INFLUENCE OF AGGREGATE SIZE ON THE BINDING AND ACTIVATION OF THE 1ST COMPONENT OF HUMAN-COMPLEMENT BY SOLUBLE IGG AGGREGATES

  • 1 January 1982
    • journal article
    • research article
    • Vol. 45  (4) , 705-713
Abstract
The interaction between small aggregates of human IgG and the 1st component of human complement C1 was studied. Stabilized soluble IgG aggregates of restricted size were prepared by heat aggregation of human IgG, followed by sucrose-density ultracentrifugation. Human C1 was isolated in its precursor form by euglobulin precipitation, followed by gel filtration and immunoadsorption. A C1 preparation was obtained of which more than 90% was still in its unactivated form. Soluble aggregates containing 20, 10 or 5 molecules IgG, and monomeric IgG were tested for their ability to bind and to activate C1. The binding of C1 was determined by C1 consumption; the activation of C1 was measured as the increased ability of the C1 preparation to consume purified human C4 after the incubation with the aggregates. The 3 aggregates tested and monomeric IgG were all able to bind and to activate C1, but the efficiency of both processes markedly increased with increasing aggregate-size. All 4 preparations activated an appreciable amount of C1 at concentrations that did not result in any detectable C1 fixation. C1 apparently can be activated during a short, transient binding to small aggregates or immune complexes that have a low avidity for C1, after which the activated form, C.hivin.1, is released into the medium.