With news that a COVID-19 is not expected for around a year, peoples are looking at building up their body defences by strengthening immune system. COVID-19 is absolutely new for our immune system. Before the recent outbreaks, no one is known to be exposed to it. Therefore, our immune systems are immature to the virus and not capable to develop immunity against it. This is one of the important reasons why this virus is spreading speedily through the populations. At the moment there is no specific treatment for COVID-19. Treatment is essentially focused on supportive care, on condition of oxygen, fluids and respiratory support for severely sick people.

Since, there is no any vaccine and specific effective clinically established treatment, preventing COVID-19 by maintaining high hygiene by washing our hands, avoiding contact with infected people and reinforcing our immune system are the best strategies. The contributions of the gut microbiota to the development of the immune system have been extensively characterized. The gut immune system is influenced by many factors, including dietary components and commensal bacteria. Probiotic bacteria can interact with our gut microbiome to reinforce our immune system, increase immune response system and promote specific immune signalling with several physiolocal and clinical importance (Yan and Pok, 2011). Nutrients that affect gut immunity and strategies that re-establish a healthy gut microbial community is novel therapeutic approaches to treat several inflammatory diseases.

The gut associated lymphoid tissue is the major component in the body and huge amounts of antigens pass everyday through the gut, make the gut mucosa the key site of lymphocyte contact with antigens in the complete body. In addition, approximately 100 trillion bacteria are associated with our gastrointestinal tract. Presence of rich gut microbial community are called microbiota. The contributions of the gut microbiota to the development of the immune system has been broadly characterized.

Gut microbiota and the immune system work in coordinated manner, allowing the host to tolerate the large amount of antigens present in the gut. The latest evidence shows that the gut microbial composition is also associated with malnourishment. The composition of the gut microbiota varies during childhood, until the individual reaches adulthood. Differences in composition of microbiota are associated to colonization; host factors, such as sex and age; genetic factors; and health status. The microbiota is essential to prevent the attachment, growth, and penetration of pathogenic microorganisms on the gut surface. The intestinal microbiota plays an important role in pathogen resistance, both by direct interaction with pathogenic bacteria and also by influencing the immune system (Kamada et al., 2013).

The presence and suitable level of gut microbiota are crucial for the improvement of the immune system. Certain commensal bacteria appear to preferentially drive regulatory T- lymphocyte development, whereas other bacteria promote it development in the gut. Thus, the regular use of probiotics and prebiotics has been anticipated to intentionally modulate the microbiota composition.The gut microbiota is the most important source of microbial stimulation and therefore plays an important role in postnatal immune maturation and development. The microflora is involved in maintaining a primed mucosal immune system, which can distinguish between pathogens and commensal organisms. Within the gut there are many complex interactions occurring, and a balance is required between appropriate immuno-surveillance and hyper sensitivity. Our gut is rich in beneficial bacteria that live in ideal hormony, helping us to digest food and eliminate toxins .These bacteria produces many biologically active molecules which educate our immune system to protect us from many dangerous microbes (Qin et al., 2010). The intestinal mucosa is the main site of interaction with the external environment and therefore play an important role in maintaining good health (Wieërs et al, 2020).

In this perspective, the increased use of prebiotic food ingredients and probiotics has become a major area of importance and seems to be a promising nutritional tool to modulate the immune system in different populations. These specific ingredients are integrated into several functional foods and may improve the functions of immune system and gut physiology. Mechanisms contributing to altered in vivo immune function induced by functional foods may include modulation of the microflora itself, improved barrier function and direct effects of bacteria on different epithelial and immune cell types (B cells, T cells, monocytes/ macrophages and NK cells) (Ng et al., 2009). In any case, despite the positive clinical effects on the prevention and treatment of several immune-related diseases, the mechanisms of this type of functional foods are still not completely understood (Marschan et al., 2008) .The colonization of the human intestine begins at birth and the composition of the intestinal microbiota is influenced by diet composition.

Probiotics represent a sizable aspect of the functional food market, which seems to be increasingly well-liked with consumers looking for non prescription alternatives which can prevent a range of disorders. Probiotics are marketed to health conscious product to prevent gut dysfunction and reinforce their innate defence mechanisms. The uses of probiotic food products are become increasingly widespread. Probiotics are traditionally found in many fermented foods, however, due to the recent commercial success manufacturers mainly involve in expanding their product ranges into new food such as cheese, ice cream, and chocolate in addition to yogurt (fig.1). Food with probiotic bacteria can interact with our gut microbiome to strengthen our immune system, increase immune response system and promote specific immune signalling with several physiolocal and clinical importance (Yan and Pok, 2011).

One mechanism to increase the number of beneficial bacteria in the gut is through the ingestion of prebiotics. Prebiotics are food ingredients which are mainly composed of oligosaccharide that are not digestible by the host and have several beneficial effects on host health during selective stimulation of the growth and activity of gut microbiota. Any food that contains carbohydrates and in particular oligosaccharides work as potential prebiotic. The prebiotic ingredients must fulfil the following criteria: It should neither be hydrolyzed nor absorbed in the upper part of the gastrointestinal tract.Prebiotics should be selectively fermented by limited number of potentially beneficial bacteria in the colon, for example, bifidobacteria and lactobacilli, which are encouraged to grow for human health.

