Effect of calcium and factor D depletion on C3 conversion by rat intestinal glycoprotein

These studies demonstrate that a rat intestinal glycoprotein fraction may activate C3 in normal human serum by the alternative complement pathway alone and by the classical pathway alone. Conversion of C3 by the rat intestinal glycoprotein fraction amounted to 55% when both the classical and the alternative pathways were intact, to 21% when the classical pathway was blocked by ethyleneglycol-bis-(beta-aminoethyl ether)N,N'-tetraacetic acid, and to 21% in Factor-D-depleted serum. Comparable figures for zymosan were 58%, 44%, and 12%, and for sheep erythrocytes sensitized with anti-sheep haemolysin, 27%, less than 1% and 21%, respectively.