The Influence of Probiotics on Animal Immunity

Mechanism of Probiotic Actions on Immunity

Probiotics are well-known in enhancing immune responses and warding off enteric pathogens in both human and animal hosts. The gut, performing a myriad of functions, not only offers a site for nutrient absorption but also restricts the invasion of pathogens and antigens. One of the crucial roles played by the gut involves the regulation of the barrier function of epithelial cells and binding protein complexes within the immune system. Various probiotics possess cell walls, such as yeasts' cell wall polysaccharides like mannose oligosaccharides and β-glucans, in addition to probiotic peptide polysaccharides. It has been observed that probiotics manipulate innate and adaptive immunity by producing metabolites, their cell wall components, and DNA through the gut.

The interactivity of probiotics and the immune system is attributed to probiotics' ability to interact directly with the recognition receptors of gut epithelial cells or immune cells. This interaction of probiotics with epithelial cells or cells-released soluble factors can trigger a cascade of signals in the immune cells. Probiotics interact with the cell and antibody-mediated immune systems, leading to reduced pro-inflammatory cytokines production. They maintain the integrity of the epithelial barrier by reducing cell apoptosis and strengthening dendritic cells and T cells' connection, as well as strengthening the connections between T cells and lymph nodes with potent Toll-like receptor signals. This eventually enhances the host's immunity.

Verification of Probiotics on Animal Immunity

Several in vivo studies on animals substantiate the above deductions. Evidence suggests an increase in the IgG and γ interferon levels in the blood of calves upon adding Bacillus subtilis natto. In addition, Saccharomyces cerevisiae and its metabolites have been found to upregulate the expression of immunity-related genes; these gene expressions are associated with the recognition of pathogen-associated molecular patterns, T cell differentiation, and other molecule patterns like CASP1. Amyloid sporangium has been proven to increase the levels of IL-10 in the small intestines of piglets but decreases the levels of TNF α. Additionally, it has been reported that adding Lactobacillus plantarum B2984 to piglets' diets can enhance their serum antibody response to Salmonella typhimurium infection. Also, adding Bacillus subtilis-based probiotics to poultry's diet stimulates its immune system and improves its antioxidant status. Furthermore, Bacillus subtilis has been reported to enhance the macrophage functionality in broilers- the production and phagocytic role of nitric oxide. The immunomodulatory and performance efficacy of yeast cultures in broilers is also confirmed.

Fig.1 Probiotics in Poultry's Diet

It has been reported that dietary probiotics have the potential to increase the numbers of IgA antibody-producing cells or improve the serum antibody concentration. This enhancement can be attributed to the immunomodulatory activity of probiotics on gut-related immunity. The gut mucosal innate immune systems generate antimicrobial peptides, such as β-defensins, which directly kill a wide range of gut pathogens. These peptides can further boost antibody-mediated or cell-mediated immune responses. For instance, the expression of different cytokines in T cells. However, not all probiotic strains appear to be universally applicable in enhancing immunity. Some studies indicate that probiotic supplements do not necessarily affect immune responses, possibly due to the absence of immunomodulatory factors among the probiotic strains.

Probiotics have shown considerable promise in enhancing animal immunity. Further investigation in this area is warranted, to draw a detailed understanding of the complex relationship between probiotics and immune responses.

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