03c: GI Immunology

Question 1

GI tract immune system faces specific challenges, namely from (X) pathogens.

Answer 1

X = food antigens and commensal bacterial (part of gut)

Question 2

List general immunological structures in GI tract that battle pathogens.

Answer 2

1. Tonsils
2. Peyer’s patches
3. Lamina propria follicles

Question 3

T/F: GI tract immunity particularly emphasizes tight regulation, though other innate and adaptive responses present.

Answer 3

True

Question 4

T/F: Humoral immunity plays little to no role in GI defenses.

Answer 4

False - major role in local defense

Question 5

GI Immunity: List the two components of the epithelial barrier.

Answer 5

Tight junctions and mucus

Question 6

List the specialized epithelial cells with immune function in GI tract.

Answer 6

1. Adsorptive epithelial cells
2. M cells
3. Paneth cells
4. Goblet cells

Question 7

GI innate Immunity: Goblet cells important for (X) and adsorptive epithelial cells for (Y).

Answer 7

X = secreting mucus
Y = secreting cytokines

Question 8

GI innate Immunity: M cells important for (X) and paneth cells for (Y).

Answer 8

X = antigen sampling/presentation
Y = secreting anti-bac peptides

Question 9

T/F: Mucus is both a chemical and physical barrier in GI immune system.

Answer 9

True

Question 10

Mucus: (hydrated/dehydrated) gel, made up of proteins that have been extensively modified via (X).

Answer 10

Hydrated

X = glycosylation

Question 11

GI Immunity: Some (X) from (Y) cells stimulate mucus production in GI tract.

Answer 11

X = cytokines
Y = epithelial

Question 12

Immune system: (X) ligands, such as LPS, bind (Y) receptors. This leads to signaling events that stimulate which responses?

Answer 12

X = PAMPs
Y = toll-like (TLRs)

Cytokines, adhesion, inflammation, adaptive immunity

Question 13

T/F: Mucus contains neutrophils.

Answer 13

True

Question 14

T/F: TLRs in GI tract are clustered together and localized to specific regions.

Answer 14

False - widely distributed

Question 15

TLR signaling in GI tract often leads to which responses?

Answer 15

Increased epithelial motility, proliferation, and tight junctions (NOT inflammation)

Question 16

There’s a (lower/higher) threshold for TLR activation in GI tract. Thus, (less/more) (X) needed to activate receptor.

Answer 16

Higher; more

X = PAMPs

Question 17

Which TLR would you expect to find on luminal surface of GI tract? And on basolateral surface? What does each bind?

Answer 17

Luminal: TLR-4 (LPS on gram-neg bac)

Basolateral: TLR-5 (flagellin on invaded bacteria)

Question 18

The (basal/luminal) surface of GI epithelium is considered “anti-inflammatory” environment, due to cell secretion of (X).

Answer 18

Basal;

X = IL-10 and TGF-beta

Question 19

List the cells in GI tract that secrete anti-inflamm agents, specifically (X).

Answer 19

X = IL-10 and TGF-beta

DCs, macrophages, epithelial cells

Question 20

T/F: Unlike other parts of immune system, GI tract has “anti-inflamm” DCs and macrophages that aren’t involved in antigen processing/killing.

Answer 20

False - they retain that function

Question 21

GI Immunity: lymphocytes are (localized/scattered) throughout (mucosa/submucosa/muscularis) layer.

Answer 21

Scattered; submucosa

Question 22

T/F: The major form of adaptive immunity in gut is humoral immunity.

Answer 22

True

Question 23

Major form of cell-mediated immunity in GI tract comes from (X) cells.

Answer 23

X = Th17 and Tregs

Question 24

GI Immunity: (X) cells are in contact with (basal/lateral/luminal) surface of epithelium. They act as shuttle/uber, dumping pathogen to (Y) cell.

Answer 24

X = M
Lateral (sandwiched between epithelial cells)
Y = DC

Question 25

GI Immunity: following DC uptake, maturation, and Ag processing, MHC presentation occurs in (X).

Answer 25

X = mesenteric lymph nodes OR Peyer's patches (follices/parafollicular zones)

Question 26

GI Immunity: (X) species of pathogens are especially good at hijacking the (Y) cell shuttle system, thus getting past epithelial barrier no problem.

Answer 26

``` X = Salmonella Y = M ```

Question 27

GI Immunity: (X) cells convert vitamin (Y) to (Z). This acts as a "homing signal" for which immune system cells?

Answer 27

``` X = DCs Y = A Z = retinoic acid ``` lymphocytes

Question 28

GI Immunity: retinoic acid allows lymphocytes to home back to GI due to its (up/down)-regulation of (X).

Answer 28

Up-regulation; | X = CCR9 and integrin (alpha-4-beta-7)

Question 29

GI Immunity: When lymphocytes home back to GI, which specific tissue layer are they returning to from circulation?

Answer 29

Lamina propria

Question 30

The dominant protective cell-mediated immune response consists of (X) cells. Which of their actions is most prominent in GI?

Answer 30

X = Th17 Secretion of IL-22 (increases epithelial barrier integrity)

Question 31

GI Immunity: plasma cell produces (mono/di/poly)-meric Ig(X). Of the (Y) g of Ig we make per day, how much of it is Ig(X)?

Answer 31

Dimeric; X = A Y = 3 2 of 3 g is IgA

Question 32

T/F: IgA Fc segment is pro-inflammatory.

Answer 32

False

Question 33

Invaded bacteria can actually be transported back across the epithelial cell. This is carried out by presence of (X) in (Y) tissue layer.

Answer 33

``` X = IgA Y = lamina propria ```

Question 34

T/F: IgA levels in blood circulation are very low.

Answer 34

True

Question 35

T/F: IgG is the only other Ab secreted in nearly same quantities as IgA in gut lumen.

Answer 35

False - secreted into gut lumen, but in lower quantities than IgA

Question 36

GI immunity: A special receptor, (X), allows bi-directional transport of Ig(Y). Which cells express this receptor?

Answer 36

X = FcRn (neonatal Fc receptor) Y = G Intestinal epithelial cells

Question 37

Major form of humoral immunity in the gut:

Answer 37

IgA, IgG, IgM

Question 38

Crohn's disease affects which part(s) of bowel? Which tissue layers?

Answer 38

Entire bowel thickness and all regions

Question 39

Ulcerative colitis affects which part(s) of bowel? Which tissue layers?

Answer 39

Colonic mucosa

Question 40

(X) disease: Unusual sensitivity to gluten proteins, manifesting as (Y) symptom in which region/tissue layers of bowel?

Answer 40

``` X = celiac Y = inflammation ``` Small bowel mucosa

Question 41

There's an abnormal (X) T cell response in celiac disease.

Answer 41

X = CD8

Question 42

There's an abnormal (X) T cell response in food allergy.

Answer 42

X = CD4 (Th2)