The long-term immunological effects of alloferon and its analogues in the mealworm Tenebrio molitor

The subject of this article is a search for the long-term immunological effects of alloferon and 3 structural analogues of alloferon, which were earlier characterized by the highest pro-apoptotic activity in Tenebrio molitor. The differences in the actions of these peptides on immune response were observed. Alloferon increased nodulation and significantly phenoloxidase activity in the hemolymph of experimentally infected T. molitor. However, [Phe(p-NH2)(1)]- and [Phe(p-OMe)(1)]-alloferon strongly inhibited cellular and humoral defense of the mealworm against Staphylococcus aureus infection. One day after injection of these peptides, the specific biochemical and morphological hallmarks of apoptosis in bacteria-challenged hemocytes were visible; in contrast, 3 days after peptides injection in all hemocytes, caspase activation was not observed. However, these new, circulating hemocytes differed from the control and the peptide-untreated bacteria-challenged hemocytes. They had an increased adhesion that led to a separation of viable, anucleated fragments of hemocytes that retain the ability to adhere and to form long filopodia. The peptide-induced separation of hemocyte fragments may resemble the formation of platelets in mammals and perhaps play a role in sealing wounds in insects. The results of in vivo studies may suggest a long half-life of studied peptides in the hemolymph of mealworm. Moreover, we showed the importance of the N-terminal histidine residues at position one of the alloferon molecule for its immunological properties in insects. The results obtained here show that alloferon plays pleiotropic functions in insects.