Human Intestinal Microbiome and the Immune System: The Role of Probiotics in Shaping an Immune System Unsusceptible to COVID-19 Infection

TLDR: Averina et al. as mentioned in this paper investigated the role of the HGM microbiome, the immunomodulatory potential of lactobacilli, as well as other probiotic bacteria, and COVID-19 infection together into a single systemic problem.

Abstract: The renaissance of interest in the bacteria inhabiting the human gastrointestinal tract (microbiota) manifested itself 10–15 years ago, after the fact of bidirectional gut–brain communication had been established (Rhee et al., 2009; Foster and Neufeld, 2013; Averina and Danilenko, 2017; Cryan et al., 2019). Along with the successful metagenomic sequencing of intestinal (fecal) samples, the obtainment of experimental data, and the simultaneous development of the techniques of bioinformatic data analysis, this interdisciplinary trend has become one of leading trends in the science of life (Klimina et al., 2020; Averina et al., 2020). Today, it is obvious that the gastrointestinal microbiota (the microbiome) communicates directly and indirectly with all human organs and systems, being one of the key integrating mechanisms for the maintenance of homeostasis (Belkaid and Harrison, 2017; Wang et al., 2017; Grosicki et al., 2018; Kastl et al., 2020). The effects of HGM bacteria, in particular, lactobacilli, on the functions of the immune system have been known since the time of discovery of this phenomenon by the academician I.I. Mechnikov (Marco et al., 2006), and they have been studied over the past 100 years. The genus Lactobacillus is an important HGM inhabitant that exerts a substantial effect on the function of the immune system (Galdeano and Perdigon, 2006; Abdo et al., 2019). Many lactobacillus strains belonging to more than 120 species have been used in probiotics and postbiotics (Shenderov, 2013; Marsova et al., 2020а, 2020b; Novik and Savich, 2020). The genomes of many thousands of Lactobacillus strains were sequenced, and the methods of transcriptomic, proteomic, and metabolomic analysis were used to detect the genes and their products responsible for interactions with the host organism, including the immune system (Zhang et al., 2018). Hence, it was possible to proceed from the era of probiotics to the development of pharmbiotics, drugs based on bacteria with the classical probiotic properties but with the identified active component(s), mechanisms of action, and an experimentally confirmed efficiency against particular nosological forms (Oleskin and Shenderov, 2019). There is an abundance of data indicating the role of microbiota in the development of various diseases (psychiatric, oncologic, autoimmune and infectious) (Blumberg and Powrie, 2012; Gilbert et al., 2016; Levy et al., 2017). Lactobacilli-based drugs are considered psychobiotics (Yunes et al., 2016a, 2016b, 2019; Cheng et al., 2019), probiotics exhibiting antioxidant potential (Marsova et al., 2018, 2020а, 2020b; Talib et al., 2019), and immunobiotics (Averina et al., 2015; Tada et al., 2016). The year of 2020 saw the COVID-19 pandemic caused by the SARS-CoV-2 coronavirus. The apparent role of the HGM in the maintenance of the immune system and the significant effect of the immune system of a particular person on the course of disease compel us to take a closer look at the neuromodulating, antioxidant, and immunomodulating potentials of the HGM. The specific properties of lactobacilli as potential immunomodulating agents for the prevention and treatment of COVID-19 require further analysis of this aspect. In the present review, we attempted to bring the HGM microbiome, the immunomodulatory potential of lactobacilli, as well as other probiotic bacteria, and COVID-19 infection together into a single systemic problem.