What is the Difference Between Type I and Type IV Hypersensitivity?

Type I and Type IV hypersensitivity reactions are both immune responses that can cause harm to the host, but they differ in their mechanisms, clinical manifestations, and response times.

Type I Hypersensitivity Reaction

• Mediated by IgE antibodies
• Produces an immediate response after exposure to an antigen
• Involves the sensitization stage and the effect stage
• Common triggers include food products, animal sources, environmental sources, and allergic conditions
• Symptoms include rash, flushing, hives, itching, edema, wheezing, rhinitis, and stomach cramps

Type IV Hypersensitivity Reaction

• Mediated by T cells as a delayed cell-mediated response
• Occurs 48–72 hours after exposure to an antigen
• Subdivided into Type IVa, IVb, IVc, and IVd based on the type of T cell involved
• Triggered by a wide variety of causes, such as contact dermatitis, poison ivy, certain metals, and drugs like antibiotics or anticonvulsants
• Clinical manifestations include contact dermatitis, tuberculin-type hypersensitivity, and granulomatous-type hypersensitivity

In summary, Type I hypersensitivity reactions are mediated by IgE antibodies and produce immediate responses, while Type IV hypersensitivity reactions are mediated by T cells and result in delayed responses. Both types of reactions can cause harm to the host, but they differ in their mechanisms, clinical manifestations, and response times.

Comparative Table: Type I vs Type IV Hypersensitivity

Here is a table comparing Type I and Type IV hypersensitivity reactions:

Type I hypersensitivity reactions are mediated by IgE antibodies and typically occur immediately after antigen exposure, such as in allergic reactions and anaphylaxis. On the other hand, Type IV hypersensitivity reactions are T-cell mediated, delayed in nature (occurring 24 to 72 hours after antigen exposure), and can involve tissue damage mediated by activated macrophages.