The possible mechanisms of the human microbiome in allergic diseases

Abstract

In the present paper, we discuss the importance of the microbiome in allergic disease. In this review paper, the data from the Medline (PubMed) and search engine of Kirikkale University were systematically searched for all relevant articles in June 15th, 2015 for the past 30 years. The keywords of "microbiome", "dysbiosis", "allergy", "allergic rhinitis", "allergic disease", "mechanisms" and "treatment" were used alone or together. In this paper, microbiomes were presented in terms of "Definition", "Influence of \the human microbiome on health", "The microbiome and allergic diseases", and "Modulation of the gut microbiota in terms of treatment and prevention". Microbiological dysbiosis is also reviewed. The microbiome is the genetic material of all microbes (bacteria, fungi, protozoa, and viruses) that live on or in the human body. Microbes outnumber human cells in a 10:1 ratio. Most microbes live in the gut, particularly the large intestine. Changes in the immune function of the respiratory tract are (at least in theory) linked to the immunomodulatory activity of the gut microbiota via the concept of a "common mucosal response". The gut microbiota shapes systemic immunity, thus affecting the lung mucosa. Alternatively, changes in the gut microbiota may reflect alterations in the oropharyngeal microbiota, which may in turn directly affect the lung microbiota and host immune responses via microaspiration. Dysbiosis is defined as qualitative and quantitative changes in the intestinal flora; and modern diet and lifestyle, antibiotics, psychological and physical stress result in alterations in bacterial metabolism, as well as the overgrowth of potentially pathogenic microorganisms. All immune system components are directly or indirectly regulated by the microbiota. The nature of microbial exposure early in life appears to be important for the development of robust immune regulation; disruption of either the microbiota or the host response can trigger chronic inflammation. Dysbiosis is also an important clinical entity. Antibiotics, psychological and physical stress, and dietary factors contribute to intestinal dysbiosis.

Expression of Toll-like Receptors, Pro-, and Anti-inflammatory Cytokines in Relation to Gut Microbiota in Irritable Bowel Syndrome: The Evidence for Its Micro-organic Basis

“…IECs act as a barrier between luminal microbiota and gutassociated immune cells. 30 In vitro, in vivo, and several intestinal epithelial cell lines express TLRs. 31 TLRs play a pivotal role in maintaining the gut homeostasis through secretion of pro-inflammatory cytokines and chemokines.…”

Paediatricians play a key role in preventing early harmful events that could permanently influence the development of the gut microbiota in childhood

“…The early microbiota of children who later developed allergies has been characterised by lower bacterial diversity, with predominant Firmicutes , higher counts of the Bacteroidaceae , increased numbers of the anaerobic Bacteroides fragilis , Escherichia coli , Clostridium difficile , Bifidobacterium catenulatum , Bifidobacterium bifidum and Bifidobacterium longum. In contrast and decreased numbers of Bifidobacterium adolescentis , Bifidobacterium bifidum and Lactobacillus have been reported . When the microbiota of children with allergies was assessed at the onset of allergic symptoms in one study, it showed a different pattern, with higher counts of Bacteroides , lower counts of Akkermansia muciniphila, Faecalibacterium prausnitzii and Clostridium and overall lower bacterial diversity .…”

“…The potential mechanisms underlying an increased risk of sensitisation and allergy development, detected as a consequence of dysbiosis in animal models, have been related to various alterations in mucosal regulatory T cells. Other reported effects were defects in the epithelial barrier function, as evidenced by increased mucosal permeability, diminished secretory immunoglobulin A production and excretion and altered dendritic and B‐cell function .…”

Association between Allergic Diseases and Irritable Bowel Syndrome: A Retrospective Study

“…Moreover, it has recently been suggested that imbalances in the composition of the intestinal microbiota might trigger allergy. The intestinal microbiota not only regulates the intestinal mucosal immune system but also takes part in systemic inflammatory responses [22]. It has been found that a reduced gut microbial diversity in infancy is associated with an increased risk of allergic manifestations in school-aged children [23].…”