Innate Immune Memory in Invertebrate Metazoans: A Critical Appraisal

Improving the odds of survival: transgenerational effects of infections

Recent studies argue for a novel concept of the role of chromatin as a carrier of epigenetic memory through cellular and organismal generations, defining and coordinating gene activity states and physiological functions. Environmental insults, such as exposures to unhealthy diets, smoking, toxic compounds, and infections, can epigenetically reprogram germ-line cells and influence offspring phenotypes. This review focuses on intergenerational and transgenerational epigenetic inheritance in different plants, animal species and humans, presenting the up-to-date evidence and arguments for such effects in light of Darwinian and Lamarckian evolutionary theories. An overview of the epigenetic changes induced by infection or other immune challenges is presented, and how these changes, known as epimutations, contribute to shaping offspring phenotypes. The mechanisms that mediate the transmission of epigenetic alterations via the germline are also discussed. Understanding the relationship between environmental fluctuations, epigenetic changes, resistance, and susceptibility to diseases is critical for unraveling disease etiology and adaptive evolution.

KDM4 Regulates the Glycolysis of Hemocytes in the Immune Priming of Eriocheir sinensis

Immune priming confers a sustained, augmented response of innate immune cells to a secondary challenge, a process that is characteristically reliant on metabolic reprogramming. Recent evidence suggests that histone demethylases play essential roles in the immune priming, while its regulation role in the metabolic reprogramming remains largely unknown. In the present study, the concentration of glucose was significantly down-regulated in the hemocytes of crab Eriocheir sinensis after secondary stimulation with Aeromonas hydrophila, while the expression levels of phosphofructokinase (EsPFK) pyruvate kinase (EsPK), hexokinase-2 (EsHK-2) and Glucose-6-phosphate dehydrogenase (EsG-6-PD), along with the concentrations of lactate and the ratio of NAD+/NADH, were elevated. Additionally, the levels of H3K9me3 and its enrichment at the promoters of EsPFK and EsG-6-PD were significantly decreased at 7 days after A. hydrophila stimulation. The lysine Demethylase 4 homologue (EsKDM4) was observed to translocate into the nucleus of crab hemocytes after A. hydrophila stimulation, and its activity markedly increased after secondary stimulation with A. hydrophila. Following RNA interference of EsKDM4, there was a significant increase in H3K9me3 levels, and the enrichment of H3K9me3 at the EsPFK and EsG-6-PD promoters, as well as the concentration of glucose, in the hemocytes of crabs after secondary stimulation with A. hydrophila. Furthermore, mRNA transcripts of EsPFK and EsG-6-PD, as well as the concentration of lactate and ratio of NAD+/NADH, significantly decreased after secondary stimulation. These results suggested that EsKDM4 mediates the enrichment of H3K9me3 at the promoters of EsPFK and EsG-6-PD, thereby regulating glycolysis during the immune priming of crabs.

The ultrastructural identity of some cells in Sphaerolaimus gracilis de Man, 1876

The fine structure of fibroblasts, lymphocytes, neurosecretory cells, stem cells, and steroidogenic cells in the nematode Sphaerolaimus gracilis was studied by transmission electron microscopy. Fibroblasts, lymphocytes, and stem cells were found in the lateral position at the level of the renette pore (ventral pore). Fibroblasts were characterized by long cellular processes. The cytoplasm consisted of a network of irregularly arranged microscopic filaments. The nucleus was large, triangular, rectangular, or oval. Occasionally, small, oval, or basket-shaped mitochondria and some cisternae of rough endoplasmic reticulum were observed in the periphery of the cell. Lymphocytes were round and had a large round nucleus encircled by a thin cytoplasmic rim. Indistinct cisternae of rough endoplasmic reticulum, an oval mitochondrion, and several ribosomes were observed in the cytoplasm. A large rectangular stem cell dorsally abutted lymphocytes on both sides of the esophagus. The cytoplasm of stem cells had tiny cisternae of the rough endoplasmic reticulum and small vesicles in the periphery of the cell. The nucleus was large and rectangular, and the nucleolus was characterized by a granular structure. Steroidogenic cells were embedded into the lateral epidermal cord of the midbody. The cell was characterized by a large nucleus, a voluminous vacuole, a mitochondrion of tubules, and several vesicles in the cytoplasm. Neurosecretory cells and interneurons were found in the lateral midbody close to the steroidogenic cells. The present study aimed to characterize the ultrastructure of the cells of Shaerolaimus gracilis with their close structural resemblance to fibroblasts, lymphocytes, stem cells, steroidogenic cells, and neurosecretory cells in other animals and evaluate their possible function when considering their morphology.

Leishmania-sand fly interactions: exploring the role of the immune response and potential strategies for Leishmaniasis control

Leishmaniasis is a neglected tropical disease caused by protozoan parasites of the genus Leishmania, affecting millions of people worldwide. The disease is transmitted by the bite of infected female sand flies, which act as vectors and hosts for the parasites. The interaction between Leishmania parasites and sand flies is complex and dynamic, involving various factors that influence parasite development, survival and transmission. This review examines how the immune response of sand flies affects vector competence and transmission of Leishmania parasites, and what the potential strategies are to prevent or reduce infection. The review also summarizes the main findings and conclusions of the existing literature and discusses implications and recommendations for future research and practice. The study reveals that the immune response of sand flies is a key determinant of vector competence and transmission of Leishmania parasites, and that several molecular and cellular mechanisms are involved in the interaction between parasite and vector. The study also suggests that there are potential strategies for controlling leishmaniasis, such as interfering with parasite development, modulating the vector's immune response or reducing the vector population. However, the study also identifies several gaps and limitations in current knowledge and calls for more comprehensive and systematic studies on vector-parasite interaction and its impact on leishmaniasis transmission and control.

The Loss of Beneficial Thermal Priming on Global Coral Reefs

Warm-season marine heatwaves (MHWs) have greatly increased in frequency, severity, and extent over the last few decades, driving more frequent and severe coral bleaching episodes. Given the grave near-term threat to coral reefs imposed by MHWs, it is important to assess the mechanisms by which corals may acquire higher thermal tolerance. Recent field and laboratory studies have demonstrated that exposure to sublethal heat stress, known as "priming," can reduce bleaching susceptibility during a subsequent MHW. Little is known, however, about how often priming conditions occur, and how effective those conditions may be at protecting coral reefs. We employed a global historical coral bleaching database and a high-resolution sea surface temperature dataset to assess the frequency of priming and examine its effect on coral bleaching sensitivity on a global scale. The analysis showed that coral reefs in parts of the western to central tropical Pacific experienced priming on average over twice a decade and had a higher likelihood of priming protection. Mixed-effects regression models indicated that priming conditions could mitigate coral bleaching response by up to 12% in advance of a moderate MHW. However, the protective effect of priming decreased, and even became harmful, with more severe MHWs. We detected spatial variations in priming frequency that could provide insight for conservation planning and explain some variations in bleaching sensitivity to MHWs. Even so, our findings suggest that thermal priming will not be sufficient to protect most coral reefs from MHWs in the future, without substantial efforts to mitigate climate change.

