Chapter 11: The intestinal immune system Flashcards
Intestinal microbiota
Many microbes (mostly bacteria, viruses, fungi and parasites).
Commensal bacteria: most bacteria in the intestine. Produces enzyme that can help with digestion of complex carbohydrates, produce vitamins and protect us against pathogenic bacteria. However, they enter the tissues that underlie the intestine
Mucus of intestinal system
- Coats the epithelial cells of the small intestine, contains antibacterial peptides (e.g. a-defensins)
- Acts as a diffusion barrier
- Produced by goblet cells and replaced in a few hours and disappear in our stool
- Highly glycosylated; many commensal bacteria feast on these and covert them into short-chain fatty acids (important energy source for the cells of the epithelium)
Gastrointestinal system under constant attack
- Bacteria intercepted by resident macrophages
- Bacteria can also be transported to a nearby lymph node from the lamina propria
- When it cannot be cleaned by the macrophages, there will be a dramatic increase in lymphocytes into the lamina propria
Non-inflammatory macrophages: in the lamina propria, macrophages only phagocytose. Normal macrophages cause inflammation (by secretion of cytokines)
Production of IgA in lamina propria
B cells in lamina propria mainly produce IgA.
- Can be transported into lumen of the intestine –> will bind to microbes and prevent them from adhering to epithelial cells –> eliminated via the feces
- Does not cause inflammation, because the Fc rortion cannot bind to receptors of the immune system cells
- In the lamina propria, IgA can bind to invaders and make sure they go back into the lumen for disposal
- Production can be driven through retinoic acids that is produced by DCs
The intestinal immune system’s response to pathogens
iTreg: found in lamina propia. EPithelial cells produce TGFB; cytokine which encourage Th cells to become iTregs.
- iTreg cells produce IL-10 and TGFB, which help to calm down the mucosal immune system
