Exam 2- Type IV Hypersensitivity Flashcards
true/false: type IV hypersensitivity reactions are categorized as cell-mediated immunity
true
how long do T cell-mediated hypersensitivity reactions take to become apparent?
24 hours
peak 48-82 hours
how is delayed-type hypersensitivity (DTH) transferred?
T-lymphocytes (not serum antibody)
delayed-type hypersensitivity consists of two main phases:
sensitization phase
effector phase
what cells are activated in the sensitization phase of delayed-type hypersensitivity?
Th1 type mostly
CD8+ cytotoxic T cells in a few cases
what are the primary effector cells of the delayed-type hypersensitivity?
macrophages
what is a granuloma?
continued activation of the delayed-type hypersensitivity leading to macrophages adhering closely to each other, assuming and epithelioid shape and sometimes forming multinucleated giant cells
what can result from a granuloma?
caseous (cheesy) necrosis from multinucleated giant cells releasing lytic enzymes
after about 24 hours, evidence of _____________ and ______________ appear, reaching maximal levels 48-72 hours after exposure to the antigen
erythema (redness)
induration (raised thickening)
what are three important cytokines of the delayed-type hypersensitivity reaction?
chemokine MCP-1
IFN-gamma
TNF-alpha
what concept explains the recognition of small molecules such as drugs by T and B cells?
hapten-carrier concept
haptens: small, can covalently adhere to larger molecules
how can a delayed-type hypersensitivity reaction be detected?
inject a small amount antigen intradermally and watching for skin lesion
what can the delayed-type hypersensitivity reaction protect from?
intracellular pathogens and contact antigens
what is a chronic granuloma?
infection fails to resolve
macrophages form epithelioid cells and giant cells
fibrosis and necrosis
what is the mechanism of contact dermatitis?
substances complex with skin proteins and form hapten-carrier complex
can also have metabolites do this (metabolites of drug)
can type IV hypersensitivity arise from allograft rejection?
yes
is type I diabetes autoimmune?
yes, in humans. at least some in dogs
what do patients who have equine polyneuritis have circulating in their blood?
antibodies to a protein found in peripheral myelin
true/false: macrophages are the main effector cells in a DTH reaction
true
true/false: in equine polyneuritis, autoimmune reaction is against central nervous system myelin protein, and involves autoimmune T cells
false: peripheral myeline protein
what is special about type IV hypersensitivity compared to types I-III hypersensitivities?
transferred by T lymphocytes, not serum antibody
what becomes apparent after about 24 hours of a delayed type hypersensitivity reaction?
erythema and induration (raised thickening- not edema)
why is induration hard?
deposition of fibrin in the lesion
what does chemokine MCP-1 do?
attracts monocytes and macrophages to the site of antigen deposition
how do B and T cell recognize drugs or chemicals?
hapten-carrier concept
hapten may also bind to MHC molecule or alter it
how is a delayed type hypersensitivity reaction measured experimentally?
by injecting antigen intradermally and watching for a characteristic skin lesion
what is contact dermatitis caused by?
substances that can complex with skin proteins forming hapten-carrier complex
how does urushiol induce a delayed type hypersensitivity reaction?
after it penetrates the skin, its metabolites act as haptens
