Article Sharing | Interactions Between the Porcine Host and Gut Microbiota — The impact of gut microbiota on the host immune system Ⅱ

Interactions Between the Porcine Host and Gut Microbiota — The impact of gut microbiota on the host immune system Ⅱ

It is well established that commensal gut microbiota activate systemic immunity following colonization in neonatal mammals. This process is primarily mediated through an increase in the levels of specific antimicrobial antibodies in the host’s circulatory system. Because feed consumed by animals contains intact antimicrobial molecules that retain activity even after irradiation or high-pressure sterilization, the generation of allergen-free pigs remains challenging.

In addition, compared with conventional animals possessing fully developed Peyer’s patches, the development of the mucosal immune system in germ-free animals is severely limited. Germ-free animals lack regulatory T cells, exhibit low expression levels of heat shock proteins (HSPs), and show reduced populations of intraepithelial T lymphocytes in the gastrointestinal tract (GIT), which play a critical role in host defense. In germ-free pigs, T lymphocyte populations in the jejunum and ileum are only approximately 35% of those observed in conventional pigs.

When the balance between host immunity and the microbiota is disrupted, dysbiosis occurs, which is a key factor in the pathogenesis of diseases such as diarrhea and classical swine fever. However, when germ-free pigs are colonized with a limited and defined microbiota, the development of most functional components of the immune system—including antigen-presenting cells (APCs), T cells, and B cells—resembles that of conventional pigs.

Furthermore, different strains of lactic acid bacteria exhibit distinct capacities to modulate host immune signaling pathways. The presence of various Lactobacillus species enhances interactions between these microorganisms and host immune cells. Communication between the microbiota and intestinal cells is essential for the proper development and function of the immune system.

In weaned piglets challenged with enterotoxigenic Escherichia coli (K88ac), the probiotic Lactobacillus fermentum was shown to promote T cell differentiation, increase pro-inflammatory cytokine production, and elevate the proportion of CD4⁺ lymphocytes in the ileum. Several studies have demonstrated the effects of different Lactobacillus species and strains on the intestinal microbiota, as well as their beneficial activities following challenges with ETEC, Salmonella, or rotavirus. These include Lactobacillus plantarum, Lactobacillus amylovorus DSM 16698, and Lactobacillus rhamnosus GG.

In porcine intestinal explant models, Lactobacillus amylovorus DSM 16698 was shown to counteract ETEC-induced increases in TLR4, phosphorylated IKKα (P-IKKα), phosphorylated IκBα (P-IκBα), and phosphorylated p65 (P-p65). At the same time, this strain upregulated the expression of TLR4 regulatory factors, including Toll-interacting protein (Tollip) and interleukin-1 receptor-associated kinase M (IRAK-M).