The binding of activated C3 to polysaccharides and immunoglobulins

The nature of the acceptors for activated C3 present on immunoglobulins was studied by using the fixation of C3 to Sepharose beads after activation with trypsin as a model system. C3 fixation to Sepharose is a property exclusively linked to the short active state of C3. This binding could be inhibited by various carbohydrates and their affinity for C3 was calculated from the extent of the inhibition of the binding of C3 to Sepharose. Mono-, di-tri- and tetrasaccharides showed on a molar basis an increasing but still weak affinity for active C3. The C3 fixation of Sepharose could be inhibited by immunoglobulins and the degree of inhibition was proportional to the hexose content of the immunoglobulin preparations. The isolated polysaccharide moiety of IgG gave the same inhibition as the intact IgG. In addition cell wall polysaccharides of Salmonella abortus equi were found to have a high affinity for active C3. Thus, the more complex polysaccharides such as those present on immunoglobulins and cell walls might function as acceptor for activated C3.