3.2 Mucosal immunity Flashcards
___ and ____ are susceptible to infection
External surfaces
Skin ( stratified squamous, thick layers, good for defense)
Mucous membranes: are particularly more due susceptible (easily infected) since they are thin Walled to allow physiological function
-respiratory tract: gaseous exchange
- GIT: absorption of nutrients
Innate immunity at mucosal sites:
Protect the respiratory epithelium:
Mucociliary escalator and alveolar macrophages
Alveolar =
Gaseous exchange
In milk-fed animals
e.g. calves, the GIT is colonised by
lactobacilli that produce lactic and butyric acid which have antimicrobial properties
Treatment of rabbits with penicillin can lead to?
fatal enterotoxaemia - can wipe out microbiome allowing gut to repopulate with bad species like clostridium
Gamma:delta T cells are found where?
Found beneath enteric mucosal epithelium
Gamma: delta T cells
Invariant receptors
– unlike conventional αβ T cells
Do not require MHC
– recognise stress proteins / symptoms
Gamma delta (gd) T cells are important for innate protection of mucosa in
in farm animals (90% of T cells in pigs are gd)
Mucosal-associated lymphoid tissues (MALT): ( common mucosal system)
– Tonsils
– Peyers patches
– Mesenteric lymph nodes
– Bronchial-associated lymphoid tissue
– Mammary gland lymphoid tissue
Antigen stimulation at one site leads to
recruitment and response in ALL mucosal lymphoid tissue.
Adaptive immunity: Antigen delivered via non-mucosal route
Ex: vaccine given SQ or IM
– IgM and IgG antibodies predominate
– Systemic protection from infection
Antigen delivered via mucosal route
– IgA and IgE antibodies predominate
– Mucosal protection from infection
Antigen exposure in the gut is usually recognised by
cells in Peyer’s patches in the ileum
Antigen exposure in the gut is usually recognised by
by cells in Peyer’s patches in the ileum
microfold (M) cells:
Specialised epithelial cells that sample luminal contents and transport antigen to underlying lymphoid tissue
M cell process:
Adaptive immunity in MALT: B cell response
– Mainly IgA production
– IgE production important against parasites
– Some IgG in case of systemic spread of infection
Adaptive immunity in MALT: T cell response
Mainly T helper type 2 (TH2) and TH3 cells
- TH2 > IL-4: stimulates B cell class-switching to IgE
- TH3 > TGF-beta: stimulates B cell class switching to IgA
IgA is produced by
plasma cells in submucosa and is transported by epithelial cells into lumen
IgA functions:
NEUTRALISING antibody on the mucosal surface
- Viruses
- Bacterial adhesins
- Microbial toxins
IgA protects against
infection (neutralisation)
___ and ___ are effective if epithelial barrier is breached
IgE and IgG
IgE allows
submucosal mast cells and eosinophils to detect and expel helmith parasites
Problem with IgE
can lead to dietary hypersensitivity
The main function of the GIT is?
Absorption of nutrients
The MALT must be able to
distinguish food antigens from pathogen antigens
Dietary proteins do not express
PAMPs:
– Initial activation which is inhibited following generation of regulatory T cells producing immunosuppressive cytokines
- mucosal tolerance
Exposure to pathogens leads to innate respond and inflammation in the GIT
– PRR detection of PAMPs by cells of innate immunity
– Pro-inflammatory cytokines amplify adaptive response
“sample” the liminal contents for mucosal tolerance
Dendritic cells
Mucosal tolerance: Harmless antigens
Produces immunosuppressive cytokines to switch off the immune response
Gluten-sensitive enteropathy (Coeliac disease)
• Dietary allergy to gluten
• Irish setter dogs
• Feed a gluten-free diet
Migration of B cells from the MALT to the mammary gland and secretion of antibodies is important for neonatal immunity:
- Neonatal immune system is poorly developed
- Mucosal surfaces of newborn animals are particularly vulnerable to infection
- Passive transfer of maternal antibody in colostrum & milk protects neonates from pathogens
Farm animal species rely on transfer of antibodies in
Colostrum and milk
Colostrum is rich in
IgG
Milk contains predominantly
IgA (mucosal protection)
IgG in colostrum is important for
systemic protection of the neonate
IgA in milk is important for
mucosal protection of the neonate
Absorption of colostrum
- Colostrum IgG binds to specialised Fc receptors expressed on intestinal epithelial cells of neonates (FcRn).
- Antibodies are actively taken up and passed into lacteals and then on to blood.
Absorption of colostrum : how long is this process active?
This process is only active for the first 24 hrs after birth (most absorption in first 6-12 hrs)
Maternally-derived antibodies (MDA) provide protection for how long?
~12 weeks. Can interfere with vaccination
Antibodies in milk;
- No longer any systemic absorption of antibodies
- But milk contains IgA which continues to protect the GIT of the neonate from enteric pathogens
Failure of Passive Transfer (FPT) =
Insufficient or poor quality colostrum produced by mother
– Premature birth
– Nutritional deficiencies
Inadequate intake by newborn
Why is FPT a major concern in foals
- Foals need at least 400 mg/dL serum IgG
- Foals are susceptible to infection
Diagnosis of FPT:
Blood test ~12 hours of age
Treatment of FPT
If tested < 400 mg/dL and foal less than 18 hours old – Administer oral colostrum to ‘top up’
If tested < 200 mg/dL and foal more than 18 hours old
– Can administer IV plasma infusion
Neonatal isoerythrolysis:
Stallion and mare have incompatible blood types:
- Foal inherits sire’s RBC antigens
- Mare makes antibodies to foetal RBCs
- Foal is born and suckles, absorbing IgG into
the circulation
- Maternal antibodies attack foals RBC’s
- Anaemia and jaundice result
