Delayed Hypersensitivity Type-IV Hypersensitivity Cell-mediated Hypersensitivity Types of delayed hypersensitivity: 1-Bacterial hypersensitivity. 3-Transplant rejection. 5-Drug hypersensitivity.
2-Contact dermatitis hypersensitivity. 4-Fleea-bite dermatitis.
Bacterial hypersensitivity: Numerous bacterial infection causes delayed hypersensitivity as tuberculosis, brucellosis and glanders. It is manifested by erythema and edema to necrosis.
Koch phenomenon It is the reaction caused by tubercle bacilli in normal and immunized guinea pigs. The normal one develops hard nodules at the site of injection within 2 weeks. These nodules are ulcerated and the animals die from generalized tuberculosis within 2 months. The tuberculous guinea pig develops inflammatory edema and necrosis at the site of injection within 1-2 days. The necrotic area sloughs and heals with scar formation, and the animal does not die. Microscopically, granulomatous reaction is seen (Macrophages, lymphocytes and epithelioid cells besides fibrous tissue capsule).