Types II, III & IV Hypersensitivity Flashcards
What are the targets of type II hypersensitivity reactions?
Cell bound antigens
Exogenous - blood group antigens, Rhesus D
Endogenous - self antigens, most common
What are some outcomes of type II hypersensitivity reactions?
Complement activation or Ab-dependent cell cytotoxicity =>
Tissue or cell damage
Receptor stimulation or blockage =>
Physiological change
What is the role of complement activation in type II hypersensitivity reactions?
Cell lysis - membrane attack complex
Neutrophil activation - C3a, C5a
Opsonisation - C3b
What is an example of a type II hypersensitivity reaction mediated by IgM?
Haemolytic transfusion reaction
Incompatible ABO or a Rhesus D
Donor RBC destroyed by recipient’s immune system
RBC lysis involving antibodies - IgM
What is an example of a type II hypersensitivity reaction mediated by IgG?
Haemolytic disease of the newborn
Rh+ father and a Rh- mother
Mother carries her first Rh+ baby => Rh antigens can enter mother’s blood during delivery
Therefore mother produces anti-Rh antibodies (IgM)
Second Rh+ baby => anti-Rh antibodies cross placenta (now IgG) => damage to foetal RBCs
How long does a type II hypersensitivity reaction take to develop?
5-12 hours
How long does a type III hypersensitivity reaction take to develop?
3-8 hrs
What does the pathophysiology of a type III hypersensitivity reaction involve?
Involves immune complexes between IgG/IgM and antigens
Results in tissue damage by immune complex deposition
What factors influence type III hypersensitivity?
Complex size
Intermediate sized IC can’t be cleared therefore cause problems
Host response
Low affinity antibody, or complement deficiency
Local tissue factors
Haemodynamic (filtration, BP, turbulence) or physiochemical reactions
Where can immune complexes be deposited?
Joints
Kidneys
Small vessels
Skin
What is the mechanism of type II hypersensitivity reactions?
1) Intermediate-sized immune complexes deposited in tissues
2) Activation of complement
3) Neutrophil chemotaxis
4) Neutrophil adherence and degranulation
What are some examples of type III hypersensitivity reactions?
Rheumatoid arthritis
Glomerulonephritis
Systemic lupus erythematous
How long does a type IV hypersensitivity reaction take to develop?
24-72 hrs
Which cells are involved in a type IV hypersensitivity reaction?
Lymphocytes
Macrophages
What are some subtypes of type IV hypersensitivity reactions?
Contact hypersensitivity - epidermal reaction
Tuberculin hypersensitivity- dermal reaction
Granulomatous hypersensitivty - persistence of antigens, walls off infected cells