The combined effect of herbicide and Bacillus thuringiensis exposure delays development in the red flour beetle

The use of herbicides and their long persistence in the environment have raised concerns about potential harm to ecosystems and human health. However, there is a gap in the knowledge regarding the effects of continuous exposure to residues or admitted field doses on non-target organisms such as insects that inhabit croplands and play key ecological roles. Furthermore, the potential impact of this exposure on host-pathogen interactions remains largely unstudied. This study adopted an eco-immunological perspective, investigating the influence of herbicides on an organism's interaction with natural pathogens. The impact of this combination of multiple stressors was studied in larvae of the red flour beetle, Tribolium castaneum Herbst, 1797, previously treated with a pendimethalin-based commercial formulation (PND) and exposed to the natural entomopathogen Bacillus thuringiensis (1x109, 1x1010 cells/mL). The effects of three PND concentrations (i.e. a recommended field rate, a soil contaminant concentration and the maximum residue limit admitted in grain in EU countries: 4L/ha, 13 and 0.05 ppm, respectively) on life history traits such as developmental time, pupation rate and survival rate and the expression levels of antimicrobial peptides (AMPs) were assessed. The results showed that even at doses considered safe for human consumption or field application, exposure to PND had an impact on beetle larvae, affecting their vulnerability to B. thuringiensis. The combined experience of exposure to PND and B. thuringiensis at the larval stage resulted in a delay of larval development, a reduction in the number of pupae and emerging adults, and alterations in their body condition. Moreover, changes in the expression levels of the analysed AMPs, including Attacin 1, Defensin 2 and Coleoptericin 2, were recorded as markers for immune activity against the bacterium. The findings of this study highlight the general need for further studies on the effects of commonly used herbicides on the physiology of non-target organisms and on host-pathogen interactions at the community level. Additionally, there is a need for the establishment of revised residual levels that are deemed non-toxic to soil organisms and humans.

Making Neurobots and Chimerical Ctenophores

Making living machines using biological materials (cells, tissues, and organs) is one of the challenges in developmental biology and modern biomedicine. Constraints in regeneration potential and immune self-defense mechanisms limit the progress in the field. Here, we present unanticipated features related to self-recognition and ancestral neuro-immune architectures of new emerging reference species - ctenophores or comb jellies. These are descendants of the earliest survival metazoan lineage with unique tissues, organs and independent origins of major animal traits such as neurons, muscles, mesoderm, and through-gut. Thus, ctenophores convergently evolved complex organization, compared to bilaterians. Nevertheless, their neural and immune systems are likely functionally coupled, enabling designs and experimental construction of hybrid neural systems and even entire animals. This report illustrates impressive opportunities to build both chimeric animals and neurobots using ctenophores as models for bioengineering. The obtained neurobots and chimeric animals from three ctenophore species (Bolinopsis, Mnemiopsis, and Pleurobrachia) were able to be autonomous and survive for days. In sum, the unification of biodiversity, cell biology, and neuroscience opens unprecedented opportunities for experimental synthetic biology.

Laboratory Replication of Ostreid Herpes Virus (OsHV-1) Using Pacific Oyster Tissue Explants

Pacific oysters (Crassostrea or Magallana gigas) are one of the most economically important aquaculture species globally. Over the past two decades, ostreid herpesvirus (OsHV-1) has become a major pathogen of cultured Pacific oysters, resulting in widespread mortality with a global distribution. Experimental use of OsHV-1 is challenging for many reasons, including both complexity of host-pathogen dynamics and a lack of functioning model systems. The goal of this study was to improve the tools available for working with OsHV-1 in both whole animals and in tissue explants established from oysters maintained in controlled laboratory conditions. Tissue explants were taken from oysters originating from two different sources that have different levels of mortality in experimental OsHV-1 infections and were exposed to OsHV-1. A whole-animal infection experiment was run concurrently as a comparison. Quantitative PCR and electron microscopy were used to confirm that the explants were capable of replicating OsHV-1. Furthermore, the quantitative PCR results suggest that the source of the oysters was significant in determining the outcome of infection in the explants, supporting the validity of the explant model for OsHV-1 infection. This tissue explant approach for studying OsHV-1 allows for the control of confounding factors in the disease outcome that is not possible in whole-animal experiments, providing a new tool for the study of OsHV-1 in Pacific oysters.

Transcriptomic analysis provides insights into the immune responsive genes in the Procambarus clarkii hepatopancreas challenged with Vibrio parahaemolyticus

Procambarus clarkii is an economically important species in China; however, its high mortality rate due to pathogenic bacteria, particularly Vibrio parahaemolyticus, results in significant economic loss. This study aimed to understand the immune response of crayfish to bacterial infection by comparing and analyzing transcriptome data of hepatopancreatic tissue from P. clarkii challenged with V. parahaemolyticus or treated with PBS. Physiological indices (TP, Alb, ACP, and AKP) were analyzed, and tissue sections were prepared. After assembling and annotating the data, 18,756 unigenes were identified. A comparison of the expression levels of these unigenes between the control and V. parahaemolyticus groups revealed 4037 DEGs, with 2278 unigenes upregulated and 1759 downregulated in the V. parahaemolyticus group. GO (Gene Ontology) enrichment analysis shows that the DGEs are mainly enriched in cellular anatomical activity, bindinga and cellular process, enrichment analysis of KEGG (Kyoto Encyclopedia of Genes and Genomes) pathways showed that DGEs were mainly enriched in Base excision repair, Phagosome and Longevity regulating pathway. At the same time, lysosome was also enriched. The phagosome and lysosome pathways play a crucial role in the immune defense of crayfish against V. parahaemolyticus injection that will be highlighted. In addition, the expression levels of six selected immune-related DEGs were measured using qRT-PCR, which validated the results of RNA-seq analysis. This study provides a new perspective on the immune system and defense mechanisms of P. clarkii and a valuable foundation for further investigation of the molecular immune mechanisms of this species.

Green Routes: Exploring Protein-Based Virus-like Nanoparticle Transport and Immune Activation in Nicotiana benthamiana for Biotechnological Applications

Viral, bacterial, fungal, and nematode infections cause significant agricultural losses, with limited treatment options, necessitating novel approaches to enhance plant defense systems and protection against pathogens. Virus-like nanoparticles (VLPs), extensively used in animal and human therapies (e.g., vaccines and immune enhancers), hold potential for novel agricultural solutions and advancing plant nanotechnology. This study employed various methodologies, including VLP production, confocal microscopy, and real-time qPCR. Our findings demonstrated the presence of 30 nm Qβ-VLPs, fluorescently labeled, within the intercellular space of Nicotiana benthamiana leaves one hour post-infiltration. Furthermore, infiltration with Qβ-VLPs led to an upregulation of key defense genes (NbPR1a, NbPR5, NbNPR, NbERF1, NbMYC2, and NbLRR2) in treated plants. Using RT-qPCR, a significant increase in the relative expression levels of defense genes was observed, with sustained high levels of NbERF1 and NbLRR2 even after 24 h. These findings suggest that Qβ-VLPs effectively upregulate genes crucial for pathogen defense in N. benthamiana, initiating PAMP-triggered immunity and launching signaling cascades that enhance defense mechanisms. This innovative application of VLPs to activate plant defense programs advances plant nanobiotechnology, offering new agricultural solutions.

Metabolism and immune memory in invertebrates: are they dissociated?

Since the discovery of specific immune memory in invertebrates, researchers have investigated its immune response to diverse microbial and environmental stimuli. Nevertheless, the extent of the immune system's interaction with metabolism, remains relatively enigmatic. In this mini review, we propose a comprehensive investigation into the intricate interplay between metabolism and specific immune memory. Our hypothesis is that cellular endocycles and epigenetic modifications play pivotal roles in shaping this relationship. Furthermore, we underscore the importance of the crosstalk between metabolism and specific immune memory for understanding the evolutionary costs. By evaluating these costs, we can gain deeper insights into the adaptive strategies employed by invertebrates in response to pathogenic challenges. Lastly, we outline future research directions aimed at unraveling the crosstalk between metabolism and specific immune memory. These avenues of inquiry promise to illuminate fundamental principles governing host-pathogen interactions and evolutionary trade-offs, thus advancing our understanding of invertebrate immunology.

