allergy and hypersensitivities Flashcards
what is hypersensitivity
damage to the host arising from the immune response- often involves inflammation
where can the immune response arise from in hypersenistitivity
- innocuous stimuli- allergy
- arise from autoimmunity or as a side effect of responses to pathogens (immunopathology)
what is type 1 hypersensitivity and what are some examples of the inflammatory mediators released
- it is immediate
- mast cells have an fc receptor which binds to contant region heavy chain of antibody- when allergen present the antibody variable region binds to it- this triggers the mast cell to release inflmmatory mediators- degranulation
- some examples of the inflammatory mediators released include histamine, serotine, tnf alpha, prostaglandins, leukotrienes
what are examples of type 1 hypersensitivity
- upper respiratory tract=hay fever
- lower respiratory tract= asthma
- mouth,throat,gut= food
-systemic= peanuts
-infections= worms - skin= eczema
why are some people more allergic than others
- genes
- environment (hygiene hypothesis)
- dietary conundrums (no peanut allergy in africa)
what are some treatments
- anti- histamines
- corticosteroids (suppress transcription of pro inflammatory genes)
- sodium chromoglycate (blocks mediator release from mast cells)
- omalizumab ( anti IgE- monoclonal antibodies)
- repeated low dose allergen infection or sublingual (slit)
what is type 2 hypersensitivity
- antibody (IgG, IgM) bind to surface of own cells which can cause inflammation by triggering the complement or macrophages
- leads to phagocytosis, cell lysis, release of cytokines
examples of type 2 hypersensitivity
- infection
- autoimmune diseases
- transplantation e.g. acute haemolytic transfusion reaction
- haemolytic disease of the new born (blue baby syndrome)
what is type 5 hypersensitivity and example of a condition
-antibody binds to host cell receptors and act like agonists
-graves disease>overstimulation of thyroid
what is type 3 hypersensitivity
- immune complex formed
- multiple antibodies and antigens needed and lattice structure formed which is the immune complex
- immune complex precipitates often onto walls which triggers inflammation and the activation of immune cells
examples of type 3 hypersensitivity
- allergies such as farmers lung> pigeon fanciers disease
- infections such as post streptococcal glomerular nephritis
- autoimmune diseases such as systemic lupus erythtematous
what is type 5 hypersensitivity - delayed type
- does not involve antibodies
- t cell mediated
-much slower pathology (hours to a few days) - tcr binds to peptide mhc leading to overactivation of t cells> activation of macrophages by release of interferon gamma
- once macrophage activated it release interleukin 1 and tumour necrosis factor (pro inflammatory cytokines)
what are examples of type 4 hypersensitivity
- allergies such as allergic contact dermatitis (nickel, poison ivy, hair dye_> coeliac disease
- infections such as tb and the granuloma, viral hepatitis, covid
- acute graft rejection
- some autoimmunity ( hashimotos thyroditis)
what can a mantoux test be used for
- test for tb- type 4 hypersensitivity
what are innate hypersensitivities divided into
- acute and chronic
