lecture 2- mucosal immunity Flashcards
any mucosal tissue is tissues…
continually bathed in a thick layer of mucus that they secrete
name a few functions of mucosal tissues
lungs- gas exchange
gut- food absorption
reproductive organs
describe mucosal surfaces
mucosal surfaces are thin, permeable barriers
- 75% of the body’s lymphocytes are in secondary lymphoid organs serving mucosal surfaces
- majority of all antibodies made by body are dimeric or secretory IgA which localize to mucosal surfaces
- huge surface area
what is the challenge to the mucosal immune system
to eliminate pathogens while limiting growth of commensals (that we do not want immune responses to and not attack our food (remain tolerant)
intestinal epithelial cells are covered by two layers of mucus- outer and inner
- inner layer typically firmly adherent & works to separate microbes from epithelial cell
- microbes (bacteria) mostly associated with outer layer - loosely adherent
- outer layer of mucus very thick in colon and ileum
- more bacteria in outer, less in inner
- mucus layer maintains barrier between organisms internal compartment of tissue
name secondary lymphoid tissues of small intestine
Peyer’s patches, lamina propria, isolated follicles - all drain to mesenteric lymph nodes
describe villus in secondary lymphoid tissues of small intestine
villus- a projection of tissue into the lumen coated with epithelial cell layer- important for absorption for food
- villus contains epithelial cells that have lots of cilia that enables absorption of food during digestion/degradation
there are many specialized cell types within epithelial layer of secondary lymphoid tissues
- intraepithelial lymphocytes
- paneth cells- produce antimicrobial peptides
- goblet cells- produce mucus- moves them from inner to outer layer and becomes more unfolded
describe peyer’s patch in secondary lymphoid tissues of small intestine
- lymphoid tissue integrated into intestinal wall
- has B and T cell zones, B cell follicles with germinal centers
- small and located right below epithelial lining of gut
what do M cells do in secondary lymphoid tissues of small intestine
transport things across lumen and into peyer’s patch
describe lamina propria as secondary lymphoid tissue in small intestine
large unorganized region under epithelial layer that contains variety of lymphoid cells
- cells in lamina propria = plasma cells (produce dimeric IgA), macrophages, mast cells, B & T cells, DC’s (acquire antigens by reaching through epithelial layer)
healthy intestinal epithelium and lamina propria are populated with ___
effector leukocytes (CD4 and CD8)
- effector cells, not naive
- also DC, macrophage, plasma, mast, dimeric IgA…
what helps with the challenge of the mucosal immune system
(challenge is must differentiate between pathogens and commensal organisms)
- all bacteria have PAMP’s that can stimulate epithelial cell response - we do not want to overreact to these, so…
- TLR & NLR do not face lumen, but face basal lateral surface of epithelial layer (this is how epithelial layer avoids overreacting to bacterial PAMP’s)
- lumen side is more absorptive, basal lateral surface more adherent to extracellular matrix
describe mechanisms of surveillance for mucosal immune system
- M cells sit directly in epithelial layer for transport of antigens - M cells are specialized to transport microorganisms to gut-associated lymphoid tissue ; they have very little degradative activity, function to transport antigens across epithelium
- DC’s also live at this epithelial layer, have projection through layer to sample luminal content to present to T cells - antigen bound by DC’s, which activate T cells
- paracellular (in between epithelial cells)
what antibody dominates the gut
dimeric IgA
