate the expression of interferons (IFNs), antiviral factors, regulatory cytokines and negative regulators of the TLR signaling as well as IFN regulatory factor 3 (IRF3) and ERK activation in porcine IECs and macrophages. The Δ cbpA mutant had a diminished capacity to protect porcine IECs against rotavirus challenge compared to the FFIG58. The ability of L. salivarius FFIG58 to differentially regulate antiviral and inflammatory factors expressions, the numbers of CD8aa + NKG2D + intraepithelial lymphocytes and the TLR3‐IL‐15‐mediated damage in the intestinal mucosa of mice was also altered with the deletion of CbpA . These results allow us to conclude that the CbpA protein is a key molecule for the beneficial functions of the L. salivarius species in the immune system of distinct hosts, and particularly for L. salivarius FFIG58 in pigs. This is a step forward in the understanding of the cellular mechanisms involved in the antiviral capabilities of L. salivarius FFIG58.