Hypersensitivity Flashcards
What is an antigen
Any molecule or molecular structure that can be recognised by an antibody or the adaptive immune system
Differen structures of antibodies
How do T cells differentiate
What is type 1 hypersensitivity known as
Immediate or anaphylactic hypersensitivity
What are types of Type 1 hypersensitivity
Asthma
Allergic rhinitis
Atopic dermatitis
What is Type 1 hypersensitivity provoked by
Re-exposure to a specific type of antigen
What are Type 1 hypersensitivity mediated by
IgE
Non allergic individuals only make IgE in response to parastic infections or potent venoms
What are some different types of allergens
Food
plants
Due to multiple sites on antigen that antibody can stick onto
How do you diagnose the allergy
Skin prick test
Wheal and flare
End result of sensitization of the immune response to allergens
Type 2 help CD4 T cells
B cell helper follicular CD4 T cells
They both produce type 2 cytokines IL-4 and IL-13
These act on B cells
B cells therefore produce IgE
Why are IgE rarely found in circulation
Normally bound to surface of innate immune cells, espeically mast cells and basophils
These granuloytic cells express high affinity IgE receptor (Fc epsilon receptor 1)
What happens when an allergen is encountered by cell bound IgE
Rapid crosslinking and degradulation of mast cell or basophil
Happens much faster and across a much broader site
Diagram of Hypersensitivity 1
What is the end product of all hypersensitivity reactiosn
Release of histamine
Host of cytokines
Further Th2 differentiation
Highly active smooth muscle contracting
What are the different phases of type 1 hpyersensitivity
Early phase: occurs within minutes
Later response: Recuitment of early inflammatory cells
Late response: Peaks 3-4 days after exposure where high frequencies of eosinophils are recruited
What is Type 2 hypersensitivity referred to as
Antibody-mediated cytotoxic hypersensitivity
Which antibodies are invovled
IgG and IgM
Examples of Type 2 hyeprsensitivity
Mismatched blood transfuction
Haemolytic disease of newborns by transfer of antibodies across placenta
Immune thrombocytopenia (antibodies develop against platelet surface proteins)
Graves disease (thyroid stimulating antibodies (thyroid stimulating antibodies that bind to thyrotropin receptor)
How does type 2 hypersentivity happen
Exposure to foreign antigen
Aberrant response to a self antigen
What are the 3 mechanisms of Type 2 Hypersensitivity
- Anti-receptor activity
- Antibody dependent cell-mediated cytotoxicity
- Classical activation of the complement cascade
What is the complement cascade
Leads to MAC formation as well as inflammation opsonisation and recruimtment and activation of immune cells
What happens in ADCC
In antibody-dependent cell mediated cytotoxicity antibody-antigen complexes on the surface of cells are bound by Fc receptors expressed by granulocytes and NK cells resulting in directed lysis
This releases inflammatory mediators, chemokines and cytokines
Type 3 hypersensitivity is sometimes known as
Immune complex driven disease
What are immune complexes
Non-cell bound antigen-antibody complexes which are normally cleared through the activity of the immune system
What happens in Type 3 hypersensitivity
Immune complexes cannot be efficiently cleared e.g. antibodies reacting against self-antigens
Immuen complexes deposited in the blood vessel walls
Causes fever, rashes, joint pain or arthritis, glomerulonephritis
What are some diseases of type 3 hypersensitivity
Rheumatoid arthritis
Multiple clerosis
Systemic lupus erythematosus (develop IgGs against DNA or proteins present in the nucleus of cells)
How does serum sickness work
Anti-serum is given for snake venom (antibodies)
Body will react to produce antibodies against venom antibodies
Doesn’t cause a problem until person is bit again
What is Type 4 hypersensitivity known as
Delayed-type or T cell mediated hypersensitivity
Why is type 4 hypersensitivity slower
It is initiated by T cells
Antigen is presented to naive T cells by dendritic cell
Results in T memory cells
Subsequent exposure means they promot inflammation
Memory T cell response is slower than antibodies
Examples of type 4 hypersensitivity (contact dermatits)
urushiol acts as a hapten
drives a T helper 1 response
Reexposure means that cytokines such as IFN-gamma are released
This promotoes pro-inflammatory activation of macrophages resulting in swelling and oedema
What are examples of type 4 hypersensitivity
Nickel salt and hair dyes
Measles and mycobacerium tuberculosis
How to test for TB
Injection of small amuonts of M.tb into skin (type 4 reaction)
What Type 4 hypersensitivity can be related to others
Asthma ( T helper cells produce soluble mediators that promote bronchoconstriction)
Tissue graft rejection (CD8 T cells)
Diagram of summary of hypersensitivity
