Type IV hypersensitivity reactions are further classified into subcategories based on T-Cell subtype, type of antigen, and the resulting effector mechanism.

Subcategories of Type IV Hypersensitivities

Type IV hypersensitivities occur when activated macrophages or cytotoxic T cells  lead to tissue damage. 

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The four types of hypersensitivity reactions are classified by their specific immune mechanism:
- Type I
- Type II
- Type III
- Type IV

Types of Hypersensitivity

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Type 1 Hypersensitivities occur when an IgE antibody reacts with an allergen and triggers mast  cell degranulation. Allergens can range from harmless substances such as pollen to hazardous substances such as insect venom or even food intolerances. 

Type 1 Hypersensitivity

Type II Hypersensitivities are also known as cytotoxic hypersensitivities. Cytotoxic hypersensitivity occurs when a IgM and IgG antibodies interact with cellular antigens. These interactions may activate the Complement System or antibody-dependent cell-mediated cytotoxicity with cytotoxic T cells.

Type II (Cytotoxic) Hypersensitivities

Type III Hypersensitivities involve the interactiosn of IgM, IgG, and sometimes IgA antibodies with antigen to form immune complexes. The accumulation of these immune complexes within tissue can lead to tissue damage.

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