Probiotics and Immune Function

Probiotics and Immune Function

By Emerson Ecologics

Probiotics interact with immune cells in the GI tract to support a healthy immune response at the gut level and throughout the body.

CONTEXT

The gastrointestinal tract is an essential site of separation between the outside and inside of the body. Immune cells at the interface of the intestinal lining continually encounter food particles, commensal bacteria, and other microorganisms.

Probiotics support these efforts via several overarching mechanisms. Probiotics compete with nutrients to crowd out non-beneficial bacteria. Probiotics also interact with immune cells to support a healthy immune response at the gut level and throughout the body.

OBJECTIVE AND STUDY DESIGN

Probiotics and immune function is the focus of this research review. 

The review article summarizes the molecular mechanisms of how probiotics interact with the gut-associated immune cells to help confer systemic health benefits.

KEY FINDINGS

Probiotics are live microorganisms consumed in foods or supplements that confer health benefits to their host. The most common probiotics are lactic acid bacteria (e.g., Lactobacilli, Streptococci, Pediococcus, Enterococcus, Bifidobacteria) and some yeast (e.g., Saccharomyces boulardii).

Our current understanding of how probiotics interact with the immune system comes mostly from studies conducted in cell cultures or animals. These studies have shown that probiotics interact with immune cells at several layers of the gastrointestinal tract: the intestinal barrier (where they interact with epithelial cells and Goblet cells), the intestinal crypts (where they interact with Paneth cells), and the lamina propria (where they interact with macrophages, dendritic cells, T cells, and antibodies).

At the level of the intestinal barrier, probiotics adhere to intestinal epithelial cells (IECs) via toll-like receptors (TLRs). Supplementation with probiotics has been shown to support tight-junction signaling and support mucus production from goblet cells. These mechanisms are evidence that probiotics help support healthy intestinal barrier and mucosal function. 

Also at the level of the intestinal barrier, fragments of probiotics are internalized by IECs, and then interact with the macrophages and dendritic cells of the lamina propria. Studies show that probiotic supplementation may affect the expression of TLR-2 and mannose on the surface of macrophages and dendritic cells, which is considered evidence that probiotics help support the innate immune response.

At the level of the intestinal crypts, probiotics have been shown to help influence the number of Paneth cells.

At the level of the lamina propria, probiotics may not only interact with macrophages and dendritic cells, they may also help influence the activity of T cells, cytokines, and antibodies. Probiotics favors the production of interleukin-10 (IL-10) and interferon-gamma, which support a healthy inflammatory response. Probiotics also favor the production of immunoglobulin G (IgG) over IgE. And probiotics may influence secretory IgA. 

The interactions between probiotics and immune function are not restricted to the gastrointestinal tract. Studies have shown that probiotics may also increase IgA in the bronchi and mammary glands, and may also increase macrophage activity in other organs of the body.

CLINICAL RELEVANCE

The mechanisms described in this research review suggest that probiotics support healthy intestinal-barrier function and gut-associated immune response. The benefits of probiotics also appear to extend beyond the walls of the gut to help support immune function in the bronchi, mammary glands, urogenital tract, and other organs of the body.

The evidence for the role of probiotics in supporting gastrointestinal and immune function is persuasive. Also, studies have found that probiotics support healthy lipid metabolism, blood-sugar metabolism, weight management, and a healthy inflammatory response.

Researchers suggest that an appropriate daily intake of probiotics ranges from 108 to 109 colony-forming units (CFUs) per day. Given that probiotics do not alter intestinal homeostasis, probiotics are generally considered safe to consume for long periods without adverse effects.

REFERENCE

Maldonado Galdeano C, Cazorla SI, Lemme Dumit JM, Vélez E, and Perdigón G. “Beneficial Effects of Probiotic Consumption on the Immune System.” Ann Nutr Metab 74, no. 2 (2019): 115–24.

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