4.1 Mucosal Immunity

Question 1

Why are mucous membranes susceptible to infection?

Answer 1

They are very thin walled to allow physiological function (e.g., gas exchange, nutrient absorption)

Question 2

What protects the respiratory epithelium?

Answer 2

Mucociliary escalator and alveolar macrophages

Question 3

Describe the role of gamma-delta T cells. What species are they most abundant in?

Answer 3

Recognise stress proteins induced by infected epithelial cells of the GIT

Found beneath enteric mucosal epithelium

Abundant in ruminants and pigs

Question 4

How do gamma-delta T cells protect mucosa?

Answer 4

Infected cell upregulates stress proteins

Recognised by 𝛾𝛿 TCR

Cytotoxic effect

Surrounding cells regenerate to fill gap

Question 5

What are the five different MALTs?

Answer 5

• Tonsils
• Peyers patches
• Mesenteric lymph nodes
• Bronchial-associated lymphoid tissue
• Mammary gland lymphoid tissue

Question 6

Why do lymphocytes migrate to other mucosal sites once they have been activated in one type of MALT?

Answer 6

Antigen stimulation at one site leads to recruitment and response in all MALTs

Question 7

What antibodies predominate when delivers via non-mucosal route

Answer 7

IgM and IgG
Systemic protection from infection

Question 8

What antibodies predominate when delivered via mucosal route?

Answer 8

IgA and IgE
Mucosal protection from infection

Question 9

What are microfolds and what do they do?

Answer 9

Specialised epithelial cells
They sample luminal contents and take up antigens by endocytosis. Antigens are released beneath M cells and taken up by antigen-presenting dendritic cells, stimulating and immune response
Activated lymphocytes migrate to other MALT

Question 10

Adaptive immunity in MALT

Answer 10

B cells - mainly IgA, some IgE and IgG
T cells - mainly Th2 and Th3

Th2 > IL-4: stimulates B cell class-switching to IgE
Th3 > TGF-𝛃: stimulates B cell class-switching to IgA

Question 11

How is IgA produced and transported to lumen?

Answer 11

• Produced and secreted by plasma cells
• pIgR binds to J chain and transcytosis into epithelial cells
• Cleavage of pIgR and secreted into lumen

Question 12

How does IgA prevent infection on mucosal surfaces?

Answer 12

Neutralising antibody
Prevents pathogen adherence to mucosal surfaces

Question 13

How do IgE and IgG act to protect mucous membranes?

Answer 13

Destroy pathogens that breach epithelial barrier

IgE = mast cell responses
IgG = neutralisation, opsonisaton, complement activation

Question 14

How do MALT distinguish between food antigen and pathogen antigen

Answer 14

Dietry proteins do not express PAMPs so regulatory T cells produce immunosuppressive cytokines for mucosal tolerance

Question 15

How are antibodies transferred to a neonate?

Answer 15

B cells migrate from MALT to mammary gland

Passive transport of maternal antibody in colostrum

Question 16

What antibodies are present in colostrum?

Answer 16

IgG in colostrum (system protection)
IgA in milk (mucosal protection)

Question 17

How are colostrum antibodies absorbed by neonates

Answer 17

IgG binds specialised Fc receptors expressed on intestinal epithelial cells
Antibodies actively taken up and passed into lacteals and then into blood

Question 18

What is neonatal isoerythrolysis?

Answer 18

• stallion and mare blood not compatible
• foal inherits sire’s RBCs
• mare makes antibodies to foetal RBCs passed in colostrum
• maternal antibodies attack foal RBCs

Anaemia and jaundice