In type II hypersensitivity reactions, complement-fixing antibody reacting with cell surface antigens may cause injury or death of the cell. This phenomenon is especially striking in the case of red blood cells, because the reaction results in rupture of the cells and a visible release of hemoglobin. The reaction can occur in response to foreign antigenic or haptenic material such as a drug that attaches to erythrocytes or to platelets, but more common examples are transfusion reactions and hemolytic disease of the newborn. In these cases, normal red cells are destroyed as a result of antibodies reacting with erythrocyte epi-topes. Cells can be destroyed in type II reactions not only by complement lysis, but also by antibody-dependent cellular cytotoxicity (ADCC). ■ epitope, p. 397 ■ complement, p. 381
Normal erythrocytes have many different antigens on their surfaces, and these antigens differ from one individual to another. When a person receives transfused red blood cells that are anti-genically different from his or her own, immune lysis (by antibody and complement) of the red blood cells often results. This
Table 18.2 Antigens and Antibodies in Human ABO Blood Groups
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