The dual roles of Bombyx mori immulectin in cuticular melanization and innate immunity

Insect immulectins are involved in various aspects of the innate immunity, including encapsulation, melanization, and phagocytosis. Although the silkworm Bombyx mori immulectin (BmIML) has been reported previously, the ligand and functions of BmIML have not been investigated. Here, we show the dual roles of BmIML in cuticular melanization and immunity of B. mori. BmIML recognizes carbohydrates in a Ca2+-dependent manner and binds to Gram-negative and Gram-positive bacteria, fungi, and yeast. BmIML was expressed in the fat body during infections and localized to the hemocytes of silkworms. Additionally, BmIML was expressed in the epidermis during the prepupal stage and localized to the cuticle of silkworms. After treatment with E. coli, dopa, dopamine, or tyrosine injections, BmIML production was induced in the fat body but not in the epidermis of silkworms. Treatment with BmIML RNAi resulted in the arrest of pupal cuticular melanization. Therefore, we concluded that BmIML is involved in pupal cuticular melanization and innate immunity responses of silkworms, suggesting dual roles for BmIML.