Transforming Aquaculture through Vaccination: A Review on Recent Developments and Milestones

Aquaculture has rapidly emerged as one of the fastest growing industries, expanding both on global and on national fronts. With the ever-increasing demand for proteins with a high biological value, the aquaculture industry has established itself as one of the most efficient forms of animal production, proving to be a vital component of global food production by supplying nearly half of aquatic food products intended for human consumption. As in classic animal production, the prevention of diseases constitutes an enduring challenge associated with severe economic and environmental repercussions. Nevertheless, remarkable strides in the development of aquaculture vaccines have been recently witnessed, offering sustainable solutions to persistent health-related issues challenging resilient aquaculture production. These advancements are characterized by breakthroughs in increased species-specific precision, improved vaccine-delivery systems, and innovations in vaccine development, following the recent advent of nanotechnology, biotechnology, and artificial intelligence in the -omics era. The objective of this paper was to assess recent developments and milestones revolving around aquaculture vaccinology and provide an updated overview of strengths, weaknesses, opportunities, and threats of the sector, by incorporating and comparatively discussing various diffuse advances that span across a wide range of topics, including emerging vaccine technologies, innovative delivery methods, insights on novel adjuvants, and parasite vaccine development for the aquaculture sector.

Innate and germline immune memory: specificity and heritability of the ancient immune mechanisms for adaptation and survival

The immune memory is one of the defensive strategies developed by both unicellular and multicellular organisms for ensuring their integrity and functionality. While the immune memory of the vertebrate adaptive immune system (based on somatic recombination) is antigen-specific, encompassing the generation of memory T and B cells that only recognize/react to a specific antigen epitope, the capacity of vertebrate innate cells to remember past events is a mostly non-specific mechanism of adaptation. This "innate memory" can be considered as germline-encoded because its effector tools (such as innate receptors) do not need somatic recombination for being active. Also, in several organisms the memory-related information is integrated in the genome of germline cells and can be transmitted to the progeny for several generations, but it can also be erased depending on the environmental conditions. Overall, depending on the organism, its environment and its living habits, innate immune memory appears to be a mechanism for achieving better protection and survival against repeated exposure to microbes/stressful agents present in the same environment or occurring in the same anatomical district, able to adapt to changes in the environmental cues. The anatomical and functional complexity of the organism and its lifespan drive the generation of different immune memory mechanisms, for optimal adaptation to changes in the living/environmental conditions. The concept of innate immunity being non-specific needs to be revisited, as a wealth of evidence suggests a significant degree of specificity both in the primary immune reaction and in the ensuing memory-like responses. This is clearly evident in invertebrate metazoans, in which distinct scenarios can be observed, with both non-specific (immune enhancement) or specific (immune priming) memory-like responses. In the case of mammals, there is evidence that some degree of specificity can be attained in different situations, for instance as organ-specific protection rather than microorganism-specific reaction. Thus, depending on the challenges and conditions, innate memory can be non-specific or specific, can be integrated in the germline and transmitted to the progeny or be short-lived, thereby representing an exceptionally plastic mechanism of defensive adaptation for ensuring individual and species survival.

Granulocyte dynamics: a key player in the immune priming effects of crickets

This study investigates immune priming effects associated with granulocytes in crickets through a comprehensive analysis. Kaplan-Meier survival analysis reveals a significant contrast in survival rates, with the heat-killed Bacillus thuringiensis (Bt)-primed group exhibiting an impressive ~80% survival rate compared to the PBS buffer-primed group with only ~10% survival 60 hours post live Bt infection. Hemocyte analysis underscores elevated hemocyte counts, particularly in granulocytes of the killed Bt-primed group, suggesting a correlation between the heat-killed Bt priming and heightened immune activation. Microscopy techniques further explore granulocyte morphology, unveiling distinctive immune responses in the killed Bt-primed group characterized by prolonged immune activation, heightened granulocyte activity, phagocytosis, and extracellular trap formation, contributing to enhanced survival rates. In particular, after 24 hours of injecting live Bt, most granulocytes in the PBS buffer-primed group exhibited extracellular DNA trap cell death (ETosis), while in the killed Bt-primed group, the majority of granulocytes were observed to maintain highly activated extracellular traps, sustaining the immune response. Gene expression analysis supports these findings, revealing differential regulation of immune-related genes such as antibacterial humoral response, detection of bacterial lipopeptides, and cellular response to bacteria lipopeptides. Additionally, the heat-killed Bt-primed group, the heat-killed E. coli-primed group, and the PBS-primed group were re-injected with live Bt 2 and 9 days post priming. Two days later, only the PBS-primed group displayed low survival rates. After injecting live Bt 9 days later, the heat-killed E. coli-primed group surprisingly showed a similarly low survival rate, while the heat-killed Bt-primed group exhibited a high survival rate of ~60% after 60 hours, with actively moving and healthy crickets. In conclusion, this research provides valuable insights into both short-term and long-term immune priming effects in crickets, contributing to our understanding of invertebrate immunity with potential applications in public health.

Context-dependent antioxidant defense system (ADS)-based stress memory in response to recurrent environmental challenges in congeneric invasive species

Marine ecosystems are facing escalating environmental fluctuations owing to climate change and human activities, imposing pressures on marine species. To withstand recurring environmental challenges, marine organisms, especially benthic species lacking behavioral choices to select optimal habitats, have to utilize well-established strategies such as the antioxidant defense system (ADS) to ensure their survival. Therefore, understanding of the mechanisms governing the ADS-based response is essential for gaining insights into adaptive strategies for managing environmental challenges. Here we conducted a comparative analysis of the physiological and transcriptional responses based on the ADS during two rounds of 'hypersalinity-recovery' challenges in two model congeneric invasive ascidians, Ciona robusta and C. savignyi. Our results demonstrated that C. savignyi exhibited higher tolerance and resistance to salinity stresses at the physiological level, while C. robusta demonstrated heightened responses at the transcriptional level. We observed distinct transcriptional responses, particularly in the utilization of two superoxide dismutase (SOD) isoforms. Both Ciona species developed physiological stress memory with elevated total SOD (T-SOD) and glutathione (GSH) responses, while only C. robusta demonstrated transcriptional stress memory. The regulatory distinctions within the Nrf2-Keap1 signalling pathway likely explain the formation disparity of transcriptional stress memory between both Ciona species. These findings support the 'context-dependent stress memory hypothesis', emphasizing the emergence of species-specific stress memory at diverse regulatory levels in response to recurrent environmental challenges. Our results enhance our understanding of the mechanisms of environmental challenge management in marine species, particularly those related to the ADS.

Supplementary Information

The online version contains supplementary material available at 10.1007/s42995-024-00228-y.

The plasticity of immune memory in invertebrates

Whether specific immune protection after initial pathogen exposure (immune memory) occurs in invertebrates has long been uncertain. The absence of antibodies, B-cells and T-cells, and the short lifespans of invertebrates led to the hypothesis that immune memory does not occur in these organisms. However, research in the past two decades has supported the existence of immune memory in several invertebrate groups, including Ctenophora, Cnidaria, Nematoda, Mollusca and Arthropoda. Interestingly, some studies have demonstrated immune memory that is specific to the parasite strain. Nonetheless, other work does not provide support for immune memory in invertebrates or offers only partial support. Moreover, the expected biphasic immune response, a characteristic of adaptive immune memory in vertebrates, varies within and between invertebrate species. This variation may be attributed to the influence of biotic or abiotic factors, particularly parasites, on the outcome of immune memory. Despite its critical importance for survival, the role of phenotypic plasticity in immune memory has not been systematically examined in the past two decades. Additionally, the features of immune responses occurring in diverse environments have yet to be fully characterized.

