Drosophila melanogaster Responses against Entomopathogenic Nematodes: Focus on Hemolymph Clots

Abstract

Several insect innate immune mechanisms are activated in response to infection by entomopathogenic nematodes (EPNs). In this review, we focus on the coagulation of hemolymph, which acts to stop bleeding after injury and prevent access of pathogens to the body cavity. After providing a general overview of invertebrate coagulation systems, we discuss recent findings in Drosophila melanogaster which demonstrate that clots protect against EPN infections. Detailed analysis at the cellular level provided insight into the kinetics of the secretion of Drosophila coagulation factors, including non-classical modes of secretion. Roughly, clot formation can be divided into a primary phase in which crosslinking of clot components depends on the activity of Drosophila transglutaminase and a secondary, phenoloxidase (PO)-dependent phase, characterized by further hardening and melanization of the clot matrix. These two phases appear to play distinct roles in two commonly used EPN infection models, namely Heterorhabditis bacteriophora and Steinernema carpocapsae. Finally, we discuss the implications of the coevolution between parasites such as EPNs and their hosts for the dynamics of coagulation factor evolution.

Transglutaminase 3 negatively regulates immune responses on the heart of the mosquito, Anopheles gambiae

“…Transglutaminases catalyze the formation of isopeptide bonds between glutamine and lysine residues, and are encoded in the genomes of bacteria, plants and animals 17 – 19 . Transglutaminases in Drosophila melanogaster perform pleiotropic functions, including cuticular morphogenesis, hemolymph coagulation, pathogen entrapment, and peritrophic matrix formation 20 , 21 . Transglutaminases in other arthropods have similar functions, and of interest to the present study is that they coagulate wounds in horseshoe crabs 22 , 23 and crayfish 24 , 25 , and are involved in immune defenses against viruses, bacteria and fungi in shrimps 26 , 27 , crabs 28 and termites 29 , 30 .…”

Immune Response of Drosophila suzukii Larvae to Infection with the Nematobacterial Complex Steinernema carpocapsae–Xenorhabdus nematophila

“…The proPO system is a complex enzymatic cascade responsible for the melanization reaction. This process leads to the production of melanin that can encapsulate invaders and opsonic factors enhancing immune reactions; moreover, drosophila phenoloxidases (PO) seem to play a role also in hemolymph clotting as a further defensive mechanism aimed to prevent the entry of nematodes and microorganisms [12][13][14]. Unlike the proPO system, which is rather well preserved and homogeneous among arthropod species, AMPs show different structural conformations among insects and various mechanisms to kill microorganisms [15].PRRs also activate cellular responses like phagocytosis and encapsulation; phagocytosis is a conserved process mediated by hemocytes against various small targets including bacteria and yeast [16,17].…”

Haemocyte‐mediated immunity in insects: Cells, processes and associated components in the fight against pathogens and parasites

“…These epithelia are normally in contact with microbes, and they serve as natural routes of microbial infection. Upon breaching or wounding of these walls, haemolymph (an aqueous medium in which the haemocytes are suspended and circulating) coagulates in the injured area and a haemolymph clot appears in this region [4,5]. Damaged epithelial cells release chemotactic cytokines like hemokinin [6] and haemocyte chemotactic peptide [7], which may be signalling molecules and/or adhesion peptides that induce rapid aggregation of haemocytes.…”