Mucosal immunity

Question 1

Most pathogens gain access by passing through

Answer 1

mucosal surfaces

Question 2

Challenge in the GI tract

Answer 2

Eliminate pathogenic organisms
Limit the growth of commensals, but don’t kill them
Don’t mount an immune response to food

Question 3

differences in the gut immune responses Vs. the “traditional” immune responses

Answer 3

traditional immune responses:

• Healthy tissue protected by systemic immunity
• surface wound introduces bacteria that activate macrophages to make inflammatory cytokines
• Cytokines released by macrophages produce an inflammatory immune response
• Infection is terminated, leaving a damaged and distorted tissue for repair
• Repaired and healthy tissue

Gut immune response:

• Healthy tissue protected by mucosal immunity
• Bacteria gain access to lamina propria by endocytosis, activate macrophages but do not cause inflammation
• local effector cells respond to limit infection, dendritic cells travel to mesenteric lymph node to activate adaptive immunity
• Effector B Cells and T cells that are highly specific for the invading bacteria colonize the infected area
• infection is terminated with either minor tissue d amage or no need for repair

Question 4

Lamina Propria of the Gut:

Answer 4

Population is dynamic
- size depends on the antigenic environment
- Germ free animals have very few lamina propria cells
- Animals in highly infectious environments the
population greatly expanded

Antigen presenting cells:

• Chief APCs are the dendritic cells
• Macrophages also abundant in the diffuse

Natural Killer (NK) and Lymphokine-Activated Killer (LAK) cells

Mast cells
Contribute to local host defense by producing important mediators of inflammation
Induce chemoattraction of inflammatory cells to mucosal tissues

Question 5

Goblet cells in GALT

Answer 5

Mucus secreting- barrier function and antibacterial, mucin glycoproteins

Question 6

Epithelial cells in GALT

Answer 6

Barrier and antibacterial functions

Question 7

Paneth cells in GALT

Answer 7

Antibacterial secreting cells

Question 8

M cells in GALT

Answer 8

Antigen sampling

Microfold cells (M cells):
Specialized epithelial cells
Do not secrete mucus or have microvilli
Take up microorganisms and antigens from the gut and transfer them to the Peyer’s patches (basal surface)
DCs inside can take up and present Ag
T cells and B cells activated locally

Question 9

GALT stratification

Answer 9

minimize direct contact between bacteria & epithelial surface
Mucins, Anti-bacterial proteins, IgA

Question 10

GALT compartmentalization

Answer 10

confine bacteria to intestinal sites and limit systemic exposure
Action of phagocytic cells in the lamina propria
Homing of activated lymphocytes to mucosal surfaces

Question 11

Small intestine is heavily invested with lymphoid tissue

Answer 11

Peyer’s Patches

• 5-200 B cell follicles with - - Germinal centers
• Only in small intestine

Isolated Lymphoid follicles

• Single follicle, mostly B cells
• Small and large intestine

Appendix

Question 12

Intra-epithelial lymphocyte

Answer 12

Special type of CD8+ T cell (1 per every 10 epithelial cells)
Limited range of antigen specificities

CD8+ T cell binds MHC 1 to see if the item is foreign or not

Question 13

Dendritic cells resident in lamina propria

Answer 13

Capture pathogens independently of M cells

Less likely to activate Th1 response

Question 14

Lymphocytes return to mucosal tissue as effector cells

Answer 14

Occurs in ways that minimize inflammation

These effector cells can now recirculate to any mucosal tissue

In nursing mothers, plasma cells from other mucosal sites will migrate to mammary glands.

This ensures that breast milk IgA represents all the antibody responses from all mucosal tissues

Question 15

Adaptive Immunity in the mucosa

Answer 15

Humoral immunity and * IgA

• • Neutralizing
• • Enhance innate immune factors
• Th17 dominant cell-mediated immunity
• • Th17 plays a role in gut colonization
• • IL-17 and IL-22 are characteristic cytokines

Suppression of cell-mediated immunity

• • High percentage of *** FoxP3+ Tregs
• • Presence of regulatory CD103+ DCs
• • TGF-β, IL-10, and IL-2 are characteristic cytokines

Question 16

Food allergies

Answer 16

Food potentially immunogenic, inflammatory reaction ensues

Sometimes allergen can be transported to another part of the body causing a skin reaction

IgE mediated: food-specific IgE

• Acute or chronic cutaneous symptoms or anaphylaxis
• Most prevalent in young children

Non-IgE mediated: Th2-cell mediated

• Chronic skin and/or GI symptoms
• Eosinophilic disorders

Mixed: both

Question 17

IgE mediated allergic reactions

Answer 17

Anaphylaxis (Edema)
Urticaria (increase in blood flow/ vascular permeability)
Seasonal allergies (sneezing)
asthma (bronchoconstriction, mucus, inflammation)
food allrgy (vomiting, diarrhea, pruritis, etc.)

