Immune responses Flashcards
What causes a Type I hypersensitivity reaction?
Free antigen cross-links IgE on presensitized mast cells or basophils
An immediate histamine reaction followed by a delayed leukotriene reaction
What causes a Type II hypersensitivity reaction?
An antibody (IgM or IgG) mediated cytotoxic event
think autoimmune to a specific tissue or site where antigen is found
What is a direct Coombs’ test?
Detects antibodies that HAVE adhered to PATIENT’S RBCs
tests an Rh+ infant of an Rh- mother
What is an indirect Coombs’ test?
Detects antibodies that CAN adhere to OTHER’S RBCs
tests an Rh- woman for Rh+ antibodies
What causes a Type III hypersensitivity reaction?
A complex of 3 things (Ag-Ab-complement)…activated complement attracts neutrophils…which come in and release lysosomal enzymes
(think vasculitis and systemic manifestations)
What causes a Type IV hypersensitivity reaction?
Sensitized T cells encounter antigen and release lymphokines…leads to macrophage activation (delayed hypersensitivity)
(NO antibodies)
What is an autograft? Syngenic graft? Allograft? Xenograft?
Autograft…from self
Syngenic graft…from identical twin (or clone)
Allograft…from nonidentical individual of same species
Xenograft…from different species
Transplant rejection happens within minutes. What kind of reaction is it?
Hyperacute.
Type II reaction…pre-existing antibodies react to donor antigen
Transplant rejection happens after weeks-months. What kind of reaction is this
Acute.
Cellular: CTLs activated against donor MHCs
Humoral: Antibodies develop after transplant (so unlike hyperacute)
Transplant rejection happens after months-years. What kind of reaction is this?
Chronic.
Recipient T cells perceive donor MHC as recipient MHC (so unlike acute); however, T cells react against donor antigens presented…both cellular and humoral components
What happens with GVHD?
Grafted immunocompetent T cells proliferate in immunocompromised host and reject HOST cells
