Microbial translocation and its clinical significance

Abstract

The literature was searched in PubMed Medline National Library of Medicine from 1990 to 2016 were used. The following words were used: ‘microbial translocation’ and ‘clinical significance,’ or ‘biomarkers,’ or ‘toll-like receptor,’ or ‘pathogen-associated molecular pattern.’ We found 3,300 published manuscripts using the above search. Of 3,300 manuscripts, we dropped 2087 and 723 manuscripts either they did not suit this review or were not in English; 490 manuscripts were selected for this review. From the literature, there is evidence that microbial translocation occurs in both animals and humans, but unlike in animals, its clinical significance remains questionable in humans. This could partly be explained by the current lack of a single acceptable sensitive and accurate biomarker to detect microbial translocation. Additionally, the extent to which microbial translocation in animals can be demonstrated cannot apply to humans for the sake of research without an underlying disease. In humans microbial translocation is associated with many conditions and microbial products may lead to systemic inflammation and immune activation. Although some of the microbial products or Pathogen-Associated Molecular Patterns (PAMPs) have been studied, their clinical importance is not well established, and the assays developed to measure PAMPs in blood have not been developed or validated for clinical use. However, a few molecules of microbial origin have been used as biomarkers of microbial translocation in many disease conditions. The innate immune system detects all PAMPs through cells such as macrophages, dendritic cells, and monocytes. Detection of PAMPs through pathogen recognition receptors such as Toll like receptors which result in the activation of the transcription factors, NK-κB, resulting in the production of pro-inflammatory cytokines. We provide a synthesis of the current understanding of the nature of microbial translocation, PAMP-receptor interaction and the health significance of microbial translocation in humans.