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Biology LibreTexts

16.2: Immediate Hypersensitivities: Type II

Skills to Develop

  1. Describe the mechanism for Type II (antibody-dependent cytotoxicity) hypersensitivity and give 2 examples.

Mechanism: Either IgG or IgM is made against normal self antigens as a result of a failure in immune tolerance , or a foreign antigen resembling some molecule on the surface of host cells enters the body and IgG or IgM made against that antigen then cross reacts with the host cell surface. The binding of these antibodies to the surface of host cells then leads to:

  1. Opsonization of the host cells whereby phagocytes stick to host cells by way of IgG, C3b, or C4b and discharge their lysosomes (see Fig. 1 and Fig. 2);
  1. Activation of the classical complement pathway causing MAC lysis of the cells (see Fig. 3 and Fig. 4); and
  1. ADCC destruction of the host cells whereby NK cells attach to the Fc portion of the antibodies. The NK cell then release pore-forming proteins called perforins and proteolytic enzymes called granzymes. Granzymes pass through the pores and activate the enzymes that lead to apoptosis of the infected cell by means of destruction of its structural cytoskeleton proteins and by chromosomal degradation. (see Fig. 5 , Fig. 5A, and Fig. 6).

 

Examples include:

  • AB and Rh blood group reactions;
  • autoimmune diseases such as:
    • rheumatic fever where antibodies result in joint and heart valve damage;
    • idiopathic thrombocytopenia purpura where antibodies result in the destruction of platelets;
    • myasthenia gravis where antibodies bind to the acetylcholine receptors on muscle cells causing faulty enervation of muscles;
    • Goodpasture's syndrome where antibodies lead to destruction of cells in the kidney;
    • multiple sclerosis where antibodies are made against the oligodendroglial cells that make myelin, the protein that forms the myelin sheath that insulates the nerve fiber of neurons in the brain and spinal cord; and
  • some drug reactions.

Type II hypersensitivity also participates in early transplant rejections.

Summary

  1. During type II (antibody-dependent cytotoxicity) hypersensitivity, either IgG or IgM is made against normal self antigens as a result of a failure in immune tolerance, or a foreign antigen resembling some molecule on the surface of host cells enters the body and IgG or IgM made against that antigen then cross reacts with the host cell surface.
  2. The binding of these antibodies to the surface of host cells then leads to opsonization of the host cells, membrane attack complex (MAC) lysis of the cells, and antibody-dependent cellular cytotoxicity (ADCC) destruction of the host cells.
  3. Examples include AB and Rh blood group reactions and autoimmune diseases such as rheumatic fever, acute glomerulonephritis, myasthenia gravis, and multiple sclerosis.

Questions

Study the material in this section and then write out the answers to these questions. Do not just click on the answers and write them out. This will not test your understanding of this tutorial.

  1. Describe the mechanism for Type II (antibody-dependent cytotoxicity) hypersensitivity and give 2 examples. (ans)

Contributors

  • Dr. Gary Kaiser (COMMUNITY COLLEGE OF BALTIMORE COUNTY, CATONSVILLE CAMPUS)