Flashcards in hypersensitivity and autoimmunity Deck (21)
mechanism of type I hypersensitivity (allergy)
principally arises from the inappropriate synthesis of IgE in response to allergen exposure. This causes the release of inflammatory mediators such as histamine and prostaglandins from mast cells.
effects of type I hypersensitivity
-smooth muscle -contraction
Mechanism of type II hypersensitivity
IgM and IgG antibodies are released against antigens on the surface of cells, these can be exogenous or self.
effects of type II hypersensitivity
causes tissue damage by:
- Fc (surface) binding of Ig and stimulation of phagocytes
-antibody dependent cytotoxicity
-stimulation or inhibition on target cell function
mechanism of type III hypersensitivity
caused by antibodies forming complexes. This is a normal process but can cause problems when they are deposited in places they shouldn't be.
effects of type III hypersensitivity
deposition of antibody complexes are deposited locally in one tissue or throughout the body in many tissues.
mechanism of type IV hypersensitivity
not caused by antibodies but by Th1 cells. An exogenous antigen with alow molecular weight binds with an endogenous protein carrier, Th1 cells rcognise the antigen and release cytokines producing an inflammatory response. The Th1 cells acn also be activated by microorganisms such as mycobacteria.
Th1 cell function
stimulate the activation of macrophages and cell-mediated immunity.
Th2 cell function
stimulate the activation of B lymphocytes
a state of sub-clinical immune sensitisation, associated with type 1 hypersensitivity.
The process whereby the immune system avoids producing damaging reactions against self antigens.
central tolerance mechanism
autoreactive T&B cells are deleted during cell maturation
peripheral tolerance mechanism
autoreactive cells that escape the immune system are inhibited
what causes autoimmunity?
a breakdown in any of the tolerance mechanisms
aetiology of autoimmunity
-genetic factors (inheritance of particular HLA (MHC) types)
-immune regulatory factors (defective tolerance induction, defective peripheral tolerance mechanisms)
-hormone factors ( particularly female hormones)
-environmental factors (infectious agents, sunlight, drugs, chemicals, nutritional factors)
-'other' factors (trauma or malignant disease)
pathogenic mechanisms of autoimmune diseases
same as in normal immune responses.
- cellular (T cell) or humoral (Bcell) activity
-autoantibody activation of complement-mediated inflammation.
-immune complex formation
-recruitment of innate immune components such as phagocytes/ cytokines/ NK cells etc.
genes that code for the MHC, if translation of these genes goes wrong along with environmental factors this can cause autoimmunity.
spectrum of clinical autoimmune disorders
spectrum from asymptomatic to chronic life-threatening disorders.
organ specific autoimmune disorders
immune system attacks one organ, eg autoimmune endocrine disorders
non-organ specific autoimmune disorders
immune system attacks more than one organ or non-organ tissues, eg. joints