Disentangling specific and unspecific components of innate immune memory in a copepod-tapeworm system

Evidence that the innate immune system can respond with forms of memory upon reinfection has been accumulating over the past few years. These phenomena of "immune priming" in invertebrates, and "trained immunity" in vertebrates, are contrary to previous belief that immune memory and specificity are restricted to the adaptive immune system. However, while trained immunity is usually a response with rather low specificity, immune priming has shown highly specific responses in certain species. To date, it is largely unknown how specificity in innate immune memory can be achieved in response to different parasite types. Here, we revisited a system where an exceptionally high degree of innate immune specificity had been demonstrated for the first time, consisting of the copepod Macrocyclops albidus and its natural parasite, the tapeworm Schistocephalus solidus. Using homologous (same family) vs. heterologous (different family) priming-challenge experiments, we first confirm that copepods exposed to the same parasite family benefit from reduced secondary infections. We further focused on exposed-but-not-infected copepods in primary exposure to employ a transcriptomic approach, distinguishing between immunity that was either specific or unspecific regarding the discrimination between tapeworm types. A weighted gene co-expression network (WGCN) revealed differences between specific and unspecific immunity; while both involved histone modification regulation, specific immunity involved gene-splicing factors, whereas unspecific immunity was primarily involved in metabolic shift. We found a functional enrichment in spliceosome in specific immunity, whereas oxidative phosphorylation and carbon metabolism were enriched in unspecific immunity. Our findings allow discrimination of specific and unspecific components of an innate immune memory, based on gene expression networks, and deepen our understanding of basic aspects of immune systems.

Invertebrate Immunity, Natural Transplantation Immunity, Somatic and Germ Cell Parasitism, and Transposon Defense

While the vertebrate immune system consists of innate and adaptive branches, invertebrates only have innate immunity. This feature makes them an ideal model system for studying the cellular and molecular mechanisms of innate immunity sensu stricto without reciprocal interferences from adaptive immunity. Although invertebrate immunity is evolutionarily older and a precursor of vertebrate immunity, it is far from simple. Despite lacking lymphocytes and functional immunoglobulin, the invertebrate immune system has many sophisticated mechanisms and features, such as long-term immune memory, which, for decades, have been exclusively attributed to adaptive immunity. In this review, we describe the cellular and molecular aspects of invertebrate immunity, including the epigenetic foundation of innate memory, the transgenerational inheritance of immunity, genetic immunity against invading transposons, the mechanisms of self-recognition, natural transplantation, and germ/somatic cell parasitism.

The Modification of H3K4me3 Enhanced the Expression of CgTLR3 in Hemocytes to Increase CgIL17-1 Production in the Immune Priming of Crassostrea gigas

Increasing evidence confirms that histone modification plays a critical role in preserving long-term immunological memory. Immune priming is a novel form of immunological memory recently verified in invertebrates. Toll-like receptor (TLR) signaling and cytokines have been reported to be involved in the immune priming of the Pacific oyster Crassostrea gigas. In the present study, the expression of Toll-like receptor 3 (CgTLR3), myeloid differentiation factor 88-2 (CgMyd88-2) and interleukin 17-1 (CgIL17-1) was found to be elevated in the hemocytes of C. gigas at 6 h after the secondary stimulation with Vibrio splendidus, which was significantly higher than that at 6 h after the primary stimulation (p < 0.05). A significant increase in histone H3 lysine 4 trimethylation (H3K4me3) enrichment was detected in the promoter region of the CgTLR3 gene at 7 d after the primary stimulation with inactivated V. splendidus (p < 0.05). After the treatment with a histone methyltransferase inhibitor (5'-methylthioadenosine, MTA), the level of H3K4me3 at the promoter of the CgTLR3 gene decreased significantly at 7 d after the primary stimulation with inactivated V. splendidus (p < 0.05), and the expression of CgTLR3, CgMyD88-2 and CgIL17-1 was significantly repressed at 6 h after the secondary stimulation with V. splendidus (p < 0.05). Conversely, the treatment with monomethyl fumarate (MEF, an inhibitor of histone demethylases) resulted in a significant increase in H3K4me3 enrichment levels at the CgTLR3 promoter at 7 d after the primary stimulation (p < 0.05), and the expression of CgTLR3, CgMyD88-2 and CgIL17-1 was observed to increase significantly at 6 h after the secondary stimulation (p < 0.05). These results suggested that H3K4me3 regulated MyD88-dependent TLR signaling in the hemocytes of C. gigas, which defined the role of histone modifications in invertebrate immune priming.

The combined effects of phenanthrene and micro-/nanoplastics mixtures on the cellular stress responses of the thick-shell mussel Mytilus coruscus

Pollution with complex mixtures of contaminants including micro- and nano-plastics (MNPs) and organic pollutants like polycyclic aromatic hydrocarbons (PAH) poses a major threat to coastal marine ecosystems. Toxic mechanisms of contaminant mixtures are not well understood in marine organisms. We studied the effects of single and combined exposures to polycyclic aromatic hydrocarbon phenanthrene (Phe) and MNPs mixture with sizes of 70 nm, 5 μm and 100 μm on the immune health and oxidative stress parameters in the thick-shell mussel Mytilus coruscus. Immune cells (hemocytes) were more sensitive to the pollutant-induced oxidative stress than the gills. In hemocytes of co-exposed mussels, elevated mortality, lower lysosomal content, high production of reactive oxygen species (ROS) and decrease mitochondrial were found. Disparate responses of antioxidant enzymes in the hemolymph (e.g. increased superoxide dismutase (SOD) activity without a corresponding increase in catalase (CAT) in Phe exposures and an increase in CAT without a change in SOD in MNPs exposures) suggests misbalance of the antioxidant defense in the pollutant-exposed mussels. Gill lacked pronounced oxidative stress response showing a decline in ROS and antioxidant levels. Tissue-specific single and combined effects of Phe and MNPs suggest variation in bioavailability and/or different sensitivity to these pollutants in the studied tissues. Notably, the combined effects of MNPs and Phe were additive or antagonistic, showing that MNPs do not enhance and occasionally mitigate the toxic effects of Phe on the hemocytes and the gills of the mussels. Overall, our study sheds light on the impact of long-term exposure to MNPs and Phe mixtures on mussels, showing high sensitivity of the immune system and modulation of the Phe toxicity by MNPs co-exposure. These findings that may have implications for understanding the impacts of combined PAH and MNPs pollution on the health of mussel populations from polluted coastal habitats.

Physicochemical properties and antimicrobial activities of MytiLec-1, a member from the mytilectin family of mussels

MytiLec-1, the recombinant form of a mussel lectin from Mytillus galloprovincialis, was purified by affinity chromatography and showed the maximum hemagglutination activity at a temperature range of 10 °C to 40 °C and at pH 7.0 to 9.0. Denaturants like urea and acidic-guanidine inhibited its hemagglutination activity significantly. MytiLec-1 was found to be metal-independent though Ca2+ slightly increased the activity of chelated MytiLec-1. The lectin suppressed 65 % growth of Pseudomonas aeruginosa (ATCC 47085) at 200 μg/ml and reduced the formation of biofilm (15 % at 200 μg/ml). Comparing to Shigella sonnei (ATCC 29930), Shigella boydii (ATCC 231903) and Shigella dysenteriae (ATCC 238135), Bacillus cereus (ATCC 14579) was slightly more sensitive to MytiLec-1. At a concentration of 200 μg/disc and 100 μg/ml, MytiLec-1 prevented the growth of Aspergillus niger and agglutinated the spores of Aspergillus niger and Trichoderma reesei, respectively. Amino acid sequences, physicochemical properties and antimicrobial activities of MytiLec-1 were compared with three other lectins (CGL, MTL and MCL from Crenomytilus grayanus, Mytilus trossulas and Mytilus californianus, respectively) from the mytilectin family of bivalve mollusks. It reconfirms the function of these lectins to recognize pathogens and perform important roles in innate immune response of mussels.

