Autoimmune Disease and Hypersensitivity Reactions Flashcards
What is autoimmunity?
A state that is present when an individual has made an immune response to self-antigens
What provides evidence for autoimmunity in many cases?
The presence of autoantibodies in serum
What can autoantibodies in serum be helpful in?
Diagonsing and monitoring autoimmune diseases
What is meant by autoimmune disease?
The term applied to a disease in which autoimmunity is thought to play a significant pathological role, i.e. when the tissue damage results from the autoimmune response
What are the types of autoimmune disease?
- Organ specific
- Non-organ specific
What is meant by organ specific autoimmunity?
The target antigen is located in one organ
What is meant by non-organ specific autoimmune disease?
The target antigen is located on many different tissues/organs
Give 10 examples of organ-specific autoimmune diseases
- Hashimoto’s
- Thyrotoxicosis
- Primary myxoedema
- Chronic atrophic gastritis
- Pernicious anaemia
- Addisons’s disease
- Myasthenia gravis
- Type 1 diabetes mellitus
- Premature ovarian failure
- Male infertility
Give 4 examples of intermediate/mixed autoimmune diseases
- Goodpasture’s syndrome
- Primary biliary cirrhosis
- Autoimmune haemolytic disease
- Ulcerative colitis
Give 4 examples of non-organ specific autoimmune diseases
- Systemic Lupus Erythematosus
- Rheumatoid arthritis
- Sjogren’s syndrome
- Progressive systemic sclerosis
What does the existence of autoimmune disesae show?
Central tolerance is not fool proof
What is central tolerance?
The mechanism by which auto-reactive B and T cells are deleted
What is peripheral tolerance?
Collective term for further immunological processes that act to avoid the activation of auto-active T and B lymphocytes
What happens when peripheral tolerance breaks down?
Autoimmunity can ensue
What are the potential mechaniams of immunologically mediated tissue injury?
- Defective immunoregulation
- Cytokine dysregulation
- Molecular mimicry
- T cell bypass
- ‘Hidden’ self antigens
What is the mechanism of injury in defective immunoregulation?
Reduction in supressor/regulatory T cell number and/or function
What diseases result from defective immunoregulation?
Thyroid, liver, GI, and other autoimmune diseases
What is the mechanism of injury in cytokine dysregulation?
Cytokines provide additional signals to activate resting or tolerised autoreactive cells
What disease results from cytokine dysregulation?
Autoimmune thyroid disease following IL-2 therapy
What is the mechanism of injury in molecular mimicry?
Pathogen has cross-reactive epitopes with autoantigen; anti-pathogen immune response leads to anti-self response
What diseases result from molecular mimicry?
- Coxsackie virus and glutamic acid decarboxylase in type 1 diabetes.
- Adenovirus 12 and gliadin in coeliac disease
What is the mechanism of injury in T cell bypass?
Novel T cell carrier supplied for an associated T or B cell epitope for which tolerance exists, so T cell help via new carrier activates tolerised cell
What disease result from T cell bypass?
Drug and virus induced auto-immune cytopenias
What is the mechanism of injury of ‘hidden’ self antigens?
Tolerance exists to cryptic antigens (‘immunological ignorence’), and release or presentation of these breaks the tolerance
What diseases result from ‘hidden’ self antigens?
- Sympathetic ophthalmia
- Post myocardial complications
- Dressler’s syndrome
- MS (myelin antigens)
What are hypersensitivity reactions?
Excessive or over zealous immune responses that can lead to tissue damage
What are hypersensitivity reactions the basis of?
Autoimmune disease
What can hypersensitivity reactions occur in response to?
- Infectious agents
- Environmental agents
- Self antigens
Give an example of a disease caused by hypersensitivity to infectious agents
Fulminant hepatitis
Give an example of a disease caused by hypersensitivity to environmental substances?
Hayfever
What are the types of hypersensitivity reactions?
- Immediate hypersensitivity
- Antibody mediated hypersensitivity
- Immune complex mediated hypersensitivity
- Delayed hypersensitivity
What happens in immediate hypersensitivity?
