Antibodies specific for cell and tissue antigens may deposit in tissues and cause injury by inducing local inflammation, they may induce phagocytosis and destruction of cells, or they interfere with normal cellular functions (Fig. 1).

Fig1. Effector mechanisms of antibody-mediated diseases. Antibodies cause disease by A, Inducing inflammation at the site of deposition; B, Opsonizing cells (such as red cells) for phagocytosis; and C, Interfering with normal cellular functions, such as hormone receptor signaling. All three mechanisms are seen with antibodies that bind directly to their target antigens, but immune complexes cause disease mainly by inducing inflammation (A). TSH, Thyroid-stimulating hormone.

• Inflammation. Antibodies against tissue antigens induce inflammation by attracting and activating leukocytes. IgG antibodies of the IgG1 and IgG3 subclasses bind to neutrophil and macrophage Fc receptors and activate these leukocytes, resulting in inflammation . The same antibodies, as well as IgM, activate the complement system by the classical pathway, resulting in the production of complement by-products that recruit leukocytes and induce inflammation. When leukocytes are activated at sites of antibody deposition, these cells release reactive oxygen species and lysosomal enzymes that damage the adjacent tissues.

 • Opsonization and phagocytosis. If antibodies bind to cells, such as erythrocytes, neutrophils, and plate lets, the cells are opsonized and may be ingested and destroyed by host phagocytes.

• Abnormal cellular responses. Some antibodies may cause disease without directly inducing tissue injury. For example, in pernicious anemia, autoantibodies specific for a protein required for absorption of vitamin B12 cause a multisystem disease due to B12 deficiency. In some cases of myasthenia gravis, antibodies against the acetylcholine receptor inhibit neuromuscular transmission, causing paralysis. Other antibodies may directly activate receptors, mimicking their physiologic ligands. The only known example is a form of hyperthyroidism called Graves disease, in which antibodies against the receptor for thyroid-stimulating hormone activate thyroid cells even in the absence of the hormone. 

مواضيع ذات صلة

Diseases Caused by T Lymphocytes

Etiology, Examples, and Therapy of Immune Complex–Mediated Diseases

Examples and Treatment of Diseases Caused by Cell- or Tissue-Specific Antibodies

Hypersensitivity Disorders Caused by Immune Responses : Clinical Syndromes and Therapy

Activation of Mast Cells and Secretion of Mediators

Activation of Th2 Cells and Production of IgE Antibody

Transplantation of Blood Cells and Hematopoietic Stem Cells

Prevention and Treatment of Graft Rejection

Monocytes–Macrophages: Host Defense Functions: Phagocytosis

Mononuclear Phagocyte System

Immune Mechanisms of Graft Rejection

Induction of Immune Responses Against Transplants