hypersensitivity Flashcards
define antigen
Any molecule or molecular structure that can be recognised by an antibody or the adaptive immune system.
what is type 1 hypersensitivity?
an allergic reaction provoked by re-exposure to a specific type of antigen referred to as an allergen.
give some example of diseases which arise from type i hypersensitivity
.asthma
.atopic dermatitis
.allergic rhinitis
what mediates type 1 hypersensitive reactions
IgE
what can diagnose allergies
skin prick test
what is the end result which causes the sensitisation of the immune response to allergens causing IgE production
.generation of type 2 helper CD4 T cells
B cell helper follicular CD4 T cells ( B CELLS THAT ASSOCIATE WITH DENDRITIC CELLS AND NEED T CELLS TO ALLOW DIFFERENTIATION)
B cell helper follicular CD4 T cells ( T cell that activates the B cell) causes production of which type 2 cytokines
IL 4, IL13
When type 2 cytokines IL 4 and IL 13 act on B cells, what happens
promote B cell to switch to producing antigen specific IgE.
true or false:IgE is very rarely found in the circulation, even in allergic individuals
true
which cells does IgE particularly rapidly bind to
mast cells and basophils (innate immune cells)
what happens if an allegern is encountered by a cell bound IgE?
rapid crosslinking and degranulation of the mast cell or basophil.
end products of type 1 reactions
release of histamine, a host of cytokines that can recruit other cells and promote further Th2 differentiation, and highly active smooth muscle contracting molecules such as leukotrienes and prostaglandins.
what is the early phase?
a result of bioactive small molecules produced directly by mast cells, occurs within minutes of allergen exposure
what is the later response
later response, is the result of the recruitment of early inflammatory cells such as neutrophils.
what is the late response
where high frequencies of eosinophils are recruited and Th2 cells are present.
what is type II hypersensitivity?
involves the destruction of cells by IgG or IgM antibody bound to antigens present on the surface of the cells.
Give examples of type ii hypersensitivity
hameolytic diseases of newborns
immune thrombocytopenia- where antibodies develop against platelet surface proteins
Graves disease where patients develop thyroid stimulating antibodies that bind the thyrotropin receptor resulting in secretion of thyroid hormones.
list the three mechanisms in which antibodies cause disease
Anti-receptor activity – blocking or activating its function
Antibody dependent cell-mediated cytotoxicity (abbreviated to ADCC)
Classical activation of the complement cascade
what is the complement cascade?
a complex process by which antibody on the surface of cells is recognised by the complement components, ultimately leading to the formation of the membrane attack complex (MAC) in the surface of the cell, and cell death due to loss of osmotic integrity.
what can activation of the complement cascade result in?
inflammation,
opsonisation
recruitment and activation of immune cells.
n ADCC antibody-antigen complexes on the surface of cells are bound by…
Fc receptors
Fc receptors are expressed by
cells such as granulocytes and NK cells
binding of the ADCC antibody-antigen complex to Fc receptors leads to…
directed lysis of the target cell, but also the release of inflammatory mediators, chemokines and cytokines.
type 2 hypersensitivity can lead to…
ocal or systemic inflammation, cell depletion leading to a loss of function or imbalance in organ function.
what are immune complexes?
immune complexes are non-cell bound antigen-antibody complexes which are normally cleared through the activity of the immune system
what happens if immune complexes aren’t cleared?
complexes end up being deposited in the blood vessel walls and tissues, promoting inflammation and tissue damage.
what symptoms arise from immune complexes not being cleared?
Fever rashes joint pain protein in urine vasculitis (blood vessel) glomerulonephritis (kidney) arthritis (joints)
what autoimmune disorders arise from type 111 hypersensitivity
rheumatoid arthritis
multiple sclerosis
systemic lupus erythematosus (SLE)
what is type IV hypersensitivity
involves T cell-antigen interactions that cause activation and cytokine secretion requiring SENSITIZATION of lymphocytes
give 2 examples of type IV hypersensitivity
dermatitis
turburcular regions
graft rejections
what causes dermatitis
caused by exposure to poison ivy, where a small molecule called urushiol acts as a hapten (and binds to proteins in the skin), drives a T helper 1 response
