Objectives: to investigate the mode of complement activation by SAG.
Methods: SAG-coated microplates were incubated with serum dilutions and C4 deposition was measured with C4 specific antibodies.
Results: We found a dose-dependent C4 deposition on SAG-coated microplates showing that either the classical or lectin pathway of complement was activated. Antibodies against mannose binding lectin (MBL) inhibited C4 deposition and MBL deficient sera were not activated by SAG. These results showed that SAG activates complement through the MBL pathway. After periodic acid treatment of SAG it could not induce C4 deposition anymore. Disappearance of complement activation corresponded with the disappearance of fucose residues on SAG.
Conclusions: SAG activates the complement system through the mannose binding lectin pathway suggesting a role for SAG as a complement activating factor at the mucosal surfaces.