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any one of a number of antibodies that cause the dissolution of various cells of an organism or bacterium. Cytolysins include hemolysins, which act on erythrocytes, leukocytolysins, which act on leukocytes, spermatolysins, which act on spermatozoa, and bacteriolysins, which act on bacteria. Their action is related to the partial destruction of the cell membrane and the release of cell contents into the surrounding fluid.

Cytolysins were discovered in 1898 by the French scientist J. Bordet in animal serums after the repeated introduction of foreign erythrocytes. Human cytolysins belong to the M and G classes of immunoglobulins, more precisely, to the classes IgM, IgG2, and IgG3. The cytolytic action of cytolysins is observed only in the presence of complement. In cytolytic reactions, the active centers of cytolysins bind to the membrane of a cell, altering the conformation of the antibody molecule; consequently, a special receptor of the molecule interacts with the first component of complement. In order to destroy the cell membrane and then “dissolve” the cell, that is, release the cell contents into the surrounding fluid, the participation of all nine components of complement is necessary.

Cytolysins play a certain role in infection immunity, transplantation immunity, and antitumor immunity and in the pathogenesis of several diseases, for example, hemolytic anemia. The cy-tolysin that acts on human lymphocytes is the active principle of antilymphocytic globulin and antireticular cytotoxic serum, both of which are preparations used in medicine. Immune cytolysis forms the basis of the binding of complement; in particular, it lies at the basis of the Wasserman reaction in syphilis. In addition to specific cytotoxic antibodies, certain cells of the immune system, namely, lymphocytes and macrophages, upon reacting with an antigen, may release nonspecific cytotoxic factors, such as proteins with a molecular weight of 80,000 to 160,000 called lymphotoxins, as well as toxic phospholipids and lysosomal hydrolases. These substances participate in cellular immunity.

In a broader sense, the term “cytolysin” is used for any substance that dissolves cells.


Kul’berg, A. Ia. Immunoglobuliny kak biologicheskie reguliatory. Moscow, 1975.
Waksman, B. H., and Y. Namba. “On Soluble Mediators of Immunologic Regulation.” Cellular Immunology, 1976, vol. 21, no. 1.


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