The costs of transgenerational immune priming for homologous and heterologous infections with different serotypes of dengue virus in Aedes aegypti mosquitoes

The immune system is a network of molecules, signaling pathways, transcription, and effector modulation that controls, mitigates, or eradicates agents that may affect the integrity of the host. In mosquitoes, the innate immune system is highly efficient at combating foreign organisms but has the capacity to tolerate vector-borne diseases. These implications lead to replication, dissemination, and ultimately the transmission of pathogenic organisms when feeding on a host. In recent years, it has been discovered that the innate immune response of mosquitoes can trigger an enhanced immunity response to the stimulus of a previously encountered pathogen. This phenomenon, called immune priming, is characterized by a molecular response that prevents the replication of viruses, parasites, or bacteria in the body. It has been documented that immune priming can be stimulated through homologous organisms or molecules, although it has also been documented that closely related pathogens can generate an enhanced immune response to a second stimulus with a related organism. However, the cost involved in this immune response has not been characterized through the transmission of the immunological experience from parents to offspring by transgenerational immune priming (TGIP) in mosquitoes. Here, we address the impact on the rates of oviposition, hatching, development, and immune response in Aedes aegypti mosquitoes, the mothers of which were stimulated with dengue virus serotypes 2 and/or 4, having found a cost of TGIP on the development time of the progeny of mothers with heterologous infections, with respect to mothers with homologous infections. Our results showed a significant effect on the sex ratio, with females being more abundant than males. We found a decrease in transcripts of the siRNA pathway in daughters of mothers who had been exposed to an immune challenge with DV. Our research demonstrates that there are costs and benefits associated with TGIP in Aedes aegypti mosquitoes exposed to DV. Specifically, priming results in a lower viral load in the offspring of mothers who have previously been infected with the virus. Although some results from tests of two dengue virus serotypes show similarities, such as the percentage of pupae emergence, there are differences in the percentage of adult emergence, indicating differences in TGIP costs even within the same virus with different serotypes. This finding has crucial implications in the context of dengue virus transmission in endemic areas where multiple serotypes circulate simultaneously.

Herbicide exposure alters the effect of the enthomopathogen Beauveria bassiana on immune gene expression in mealworm beetles

Concerns have grown worldwide about the potentially far-reaching effects of herbicides on functional biodiversity in agroecosystems. Repeated applications over time can lead to accumulation of residues in soil, water, and food and may have negative impacts on non-target organisms. However, the effects of herbicide residues on interspecific relationships, such as host-pathogen interactions, are poorly studied. In this study, we evaluated the effects of two different concentrations of a commercial pendimethalin-based formulation (PND), the residual contamination (S, 13 ppm) in treated soils and the maximum residue level allowed by the European Commission in cereals (EU, 0.05 ppm). We tested the effect of PND on the biological interaction between the mealworm beetle Tenebrio molitor Linnaeus, 1758 and the entomopathogenic fungus Beauveria bassiana Vuillemin, 1912 (Bb, strain KVL 03-144) at two concentrations (LC50 5 × 105 conidia mL-1 and LC100 1 × 107 conidia mL-1). We checked the survival of beetles exposed to PND or/and inoculated with B. bassiana, the expression of four antimicrobial peptides (AMPs), and finally how PND affects in vitro germination of fungus. The exposure to PND had no significant effects on the survival of either control or Bb-exposed beetles. In the mealworm beetle, upregulation of gene expression of the inducible AMPs Tenecin 1, 2, and 4 was observed in PND-treated beetles after inoculation with Bb, while the levels of the non-inducible AMP Tenecin 3 were similar between treatments. In conclusion, our findings demonstrate that admitted residual doses of currently used herbicides modify an important component of the inducible immune response of an insect. This did not translate into an effect on the survival to B. bassiana in our system. However, residual doses of the herbicide at 13 ppm may temporarily affect fungal germination. These results raise questions about the compatibility of bioinsecticides with synthetic pesticides and the effects of herbicide residues on host-pathogen interactions.

The Role of Human and Animal Monocytes and Macrophages in Homeostasis and Disease

Monocytes and macrophages are the innate immune cells that are the first-line responders to invading pathogens or foreign objects[...].

Evolutionary trade-off between innate and acquired immune defences in birds

BACKGROUND

The development, maintenance, and use of immune defences are costly. Therefore, animals face trade-offs in terms of resource allocation within their immune system and between their immune system and other physiological processes. To maximize fitness, evolution may favour investment in one immunological defence or subsystem over another in a way that matches a species broader life history strategy. Here, we used phylogenetically-informed comparative analyses to test for relationships between two immunological components. Natural antibodies and complement were used as proxies for the innate branch; structural complexity of the major histocompatibility complex (MHC) region was used for the acquired branch.

RESULTS

We found a negative association between the levels of natural antibodies (i.e., haemagglutination titre) and the total MHC gene copy number across the avian phylogeny, both at the species and family level. The family-level analysis indicated that this association was apparent for both MHC-I and MHC-II, when copy numbers within these two MHC regions were analysed separately. The association remained significant after controlling for basic life history components and for ecological traits commonly linked to pathogen exposure.

CONCLUSION

Our results provide the first phylogenetically robust evidence for an evolutionary trade-off within the avian immune system, with a more developed acquired immune system (i.e., more complex MHC architecture) in more derived bird lineages (e.g., passerines) being accompanied by an apparent downregulation of the innate immune system.

The characterization of toll-like receptor repertoire in Pinna nobilis after mass mortality events suggests adaptive introgression

The fan mussel Pinna nobilis is currently on the brink of extinction due to a multifactorial disease mainly caused to the highly pathogenic parasite Haplosporidium pinnae, meaning that the selection pressure outweighs the adaptive potential of the species. Hopefully, rare individuals have been observed somehow resistant to the parasite, stretching the need to identify the traits underlying this better fitness. Among the candidate to explore at first intention are fast-evolving immune genes, of which toll-like receptor (TLR). In this study, we examined the genetic diversity at 14 TLR loci across P. nobilis, Pinna rudis and P. nobilis × P. rudis hybrid genomes, collected at four physically distant regions, that were found to be either resistant or sensitive to the parasite H. pinnae. We report a high genetic diversity, mainly observed at cell surface TLRs compared with that of endosomal TLRs. However, the endosomal TLR-7 exhibited unexpected level of diversity and haplotype phylogeny. The lack of population structure, associated with a high genetic diversity and elevated dN/dS ratio, was interpreted as balancing selection, though both directional and purifying selection were detected. Interestingly, roughly 40% of the P. nobilis identified as resistant to H. pinnae were introgressed with P. rudis TLR. Specifically, they all carried a TLR-7 of P. rudis origin, whereas sensitive P. nobilis were not introgressed, at least at TLR loci. Small contributions of TLR-6 and TLR-4 single-nucleotide polymorphisms to the clustering of resistant and susceptible individuals could be detected, but their specific role in resistance remains highly speculative. This study provides new information on the diversity of TLR genes within the P. nobilis species after MME and additional insights into adaptation to H. pinnae that should contribute to the conservation of this Mediterranean endemic species.

