Cytokines are central importance in the regulations of many physiological and morphological events such as immunity, inflammation, tissue remodeling, and embryonic development. While a large number of cytokines have been extensively studied in mammals, little is known in the insect system. The first family of insect cytokines found recently was temporarily referred to as the ENF peptides, which is based on their common N terminal sequence, Glu-Asn-Phe-. These are 23-25 amino acid peptides whose functions are diverse: insect growth regulation, paralysis induction, cardioacceleration, morphogenesis and immune cell stimulation. Growth-blocking peptide (GBP) was the first member ever known as this family. Today, at least 16 members belong to this cytokine family, but all of them were found only in Lepidoptera. Recently, we succeeded in identifying orthologous peptides from Drosophila melanogaster.
Recently we found that expression of antimicrobial protein genes was enhanced by injection of GBP into silkworm larvae. Further, we demonstrated that GBP enhances antimicrobial protein gene expression in Drosophila by using transgenic flies. Although we do not know yet whether the GBP effect on this gene expression is direct or indirect, further studies of this topic will improve our understanding of the role of insect cytokines in their innate immunity.