Conservation of Cell Communication Systems in Invertebrate Host–Defence Mechanisms: Possible Role in Immunity and Disease

Abstract

Innate immunity is continuously revealing multiple and highly conserved host–defence mechanisms. Studies on mammalian immunocytes are showing different communication systems that may play a role in coordinating innate immune responses also in invertebrates. Extracellular traps (ETs) are an immune response by which cells release net-like material, including DNA, histones and proteins. ETs are thought to immobilise and kill microorganisms, but are also involved in inflammation and autoimmune disease. Immune cells are also known to communicate through extracellular vesicles secreted in the extracellular environment or exosomes, which can carry a variety of different signalling molecules. Tunnelling nanotubes (TNTs) represent a direct cell-to-cell communication over a long distance, that allow for bi- or uni-directional transfer of cellular components between cells. Their functional role in a number of physio-pathological processes, including immune responses and pathogen transfer, has been underlined. Although ETs, exosomes, and TNTs have been described in invertebrate species, their possible role in immune responses is not fully understood. In this work, available data on these communication systems are summarised, in an attempt to provide basic information for further studies on their relevance in invertebrate immunity and disease.

Extracellular DNA traps in a ctenophore demonstrate conserved immune cell behaviors in a non-bilaterian

“…ETosis can be induced in vertebrate granulocytes and leukocytes with pharmacological agents that activate production of ROS via discrete intracellular signaling pathways 10,11,16 . Though ctenophore genomes appear to lack predicted gene homologs to many classic innate immunity pathway cell surface receptors and signaling intermediaries, many components of metazoan stress response pathways, as well as secondary messenger machinery, are present 20,26,27 .…”

“…The release of extracellular DNA traps (ETs) is a morphologically and molecularly distinct immune-based process of cell death during which ETosis-competent immune cells cast nuclear chromatin material into the surrounding extracellular space in filamentous nets, trapping and killing invading microbes 8,9 . ETosis can be initiated by activation of specific signaling cascades following exposure to cytokines, microbes, pathogen-associated molecular patterns (PAMPs), or pharmacological agents 10,11 . Initially believed to be a behavior exclusive to vertebrate immune cells, a number of recent studies have highlighted ETosis as an antimicrobial behavior also present in non-vertebrate taxa 3,4,[12][13][14][15] .…”

Functional and Morphological Changes Induced in Mytilus Hemocytes by Selected Nanoparticles

“…The presence and roles of TNTs have been mainly described in mammalian cells, including immune cells, where they play several roles in responding to stress, including the transport of nanomaterials [ 46 , 47 ]. Interestingly, we have recently reported the presence of similar structures exchanging lysosomal vesicles and mitochondria in live M. galloprovincialis hemocytes [ 48 ]. The results here obtained suggest that, under certain experimental conditions, NPs may induce TNT formation in invertebrate immune cells, thus probably allowing for an intercellular communication system that may participate in the protection against NP toxicity.…”

In Vitro and In Vivo Models to Assess the Immune-Related Effects of Nanomaterials

“…Conversely, several basic mechanisms of innate recognition (through innate receptors and sensors) and engulfment/degradation by phagocytes are largely conserved and active with very similar mechanisms in every species. Thus, the model plant Arabidop-sis thaliana, the woodlouse Porcellio scaber, the fruit fly Drosophila melanogaster, the nematode Caenorhabditis elegans, the earthworm Eisenia fetida, the blue mussel Mytilus galloprovincialis, the sea squirt Ciona intestinalis, the sea urchin Paracentrotus lividus, the cephalopod Octopus vulgaris and many others can be used for environmental nanoimmunosafety studies, but also as a proxy for human innate responses [26,30,[74][75][76][77][78][79][80][81][82][83].…”