Immunity and Microbiome
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The default response to oral administration of a protein antigen is the development of this phenomenon
Oral tolerance
Renders the systemic and mucosal immune systems relatively unresponsive to the same antigen
Peripheral tolerance
Suppression of subsequent immune responses is observed after the administration of proteins into the respiratory tract, giving rise to this concept
Mucosal tolerance
How does oral tolerance impact peripheral immune response?
Affects T cell dependent effector responses and IgE production
What mechanisms account for oral tolerance to protein antigens?
• anergy • deletion of antigen specific T cells • the generation of regulatory T cells induced in the mesenteric lymph node
Intestinal microbiota normally exist in a mutually beneficial or symbiotic relationship
Mutualism
Enterocytes starved of short chain fatty acids (SCFAs) undergo inflammation and necrosis
Diversion colitis
How can commensal organisms inhibit pathogens?
Interfere with the ability of pathogenic bacteria to colonize and invade the guy by competing for space and nutrients Also directly inhibit the pro inflammatory signaling pathways that pathogens stimulate in epithelial cells and that are needed for invasions
Perturbations in the balance between the various spaces of bacteria present in the microbiota Increase susceptibility to diseases
Dysbiosis
Grows in the antibiotic treated gut Can cause severe infection Produces toxins that cause severe diarrhea and mucosal injury
Clostridium difficile
When are commensal bacteria a potential threat?
When the integrity of the intestinal epithelium is damaged Can cross the mucosa, invade the bloodstream and cause fatal systemic infection
What do commensal bacteria do to maintain balance?
Elicit antigen specific responses that maintain the local balance between host and microbiota and are largely confined to the intestine
What is the recognition of microbiota by the adaptive immune system dependent on?
On the uptake and intracellular transport of organisms by local dendritic cells that remain in Peyer’s patches or migrate no further than the mesenteric lymph node
No colonization of the gut by microorgnanisms Marked reductions in size of lymphoid organs, low serum immunoglobulin levels, fewer mature T cells and reduced immune responses, especially Th1 and Th17 responses
Germ free or gnotobiotic
Enhances IgA production, accumulation of IELs and the number of intestinal effector Th17 T cells
Segmented filamentous bacteria (SFB)
What happens if aggressive T cells are not kept in check by active regulation?
Unrestricted immune responses to commensal bacteria can lead to inflammatory bowel diseases
True or false: immune tolerance is usually the cause of allergic reactions
False
True or false: immune tolerance is the reason why oral immunization is more difficult to accomplish
True
True or false: the human microbiota has only bacteria
False
True or false: dysbiosis in the microbiota often leads to increased susceptibility to disease
True
True or false: both the quantity and diversity of the microbiota are important for human health
True
True or false: intestinal IgA production is stimulated by the presence of microbes
True
True or false: any bacterium that can penetrate the mucus layer is considered a pathogen
False