GALT Flashcards
what are peyers patches
organised lymphoid structures localised in the intestinal tissue
where will you find peyers patches
in the intestinal Jejunum and ileum
are peyers patches visible grossly
maybe visible in surgery/endoscopy but usually only if enlarged due to infection
what is GALT
gut associated lymphoid tissue
- lymphoid tissue associated with the lining of the intestinal tract
- located immediately below the epithelium of the mucosal tissue
- primary lymphoid organ in ruminants (site of B cell proliferation)
- secondary lymphoid organ in other species
what does GALT contian
organized structures such as:
- peyers patches
- isolated lymphoid follicles
- cryptopatches
- scattered lymphocytes in the intestinal villi
where does the lymphatic drainage of peyers patches and villus lamina propria go
mesenteric lymph nodes
discuss the difference between development of peyers patches in rabbits and rodents compared to other species
- in most species (ruminants, pigs, horses, dogs cats) reach max size and maturity before birth prior to encountering gut microbiota
- in rabbits and rodents, development doesnt start until exposure to gut microbiota (2-4 weeks after birth) and therefore if raised in sterile environment wont develop them
discuss the histologival features of peyers patches and label the diagram below
- extend from the lamina propria to the submucosa
what structures are in the follicle associated epithelium
M cells in between vilous epitheliumn
what cells exist within the subepithelial dome of a peyers patch
- dendritic cells
- macrophages
- neutrophils
- B cells
- T cells
what immunocytological content exists in the interfollicular area of a peyers patch
T cells
what immunolocytological content exists in the lymph follicle with germinal centre in a peyers patch
B cells
what immunocytological content exists in the lamina propria of a peyers patch
T cells
what are M cells
microfold cells
- have apical microfolds with adhesion molecules inside the lumen of intestines
- antigen uptake cells on lumen side transport particles and intact bacteria to allow for contact of antigens with immune cells on the other side of the intestinal barrier
- basolateral pocket occupied by immune cells (antigen presenting cells and lymphocytes
- cannot present the antigen to lymphocytes. they are strictly transporter cells which transport antigens to dendritic cells and dendritic cells then present the antigen to lymphocytes
compare and contrast peyers patches and lymph nodes in terms of:
- arrival of naive lymphocytes
- arrival of antigens
- lymphocytes leave
- B cells
- T cells
- capsule
what are the 3 pathways of luminal intestinal antigen uptake
-intestinal epithelial cells
M cells
dendritic cells that interdigitize the lamina propria
how does antigen sampling occur
- follicle associated epithelium sample soluble antigens
- M cells and dendritic cells sample particulate antigens
- antigens is captured by dendritic cells and presented to T cells in peyers patches
- activated T helper cells secrete cytokines to promote differentiation and proliferation of B cells and T cells
discuss how B cells in secrete IgA
- B cells are activated by cytokines from the T helper lymphocytes
- differentiate into plasma cells
- IgM secreted first (but too large and vulnerable to enzymes)
- cytokines stimulate plasma cells to swtich to produce different class of antobody from IgM to secretory IgA
- secretion of IgA from lamina propria into lumen is complex but end result is secretory IgA which is protected from enzymatic digestion
- IgA binds to receptor on the basolateral aspect of the epithelial cell
- IgA/receptor complex is translocated to the apical aspect where the secretory component is wrapped around the IgA molecule
- on the mucosal surface of the cell, secretory IgA is either released into the lumen or captures anitgen directly
what are the 2 isotypes of IgA
- IgA1 = found in serum
- IgA2 = found in secretory lymphoid tissues (GALT)
where is the secretory component of IgA added and what does it achieve
- added to IgA in the lamina propria as it passes through the mucosal epithelial cells
- protected from enzymatic digestion
what does secretory IgA do to the pathogen
- interferes with binding of pathogen to receptors on the epithelial cells to prevent invasion of pathogen
- immune exclusion rather than elimination (doesnt eliminate the antigen just prevents it from binding to epithelial cells)
what does IgG do in GALT
- neutralises bacterial toxins
- opsonises invading pathogens, enhancing their phagocytosis or complement mediated lysis
where is IgG found in GALT
mostly in serum and lamina propria, some transported to lumen
which pathogens exploit M cells and use them as portals of entry to the body
- slamonella
- listeria
- yersinia
- some E coli
- rotavirus
- cryptosporidium
IgA acts via:
immune exclusion
antigen sampling occurs mainly via:
M cells, captured by DCs and presented to T cells. Activated T cells secrete cytokines, B cells differentiate into plasma cells and produce mainly IgA
