Inhibition of human factor B activity of the properdin system by human and guinea-pig sera.

The activity of factor B of the alternative pathway of complement activation was assayed in human and guinea-pig sera using the radial haemolytic assay with various MgCl2 and RB concentrations. RB were prepared by heating at 50 degrees C human or guinea-pig sera to render them deficient in factor B. Whatever concentrated RB and MgCl2 were, guinea-pig sera seemed unable to react while human sera gave an haemolytic reaction with both human and guinea-pig RB. We described an inhibition of human factor B activity by human and guinea-pig RB under certain conditions. This inhibition is more pronounced in the case of guinea-pig RB.