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Flashcards in Immune responses Deck (11):

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?


Type II reaction...pre-existing antibodies react to donor antigen


Transplant rejection happens after weeks-months. What kind of reaction is this


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?


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