Which type of hypersensitivity reaction involves T cell-mediated immune responses?

Type 4 hypersensitivity reactions, also known as delayed-type hypersensitivity, are characterized by T cell-mediated immune responses. Unlike other types of hypersensitivity that primarily involve antibodies, Type 4 reactions are orchestrated by T lymphocytes and occur hours to days after exposure to the antigen.

In this type of hypersensitivity, specific CD4+ T helper cells or CD8+ cytotoxic T cells recognize and respond to antigens presented by major histocompatibility complex (MHC) molecules on antigen-presenting cells. This activation leads to a cascade of immune responses, including the recruitment of other immune cells such as macrophages, which ultimately results in inflammation and tissue damage. Conditions such as contact dermatitis and tuberculin reactions are classic examples of Type 4 hypersensitivity.

Understanding the mechanism of Type 4 hypersensitivity is crucial because it highlights the role of T cells in mediating immune responses and differentiating it from other types of hypersensitivity that involve antibodies. This distinction is fundamental in various clinical scenarios, such as managing allergic reactions and autoimmune disorders.