BINDING OF AGGREGATED HUMAN GAMMA-GLOBULIN BY RAJI CELLS - C1Q WILL ENHANCE ONLY IF IT IS DISSOCIATED FROM THE C1 MACROMOLECULAR COMPLEX

  • 1 January 1981
    • journal article
    • research article
    • Vol. 43  (2) , 287-292
Abstract
The role of complement components in binding of aggregated human .gamma.-globulin (AHG) to [human Burkitt''s lymphoma] Raji cells was examined using the Raji cell radioimmunoassay. AHG incubation in normal human serum enhanced up to 5-fold the binding of these complexes by Raji cells. This enhanced binding was mediated primarily be C3 [complement component 3] receptors, however, as much as 30% of the enhanced binding was due to a heat-labile protein in serum. AHG incubated with serum-EDTA bound to Raji cells up to 2-fold more than AHG incubated with unchelated serum. Since purified Clq also enhanced binding, AHG binding after incubation with serum-EDTA was probably mediated by C1q. The enhancement effected by Clq occurred only if C1q bound 1st to AHG, not to the Raji cells, and if Clq bound in the absence of C1r and C1s. Speculations on a role for C1q in biological processes must consider whether the C1q in serum is available to participate. Apparently, whole serum activated by AHG contained only a small C1q amount available for cross-linking of particles. Thus, the potential C1q involvement in biological reactions in vivo is probably limited.