In recent years, the number of individuals suffering from allergic diseases has been rising globally. Allergies are thought to be caused by a combination of genetic, lifestyle-related, and environmental factors. Both the activation of T-helper-2 (Th2) cell immune responses and the immune regulation of regulatory T cells (Tregs) have been implicated in the pathogenesis of allergic reactions.
An allergy is an excessive immune response to a specific environmental antigen that normally is tolerated by the general population; the term also has become synonymous with hypersensitivity. Th2 cells are thought to play a key role in the onset of allergic reactions, given that this class of cells produces the pro-inflammatory cytokines interleukin and induce the differentiation of B cells into plasma cells.
Therefore Tasuku Ogita, from Shinshu University, and his team theorised that oral administration of Flavonifractor plautii (FP) bacteria (found in the gut) may inhibit the Th2 immune response by incorporation into the mesenteric lymph nodes (MLNs) or by inducing changes in the gut microbiota. Thus, FP may be useful in alleviating antigen-induced Th2 immune responses.
FP is a strain of the Clostridia family of bacteria, which is known to have effects on the immune system, notably inhibiting inflammation. Some Clostridia strains show promise of lowering blood pressure and some are known to be abundant in lean people and not in heavier people, leading researchers to believe they can be used to regulate weight.
FP has been reported to be a part of the catechin metabolism in the intestines and catechin is an antioxidant found in a variety of foods including green tea, of which 30 to 42% of its dry weight is catechin.
Ogita, an expert on teas and their effects on gut bacteria, and his team, therefore looked into the influence of green tea.
OVA-sensitized mice were randomly allocated into three groups: OVA-non-sensitized mice (NT group), OVA-sensitized mice orally administered with phosphate-buffered saline (PBS group), and OVA-sensitized mice orally administered with FP (FP group).
Through multiple tests, the researchers measured how the population of different cells varied between the different groups post FP administration.
They concluded that drinking green tea increases the abundance of FP (Flavonifractor plautii) which suppresses the Th2 immune response.
The report states: "The collection of FP in MLNs may be involved in inhibition of the Th2 immune response. Our results demonstrated that FP mediates the inhibition of OVA-specific IgE production in a Th2-dominant environment.
"Given that allergy is closely associated with the production of antigen-specific IgE, FP may be useful in alleviating antigen-specific Th2 immune responses in a Th2-dominant environment.
"The results described here suggest that FP might be employed as a probiotic in the treatment of allergy. However, other work has suggested this organism as a possible causative agent of acute cholecystitis in a patient with a bloodstream infection. Clearly, further studies addressing the safety of FP will be needed before this bacterium can be employed as an anti-allergy probiotic."
Previous research
Several reports have shown that the gut microbiota of Clostridia cluster IV is capable of inhibiting inflammation. Li et al. reported that Clostridium leptum induces proliferation of Treg cells; Rossi et al. reported that Faecalibacterium prausnitzii (a member of the Ruminococcaceae family) strongly induces IL-10 production; and Wu et al. reported that decreases in the proportion of the Ruminococcaceae family induce IgE-associated eczema in infants.
It has previously been reported that Tregs are induced and Th2 responses are suppressed under conditions that lead to increases in the number of CD103+ DCs that are tolerant to the gram-positive bacteria Bifidobacterium and Lactobacillus (L.) rhamnosus GG as well as to the FP strain.
Inspired by Japanese heritage
Shinshu University is located in Nagano prefecture, known throughout Japan for having a variety of fermented food items with positive health outcomes. Nagano is unusual in that it does not have direct access to an ocean, so the food culture that has developed here has been unique. Due to its mountainous terrain, residents have had to survive long winters without access to the outside world, cultivating a rich food culture of natural preserves including miso and lacto-fermented pickles.
Nowadays, its residents have the best health and highest longevity in Japan, meaning it is likely a great contender for the area with some of the best health lifestyles in the world. Nagano manages to do this with some of the lowest costs for medical care for the elderly in Japan, meaning people live long but are also healthier longer. Researchers at Shinshu University continue to work to study unique foods indigenous to Nagano and Japan, and metabolic processes in the body scientifically to share this knowledge with others around the world with the hope that they too, can benefit from this culture.
The authors of the study suggest there is potential for the FP strains of bacteria to follow in the steps of lactic acid bacteria and bifidobacterium in being added to foods for their desired functionality but more studies are needed to look into the safety of FP before it can be used as an anti-allergy probiotic.
Source: Frontiers in Immunology
Shimosato. T., et al
"Oral Administration of Flavonifractor plautii Strongly Suppresses Th2 Immune Responses in Mice"