Type I. „immediate” Type II.Type III.Type IV. „late” Antibody mediatedT cell mediated AN OVERVIEW OF HYPERSENSITIVITY REACTIONS

Types of antibody mediated hypersensitivity reactions Fc  RIα)

TYPE II HYPERSENSITIVITY IgG or IgM antibodies bound to antigens of particular cells or the extracellular matrix

Mechanisms of type II hypersensitivity reactions Cellular and Molecular Immunology, 7th ed., 2012 Elsevier

The target, which cannot be phagocytosed, is damaged Absorbed antigen (drug) Binding Opsonization Internalization Enzyme release Opsonized surface Binding Frustrated Enzyme release phagocytosis Frustrated phagocytosis mediated by IgG antibodies

Examples of type II hypersensitivity

Pemphigus vulgaris

Development of drug sensitivity I.

Development of drug sensitivity II.

TYPE III HYPERSENSITIVITY Antibodies form immune complexes in the circulation, and the complexes are subsequently deposited in tissues, particularly in blood vessels, and cause injury

Immune complex–mediated tissue injury Cellular and Molecular Immunology, 7th ed., 2012 Elsevier

Tissue damage caused by deposited immune complexes Immune complexes activate the complement system, neutrophils, basophils and thrombocytes Frustrated phagocytosis

Examples of human immune complex–mediated diseases

Symptoms caused by type III hypersensitivity reactions depend on the site of immunecomplex deposition

Arthus-reaction Localized Type III hypersensitivity Local vasculitis develops as a result of immune complex deposition Inhaled antigens (fungi, animal feces) may induce similar reaction in the lung (Farmer’s lung and piegeon-breeder’s lung)

Localized deposition of immune complexes within a tissue causes a type III hypersensitivity reaction

Facial, malar "butterfly" rash with characteristic shape across the cheek Manifestation of type III hypersensitivity in lupus erythematosus

Pathologic features of antibody-mediated glomerulonephritis Cellular and Molecular Immunology, 7th ed., 2012 Elsevier

TYPE IV HYPERSENSITIVITY REACTION T lymphocytes injure tissues either by triggering inflammation or by directly killing target cells

Type IV hypersensitivity reactions

Mechanisms of T cell–mediated hypersensitivity reactions Cellular and Molecular Immunology, 7th ed., 2012 Elsevier

T H 1 from a previous immunization (memory) Delayed-type hypersensitivity (DTH) Delayed-type hypersensitivity (DTH) (e.g. tuberculin skin test)

Tuberculin skin test Ag = antigen Purified protein derivate (PPD) Introduction of Ag

Most type IV hypersensitivity reactions are orchestrated by the cytokines released by T H 1 CD4 cells in response to antigen

*a contact-sensitizing agent is usually a small molecule that penetrates the skin then binds to self-proteins, making them “look” foreign DTH as a result of a contact-sensitizing agent* CONTACT DERMATITIS

Poison ivy Anacardiaceae (family), Toxicodendron (genus) Toxicodendron radicans or Rhus toxicodendron

Physical contact with poison ivy transfers pentadecacatechol, which causes dermatitis

CELIAC DISEASE

Delayed-type hypersensitivity