Drosophila immune priming to Enterococcus faecalis relies on immune tolerance rather than resistance

Innate immune priming increases an organism's survival of a second infection after an initial, non-lethal infection. We used Drosophila melanogaster and an insect-derived strain of Enterococcus faecalis to study transcriptional control of priming. In contrast to other pathogens, the enhanced survival in primed animals does not correlate with decreased E. faecalis load. Further analysis shows that primed organisms tolerate, rather than resist infection. Using RNA-seq of immune tissues, we found many genes were upregulated in only primed flies, suggesting a distinct transcriptional program in response to initial and secondary infections. In contrast, few genes continuously express throughout the experiment or more efficiently re-activate upon reinfection. Priming experiments in immune deficient mutants revealed Imd is largely dispensable for responding to a single infection but needed to fully prime. Together, this indicates the fly's innate immune response is plastic-differing in immune strategy, transcriptional program, and pathway use depending on infection history.

Preventing bacterial disease in poultry in the post-antibiotic era: a case for innate immunity modulation as an alternative to antibiotic use

The widespread use of antibiotics in the poultry industry has led to the emergence of antibiotic-resistant bacteria, which pose a significant health risk to humans and animals. These public health concerns, which have led to legislation limiting antibiotic use in animals, drive the need to find alternative strategies for controlling and treating bacterial infections. Modulation of the avian innate immune system using immunostimulatory compounds provides a promising solution to enhance poultry immune responses to a broad range of bacterial infections without the risk of generating antibiotic resistance. An array of immunomodulatory compounds have been investigated for their impact on poultry performance and immune responses. However, further research is required to identify compounds capable of controlling bacterial infections without detrimentally affecting bird performance. It is also crucial to determine the safety and effectiveness of these compounds in conjunction with poultry vaccines. This review provides an overview of the various immune modulators known to enhance innate immunity against avian bacterial pathogens in chickens, and describes the mechanisms involved.

New insights into inflammatory memory of epidermal stem cells

Inflammatory memory, as one form of innate immune memory, has a wide range of manifestations, and its occurrence is related to cell epigenetic modification or metabolic transformation. When re-encountering similar stimuli, executing cells with inflammatory memory function show enhanced or tolerated inflammatory response. Studies have identified that not only hematopoietic stem cells and fibroblasts have immune memory effects, but also stem cells from various barrier epithelial tissues generate and maintain inflammatory memory. Epidermal stem cells, especially hair follicle stem cells, play an essential role in wound healing, immune-related skin diseases, and skin cancer development. In recent years, it has been found that epidermal stem cells from hair follicle can remember the inflammatory response and implement a more rapid response to subsequent stimuli. This review updates the advances of inflammatory memory and focuses on its mechanisms in epidermal stem cells. We are finally looking forward to further research on inflammatory memory, which will allow for the development of precise strategies to manipulate host responses to infection, injury, and inflammatory skin disease.

Morphological and functional alterations in hemocytes of Mytilus galloprovincialis exposed in high-impact anthropogenic sites

The work aimed to study the induction of morphological alterations in M. galloprovincialis in the field and its suitability to be integrated into a sensitive, simple, and cost-effective cell-based multimarker approach for the detection of the stress status induced by pollution in coastal marine environments in view of ecotoxicological biomonitoring and assessment application. Cellular morphometric alterations was paralleled by the analysis of standardized biomarkers such as lysosomal membrane destabilization, and genotoxocity biomarkers such as micronuclei and binuclated cells frequencies were investigated. The study was carried out by means of a transplanting experiment in the field, using caged organisms from an initial population exposed in the field in two multi-impacted coastal sites of the central Mediterranean area, Bagnoli in the eastern Tyrrhenian Sea and Augusta-Melilli-Priolo in the western Ionian Sea. Capo Miseno (NA) for the Tyrrhenian area and Brucoli (ME) for the Ionian area were chosen as control sites. Hemocyte enlargement and filopodial elongation increased frequencies were observed in organisms exposed to the impacted sites. These morphometric alterations showed strong agreement with the lysosomal membrane destabilization and biomarkers of genotoxicity, suggesting their usefulness in detecting the pollutant-induced stress syndrome related to genotoxic damage.

Association between Microorganisms and Microplastics: How Does It Change the Host-Pathogen Interaction and Subsequent Immune Response?

Plastic pollution is a significant problem worldwide because of the risks it poses to the equilibrium and health of the environment as well as to human beings. Discarded plastic released into the environment can degrade into microplastics (MPs) due to various factors, such as sunlight, seawater flow, and temperature. MP surfaces can act as solid scaffolds for microorganisms, viruses, and various biomolecules (such as LPS, allergens, and antibiotics), depending on the MP characteristics of size/surface area, chemical composition, and surface charge. The immune system has efficient recognition and elimination mechanisms for pathogens, foreign agents, and anomalous molecules, including pattern recognition receptors and phagocytosis. However, associations with MPs can modify the physical, structural, and functional characteristics of microbes and biomolecules, thereby changing their interactions with the host immune system (in particular with innate immune cells) and, most likely, the features of the subsequent innate/inflammatory response. Thus, exploring differences in the immune response to microbial agents that have been modified by interactions with MPs is meaningful in terms of identifying new possible risks to human health posed by anomalous stimulation of immune reactivities.

Innate Immune Memory in Macrophages

Macrophages have been recognized as the primary mediators of innate immunity starting from embryonic/fetal development. Macrophage-mediated defenses may not be as antigen-specific as adaptive immunity, but increasing information suggests that these responses do strengthen with repeated immunological triggers. The concept of innate memory in macrophages has been described as "trained immunity" or "innate immune memory (IIM)." As currently understood, this cellular memory is rooted in epigenetic and metabolic reprogramming. The recognition of IIM may be particularly important in the fetus and the young neonate who are yet to develop protective levels of adaptive immunity, and could even be of preventive/therapeutic importance in many disorders. There may also be a possibility of therapeutic enhancement with targeted vaccination. This article presents a review of the properties, mechanisms, and possible clinical significance of macrophage-mediated IIM.

Induction of Innate Memory in Human Monocytes Exposed to Mixtures of Bacterial Agents and Nanoparticles

We assessed whether concomitant exposure of human monocytes to bacterial agents and different engineered nanoparticles can affect the induction of protective innate memory, an immune mechanism that affords better resistance to diverse threatening challenges. Monocytes were exposed in vitro to nanoparticles of different chemical nature, shape and size either alone or admixed with LPS, and cell activation was assessed in terms of production of inflammatory (TNFα, IL-6) and anti-inflammatory cytokines (IL-10, IL-1Ra). After return to baseline conditions, cells were re-challenged with LPS and their secondary "memory" response measured. Results show that nanoparticles alone are essentially unable to generate memory, while LPS induced a tolerance memory response (less inflammatory cytokines, equal or increased anti-inflammatory cytokines). LPS-induced tolerance was not significantly affected by the presence of nanoparticles during the memory generation phase, although with substantial donor-to-donor variability. This suggests that, despite the overall lack of significant effects on LPS-induced innate memory, nanoparticles may have donor-specific effects. Thus, future nanosafety assessment and nanotherapeutic strategies will need a personalized approach in order to ensure both the safety and efficacy of nano medical compounds for individual patients.

Antibacterial responses and functional characterization of the interferon gamma inducible lysosomal thiol reductase (GILT) protein in Chinese mitten crab (Eriocheir sinensis)

The inducible reductase of interferon gamma (IFN- γ), IFN-γ-induced lysosomal thiol reductase (GILT) is important in antiviral immunity, but its mechanism in invertebrate antimicrobial immunity is unclear. We determined that GILT protein was involved in the antibacterial immunity of Chinese mitten crab (Eriocheir sinensis). GILT protein was highly expressed in crab hemocytes and was significantly upregulated 6 h after bacterial stimulation. Recombinant E. sinensis GILT (rEsGILT) contained a CXXS active site that catalyzed disulfide bond reduction. Vibrio parahaemolyticus and Staphylococcus aureus were bound through interaction with peptidoglycan and lipopolysaccharide, respectively, and bacterial agglutination and clearance in the crabs was markedly promoted. Nevertheless, EsGILT exhibited no direct antibacterial or bactericidal activity. EsGILT also promoted crab hemocyte phagocytosis and played an anti-bacterial role, and inhibited hemocyte apoptosis. In summary, EsGILT promoted bacterial agglutination, clearance, and phagocytosis by recognizing and agglutinating pathogenic microorganisms and reduced the apoptosis level, indirectly participating in antibacterial reactions.

