The role of microbiota in the regulation of homeostasis in the human body during infection

Abstract

The review considers the regulatory capabilities of the human microbiota to preserve human health. The problem is not new, but it has expanded with the inclusion of new “findings” since the time of I.I. Mechnikov, a staunch supporter of the useful (protective) function of the normal flora.The study of the integration of human metabolism and microbes inhabiting human body revealed the participation of microbial metabolites — “signaling molecules” — in providing the homeostasis of the host. Particular attention is paid to the metabolic products aromatic amino acids as regulators of the physiological functions of humans and microbes. “Signal” molecules regulate the microbial “quorum”, the immune system (its cellular and humoral components). Opiates, hormonal peptides, in particular, natriuretic hormone, hypothalamic nonapeptides (oxytocin and vasopressin), which have both a direct antimicrobial and an indirect effect in the host's body, are not ignored. Researchers are also showing interest in the products of adipose tissue — “adipokines” (in particular, leptin), which turned out to be a multipurpose regulator showing a pro-inflammatory nature.The category of “signaling” molecules also includes cytokines that interact with gram-positive bacteria, which is actively discussed in the literature.In the evaluation of the material presented on various models of infections, a general pattern is observed: under the conditions of symbiosis, a “single regulatory environment” is formed, in which a variety of connections from immediate (direct) interactions are noted, i.e. the destruction of “signaling” molecules, induction of physiological functions due to the presence of similar receptors with ligands and, finally, modification of “signaling” molecules, i.e. expansion of the spectrum of action. The combination of this variety of integration mechanisms in this “single regulatory environment” (microorganism-host) probably leads to the formation of homeostasis, i.e. dynamic balance of the “signaling” systems of the microbiota and humans in the conditions of associative symbiosis, where an infection is its model system.This concept fits well our method of intermicrobial recognition of friend-foe in the dominant-associate pair and the described triangle: microbiota-hypothalamic-pituitary neurosecretion-oxytocin, organically constituting the gut-brain axis.