Phases of type IV hypersensitivity

What is required for Type IV hypersensitivity?

Type IV hypersensitivity requires antigen-presenting cells (APCs) to present the antigen to T cells.

What occurs during the sensitization phase of Type IV hypersensitivity?

During the sensitization phase, APCs present the antigen to T cells via MHC molecules, activating the T cell that recognizes the MHC-antigen complex. This activation usually occurs due to the action of localized APCs.

What happens during the effector phase of Type IV hypersensitivity?

After T cell sensitization, subsequent exposure to the antigen drives the differentiation of the T cell into an effector T cell. Typically, this is a TH1 helper T cell, which secretes IFN-γ and CXCL8, activating and recruiting macrophages.

How long does it take for symptoms of Type IV hypersensitivity to appear?

Symptoms associated with delayed-type hypersensitivity appear 48 to 72 hours after antigen exposure, when maximal T cell activation occurs.