Probiotics and the Gut Immune System: Indirect Regulation

Abstract

The gastrointestinal tract (GIT) represents the largest interface between the human organism and the external environment. In the lumen and upper part of the mucus layer, this organ hosts an enormous number of microorganisms whose composition affects the functions of the epithelial barrier and the gut immune system. Consequentially, the microorganisms in the GIT influence the health status of the organism. Probiotics are living microorganisms which, in specific conditions, confer a health benefit to the host. Among others, probiotics have immunomodulatory properties that usually act directly by (a) increasing the activity of macrophages or natural killer cells, (b) modulating the secretion of immunoglobulins or cytokines, or indirectly by (c) enhancing the gut epithelial barrier, (d) altering the mucus secretion, and (e) competitive exclusion of other (pathogenic) bacteria. This review focuses on specific bacteria strains with indirect immunomodulatory properties. Particularly, we describe here the mechanisms through which specific probiotics enhance the gut epithelial barrier and modulate mucus production. Moreover, we describe the antimicrobial properties of specific bacteria strains. Recent data suggest that multiple pathologies are associated with an unbalanced gut microflora (dysbiosis). Although the cause-effect relationship between pathology and gut microflora is not yet well established, consumption of specific probiotics may represent a powerful tool to re-establish gut homeostasis and promote gut health.

Ulcerative colitis: understanding its cellular pathology could provide insights into novel therapies

“…Probiotics act as a barrier, as they line the intestinal tract and through competitive inhibition, prevent other luminal bacteria from reaching the lamina propria and stimulating the mucosal immune system [62]. Probiotics also enhance mucus production which protects against invasive bacteria, induce protective cytokines and suppress pro-inflammatory cytokines and can modulate the immune system in the gut [63,64]. In addition, faecal microbiota transplantation (FMT), the transfer of stool from a healthy donor to a UC patient is emerging as a promising approach to alleviating UC severity.…”

Probiotics as alternatives to antibiotics in treating post-weaning diarrhoea in pigs: Review paper

“…In addition, the GIT lumen and the upper part of its mucous layer harbour a large population of microorganisms whose composition affects the epithelial barrier and immune system functionality. Probiotic bacteria modulate the immune system directly through adjusting the secretion of immunoglobulins or cytokines, increasing the activity of macrophages or natural killer cells, or through indirect mechanisms such as enhancing the gut epithelial barrier, and altering the mucus secretion or through competitive exclusion of other pathogenic bacteria (La Fata et al, 2017). Immunoglobulins A and G are among those whose production and circulation can be stimulated by probiotic bacteria (Vondruskova et al, 2010;Bajaj et al, 2015).…”

Dietary Fatty Acids and Microbiota-Brain Communication in Neuropsychiatric Diseases

“…The notion that the alterations of microbiota ecosystem may negatively affect brain physiology has been suggested by the observation that chronic antibiotic treatment is associated with an increased risk of psychiatric illness [24]. Moreover, the link between microbiota alteration and brain disease is corroborated by the comorbidity between psychiatric disorders and several GI disease such as irritable bowel syndrome (IBS) and enteropathies as well as by the efficacy of specific classes of probiotics (i.e., psychobiotics) on stress-induced GI symptoms, anxiety and depression [25][26][27]. Even more unexpected, is the demonstration that the pathophysiology of GI disorders or systemic inflammation can be spread between organisms by transferring the microbiota either from patients or pathological animal models to germ-free (GF) mice [28,29].…”

“…If the depletion of commensal microbiota increases the risk of maladaptive behaviors and can be fully reverted only within the maturational period, the strong influence of microbiota on neuron plasticity and circuitry wiring during the neurodevelopment may also increase the susceptibility to stress-induced psychiatric disorders. In any case, during development [37] and adulthood, probiotics supplementation may mitigate social stress-induced cognitive, behavioral (e.g., anxiety, depression) and immune alterations [27,38,39]. From this view, prototypical appears one animal study in which stress-induced hyperthermia, increase of corticosterone levels, anxiety-and depression-like behaviors were reduced by the chronic treatment with Lactobacillus rhamnosus (JB-1) probiotic [14,34].…”