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

Introduction

Mediated by T-lymphocytes.

Pathology

• chemical haptens bind to endogenous proteins which act as hapten carriers
• Langerhans' cells act as antigen-presenting cells
  • internalization & processing of hapten-carrier
  • migration to regional lymph node
  • antigen epitopes are presented to T-cell receptors of CD4 cells
• T-cell activation
  • specific recognition of peptide antigen determinants
  • class II MHC molecules on the surface of antigen- presenting cells
• T-cell proliferation into antigen-specific memory cells
• upon re-exposure to antigen, <A19396>T-cells</A19396> are activated to produce cytokines that promote
  • macrophage-mediated inflammatory reactions
  • CD8 T-cell infiltration & activation
  • granuloma formation

More general terms

• hypersensitivity

More specific terms

• 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