Читать книгу Diagnostics and Therapy in Veterinary Dermatology - Группа авторов - Страница 24

Delayed hypersensitivity reactions involve Th lymphocytes, macrophages, and cytotoxic T lymphocytes. Delayed‐type hypersensitivities are induced by chronic intracellular infectious disease agents such as Mycobacteria spp. or Leishmania spp., as well as contact allergens. For dermatology, contact allergy is the perfect example of a type IV reaction. In contact allergic dermatitis, small molecules from plants or chemicals are absorbed into the skin. These molecules by themselves do not elicit a response from the immune system and are called haptens. Once these haptens attach to a host protein, this larger complex can then be recognized, processed, and presented as a complete antigen by Langerhans cells. During presentation to naïve T cells in the lymph node, the Langerhans cell releases cytokines that induce the formation of Th1 and Th17 cells. These cells then return to the skin and upon reexposure release Th1 cytokines and activate macrophages, causing the clinical signs associated with delayed hypersensitivity.