Immulectin-2, a lipopolysaccharide specific lectin from an insect, Manducasexta, is induced in response to gram-negative bacteria

A lipopolysaccharide-specific lectin, immulectin-2, was isolated from plasm a of the tobacco hornworm, Manduca sexta. Immulectin-2 has specificity for xylose, glucose, lipopolysaccharide, and mannan, A cDNA clone encoding immu lectin-2 was isolated from an Escherichia coli-induced M. sexta larval fat body cDNA library. The cDNA is 1253 base pairs long, with an open reading f rame of 981 base pairs, encoding a 327-residue polypeptide, Immulectin-2 is a member of the C-type lectin superfamily, It consists of two carbohydrate recognition domains, which is similar to the organization of M, sexta immu lectin-1, Immulectin-8 was present at a constitutively low level in plasma of control larvae and increased 3-4-fold after injection of Gram negative b acteria or lipopolysaccharide, Immulectin-2 mRNA was detected in fat body o f control larvae, and its level increased dramatically after injection of E . coli. The concentration of immulectin-2 in plasma did not change signific antly after injection of Gram-positive bacteria or yeast, even though its m RNA level was increased by these treatments. Compared with immulectin-1, im mulectin-2 has a more restricted specificity for binding to Gram-negative b acteria. Immulectin-2 at low physiological concentrations agglutinated E, c oli in a calcium-dependent manner. It also bound to immobilized lipopolysac charide from E, coli, Binding of immulectin-2 to lipopolysaccharide stimula ted phenol oxidase activation in plasma. The properties of immulectin-2 are consistent with its function as a pattern recognition receptor for detecti on and defense against Gram-negative bacterial infection in M. sexta.