The microbiome–systemic diseases connection

Abstract

The human microbiome consists of all microorganisms occupying the skin, mucous membranes and intestinal tract of the human body. The contact of the mucosal immune system with the human microbiome is a balanced interplay between defence mechanisms of the immune system and symbiotic or pathogenic microbial factors, such as microbial antigens and metabolites. In systemic autoimmune diseases (SADs) such as rheumatoid arthritis, systemic lupus erythematosus and Sjögren's syndrome, the immune system is deranged to a chronic inflammatory state and autoantibodies are an important hallmark. Specific bacteria and/or a dysbiosis in the human microbiome can lead to local mucosal inflammation and increased intestinal permeability. Proinflammatory lymphocytes and cytokines can spread to the systemic circulation and increase the risk of inflammation at distant anatomical sites, such as the joints or salivary glands. Increased intestinal permeability increases antigen exposure and the risk of autoantibody production. If the human microbiome indeed plays such a critical role in SADs, this finding holds a great promise for new therapeutic strategies, such as diet interventions and probiotics and prebiotics. This review provides a background on the human microbiome and mucosal immunity in the gut and oral cavity and gives a summary of the current knowledge on the microbiome–SADs connection.

The microbiome in autoimmune diseases

“…Furthermore, Porphyromonas gingivalis, a bacterium linked to the pathogenesis of the periodontitis, has the unique ability to convert the amino acid arginine to the amino acid citrulline: a process called citrullination, through the production of peptidylarginine deiminase. The protein, which contains the amino acid citrulline, is recognized by the autoantibodies ACPA that are highly specific for RA [49]. Recently, Brusca et al [50] found that there were more organisms than simply P. gingivalis which cause periodontal disease (i.e.…”

The autoimmunity–oral microbiome connection

“…In addition, the presence of pathogens may worsen the symptoms of these diseases. In the oral cavity, saliva is the main factor that maintains microbial homeostasis and this is exemplified in SS where the reduction in saliva disturbs the oral community and leads to dental caries and oral candidiasis (Zarco et al, 2012;Krishnan et al, 2016;van der Meulen et al, 2016).…”

“…We believe that the realization of the complexity of interactions between the microbiome and the host, that is, this dynamic interface, is of paramount importance for developing precision diagnostics and therapies. Nevertheless, there is still much work to be carried out in order to establish the role of the microbiome in the pathogenesis of autoimmune disease (Krishnan et al, 2016;van der Meulen et al, 2016). We and others think that future research in this area will provide the bases for relevant personalized medicine (Zarco et al, 2012).…”

Porphyromonas gingivalis in the tongue biofilm is associated with clinical outcome in rheumatoid arthritis patients

“…In recent years, several studies have suggested a link between human microbiome and the development of a number of pathological conditions, including autoimmune diseases [1,2]. In particular, the advent of new technologies allowed the characterization of functional properties and composition of microbial communities [3].…”