hypersensitivity Flashcards
what type of hypersensitivity is asthma?
type 1 (allergic reaction provoked by re-exposure to a specific type of antigen)
hallmarks of type II hypersensitivity?
antibody-mediated cytotoxic
destruction of cells by IgG or IgM antibodies
complement pathway etc
hallmarks of type III hypersensitivity
immune complex driven disease
when immune complexes are not effectively cleared
serum sickness (snake bite)
what are immune complexes
non cell bound antigen/antibody complexes
symptoms of type III
fever rashes joint pain protein in urine vasculitis glomerulonephritis arthritis
autoimmune disorders w type III
rheumatoid arthritis, MS, SLE (lupus)
SLE- IgGs developed against DNA or proteins
type IV
delayed type, T-cell mediated hypersensitivity
Rate limiting step of all hypersensitivity reaction?
Antigens
What is a hapten
A small molecule which is not antigenic on its own but can form an antigen when associated with a large carrier like a protein
Which hypersensitivity reaction causes a characteristic “wheal and flare”
Type 1
What happens in type 1 hypersensitivity when IgE binds to the surface of innate immune cells eg mast cells
Rapid cross linking and degranulation of mast cells/basophils
End product is the release of histamine, also leukotrienes and prostaglandins
What do leukotrienes and prostaglandins do?
They are smooth muscle contracting molecules
What are the phases of response of a type 1 reaction?
Early phase- caused by bioactive small molecules produced directly by mast cells within minutes of allergen exposure
Later phase- recruitment of early inflammatory cells like neutrophils (few hours later)
Late response- peaks 3-4 days after exposure, high frequencies of eosinophils are recruited, Th2 cells present
Examples of type II hypersensitivity reactions
Mismatched blood transfusion
Haemolytic disease of newborns
Immune thrombocytopenia- antibodies against platelet surface proteins
Graves’ disease - thyroid stimulating antibodies developed
3 possible mechanisms of type II hypersensitivity reactions?
1- anti-receptor activity (blocking/activating function)
2- antibody dependent cell-mediated cytotoxicity (ADCC)
3- classical activation of the complement cascade
Results of type II reactions
Tissue injury eg local/systemic inflammation, cell depletion leading to a loss of function/ imbalance in organ function
what’s an immune complex
an antibody which is bound to its antigen
what is immunogenicity?
the ability of a substance to elicit an immune response
what are DAMPs?
molecules released as a result of non-apoptotic cell death
what are PAMPs?
common molecular patterns found in pathogens and microbes but not in host cells (normally)
what do PRRs do?
host proteins which recognise DAMPs and PAMPs and activate the innate immune system
what is a type 1 response mediated by?
antigen specific IgE antibodies
what is the process of IgE production in type 1 responses?
due to genetics, environment etc..
CD4 cells produce cytokines which act on B cells, causing them to produce IgE
which type of hypersensitivity reaction is also known as antibody-mediated cytotoxic hypersensitivity?
type II
