Hypersensitivity and Autoimmunity Flashcards
What is hypersensitivity?
A group of disorders where the normally beneficial components of the immune response act in an inappropriate or exaggerated way to environmental antigens which do not normally cause tissue damage. The exaggerated response is responsible for tissue damage.
What is type one hypersensitivity caused by?
It arises through the inappropriate synthesis of IgE by the immune system. The IgE is directed against allergens (environmental antigens).
It bursts open mast cells to release inflammatory mediators.
Synthesis of IgE on its own is not enough to cause an allergic reaction, environmental and hormonal aspects also play a part.
What is atopy?
A state of sub clinical immune sensitisation so the patient experiences no symptoms.
40-50% of the population are atopic but only around half of these will have symptoms.
What causes type two hypersensitivity?
Damage is caused to the tissue by complement activation, Fc binding of Ig and stimulation of phagocytes, antibody dependant cellular cytotoxicity and effects on target cell function.
It’s difficult to distinguish between autoimmunity and type two.
It is mediated via IgG or IgM antibodies which are directed against antigens on cell surface or in certain tissues. The antigens can be either self or exogenous which is why it’s difficult to distinguish. The mechanisms for tissue damage are the same no matter the type of antigen though.
What causes type three hypersensitivity?
Arises as a result of of abnormal deposition of formed antigen and antibody complexes in tissues. Could be a self or exogenous antigen in the complex.
Immune complex formation can be normal physiological or pathological (problem).
Causes inflammation either as systemic problem (serum sickness) or local in local tissues (Arthus reaction).
What causes type four hypersensitivity?
Doesn’t have an antibody component and is mediated by Th1 cells and their cytokine products like interleukin-2 and gamma interferon. Happens due to body’s inability to destroy environmental agents. The environmental agents don’t cause the harm, it is the immune responses reaction that damages tissue.
Non infectious agents are too small to cause a reaction so they bind to a protein (hapten bound to carrier).
Delay of 48-72 hours between antigen exposure and clinics effect so is often called delayed type hypersensitivity.
What is an autoimmune disease?
A group of clinical disorders characterised by tissue or organ damage mediated through aberrant cellular and/or humoral immunological mechanisms which are directed against autoantigens (self). Can be organ specific or non organ specific due to location of autoantigens so autoimmune diseases are very complex.
What is tolerance?
Process whereby the immune system avoids producing reactions against self antigens.
Central tolerance is deletion of autoreactive T and B cells during maturation.
Peripheral tolerance is inhibiting activity of autoreactive cells which escape central tolerance process.
Breakdown of process causes autoimmune disease.
What are some causes for autoimmune diseases?
Genetic factors Immune regulatory factors Hormonal factors Environmental factors Other factors like malignancy or trauma
What are the effector mechanisms of autoimmune diseases?
Identical to those of normal immune response.
Cellular or antibody activity
Antibody activation of complement mediated inflammation
Immune complex formation
Recruitment of innate immune components
Can get different combinations of these.
