About this Research Topic
Marine invertebrates (MIs) defense strategies are heterogeneous in terms of effector mechanisms and are strictly correlated to the surrounding environment challenges. However, the effector molecules that elicit specific immunological functions have not been deeply addressed so far. Studying the molecular mechanisms involved in the immune performance of MIs is crucial to figure out the way they deal with biotic and abiotic stressors and helps to better understand the whole animal physiology in different environmental conditions. MIs immune system mainly encompasses: 1) physical and chemical barriers that prevent the entry of pathogens into the body and 2) specialized cells and humoral factors that avoid the spread of infections. The microbial clearance can be accomplished either intracellularly, through phagocytosis, or extracellularly, by means of cytotoxic factors which are stored in granules of specialized cells and released (degranulation) upon a microbial challenge. These factors include complement molecules, lectins, agglutinins, lysins, antimicrobial peptides, prophenoloxidase activating system, as well as metabolites and enzymes involved in tuning antioxidant cell activity. Each of them targets different cellular structures and metabolic pathways (e.g., wall permeability changes, lysis, agglutination, opsonization, growth inhibition) to accomplish the clearance of invaders.
Currently, many studies rely on the measure of the transcription level of immune-related genes to define the protein component of the immune system of MIs: this approach conflicts with the promptness that an innate immune defense should display. Moreover, the functional characterization of the products of these genes (e.g., the Pattern Recognition Receptors (PRRs) and related ligand identification) is often missing, as well as the metabolic signals and mechanisms activating pro-proteins (prophenoloxidase and complement systems). On the same line, regarding the soluble immune effectors, a clear picture of secreting cells identity (e.g. some MIs don't have cells in the haemolymph) or the anatomical/physiological degranulation site (several cytotoxic factors are harmful for animal tissues) it's still missing. Similarly, the rate of immunocompetent cells replenishment is not investigated, since many of those cells participating in the first line of response usually dye. Another aspect that should be considered is "the immunometabolism", an emerging field that couples several metabolic pathways to immune effector functions, with the rationale that any changes in metabolites could shape the immune cells activity.
In this Research Topic we aim to provide a comprehensive overview of the biological molecules required for the function and regulation of the MI immune system obtained through a wide-ranging approaches, which integrates advanced cell biology, biochemistry and physiology advanced techniques (i.e., proteomics, metabolomics) with genomics and transcriptomics data. This will help to define the function and the extent of contribution of each effector to the defence strategies of MIs. We welcome the submission of Original Research, Review, Mini-Review, Methods and Perspective articles covering, but not limited to, the following sub-topics on the immunity of marine invertebrates:
1. PRRs and immune receptor functional characterization.
2. Identification of cell-surface markers and their changes upon insult.
3. Lectins, agglutinins and cytokines recognition and function.
4. Hemolymph (cell-free) composition, pH and redox potential in healthy and stressed animals.
5. Immunometabolism of cells interacting with pathogens.
Since the molecular mechanisms of MIs immune defense are highly conserved throughout all animals, a better and deeper knowledge of such mechanisms will shed light also on innate immune defense strategies in more evolved species.
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