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Review
. 2015 Nov 18:6:1285.
doi: 10.3389/fmicb.2015.01285. eCollection 2015.

Molecular Players Involved in the Interaction Between Beneficial Bacteria and the Immune System

Arancha Hevia  1 , Susana Delgado  1 , Borja Sánchez  1 , Abelardo Margolles  1
Affiliations
Review

Molecular Players Involved in the Interaction Between Beneficial Bacteria and the Immune System

Arancha Hevia et al. Front Microbiol. .

Abstract

The human gastrointestinal tract is a very complex ecosystem, in which there is a continuous interaction between nutrients, host cells, and microorganisms. The gut microbiota comprises trillions of microbes that have been selected during evolution on the basis of their functionality and capacity to survive in, and adapt to, the intestinal environment. Host bacteria and our immune system constantly sense and react to one another. In this regard, commensal microbes contribute to gut homeostasis, whereas the necessary responses are triggered against enteropathogens. Some representatives of our gut microbiota have beneficial effects on human health. Some of the most important roles of these microbes are to help to maintain the integrity of the mucosal barrier, to provide nutrients such as vitamins, or to protect against pathogens. In addition, the interaction between commensal microbiota and the mucosal immune system is crucial for proper immune function. This process is mainly performed via the pattern recognition receptors of epithelial cells, such as Toll-like or Nod-like receptors, which are able to recognize the molecular effectors that are produced by intestinal microbes. These effectors mediate processes that can ameliorate certain inflammatory gut disorders, discriminate between beneficial and pathogenic bacteria, or increase the number of immune cells or their pattern recognition receptors (PRRs). This review intends to summarize the molecular players produced by probiotic bacteria, notably Lactobacillus and Bifidobacterium strains, but also other very promising potential probiotics, which affect the human immune system.

Keywords: Bifidobacterium; Lactobacillus; immunomodulation; molecular players; probiotic.

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Figures

Figure 1
Figure 1
Schematic representation of the interactions established between the intestinal microbiota and the host immune system. (A) General overview of the epithelium in contact with multiple species of microorganisms that constitute the intestinal microbiota: (1) enterocytes; (2) M cells; (3) Goblet cells; antigen presentation cells (APC): (4) dendritic cells and (5) macrophages; (6) defensins, bacteriocins, and secreted IgA (sIgA) also play an important role in controlling the levels of the different populations of microorganisms. A fine-tuned balance of Tcell maturation toward Treg or Thelper cells must be established to assure the tolerogenic response of the host immune system. (B) Examples of molecular interactions between microbial antigens and host cells through Pattern Recognition Receptors (PRRs). LPS, lipopolysaccharide; PGN, peptidoglycan; dsRNA, double-strand RNA; TLR, toll-like receptor; NODLR, nucleotide-binding oligomerization domain-like receptors; RIG-like helicases, retinoic acid-inducible gene 1 like helicases.
Figure 2
Figure 2
Main molecular effectors that are able to trigger immunomodulatory responses in the host: Bifidobacterium (A) and Lactobacillus (B). Some of these effectors are species-specific, such as the S-layer protein A from Lactobacillus acidophilus, whereas others, such as short chain fatty acids, are secreted by the vast majority of strains. Detailed information about the mechanisms and the molecular effectors is included in Section Immunomodulatory Effectors.
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