When the immune system goes wrong Flashcards
Define Hypersensitivity Reactions.
Hypersensitivity is the triggering of an immune response to a harmless antigen or molecule. The inappropriate response leads to tissue damage and sometimes death.
There are 4 main types of Hypersensitivity reactions.
Type I - IgE mediated, allergic response
Type II - Antibody-dependent, cytotoxicity IgM, IgG mediated
Type III - IgG binds to soluble Antigens and forms immune complexes.
Type IV - Delayed-type, cell mediated (Th activated by APC and in the future, T memory cells activate macrophages) antibody-independent
Define Type I Hypersensitivity.
Also known as ‘Immediate hypersensitivity’, Type I is commonly associated with allergic responses.
Atopy (30-50% UK population) is an inherited tendency to make Type I responses
These responses to ‘allergens’ are mediated by IgE, Mast cells (Degranulation causes the release of Histamine) and Th2 responses.
Describe the Th2 response that occurs during Type I hypersensitivity reactions.
Allergen is picked up by an APC and presented on MHC class II to naice CD4+ T cells.
In response to IL-4 released by the APC, the naive CD4+ T cell differentiates into a Th2 helper cell.
Th2 cells release IL-4, IL-5 and IL-13 that act on B cells to causes them to differentiate into plasma cells that produce allergen-specfic IgE antibodies
IgE causes Mast cells to degranulate and release histamine.
Give examples of diseases that cause Type I hypersensitivity reactions and their respective treatments.
Asthma - ß2-adrenoceptor agonist
Perennial rhinitis (Hay fever) - Antihistamines
Allergic eczema - Corticosteroids
Anaphylaxis
What is omalizumab and for which type of hypersensitivity reactions is it used?
A monoclonal antibody against IgE for Type I hypersensitivity reactions.
What does the presence of autoantibodies indicate?
Autoimmune disease affecting B cell activity.
What is Grave’s thyroiditis?
An autoimmune disease characterised by the production of anti-thyroid autoantibodies that bind to the TSH receptor.
Breakdown of the normal negative feedback loop results in the continuous production of thyroid hormones - ‘Hyperthyroidism’
Why is there a risk of baby being born with Grave’s tyroiditis if the mother has the disease?
Just prior to birth, maternal IgG is transferred to the foetus.
Which subsets of T helper cells are involved in Type I diabetes?
Th1 and Th17 which recruit monocytes/macrophages and CD8+ T cells.
Define the types of immunodeficiencies.
Primary - Rare - Cellular or molecular defect
Secondary - More common - Arises as a result of cytotoxic or irradiation therapy, or acquired by a disease (HIV, Leukaemia)
An absent thymus causes what disease?
Di George syndrome
Characterised by severely reduced number and function of T cells
A mutation in CD3-gamma chain is likely to have what effect?
Reduced number of T cells and thus reduced T cell responses.
Give an example of a disease where the number of B cells is normal but there is abnormal production of immunoglobulins.
Hyper-IgM syndrome.
What might cause defective APC/T cell interaction?
IFN-gamma receptor deficiency.
What is the disease characterised by reduced killing activity and migration of Neutrophils?
Chronic granulomatous disease.
