hypersensitivities Flashcards
what are autoimmune diseases a type of ?
hypersensitivity
what are hypersensitivities ?
when the immune system has an over reaction , the harmful immune responses are what produce tissue injury and may cause serious disease.
how many hypersensitivities are there ?
four
what do type one to three immediate hypersensitivity all involve ?
involve antibodies
what does type four delayed hypersensitivity not involve ?
antibodies
type 1 ?
IgE mediated
Type II ?
IgG mediated
Type III ?
immune complex mediated hypersensitivity
Type IV ?
cell mediated
what is type I induced by ?
allergens
can type I be genetically predisposed ?
yes
what can the cutaneous reactions involve ?
on the skin include urticaria which is a rash and this can occur in minutes
pathological reactions ?
oedema which is swelling , vasodilation which is when the blood vessels relax , smooth muscle contraction and anaphylaxis ( Lack of oxygen supply due to contraction of smooth muscle)
how is type one transferred ?
by serum and IgE
what are the effector cells ?
mast cells and basophils that contain granules
what are the secreated mediators ?
mast cell mediators such as histamine , vasoactive amine lipid mediators and cytokines.
why does the mast cell degranulate ?
the IgE antibody and antigen cross link.
what are type II ( IgG) and Type III ( immune complex ) induced by ?
antigens that induce IgG and IgM. These antigens can be anything from food , self antigens and even viral antigens
what are the cutaneous reactons ?
arthus reaction which is a hypersensitivity reaction that occurs several hours to days following the exposure and is marked by the formation of antigen-antibody complexes accompanied by localized inflammation, pain, redness, and sometimes tissue destruction.
what are the pathological responses ?
necrotizing vasculitis is an inflammation of blood vessel walls
How is it transferred ?
by serum and complement fixing IgG and IgM
what are the effector cells ?
neutrophils and monocytes
what are the secreated mediators
products of the complement activation
give a of disease due to type II hypersensitivity ?
haemolytic disease of the newborn
describe it ?
the Rh- mother gives birth to a Rh+ baby with a Rh+ father. The mothers IgG antibody crosses the placenta and responds to the RBC on the baby to destroy them. This destruction of the RBC releases viral toxins which affect the brain. Considerable enlargement of the liver and spleen associated with erythrocyte destruction caused by maternal anti-erythrocyte antibody in the fetal circulation.
what is ADCC ?
antibody dependent cellular cytotoxicity
how can the haemolytic disease be prevented ?
administering Rhogam at the time of delivery
what is type II mediated by ?
immune complexes and resulting complement activation.
what do the complement products elicit ?
localised vasodilation and attract neutrophils.
when are lytic enzymes released ?
due to frustrated phagocytosis
what is frustrated phagocytosis ?
a phagocyte fails to engulf its target, these toxic agents can be released into the environment .
how is tissue damage occured ?
by the complement membrane attack complex
when does serum sickness occur ?
immune complexes are deposited throughout the body so type III
type IV does not involve antibodies , what instead ?
proteins and haptens as well as specific activation of T cells
what is the cutaneous reaction and how long.
contact hypersensitivty and one to two days so longer than type I , II and III
what is the patholgocial reactions ?
perivascular cellular infiltration and oedema occurs
how is it transferred ?
lymphocytes
effector cells ?
CD4+ T cells and activated macrophages
secreated mediators ?
cytokines such as TNF alpha and IFN gamma
summary of hypersensitivty ?
are inflammatory reactions within the humoral or cell-mediated branches of the immune system. Lead to extensive tissue damage and even death. Reactions are classified into four main types according to the mechanism that induces them. Each type generates characteristic effector molecules and clinical manifestation.
what is an allergy a type of ?
hypersensitivity
defintion of allergy ?
disease following a response by the immune system to an otherwise innocuous antigens.
when is IgE produced ?
following a Th2 response
effect of IgE ?
IgE binds to high affinity receptor FceRI on mast cells, basophils and eosinophils. This triggers degranulation of mast cells, basophils and eosinophils and release of mediators and cytokines. This degranulation occurs only when the antigen arrives and crosslinks with the antibody.
why can type I hypersensitive reactoins occur ?
so that parasite killing can occur
where are mast cells most abundant ?
near the body surface
what do mast cells contain ?
granules
role of mast cells ?
provide alert to the immune system and provide a rapid response
what are mast cells important for controlling ?
bacterial infection and parasites
what are the features of an allergen that promote the induction of an allergy ?
- Protein
- Enzymatically active
- Low dose
- Low molecular weight
- Highly soluble
- Stable
- MHC class II binding peptides
effects of degranulation of mast cells ?
Smooth muscle contraction Increased vascular permeability Vasodilation Platelet aggregation Eosinophil chemotoaxins Mucus secretion Circulatory collapse – heart attack
how can you treat type I hypersensitivites with epinepthrine ?
Anaphylactic reactions are treated with epinephrine ( shot adrenaline).
bronchodilators ?
relax the constricted airways during an asthma attack
anti histamines ?
reduce urticaria induced by mast cell and eosinophil degranulation
cromolyn ?
blocks production and release of mediators such as histamine
topical and systemic corticosteroids ?
suppress chronic inflammation associated with asthma and eczema
desensitisation ?
injection of increasing doses of allergen which switches off response .