Drosophila melanogaster as a model to study innate immune memory

Over the last decades, research regarding innate immune responses has gained increasing importance. A growing body of evidence supports the notion that the innate arm of the immune system could show memory traits. Such traits are thought to be conserved throughout evolution and provide a survival advantage. Several models are available to study these mechanisms. Among them, we find the fruit fly, Drosophila melanogaster. This non-mammalian model has been widely used for innate immune research since it naturally lacks an adaptive response. Here, we aim to review the latest advances in the study of the memory mechanisms of the innate immune response using this animal model.

Transcriptome features of innate immune memory in Drosophila

Immune memory is the ability of organisms to elicit potentiated immune responses at secondary infection. Current studies have revealed that similar to adaptive immunity, innate immunity exhibits memory characteristics (called "innate immune memory"). Although epigenetic reprogramming plays an important role in innate immune memory, the underlying mechanisms have not been elucidated, especially at the individual level. Here, we established experimental systems for detecting innate immune memory in Drosophila melanogaster. Training infection with low-pathogenic bacteria enhanced the survival rate of the flies at subsequent challenge infection with high-pathogenic bacteria. Among low-pathogenic bacteria, Micrococcus luteus (Ml) and Salmonella typhimurium (St) exerted apparent training effects in the fly but exhibited different mechanisms of action. Ml exerted training effects even after its clearance from flies, while live St persisted in the flies for a prolonged duration. RNA sequencing (RNA-Seq) analysis revealed that Ml training enhanced the expression of the immune-related genes under the challenge condition but not under the non-challenge condition. In contrast, St training upregulated the expression of the immune-related genes independent of challenge. These results suggest that training effects with Ml and St are due to memory and persistence of immune responses, respectively. Furthermore, we searched for the gene involved in immune memory, and identified a candidate gene, Ada2b, which encodes a component of the histone modification complex. The Ada2b mutant suppressed Ml training effects on survival and disrupted the expression of some genes under the training + challenge condition. These results suggest that the gene expression regulated by Ada2b may contribute to innate immune memory in Drosophila.

Pre-exposure to Candida albicans induce trans-generational immune priming and gene expression of Musca domestica

Insects have the phenomenon of immune priming by which they can have enhanced protection against reinfection with the same pathogen, and this immune protection can be passed on to their offspring, which is defined as “trans-generational immune priming (TGIP).” But whether housefly possesses TGIP is still unclear. Therefore, we used the housefly as the insect model and Candida albicans as the pathogen to explore whether the housefly is capable of eliciting TGIP, and RNA sequencing (RNA-seq) was performed to explore the molecular mechanism of TGIP of the housefly. We found that the housefly possesses TGIP, and adults pre-exposed to heat-killed C. albicans could confer protection to itself and its offspring upon reinfection with a lethal dose of C. albicans. RNA-seq results showed that 30 and 154 genes were differentially expressed after adults were primed with heat-killed C. albicans (CA-A) and after offspring larvae were challenged with a lethal dose of C. albicans (CA-CA-G), respectively. Among the differentially expressed genes (DEGs), there were 23 immune genes, including 6 pattern recognition receptors (PRRs), 7 immune effectors, and 10 immunoregulatory molecules. More importantly, multiple DEGs were involved in the Toll signaling pathway and phagosome signaling pathway, suggesting that the Toll signaling pathway and phagocytosis might play important roles in the process of TGIP of housefly to C. albicans. Our results expanded on previous studies and provided parameters for exploring the mechanism of TGIP.

Common aquatic pollutants modify hemocyte immune responses in Biomphalaria glabrata

Disruptions to reproductive health in wildlife species inhabiting polluted environments is often found to occur alongside compromised immunity. However, research on impacts of aquatic pollution on freshwater mollusc immune responses is limited despite their importance as vectors of disease (Schistosomiasis) in humans, cattle and wild mammals. We developed an in vitro 'tool-kit' of well-characterized quantitative immune tests using Biomphalaria glabrata hemocytes. We exposed hemocytes to environmentally-relevant concentrations of common aquatic pollutants (17β-estradiol, Bisphenol-A and p,p'-DDE) and measured key innate immune responses including motility, phagocytosis and encapsulation. Additionally, we tested an extract of a typical domestic tertiary treated effluent as representative of a 'real-world' mixture of chemicals. Encapsulation responses were stimulated by p,p'-DDE at low doses but were suppressed at higher doses. Concentrations of BPA (above 200 ng/L) and p,p'-DDE (above 500 ng/L) significantly inhibited phagocytosis compared to controls, whilst hemocyte motility was reduced by all test chemicals and the effluent extract in a dose-dependent manner. All responses occurred at chemical concentrations considered to be below the cytotoxic thresholds of hemocytes. This is the first time a suite of in vitro tests has been developed specifically in B. glabrata with the purpose of investigating the impacts of chemical pollutants and an effluent extract on immunity. Our findings indicate that common aquatic pollutants alter innate immune responses in B. glabrata, suggesting that pollutants may be a critical, yet overlooked, factor impacting disease by modulating the dynamics of parasite transmission between molluscs and humans.

Single cell RNA sequencing reveals hemocyte heterogeneity in Biomphalaria glabrata: Plasticity over diversity

The freshwater snail Biomphalaria glabrata is an intermediate host of Schistosoma mansoni, the agent of human intestinal schistosomiasis. However, much is to be discovered about its innate immune system that appears as a complex black box, in which the immune cells (called hemocytes) play a major role in both cellular and humoral response towards pathogens. Until now, hemocyte classification has been based exclusively on cell morphology and ultrastructural description and depending on the authors considered from 2 to 5 hemocyte populations have been described. In this study, we proposed to evaluate the hemocyte heterogeneity at the transcriptomic level. To accomplish this objective, we used single cell RNA sequencing (scRNAseq) technology coupled to a droplet-based system to separate hemocytes and analyze their transcriptome at a unique cell level in naive Biomphalaria glabrata snails. We were able to demonstrate the presence of 7 hemocyte transcriptomic populations defined by the expression of specific marker genes. As a result, scRNAseq approach showed a high heterogeneity within hemocytes, but provides a detailed description of the different hemocyte transcriptomic populations in B. glabrata supported by distinct cellular functions and lineage trajectory. As a main result, scRNAseq revealed the 3 main population as a super-group of hemocyte diversity but, on the contrary, a great hemocytes plasticity with a probable capacity of hemocytes to engage to different activation pathways. This work opens a new field of research to understand the role of hemocytes particularly in response to pathogens, and towards S. mansoni parasites.

Harsh intertidal environment enhances metabolism and immunity in oyster (Crassostrea gigas) spat

The Pacific oyster Crassostrea gigas is established in the marine intertidal zone, experiencing rapid and highly dynamic environmental changes throughout the tidal cycle. Depending on the bathymetry, oysters face oxygen deprivation, lack of nutrients, and high changes in temperature during alternation of the cycles of emersion/immersion. Here we showed that intertidal oysters at a bathymetry level of 3 and 5 m delayed by ten days the onset of mortality associated with Pacific Oyster Mortality Syndrome (POMS) as compared to subtidal oysters. Intertidal oysters presented a lower growth but similar energetic reserves to subtidal oysters but induced proteomic changes indicative of a boost in metabolism, inflammation, and innate immunity that may have improved their resistance during infection with the Ostreid herpes virus. Our work highlights that intertidal harsh environmental conditions modify host-pathogen interaction and improve oyster health. This study opens new perspectives on oyster farming for mitigation strategies based on tidal height.

