Complement (C3) conversion by rat intestinal glycoprotein and its degradation products.

Abstract

Several fragments obtained from alkaline borohydride degradation of a rat intestinal glycoprotein fraction have been tested for anti-complementary activity. Oligosaccharide alditols with a molecular weight of less than about 1 X 10(3) daltons showed no activity, whereas reduced oligosaccharides in the molecular weight range of about 1 X 10(3) to 3 X 10(3) daltons exerted a minor conversion of C3 by the alternative pathway. The low molecular weight fragments tested did not influence C3 conversion induced by the intact intestinal glycoprotein fraction. Of the fragments, a peptide fraction, with an 'average' molecular weight of 2 X 10(3) daltons, and peptide-containing glycoconjugates exerted activation by C3 by both the classical and alternative pathways. Classical pathway activation by the intestinal glycoproteins depended on antibody, whereas alternative pathway activation did not. Alternative pathway activation appeared to require Factor B in that the intestinal glycoproteins induced no C3 conversion in serum heated to 50 degrees C for 20 min. The rat intestinal glycoproteins had no protease activity on casein and no stimulating effect on human lymphocytes in vitro. Branching of oligosaccharide chains was not indicated by the methylation analyses carried out.