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A term used in serology to describe a reaction that leads to the disruption or lysis of a cell. The best example is the lysis of sheep red blood cells by specific antibody and complement in the presence of Ca2+ by (calcium ion) and Mg2+ (magnesium ion), a reaction that forms the indicator system of the standard Wassermann test for syphilis, as well as other complement-fixation reactions. In this example lysis results in the release of cellular hemoglobin into the medium; the reaction may be followed by visual or instrumental estimation of the decreased cell turbidity or the increased color of the medium due to the free hemoglobin. The initiation of lysis by complement can apparently proceed after the attachment of only one molecule of IgM or two molecules of IgG antibody to the red blood cell. IgM and IgG are both immunoglobulins. See Antibody, Complement, Complement-fixation test, Serology