Complement

Abstract

Pfeiffer and Issaeff observed in 1894 that cholera vibrios disintegrated when injected into the peritoneal cavities of previously immunized guinea pigs. Bordet demonstrated that the microorganisms also were lysed within minutes when placed in vitro in the presence of serum obtained from immunized animals; however, if the serum was heated to 56 °C for 30 min, or simply allowed to age for a few days, it lost its lytic activity even though the antibodies were preserved. The addition of fresh serum obtained from nonimmune animals restored the lytic activity of serum. This experiment demonstrated that the bacteriolytic action of serum of immunized animals depended upon two factors, one (the antibody) specific and ther- mostabile, and another that was thermolabile and nonspecific, existing in immune serum as well as in normal serum. The latter, initially termed alexin, is now called complement (C). Any immunologic reaction, as in the example cited above (Pfeiffer’s phenom-enon), is initiated by a specific combination of antigens and antibodies. From this point, a series of reactions is unleashed, humoral or cellular in nature, whose final expression is the production of tissue injury.