Type IV hypersensitivity is also known as what type of hypersensitivity?

Type IV hypersensitivity is also referred to as delayed-type hypersensitivity because it typically takes hours to days for the immune reaction to develop after exposure to an antigen. This reaction is primarily mediated by T lymphocytes (T cells), rather than antibodies, which distinguishes it from the other types of hypersensitivity.

In delayed-type hypersensitivity, upon first exposure to the antigen, memory T cells are generated. Upon subsequent exposure, these T cells become activated and orchestrate an immune response, resulting in inflammation and tissue damage. Common examples include reactions to poison ivy, tuberculosis skin tests, and graft-versus-host disease.

The other types of hypersensitivity are characterized by different mechanisms: immediate hypersensitivity (Type I) involves IgE-mediated responses that occur rapidly; autoimmune conditions (often considered separate from the hypersensitivity classifications) can involve multiple types of hypersensitivity, but are not synonymous with Type IV; and non-specific responses do not accurately describe the targeted nature of Type IV reactions. Thus, identifying Type IV as delayed-type hypersensitivity aligns with its mechanistic process and timing in the immune response.