Cross-linking of Antigen-specific IgE molecules on surface of mast cells or basophils
What does the cross-linking lead to in immediate hypersensitivity?
Degranulation of the cells and the release of vasoactive substances
Over what time scale to immediate hypersensitivity reactions typically occur?
In minutes
What do immediate hypersensitivity reactions form the basis of?
Most common types of allergies
What does immediate hypersensitivity represent a component of?
Childhood asthma
What is anaphylaxis?
A severe form of type I hypersensitivity reaction
What triggers anaphylaxis?
The exposure of a pre-sensitised individual to an allergen, causing mast cell degranulation
What does systemic mast cell degranulation lead to?
- Vasodilation
- Tissue oedema
- Airways obstruction
- Fall in blood pressure
- Shock
How should acute anaphylaxis be treated?
Intramuscular adrenaline
What is the purpose of intramuscular adrenaline in acute anaphylaxis?
It promptly reverses the symptoms and signs with an increase in blood pressure and reversal of airways obstruction
What happens in antibody mediated hypersensitivity?
IgG antibodies reacting with antigen present on tissues or on the surfaces of cells
What happens once the antibodies have bound with the antigens in antibody mediated hypersensitivity?
They interact with complement or the FC receptor on phagocytic cells, activating these innate mechanisms leading to the induction of localised inflammatory response and tissue damage
What is the timescale for antibody mediated hypersensitivity?
The reactions may occur very quickly, but may also lead to prolonged activation
Give 4 examples of antibody mediated hypersensitivity reactions
- Goodpasture’s syndrome
- Haemolytic anaemias / Rhesus disease
- Stimulating Ab’s
- Blocking Ab’s
What happens in Goodpastures syndrome?
There are autoantibodies to the basement membrane in the lung and kidney
What disease is caused by the stimulation of antibodies?
Grave’s disease (stimulates TSH)
What diseases are caused by blocking antibodies?
- Myasthenia gravis (Blocks AchR)
- Diabetes (blocks insulin receptor)
What happens in immune complex mediated hypersensitivity?
Deposition of immune complexes, usually IgG antibodies
What happens when immune complexes are deposited in various tissues in immune complex mediated hypersensitivity?
They set up inflammatory reactions similar to Type II reactions (complement activation, phagocyte Fc receptor)
What are the most common sites of Type III reactions?
- Skin
- Joints
- Kidney
How does type III hypersensitivity in the skin present?
Rash
How does type III hypersensitivity in the joints present?
Arthritis
How does type III hypersensitivity in the kidney present?
Nephritis
Give 3 examples of diseases caused by type III hypersensitivity
- Systemic Lupus Erythematosus
- Farmer’s lung
What happens in delayed hypersensitivity?
T cells activate macrophages or cytotoxic T cells
What do activated macrophages/cytotoxic T cells cause?
Tissue damage
What time scale do delayed hypersensitivity reactions typically occur over?
Two to three days after exposure to antigen
What can cause delayed hypersensitivity reactions?
- External agents
- Autoimmune reactions
Give two examples of diseases that are caused by a delayed hypersensitivity reaction to external agents
- Tuberculoid leprosy
- Contact dermatitis
Give two examples of autoimmune diseases caused by delayed hypersensitivity
- Coeliac disease
- Multiple sclerosis
What causes coeliac disease?
A delayed type hypersensitivity reaction taking place in the intestinal wall
What facilitates the reaction taking place in coeliac disease?
The allele HLA-DQ2
What is the mechanism of disease in coeliac disease?
Gluten is digested to gliadin, which is recognised as an antigen by HLA-DQ2 and presented to T cells. B cells then make autoantibodies to the transglutamase that is attached to the gliadin. The T cells interact with macrophages, activating them and causing the hypersensitivity, damaging the intestinal villi
What is the appearance of the damaged intestinal villi in coaelic disease?
Flattened
What happens if gluten is withdrawn from the diet in coeliac disease?
It reverses the process and the villi return to normal architecture
What is immunotherapy?
The manipulation of the immune response to treat disease
What can immunotherapy involve?
- Enhancing immunity
- Suppressing immunity
What immunotherapy enhances immunity?
Vaccination