GALT

Question 1

what are peyers patches

Answer 1

organised lymphoid structures localised in the intestinal tissue

Question 2

where will you find peyers patches

Answer 2

in the intestinal Jejunum and ileum

Question 3

are peyers patches visible grossly

Answer 3

maybe visible in surgery/endoscopy but usually only if enlarged due to infection

Question 4

what is GALT

Answer 4

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

Question 5

what does GALT contian

Answer 5

organized structures such as:
- peyers patches
- isolated lymphoid follicles
- cryptopatches
- scattered lymphocytes in the intestinal villi

Question 6

where does the lymphatic drainage of peyers patches and villus lamina propria go

Answer 6

mesenteric lymph nodes

Question 7

discuss the difference between development of peyers patches in rabbits and rodents compared to other species

Answer 7

• 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

Question 8

discuss the histologival features of peyers patches and label the diagram below

Answer 8

• extend from the lamina propria to the submucosa

Question 9

what structures are in the follicle associated epithelium

Answer 9

M cells in between vilous epitheliumn

Question 10

what cells exist within the subepithelial dome of a peyers patch

Answer 10

• dendritic cells
• macrophages
• neutrophils
• B cells
• T cells

Question 11

what immunocytological content exists in the interfollicular area of a peyers patch

Answer 11

T cells

Question 12

what immunolocytological content exists in the lymph follicle with germinal centre in a peyers patch

Answer 12

B cells

Question 13

what immunocytological content exists in the lamina propria of a peyers patch

Answer 13

T cells

Question 14

what are M cells

Answer 14

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

Question 15

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

Answer 15

Question 16

what are the 3 pathways of luminal intestinal antigen uptake

Answer 16

-intestinal epithelial cells
M cells
dendritic cells that interdigitize the lamina propria

Question 17

how does antigen sampling occur

Answer 17

• 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

Question 18

discuss how B cells in secrete IgA

Answer 18

• 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

Question 19

what are the 2 isotypes of IgA

Answer 19

• IgA1 = found in serum
• IgA2 = found in secretory lymphoid tissues (GALT)

Question 20

where is the secretory component of IgA added and what does it achieve

Answer 20

• added to IgA in the lamina propria as it passes through the mucosal epithelial cells
• protected from enzymatic digestion

Question 21

what does secretory IgA do to the pathogen

Answer 21

• 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)

Question 22

what does IgG do in GALT

Answer 22

• neutralises bacterial toxins
• opsonises invading pathogens, enhancing their phagocytosis or complement mediated lysis

Question 23

where is IgG found in GALT

Answer 23

mostly in serum and lamina propria, some transported to lumen

Question 24

which pathogens exploit M cells and use them as portals of entry to the body

Answer 24

• slamonella
• listeria
• yersinia
• some E coli
• rotavirus
• cryptosporidium

Question 25

IgA acts via:

Answer 25

immune exclusion

Question 26

antigen sampling occurs mainly via:

Answer 26

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