Disorder Of The Immune System Flashcards
What causes type I hypersensitivity?
Examples of substances that causes it are pollen, animal hair, house dust mite, mounds, insect bites, food, latex and medicine.
What happens with type I hypersensitivity?
First exposure to pollen is the sensitivity phase. This is followed by B lymphocytes recognise the antigen. They internalise the antigen and present it to TH 2 cells which then secret IL4 which induce B cells to switch class and become IgE producing cells.
Next stage is the the effector phase. This is when IgE that was produced previously diffuses throughout the body l. IgE comes in contact with mast cells and bind to the Fc region of the antibody by taking tail.
During second exposure to pollen there will already be mast cells with antibodies attached to them. Pollen then enters and bind to the antigen which cause granules of histamine released.
What is late phase reaction in type I hypersensitivity.
This is when mast cells generate other cytokines and they encourage T helper cells to produce cytokines as well and this is what cause the allergic reaction to pro long.
How is type II and type III hypersensitivity different to type I?
Type II and type III hypersensitivity is initiated by antigen and antibody interaction which is IgM and IgG mediated.
What is an example of a type II hypersensitivity.
Example of type II hypersensitivity is myasthenia Gravis, rhesus isoimmunisation, haemolytic disease of the new born and Graves’ disease.
What is myasthenia Gravis?
In myasthenia Gravis, autoantibodies to acetylcholine receptors are produced. These block acetylcholine receptors at the post synaptic neuromuscular junction. Muscle contraction is therefore diminished.
What is rhesus isoimmunisation
Rhesus antigen is carried on red blood cells. If the mother is Rh D negative and the father is RhD positive. During the first pregnancy the mother is sensitises and often sensitisation happens at birth of the first infant. In this case the mother will make antibodies to RhD.
Come second pregnancy and the Foetus is Rh positive, small amounts of erythrocytes will pass through placenta which stimulate memory cells. More anti-RhD antibodies are then produced and cross the placenta. The newborn will have a haemolytic disease.
What is Graves’ disease?
This is a autoimmune thyroid disease. In healthy individuals pituitary makes thyroid stimulating hormone TSH. TSH binds to TSH receptors on cells of the thyroid follicle which gets triggered to produce thyroid hormones. Thyroid hormones then engage in an inhibiting feedback loop to stop more TSH from being produced.
In Graves’ disease there will be circulating autoantibodies to TSH receptors. These bind to TSH receptors and trigger the cell to release thyroid hormones so the control system is not working anymore.
What is an example of hypersensitivity III?
An example is Systemic lupus erythematosus.
This disease involves autoantibody directly against several self molecules such as DNA and nuclear ribonucleo proteins. This causes immune complexes to form. The antibodies in these immune complexes can fix complement which result in tissue injury.
Complexes are trapped in kidney so it cause glomerulonephritis. B cell activation are abnormal in patients with SLE. There is a higher number of B cells at all stage of activation in SLE patients.
B cells in these patients are more sensitive to stimulating cytokines.
There are changes in T cell function where one of which is T helper 1 cell response is reduced. There are problem with phagocytes cells where immune complexes are not cleared by phagocytes.
It affects 40 in 100,000 people in Europe 9/10 affected are women.
What is type IV hypersensitivity?
Type 4 hyperventilate is delayed hypersensitivity. This is mainly T cell mediated but dendritic cells, macrophages and cytokines contribute to the disease process.
What is an Mantoux test?
This test involves a patient being injected with an extract of mycobacterial antigen in the skin. Then macrophages present antigen which is followed by T helper cells being activated. T helper cells in response to it by releasing cytokines which activate macrophages to release cytokines. This cause firm red swelling of skin.
What is endocrine autoimmune disease?
This is another type IV hyper sensitivity disease. This is insulin dependent disease more specifically type I diabetes.
Beta cells in the islet of Langerhans act as auto antigen. These auto antigens are presented by antigen presenting cells in the context of MHC class II, this stimulate CD4+ T helper cells. T helper I cells release cytokines and activate T cytotoxic cells which damage beta cells.
What are hypersentivity gastrointestinal disease?
In coeliac disease small intestines are intolerant for gluten. Patients produce antibodies which may have originated from intestinal mucosa. T cells become present in the intestines and this lead to Vilnius atrophy.
