A cytolytic function for a sialic acid-binding lectin that is a member of the pentraxin family of proteins

A variety of invertebrates possess plasma lectins with sialic acid recognition capabilities, One of the best studied of these lectins is limulin, which is a member of the pentraxin family of proteins and is found in the plasma of the American horseshoe crab, Limulus polyphemus, We find that limulin is one of several sialic acid-binding lectins of limulus plasma and is present at a much lower abundance than Limulus C-reactive protein, the other plasma pentraxin, Limulin was purified by sequential affinity chromatography on phosphorylethanolamine agarose, which isolates the pentraxins and separates limulin from the other sialic acid-binding lectins of the plasma, followed by fetuin-Sepharose, which binds limulin and separates it from Limulus C-reactive protein, the most abundant pentraxin of the plasma, We show here that limulin is the mediator of the Ca+2-dependent hemolytic activity found in the plasma of Limulus, Plasma that was depleted in the pentraxins by passage over phosphorylethanolamine-agarose or was depleted in the sialic acid-binding lectins by passage over fetuin Sepharose lacked hemolytic activity, Purified limulin was hemolytic at concentrations of 3-5 nM. The other sialic acid-binding lectins of Limulus plasma and Limulus C-reactive protein were nonhemolytic. Foreign cell cytolysis by limulin represents a novel function for a plasma lectin and is the first documented function for limulin.