Abstract: Our research group previously found that destruxin A interacts with the hemocytin of the silkworm, Bombyx mori, and strongly suppresses hemolymph immunity, suggesting that hemocytin may become a novel target for pesticide. Therefore, it is necessary to further understand hemocytin. Hemocytin, as a lectin, is an important factor in insect hemolymph immunity to mediate the process of coagulation, nodulation and encapsulation and prevent hemolymph spillage and microbial invasion caused by epidermal breakage, as well as be involved in the fixation and removal of invaded pathogens. Insect hemocytin generally consists of 3 000-4 000 amino acids with multiple and repeatedly arranged domains including FA58C (coagulation factor 5 or 8 C-terminal), VWD (von Willebrand factor type D), TIL (trypsin inhibitor like cysteine rich), VWC (von Willebrand factor type C), CT (C-terminal cystine knotlike), C8 (8 conserved cysteine residues), ChtBD2 (chitin-binding domain type 2), and MUC (mucin-2 protein WxxW repeating region). The amino acid sequence similarity of hemocytin between different insects is quite low, but the domain sequence is highly conserved. Hemocytin is biosynthesized by hemocytes and secreted into the hemolymph in mature form. Hemocytin is the main component of blood clot, forming soft clot by coagulating hemocytes and clotting factors through its fibrous structure to seal the wound, and then forming hard clot and scab through crosslinking. Hemocytin plays an important role in the process of nodulation and encapsulation, agglutinating hemocytes, immune factors and pathogens, and finally combining with melanization to isolate and kill pathogens. Overall, insect hemocytin has not been studied in depth. Analysis of the molecular mechanism of hemocytin regulation of insect immunity is important to enrich the basic research of insect immunology and promote the development of new insecticides based on hemocytin as the target.

Key words:  Hemocytin, hemolymph immunity, lectin, coagulation, encapsulation