Question 18

Sensitization (Priming) and repeat exposures to allergen

Answer 18

1st time: no allergic symptoms
2nd time: sensitized. mild
3rd and more: hypersensitized, overt allergic symptoms

Question 19

Immediate hypersensitivity

Answer 19

Cross linking of FcR1 on mast cells by IgE causes mast cell activation
Immediate hypersensitivity
Varying severity - runny nose to asphyxiation
Early phase (minutes after repeat exposure to allergen)

and late phase (6-24 hours after repeat exposure to allergen)

Question 20

Why Do Food Allergies Arise?

Answer 20

Inappropriate Digestion Hypothesis

• Normal: di & tri-peptides, non-immunogenic
• Abnormal: longer peptides, some maybe immunogenic
• Caused by: genetics, diet, drugs, toxins, age?

Hygiene Hypothesis

Microflora Hypothesis

Question 21

Hygiene Hypothesis

Answer 21

Lack of early childhood exposure to infectious agents, including parasites, increases susceptibility to allergic diseases

“Poorly developed” immune systems – can’t perceive real danger

Fail to induce Th1 polarized responses early in life, grow up more prone to Th2 responses

Increase due to better hygiene, vaccination, increased use of drugs and antibiotics

Some studies have shown that children exposed to more infections at a younger age have reduced propensity for allergic reactions

Question 22

IBD

Answer 22

Autoimmune disease partially mediated by the absence of Treg cells

Inflamed, ulcerated, damaged bowel
* Crohn’s disease
affects the entire thickness of the bowel wall
most frequent, but not restricted, to the terminal ileum
* Ulcerative colitis
restricted to the colonic mucosa
Recent study demonstrated that Celiac and Crohn’s share genetic risk loci

Question 23

Differences between Crohns and Ulcerative colitis

Answer 23

Crohns: anywhere along the digestive tract
inflammation may occur in patches
pain commonly in RLQ
colon may be thickened and may have a rocky appearance
ulcers along the digestive tract are deep and may extend into all layers of the bowel wall
Bleeding from the rectum during bowel movements is NOT common

Ulcerative colitis: large intestine is typically the only affected site
inflammation continuous
pain common in LLQ
colon wall thinner, continuous inflammation
mucus lining may have ulcers, but they do not extend beyond the inner lining
bleeding from rectum during bowel mvts

Question 24

IBD treatment

Answer 24

IBD and colitis result from autoreactive T cells in the lamina propria

The disease can be treated by transfer of CD4 CD25 Treg cells, which home to mesenteric lymph nodes and the colon

CD4 CD25 Treg cells proliferate and inhibit the pathogenic effector T cells

After inflammation resolves, CD4 CD25 Treg cells remain in clusters with dendritic cell and pathogenic effector T cells

Question 25

Immunologic Abnormalities in IBD

Answer 25

Defective Treg cell function - FoxP3 and IL-2 or IL-2R deficiencies result in inflammatory bowel disease Dysregulated innate immune response - Defective defensin expression - Inadequate negative immune regulation to commensal organisms Abnormal cell-mediated immunity - Overactive Th17 response - Granulomatous inflammation by IFN-γ-producing Th1 cells Defective autophagy

Question 26

Epithelial Host Defense- Regulated Expression of TLRs and NLRs

Answer 26

The first susceptibility gene identified for Crohn’s disease was a NOD family member NOD2, a receptor for the muramyl dipeptide structural unit of bacterial peptidoglycan. Expression of TLRs and NLRs (nod-like receptor) is restricted in the gut and the location of receptors is altered. Furthermore, the functional response of these receptors is biased towards an anti-inflammatory response. The purpose of these alterations is to limit inflammation in the gastrointestinal tract.

