|Results 1-1||<< Back|
Mentions: In this review, we have highlighted several bacterial groups and specific species that have an immunomodulatory impact on their hosts (summarized in Figure 1). There are an incredible 1014 bacteria in the intestine and the mammalian immune system must be able to sustain these constant visitors without eliciting a strong reaction, yet at the same time, be primed to react to incoming and invading pathogens. We have described several different instances in which intestinal bacteria prime responses that mirror and enhance this vital balance by either promoting inflammatory (SFB and Th17 cells) or anti-inflammatory conditions (Clostridium, Bacteroides fragilis, Bifidobacterium, and Lactobacillus).
The Starting Lineup: Key Microbial Players in Intestinal Immunity and Homeostasis
Bottom Line: These models have not only allowed us to tease out the roles of individual species, but have also allowed the discovery and characterization of functionally unknown organisms.Prior to linking their key role in immune system development, little was known about these organisms.Additionally, Clostridium species have most recently been shown to expand regulatory T-cell populations leading to anti-inflammatory conditions.
Affiliation: Channing Laboratory, Department of Medicine, Brigham and Women's Hospital Boston, MA, USA.
The complexity of microbiota inhabiting the intestine is increasingly apparent. Delicate balance of numerous bacterial species can affect development of the immune system, how susceptible a host is to pathogenic organisms, and the auto-inflammatory state of the host. In the last decade, with the increased use of germ-free mice, gnotobiotic mice, and animal models in which a germ-free animal has been colonized with a foreign microbiota such as humanized mice, it has been possible to delineate relationships that specific bacteria have with the host immune system and to show what role they may play in overall host health. These models have not only allowed us to tease out the roles of individual species, but have also allowed the discovery and characterization of functionally unknown organisms. For example, segmented filamentous bacteria (SFB) have been shown to play a vital role in expansion of IL-17 producing cells. Prior to linking their key role in immune system development, little was known about these organisms. Bacteroides fragilis can rescue some of the immune defects of gnotobiotic mice after mono-colonization and have anti-inflammatory properties that can alleviate colitis and experimental allergic encephalitis in murine models. Additionally, Clostridium species have most recently been shown to expand regulatory T-cell populations leading to anti-inflammatory conditions. This review will highlight and summarize some of the major findings within the last decade concerning the role of select groups of bacteria including SFB, Clostridium, Bacteroides, Bifidobacterium, and Lactobacillus, and their impact on host mucosal immune systems.