HUMAN ALTERNATIVE COMPLEMENT PATHWAY-MEDIATED LYSIS OF RABBIT ERYTHROCYTES IS ENHANCED BY NATURAL ANTI-GAL-ALPHA-1-3GAL ANTIBODIES

Human serum is effective at lysing unsensitized rabbit erythrocytes du e to activation of the alternative complement pathway. Hemolysis is kn own to be enhanced by the addition of human IgG, We demonstrate that t he enhancement of alternative pathway-mediated rabbit E lysis by human Ig is due to natural Abs specific for galactosyl (Gal)alpha 1-3Gal. D epletion of normal human serum (NHS) of anti-Gal alpha 1-3Gal Abs remo ves almost all hemolytic activity from NHS, and activity can be restor ed by repletion with anti-Gal alpha 1-3Gal affinity-purified Abs, Fact or B-depleted serum (inactive alternative pathway) did not lyse rabbit erythrocytes. Although C2-depleted serum was fully hemolytic, activit y was removed by depletion of anti-Gal alpha 1-3Gal Abs, Of the total anti-Gal alpha 1-3Gal Abs affinity isolated from NHS, about one-third were IgM and two-thirds were IgG. Both anti-Gala1-3Gal IgG and IgM enh anced alternative pathway-mediated erythrocyte lysis.