Hypersensitivity I/II Flashcards
What are hypersensitivities?
Hypersensitivities are undesirable reactions produced by the normal immune system. Can be triggered from autoimmunity, microbes or environmental factors.
What is Type I hypersensitivity?
Type I hypersensitivity is the triggering of the immune system that normally responds to helminths/ multicellular parasites.
*Involves the classic allergic response and production of IgE antibody as mediated by Th2
What is involved in the classic allergic response?
The classic allergic response involves…
- Exposure to innocuous antigen
- antigen presenting cells activate th2
- IL-4 causes class switching of Th2 to IgE
- IL-5 recruits eosinophils
- IL-13 triggers mucous secretion
- IgE production
- IgE opsonises mast cells and basophils via FceRI (sensitization)
- release granuales
What is the classical allergic response upon re-exposure?
Re-exposure:
- Allergens bind to IgE on mast cells
- Inflammatory mediators quickly release granules
- Drives pathology
What are allergens?
Allergens are protein/ chemical Ags, which the individual is exposed to.
What are some tissue specific symptoms of Type 1 Hypersensitivity (gastrointestinal tract, airways, blood vessels + skin)?
Gastrointestinal tract - increased fluid secretion and peristalsis. Causes diarrhea and vomiting
Airways - constriction of airways and increased mucous secretion. Causes wheezing, coughing and phlegm
Blood Vessels - Increased permeability and blood flow. Causes more fluid in tissues
Skin - Increased fluid secretion and vasodilation. Causes swelling, itching and drop in overall blood pressure.
What are some factors towards the susceptibility of type 1 hypersensitivity?
Environmental -> Richer nations have more allergic diseases
Hygiene hypothesis -> Cleaner during childhood = less exposure to allergens
Counter regulation hypothesis -> Less infection causes less efficient Treg production.
Genes -> Linked genomes
HLA Molecules -> IgE production is causes by haplotypes
What is a Type II hypersensitivity?
A type II hypersensitivity is an immune response by IgM/ IgG directed at normal or modified cell surface antigens/ antigen tissue.
Causes cell apoptosis, tissue damage or preventing the function of the antigen.
What mechanism of Type II hypersensitivity causes myasthenia gravis?
Myasthenia gravis is a type II hypersensitivity that results from a blocking of an antigen’s normal function. Antibodies block the ACh receptors in the motor end plates which causes muscular weakness.
What mechanism of Type II hypersensitivity causes Graves Disease?
Graves disease is a type II hypersensitivity that results from a change in the antigen’s normal function. Autoantibodies activate the TSH receptors on the thyroid, causing excessive production of thyroid hormone.
What is the mechanism that causes Rh disease in a newborn?
Rh disease is a type II hypersensitivity where a rehesus negative woman, carries a rehesus positive baby. The maternal IgG antibody reacts with the baby’s. This causes the removal of red blood cells due to activation of the complement system. Can be prevented if the baby is given anti-D antibodies.
What are is the mechanism that causes rheumatic heart disease?
Rheumatic heart disease follows a StrepA infection, where the host’s antibodies cross react with their own antigens. This damages tissue and causes inflammation of the valves, myocardium or pericardium.
