In Vitro Damage of Rabbit Platelets by an Unrelated Antigen-Antibody Reaction I. General Characteristics of the Reaction

Summary An in vitro experimental system for the study of mechanisms by which an antigen-antibody system unrelated to the platelet produces platelet damage has been described. The system involves the fluorometric measurement of histamine release from a standarized suspension of washed normal rabbit platelets by various rabbit antibodies and their homologous antigens. Some of the general characteristics of this reaction are that 50% of the histamine release is obtained with antibody concentrations of 0.5 to 1.0 µg/ml and that optimal release occurs with ratios of antibody to antigen in antibody excess in relation to precipitin data. Pepsin digests of rabbit anti-human serum albumin are ineffective. The reaction requires the presence of fresh rabbit plasma. The plasma activity is present in low titer, is heat labile and is removed by absorption with an immune precipitate. Guinea pig plasma does not mediate the reaction with rabbit platelets and rabbit antibody. The time course of the reaction, the effect of varying platelet concentration, and the calcium and magnesium requirements are described. Observations are presented which suggest that the reaction begins in the fluid phase. No evidence of fixation of antibody to the platelet could be found. The primary effect of the reaction on the platelet appears to be lysis, rather than agglutination. The histamine-releasing activity generated by the antigen-antibody reaction is unstable, half the activity being lost in 7 to 8 min at 37°C.