Hypersensitivity and Autoimmunity Flashcards
What is hypersensitivity?
A group of disorders in which the normally beneficial components of the immune response act in an exaggerated or inappropriate fashion to environmental antigens which do not normally cause tissue damage.
Describe Type 1 hypersensitivity?
Principally arises due to unnecessary synthesis of IgE by the immune system. The IgE is directed against environmental antigens which may be airborne, ingested, injected or encountered through skin contact.
What is involved in the early phase response to allergic reactions?
Preformed mast cell mediators - histamine, eosinophil and neutrophil factors
What is involved in the late phase response to allergic reactions?
Newly synthesised mediators - prostaglandins, leukotrienes
Th2 cytokines
Eosinophil mediators
Describe type 2 hypersensitivity?
Production of IgG and/or IgM antibodies which are directed against cell surface antigens or antigens fixed in tissues.
Antigens can be exogenous (external) or derived from self antigens.
What are the 4 basic stages of a type 2 reaction?
Complement dependent lysis
Fc receptor mediated damage
Antibody dependent cellular cytotoxicity
Effects on target cell function - inhibition or stimulation.
What is immune complex formation?
A molecule formed from the integral binding of an antibody to a soluble antigen.
What are the 3 stages of normal immune complex formation?
Opsonisation - tagging cells so they become desirable to phagocytes and NK cells.
Transportation
Destruction
Describe the basic outline of type 3 hypersensitivity?
Abnormal immune complex formation occurs in either local or systemic tissue.
Complement system is activated and inflammatory cells are recruited.
This leads to tissue damage.
Describe type IV sensitiivity?
Delayed type hypersensitivity as the reaction takes several days to develop.
Not antibody-mediated but rather is a type of cell-mediated response. Mediated by Th1 cells.
What is autoimmunity?
A misdirected immune response that occurs when the immune system goes awry and attacks the body itself.
What are some factors in the aetiology of an autoimmune disease?
Environment Genes Regulatory defects Internal milieu Other factors
What is a hapten?
A small molecule that when combined with a larger carrier (usually a protein) will cause the production of antibodies that are specific to it.
What is an antigen presenting cell?
A cell that displays antigen complexed with major histocompatibility complexes (MHCs) on their surfaces.
T-cells may recognize these complexes.
What is immunological tolerance?
Failure to mount an immune response to an antigen.
T helper cells cause this - if they are deleted or suppressed or rendered inactive they can no longer signal for the production of B cells and CD8+ T cells.