Currently, only inulin and galacto- oligosaccharides, present in many natural food as ingredients do all of the criteria for prebiotic classification. Fiber carbohydrates i.e cellulose, pectin, gums, beta- glucan, and lignin are not digested in the upper gastrointestinal tract due to absence relevant enzymes and unable to degrade these carbohydrates (Gibson et al,.2004).However, these substances are attention to be selectively ferment by inhabited bacteria into SCFAs, and particularly acetate, propionate, butyrate, and lactate, once in the colon. Diet alone has the strongest and most direct effects on gut microbial colonization because bacteria have different preferences for energy sources. Thus, diet is closely related to the species present in the gut microbiota. Dietary fibbers can utilized as effective prebiotics for maintaining gut microbial composition which directly affecting the mucosal immune system, resulting in systemic immune response. Prebiotics can also provide resistance to colonization of pathogenic bacteria by inhibiting the adherence of pathogens to the gut epithelium (Gibson and Roberfroid 1995). The mechanisms of action of prebiotic-induced alterations are not yet known. Substantial experimental data suggest that prebiotics immunological effects by several ways as mention in table 1.

Table.1. Potential Mechanisms of Prebiotic-Induced Immune Alterations

During last few decades,  probiotics were found effective in preventing and decreasing the duration of either bacterial colony or their function (Gabryszewski et al., 2011). Although in some cases the pattern are common but not all the probiotics show similar mechanism of action. Probiotics and prebiotics have been shown to be effective in elevating immunogenicity by influencing seroconversion and seroprotection rates in adults inoculated with influenza virus (Lei et ., 2017). Currently there is no any scientific justification of using prebiotic and probiotic the COVID-19 prevention. Apart from prebiotic and probiotics  a study reported stretching exercises for 90 minutes enhances the ability of immune system to fight against infection. This study explained the stretching exercises of yoga caused increase in expression of salivary human β-defensin 2 (HBD-2), which disrupts hydrophobic core of lipid bilayers of microbes causing enhancement of body immune system to fight against infections (Eda N et al 2013).

 Another study supported the positive effect of yogic breathing practices in increasing Nk cells of immune system. The increment in concentration of Nk cells can relieve viral infections, and cancer generated cytotoxic stress. This process also leads to the regulation of cytokines which results in regulation of immune system, cell differentiation and cell growth during cancer (Kochupillai V, 2005). Specific positions of Yoga are recommended for the initiation and regulation of repairing mechanism in the body.

We strongly support that any food ingredients which building up our body defences by support the immune system is important. Prebiotic and probiotic in combination to Yoga gives synergistic effects. Combining healthy and balanced food ingredients together with prebiotics and probiotics could help us to reinforce our immune system during COVID-19 outbreak.

Reference;

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Gabryszewski SJ, Bachar O, Dyer KD, et al. Lactobacillus-mediated priming of the respiratory mucosa protects against lethal pneumovirus infection. J Im- munol (2011); 186:1151 – 1161.

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Gibson G R, Roberfroid M B.Dietary modulation of the human colonic micro- biota: introducing the concept of prebiotics. J Nutr (1995) 125:1401-12.

Kamada N,Chen G Y,InoharaN,Nunez G. Control of pathogens by the gut microbiota. Nat Immunol (2013) 14:685–90.doi:10.1038/ni. 2608ni.2608.

Marschan E, Kuitunenw M, Kukkonenw K, Poussaz T, Sarnesto A, Haahtelaw V, Korpela R, Savilahti E, Vaarala O. Probiotics in infancy induce protective immune profiles that are characteristic for chronic low-grade inflammation. Clin Exp Allergy (2008) 38: 611-18.

 Ng SC, Hart AL, Kamm MA, Stagg AJ, Knight SC. Mechanisms of action of  probiotics: recent advances. Inflamm Bowel Dis (2009) 15 (2): 300-10.

Qin J, Li R, Raes J, Arumugam M, Burgdorf KS, Manichanh C et al. A human gut microbial gene catalogue established by metagenomic sequencing. Nature (2010).  464: 59-65.

Yan F, Polk DB. Probiotics and immune health. Curr Opin Gastroenterol. (2011) Oct; 27(6):496-501. doi: 10.1097/MOG.0b013e32834baa4d.

Wieërs G, Belkhir L, Enaud R, Leclercq S, Philippart de Foy JM, Dequenne I, de Timary P, Cani PD. How Probiotics Affect the Microbiota. Front Cell Infect Microbiol. (2020) Jan 15; 9:454. doi: 10.3389/fcimb.2019.00454.

Kochupillai V. Effect of Rhythmic Breathing (Sudarshan Kriya and Pranayam) on Immune Functions and Tobacco Addiction. Annals of the New York Academy of Sciences. (2005); 10, 56(1):242-252