Activation of the classical and properdin pathways of complement by bacterial lipopolysaccharides (LPS)

Bacterial lipopolysaccharides (LPS) have been demonstrated to activate both the classical and the properdin pathways of complement. The lipid A region of the LPS is responsible for classical pathway activation and the polysaccharide region responsible for properdin pathway activation. Classical pathway activation by lipid A does not depend upon antibody to the lipid A and properdin pathway activation proceeds by a lipid A-independent mechanism. The polysaccharide portion of the LPS molecule exerts a modifying influence on the potential anticomplementary activity of the lipid A.