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type 4 hypersensitivity; T-cell-mediated (delayed) hypersensitivity

Mediated by T-lymphocytes. Pathology: 1) chemical haptens bind to endogenous proteins which act as hapten carriers 2) Langerhans' cells act as antigen-presenting cells a) internalization & processing of hapten-carrier b) migration to regional lymph node c) antigen epitopes are presented to T-cell receptors of CD4 cells 3) T-cell activation a) specific recognition of peptide antigen determinants b) class II MHC molecules on the surface of antigen- presenting cells 4) T-cell proliferation into antigen-specific memory cells 5) upon re-exposure to antigen, T-cells are activated to produce cytokines that promote a) macrophage-mediated inflammatory reactions b) CD8 T-cell infiltration & activation c) granuloma formation

Specific

contact dermatitis (exogenous eczema) exanthematous drug eruption (morbilliform exanthem) hypersensitivity pneumonitis; extrinsic allergic alveolitis; pigeon breeder's lung; bird fancier's lung; farmer's lung; allergic pneumonitis tuberculid

General

hypersensitivity

References

  1. Medical Knowledge Self Assessment Program (MKSAP) 11, 16. American College of Physicians, Philadelphia 1998, 2012