Hypersensitivity, allergy and inflammation Flashcards
what mediates type 1 hypersensitivity reactions
immediate hypersensitivity
IgE
what mediates type 2 hypersensitivity reactions
antibody-dependent cytotoxicity
IgM, IgG
what mediates type 3 hypersensitivity reactions
immune complex mediated
IgM, IgG
compliment activation
what mediates type 4 hypersensitivity reactions
delayed cell mediated
T cells
3 varieties: Th1, cytotoxic, (Th2)
name some examples of type 1 hypersensitivity reactions
anaphylaxis
asthma
rhinitis
food allergy
name some examples of type 2 hypersensitivity reactions
myasthenia graves
glomerulonephritis
pernicious anaemia
name some examples of type 3 hypersensitivity reactions
SLE
vasculitides
name some examples of type 4 hypersensitivity reactions
chronic graft rejection
coeliac disease
contact hypersensitivity (nickel allergy)
what is the mechanism of type 1 hypersensitivity reactions
primary antigen exposure:
sensitisation occurs because IgE antibodies are produced which bind to mast cells and basophils
secondary antigen exposure:
more IgE antibodies are produced and the offending antigen cross-links IgE on the mast cells/basophils
this leads to degranulation
(CD4 binding leads to a Th1 response rather than Treg)
what is the mechanism of type 2 hypersensitivity reactions
depends on the interaction of antigen with antibody
what is the mechanism of type 3 hypersensitivity reactions
antigen-antibody complexes form within the blood and these are deposited
compliment and cell recruitment/activation occurs and activates other cascades
overall leads to tissue damage
what is the mechanism of type 4 hypersensitivity reactions
the offending antigens cause T cells to activate macrophages and cytotoxic T-lymphocytes
tissue damage is dependant on TNF
what is a chemokine
a cytokine which attracts inflammatory cells
what are the clinical features of asthma
reversible generalised airway obstruction bronchial hyper-responsiveness cough mucus production chest tightness chronic inflammation of the airways
what are the clinical features of hay fever
can be seasonal or perennial sneezing
rhinorrhoea
itchy nose/eyes
nasal blockage, sinusitis, loss of smell/taste
what are the clinical features of allergic eczema
chronic itchy skin rash in flexures of arms and legs
what are the clinical features of anaphylaxis
severe generalised allergic reaction - medical emergency
itching around mouth, pharynx, lips
swelling of lips, throat, other parts of body
wheezing, chest tightness, dyspnoea
faintness, collapse
diarrhoea and vomiting
death
what factors affect development of allergy
genetic risk
environment - age, gender, family size, infections, animals around, diet
what is the pathogenesis of acne
hyperkeratinisation of the epidermis in the infundibulum of hair follicles
accumulation of dead keratinocytes in the lumen of the hair follicle
increased sebum production stimulated by androgens
proliferation of bacteria within pilosebaceous unit
rupture of this unit with further inflammation of the surrounding skin
what is the pathogenesis of eczema
defects in lipids which hold the skin cells together and maintain its barrier function
filagrin gene mutation is present in 10% of cases
what is the pathogenesis of psoriasis
T lymphocytes move into the dermis and initiate cytokine release which leads to keratinocyte over-proliferation
keratinocyte layer becomes much thicker and results in layers which come off at the surface
genetic susceptibility (PSOR1 gene) and environmental trigger
what is the pathogenesis of bullous pemphigoid
blistering condition caused by IgG antibodies directed against BP180 or BP230 (basement membrane antigens)
splits epidermis away from dermis
what is the pathogenesis of pemphigus vulgarisms
autoimmune condition with IgG auto-antibodies directed against epidermal cell surface proteins - desmogleins 1 and 3
loss of cell-cell adhesion within epidermis which causes blisters
what are the significant symptoms of acne
closed comedone open comedone papule nodule pustule
