Type IV hypersensitivity reaction (DTH)

Type IV hypersensitivity reaction, commonly referred to as delayed-type hypersensitivity (DTH), is an overreaction of the immune system mediated by T-lymphocytes rather than antibodies (StatPearls, NBK562228). This process involves the activation, proliferation, and mobilization of antigen-specific T-cells, which release pro-inflammatory cytokines like interferon-gamma and tumor necrosis factor-alpha to recruit macrophages and cause tissue damage (Janeway's Immunobiology). It is the underlying mechanism for clinical conditions such as allergic contact dermatitis, the Mantoux tuberculin test, and chronic transplant rejection (NIH, PMC7151780). Pharmacological management typically involves immunosuppressive agents like corticosteroids, which inhibit multiple inflammatory pathways, or calcineurin inhibitors like cyclosporine that specifically block T-cell activation (Britannica). While these therapies are essential for controlling the pathological immune response, they pose significant safety challenges, including an increased risk of opportunistic infections and potential long-term toxicity (PubMed, 30035130). This reaction is characterized by its delayed onset, typically appearing 24 to 72 hours after exposure to the offending antigen. It is further classified into subtypes based on the specific immune cells and cytokines involved, such as Th1, Th2, or cytotoxic T-cells (Journal of Allergy and Clinical Immunology).

Other names

Delayed-type hypersensitivityCell-mediated hypersensitivityT-cell mediated hypersensitivityType 4 hypersensitivity

Therapeutic agents target Type IV hypersensitivity by inhibiting T-cell activation (e.g., calcineurin inhibitors), neutralizing effector cytokines like TNF-alpha or IL-12/23 (e.g., monoclonal antibodies), or broadly suppressing inflammatory gene expression (e.g., glucocorticoids).