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AN OVERVIEW OF HYPERSENSITIVITY
REACTIONS
Type I.
Type II.
„immediate”
Type III.
Type IV.
„late”
Antibody mediated
T cell mediated
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
Frustrated phagocytosis mediated by IgG antibodies
Binding
Opsonization Internalization
C3b
C3b
C3b
C3b
Enzyme
release
C3b
C3R
FcR
The target, which
cannot be
phagocytosed, is
damaged
C3b
Absorbed antigen
Opsonized surface Binding Frustrated
(drug)
phagocytosis
Enzyme release
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
Frustrated
phagocytosis
Immune complexes activate the complement system, neutrophils, basophils and
thrombocytes
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
Manifestation of type III hypersensitivity
in lupus erythematosus
Facial, malar "butterfly" rash with characteristic shape across the cheek
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
Delayed-type hypersensitivity (DTH)
(e.g. tuberculin skin test)
TH1 from a previous
immunization (memory)
Tuberculin skin test
Introduction of Ag
Ag = antigen
Purified protein derivate (PPD)
Most type IV hypersensitivity reactions are
orchestrated by the cytokines released by TH1 CD4
cells in response to antigen
DTH as a result of a contact-sensitizing agent*
CONTACT DERMATITIS
*a contact-sensitizing agent is usually a small molecule that penetrates
the skin then binds to self-proteins, making them “look” foreign
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