Displays several functions associated with host defense: it promotes agglutination, bacterial capsular swelling, phagocytosis, and complement fixation through its calcium-dependent binding to phosphorylcholine. Homodimer; disulfide-linked. It is not known if it assembles into a pentraxin (or pentaxin) structure. Pentraxins have a discoid arrangement of 5 non-covalently bound subunits. Glycosylated. Belongs to the pentraxin family.