Question 27

Celiac Disease - Introduction

Answer 27

Celiac disease is an immune-mediated disease mediated by T cells Estimated frequency 1:100 to 1:150 Associated with other autoimmune diseases Type 1 diabetes, autoimmune thyroid * Clinical symptoms can vary from abdominal pain, diarrhea, growth failure, anemia, osteoporosis, or asymptomatic

Question 28

celiac disease antibodies and triggers

Answer 28

Antibodies to tissue transglutaminase (IgA) are seen in individuals with celiac disease - 10% of type 1 diabetics will develop celiac disease autoantibodies Gluten is the environmental trigger - Found in wheat, rye, and barley Treatment is lifelong dietary avoidance of gluten (gluten-free diet) - Found in pastas, bread, most marinated meats, salad dressings, & beer Gluten-free diet completely reverses clinical and histological findings

Question 29

Celiac Disease is an autoimmune disease

Answer 29

Inflammatory autoimmune disease of gut mucosa Genetic and environmental factors CD4 T cells, chronic inflammation, atrophy of intestinal villi, malabsorption of nutrients, diarrhea Genetic predisposition - 75% monozygotic twins - Strong association with HLA-DQ2 or 8 Gluten specific T cells found in gut of celiacs but not healthy controls BUT peripheral blood T cells from celiac and non-celiac patients contain cells that react to gluten in culture

Question 30

What happens to gluten in the gut

Answer 30

gluten is degraded in the gut lumen to give a resistant fragment gluten fragment enters gut tissue and is deaminated by transgluatminase In celiac: Naive CD4 T cell responds to deaminated peptides presented by HLA-DQ inflammatory effector T cells cause villous atrophy

Question 31

one of the first thing that starts to damage tissue in celiac disease

Answer 31

intra-epithelial lymphocytes

Question 32

genetics of celiac disease

Answer 32

All Celiac disease patients have HLA - DQ2 or DQ8 30% of the Caucasian population has DQ2 3-5% of DQ2/DQ8 individuals develop Celiac disease HLA genes are necessary but not sufficient to develop disease

Question 33

Gluten is broken down into

Answer 33

Gliadin (alpha, gamma and omega)- alcohol soluble Glutenins (alcohol insoluble)

Question 34

Tissue Transglutaminase (TTG)

Answer 34

TG recognizes certain motifs: QXXF and QXPF → EXXP and EXPF Deamidation creates a negative charge on specific aa residues to better fit in DQ pockets. No evidence that TG antibodies cause disease.

Question 35

Celiac Disease Antibodies

Answer 35

Tissue Transglutaminase - IgA – sensitive and specific - IgG – check if IgA deficiency Endomysium (IgA) Gliadin (IgA & IgG) Deamidated Gliadin

Question 36

Gluten Free Diet

Answer 36

Very difficult to maintain a completely gluten free diet “Hidden Gluten” – protein filler in sausage, soups, soy sauce, & ice cream Cross-contamination – gluten free products encounter gluten during milling & storage 50 mg/day of gluten for 3 months can cause intestinal changes (this amount can come from 250 grams of gluten free food) - No change in clinical symptoms or autoantibodies levels

Question 37

Novel Therapies for Celiac disease

Answer 37

Enzyme Therapy - Bacterial prolyl endopeptidase can digest the 33-mer of gliaden - Pretreatment of gluten containing food with these peptidases Zonulin Antagonists - Zonulin is a protein that increases intestinal permeability - Zonulin antagonist (AT-1001) has been used in a small clinical trial resulting in no increased intestinal permeability after a gluten challenge (Paterson BM, Aliment Pharmacol Ther 2007) Inhibiting DQ2/DQ8 antigen presentation - Small molecules to block basic binding pockets of gluten peptides

Question 38

Immunodeficiencies that can affect the GI tract

Answer 38

Selective IgA deficiency | IPEX

Question 39

Selective IgA deficiency

Answer 39

``` Most common primary immunodeficiency Majority are asymptomatic People are relatively healthy - - Compensated for by IgM, IgG - Could reflect developed countries, few parasitic infections ``` Caucasians: 1/500 persons little or no IgA African-Americans: 1/10,000 Japanese: even lower

Question 40

Immune dysregulation, polyendocrinopathy, enteropathy X-linked disease (IPEX)

Answer 40

Arises due to mutations in the transcription factor Foxp3 The phenotype in humans results in a loss of functional Treg cells Lack of T cell inhibitory activity results in widespread autoimmunity Symptoms include intractable watery diarrhea, failure to thrive, dermatitis, and autoimmune diabetes Immunoglobulin levels are normal with the exception of IgE which is elevated

Question 41

Building on hygiene hypothesis – “microflora hypothesis”

Answer 41

Western lifestyle alters gut microflora which leads to allergies and other inflammatory diseases