Mucosal Immunity (Lec 8) Flashcards
Most infections actually occur through…
- mucosal surfaces rather than our skin
bc larger surface of skin means there are more immune cells to fight it
what is found in the Gastrointestinal Tract?
- Mucus lines all of the areas
- Commensal bacteria also populate all
the areas, help us degrade and digest food
Waldeyer’s ring
- Tonsils and adenoids (secondary lymphoid tissues) surround the entry point to the gastrointestinal and respiratory tracts
- serves as the first line of defense against inhaled or ingested pathogens
Villi
- line the inner wall of the small intestine
- projections that aid in nutrient absorption
Parts of the Gut-associated lymphoid tissue (GALT)
- villi
- Peyer’s patches (only in small intestine)
- isolated lymphoid follicles (small intestine and large intestine)
IgG is dominant in…
the nose, lower respiratory tract and urogenital tracts
IgG is transported from the blood to mucosal secretions by…
the Fc receptor (FcRn)
Mucus
made of glycoproteins, Mucins, that provide viscous and protective features
Mucins
- family of glycoproteins that have simple sequence repeats
- polypeptides are linked by disulfide bonds and form huge networks
- Carbohydrates have ionic charge that retains antimicrobial peptides (e.g. defensins) and IgA
What are the different intestinal barrier structures?
- mucosa
- goblet cell
- paneth cell
What is mucosa comprised of?
epithelial cells and lamina
propria (connective tissue with immune cells and structures)
what do goblet cells do?
secret mucus
What do paneth cells do?
produce antimicrobial peptides (AMPs)
M (microfold) cells
- help us constantly monitor the gut lumen
- Antigen undergoes transcytosis in M cells to reach Peyer’s Patch where immune cells can recognize pathogens and mount an immune response
What protect the mucosal tissues even when there is no infection?
activated (effector) immune cells
What capture antigen from the gut lumen by extending processes between intestinal epithelial cells?
dendritic cells
Healthy gut environment vs altered gut environment
Healthy:
- “peace keeping” bacteria present, more than pathobiont bacteria
- homeostasis
Altered gut environment:
- ie. from antibiotics, diet, pollutants
- dysbiosis: decrease in “peace-keeping” bacteria and increase in pathobionts and invaders
- leads to pathological inflammation
Immune Response to Mucosal Infection
- starts with healthy tissue protected by mucosal immunity
- bacteria gain access to lamina propria by endocytosis
- this activates macrophages but does not cause inflammation
- local effector cells respond to limit infection
- dendritic cells travel to mesenteric lymph node to activate adaptive immunity
- highly specific effector B and T cells colonize infected area
- infection is terminated with either minor tissue damage or no need for repair
Lamina propria
- layer of loose connective tissue found just beneath the epithelium of mucosal surfaces
- Rich in immune cells
- Works with the epithelium and gut-associated lymphoid tissue (GALT) to defend against pathogens
If the mucosal surface is breached, what is a source of infection?
- Commensal bacteria
- Mucosal immunity tries to prevent a massive influx of this bacteria during barriers being breached
Mucosal immunity employs 2 unique strategies…
- Low inflammation: avoid tissue damage and prevent worse infections
- Proactive: Constantly producing an adaptive immune response towards commensal bacteria
Intestinal Macrophages
- phagocytic cells
- do not contribute to inflammation
- have MHC class II but cannot activate naïve T cells (not professional antigen presenting cells)
- inflammation-anergic
Inflammation anergic
immune cells like macrophages in the intestines are unresponsive to inflammation-inducing signals, even when exposed to pathogens or inflammatory stimuli
