Abstract
In a model system, immune complexes formed in vitro (NIP–BSA conjugate/anti-NIP antibody) were analysed by platelet aggregation (Pl.A.) and gradient centrifugation. The addition of specific antibody or antigen to immune complexes alters their composition towards different Ag/Ab ratios. This may result in increased, decreased or complete loss of Pl.A. titre. Adding antibody to mixtures of free antigen and antigen excess complexes increased the Pl.A. titre greatly (≥64-fold). The smallest complexes produced in antigen excess Ag/Ab>4 were only weakly Pl.A. active, and the complex could not be separated by gradient centrifugation from the free antigen. The S value of the complex with antigenic activity was greater than that of the original antigen. The titre of antibody excess complexes tended to decrease slightly after addition of low dilutions of antibody. Adding antigen to complexes produced smaller changes in Pl.A. titres than adding antibody. Pl.A. active complexes were also found after refractionation in sucrose gradient of a 20S complex (Ag/Ab∼4), but most of the activity was lost during manipulations. The lost activity could be restored by adding antibody. The possibility of using the Pl.A. technique and sucrose gradient centrifugation to detect and analyse natural immune complexes is discussed.
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Selected References
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