The allatotropin/orexin system as an example of immunomodulatory properties of neuropeptides.

The central nervous system (CNS) plays a critical role in signal integration in animals and allows the orchestration of life processes to maintain homeostasis. Current research clearly shows that inflammatory processes can also be modulated by the CNS via the neuroendocrine system. One of the neuropeptide families that participate in vertebrates in this process is orexins (OXs). Interestingly, our previous results suggested that a similar dependency may also exist between neuropeptides and immune system activity in insects. Due to the structural homology of orexin and allatotropin receptors and the functional similarity between these two neuropeptide families, the main aim of this research was to perform a complex analysis of the relationships between allatotropin (AT) and the insect immune response. Our results revealed functional similarities between vertebrate OXs and insect ATs. Similar effects were observed in the profile of the expression level of the gene encoding the AT precursor in the Tenebrio molitor nervous system and in the general action of Tenmo-AT on selected immune parameters of the tested beetles. Moreover, for the first time in insects, we confirmed the role of cytokines in the modulation of neuroendocrine system by determining the effect of Spätzle-like protein injection on the expression of genes encoding AT precursor and receptor. All these results are important for understanding the evolutionary basis of hormonal regulation of the immune response.

Solanum nigrum Fruit Extract Modulates Immune System Activity of Mealworm Beetle, Tenebrio molitor L.

Here, we report the first evidence concerning the modulation of insect immune system activity after applying Solanum nigrum fruit extract (EXT). We focused on two main issues: (1) is EXT cytotoxic for Tenebrio molitor haemocytes? and (2) how EXT affects the basic immune mechanisms of T. molitor. The results indicate cytotoxic action of 0.01 and 0.1% EXT on beetle haemocytes. Both the injection of EXT and incubating haemocytes with the EXT solution on microscopic slides significantly increased the number of apoptotic cells. However, 24 h after injection of 0.1% EXT cytotoxic effect of the tested extract probably was masked by the increased number of circulating haemocytes. Application of 0.01 and 0.1% EXT led to impairment of the activity of basic immune mechanisms such as phenoloxidase activity and the lysozyme-like antimicrobial activity of T. molitor haemolymph. Moreover, the EXT elicited significant changes in the expression level of selected immune genes. However, some of the immunomodulatory effects of EXT were different in beetles with and without an activated immune system. The obtained results are an essential step toward a complete understanding of the EXT mode of action on the T. molitor physiology and its potential usage in pest control.