Type IV hypersensitivity
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31 terms
Terms | Definitions |
|---|---|
 Delayed type hypersensitivity, Type IV | T cell mediated hypersensitivity reaction occuring more then 24 hrs after contact with the antigen |
| Delayed type hypersensitivity characeristics | an influx of nonspecific inflammatory cells, mostly macrophages into tissues. Lacks antibody involvement |
| DTH response | not always detrimental - but can cause extensive tissue damage and plays an important role in host defense against intracellular pahtogens and contact antigens |
| causative agents of type IV hypersensitivity rxn | bacteria, fungi, protozoa, noninfectious agents (chemicals) |
| transfer of DTH rxn | cannot be transferred via serum, only by T lymphocytes |
| sensitization phase of DTH | 1-2 wks after primary contact with antigen |
| peptide epitopes and MHC class II proteins, CD4+ T cells associate to result in | a ell mediated response and the generation of memory Tdth cells |
| PPD | purified protein derivative, results in activation nof memory Th1 cells by APC and intiation of DTH |
| activated Tdth cells | secrete cytokines that result in vasodilation, increased vascular permeability, and recruitment/activation of macrophages |
| neutrophil appearence | early, 6-12 hrs |
| blood monocyte and T cell appearence | 24-48 hrs after antigen exposure |
| crucial cytokines | TNF-alpha, IFN-y, MCF, MIF, IL-1, TNF-beta |
| tissue damage in DTH | results from release of hydrolytic enzymes and reactive oxygen intermediates from macrophages |
| the most important clinical form of DTH | granulomatous hypersensitivity |
| granulomas formation due to | 1. persistance of particles in macrophage, 2. persistant immune complexes, 3. chronic irritants |
| ACD | allergic contact dermatitis, a T cell mediated eczematous disease |
| ACD characterized by | 48-72 hr delayed eczematous response to the epicutaneous application of the antigen |
| ACD sensitization phase | 10-14 days, haptens form complexes with skin proteins |
| epidermal langerhans cells | modified self proteins in ACD internalized by these cell and then migrate as veiled cell to regional lymph nodes |
| veiled cells produce | in the lumph node present to CD4+ and form memory CD4+ Th1 cells |
| Tdth | Th1 cell |
| elicitation phase | occurs with 48-72 hrs, activation of the Tdth cells and cytokines |
| CD8+ T cells role | contribute to tissue damage by cell-mediated cytotoxicity |
| lipid soluable chemicals | can cross the cell membrane and modify intracellular proteins |
| lesion | acute and chronic eczematous rxn observed in a hairless area |
| DDX of DTH | patch testing, positive test = local erythema and vesiculation |
| poison ivy exposure | oils (urushiol) leads to rash within 12-48hr and persists 2-4wks |
| pentadecacatechol | lipid soluable hapten, formed intermediate of urushiol |
| poison ivy lesion origin | lysis of altered epidermal cells by CD8+ T cells and lytic enzymes released from activated macrophages |
| treatment for ACD | steroids |
| pathology of ACD | mononuclear cell infiltration |
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