Innate Immunity Mechanisms in Marine Multicellular Organisms

The innate immune system provides an adequate response to stress factors and pathogens through pattern recognition receptors (PRRs), located on the surface of cell membranes and in the cytoplasm. Generally, the structures of PRRs are formed by several domains that are evolutionarily conserved, with a fairly high degree of homology in representatives of different species. The orthologs of TLRs, NLRs, RLRs and CLRs are widely represented, not only in marine chordates, but also in invertebrates. Study of the interactions of the most ancient marine multicellular organisms with microorganisms gives us an idea of the evolution of molecular mechanisms of protection against pathogens and reveals new functions of already known proteins in ensuring the body’s homeostasis. The review discusses innate immunity mechanisms of protection of marine invertebrate organisms against infections, using the examples of ancient multicellular hydroids, tunicates, echinoderms, and marine worms in the context of searching for analogies with vertebrate innate immunity. Due to the fact that mucous membranes first arose in marine invertebrates that have existed for several hundred million years, study of their innate immune system is both of fundamental importance in terms of understanding molecular mechanisms of host defense, and of practical application, including the search of new antimicrobial agents for subsequent use in medicine, veterinary and biotechnology.

Host-pathogen coevolution drives innate immune response to Aphanomyces astaci infection in freshwater crayfish: transcriptomic evidence

BACKGROUND

For over a century, scientists have studied host-pathogen interactions between the crayfish plague disease agent Aphanomyces astaci and freshwater crayfish. It has been hypothesised that North American crayfish hosts are disease-resistant due to the long-lasting coevolution with the pathogen. Similarly, the increasing number of latent infections reported in the historically sensitive European crayfish hosts seems to indicate that similar coevolutionary processes are occurring between European crayfish and A. astaci. Our current understanding of these host-pathogen interactions is largely focused on the innate immunity processes in the crayfish haemolymph and cuticle, but the molecular basis of the observed disease-resistance and susceptibility remain unclear. To understand how coevolution is shaping the host's molecular response to the pathogen, susceptible native European noble crayfish and invasive disease-resistant marbled crayfish were challenged with two A. astaci strains of different origin: a haplogroup A strain (introduced to Europe at least 50 years ago, low virulence) and a haplogroup B strain (signal crayfish in lake Tahoe, USA, high virulence). Here, we compare the gene expression profiles of the hepatopancreas, an integrated organ of crayfish immunity and metabolism.

RESULTS

We characterised several novel innate immune-related gene groups in both crayfish species. Across all challenge groups, we detected 412 differentially expressed genes (DEGs) in the noble crayfish, and 257 DEGs in the marbled crayfish. In the noble crayfish, a clear immune response was detected to the haplogroup B strain, but not to the haplogroup A strain. In contrast, in the marbled crayfish we detected an immune response to the haplogroup A strain, but not to the haplogroup B strain.

CONCLUSIONS

We highlight the hepatopancreas as an important hub for the synthesis of immune molecules in the response to A. astaci. A clear distinction between the innate immune response in the marbled crayfish and the noble crayfish is the capability of the marbled crayfish to mobilise a higher variety of innate immune response effectors. With this study we outline that the type and strength of the host immune response to the pathogen is strongly influenced by the coevolutionary history of the crayfish with specific A. astaci strains.

Effect of Bauhinia monandra Kurz Leaf Preparations on Embryonic Stages and Adult Snails of Biomphalaria glabrata (Say, 1818), Schistosoma mansoni Cercariae and Toxicity in Artemia salina

Biomphalaria glabrata snails constitute the main vector of schistosomiasis in Brazil, and Bauhinia monandra Kurz, the leaves of which contain BmoLL lectin with biocidal action, is a plant widely found on continents in which the disease is endemic. This work describes the composition of B. monandra preparations and the effect on embryos and adult snails, their reproduction parameters and hemocytes. We also describe the results of a comet assay after B. glabrata exposure to sublethal concentrations of the preparations. Additionally, the effects of the preparations on S. mansoni cercariae and environmental monitoring with Artemia salina are described. In the chemical evaluation, cinnamic, flavonoid and saponin derivatives were detected in the two preparations assessed, namely the saline extract and the fraction. Both preparations were toxic to embryos in the blastula, gastrula, trochophore, veliger and hippo stages (LC50 of 0.042 and 0.0478; 0.0417 and 0.0419; 0.0897 and 0.1582; 0.3734 and 0.0974; 0.397 and 0.0970 mg/mL, respectively) and to adult snails (LC50 of 6.6 and 0.87 mg/mL, respectively), which were reproductively affected with decreased egg deposition. In blood cell analysis, characteristic cells for apoptosis, micronucleus and binucleation were detected, while for comet analysis, different degrees of nuclear damage were detected. The fraction was able to cause total mortality of the cercariae and did not present environmental toxicity. Therefore, B. monandra preparations are promising in combating schistosomiasis since they can control both the intermediate host and eliminate the infectious agent, besides being safe to the environment.

AKT regulates hemocyte proliferation via glucose metabolism in Eriocheir sinensis

Threonine-serine protein kinase (AKT) plays an important role in the regulation of essential biological processes such as cell metabolism and cell proliferation in several organisms. Eriocheir sinensis is a widely distributed crab that is exposed to complex and diverse biological environments and various diseases. We aimed to elucidate the immune function of AKT and the underlying mechanism in E. sinensis. In this study, we performed bioinformatics analysis of E. sinensis AKT (EsAkt) and found that the AKT protein was highly conserved across species. qRT-PCR showed high AKT expression in the liver and muscle tissues, and low expression in hemocytes. After stimulation with gram-positive Staphylococcus aureus or gram-negative Vibrio parahaemolyticus, E. sinensis AKT (EsAkt) was significantly up-regulated in hemocytes. Further, knockout of the EsAkt gene weakened cell glucose metabolism and inhibited cell proliferation. Taken together, these results suggest that EsAkt plays a key role in regulating hemocyte glucose metabolism and cell proliferation in Eriocheir sinensis.

Searching for the Origin and the Differentiation of Haemocytes before and after Larval Settlement of the Colonial Ascidian Botryllus schlosseri: An Ultrastructural Viewpoint

The colonial ascidian Botryllus schlosseri possesses an innate immunity, which plays fundamental roles in its survival, adaptability, worldwide spread and ecological success. Three lines of differentiation pathways of circulating haemocytes are known to be present in the haemolymph, starting from undifferentiated haemoblasts: (i) the phagocytic line (hyaline amoebocytes and macrophage-like cells), (ii) the cytotoxic line (granular amoebocytes and morula cells) and (iii) the storage cell line (pigment cells and nephrocytes). Many questions remain about their origin, and thus, observations during various stages of development were undertaken in this study. Haemocytes were detected beginning from the early tailbud embryo stage. Haemoblasts were always present and morula cells were the first differentiated haemocytes detected. In both the next stage, just before hatching, and the swimming tadpole larva stage, hyaline amoebocytes and pigment cells were also recognisable. Some morula cells containing active phenoloxidase migrated from the haemolymph into the tunic after having crossed the epidermis, and this behaviour could be related to the preparation of a defensive function for spatial competition. During larval metamorphosis, macrophage-like cells appeared with their phagosomes positive to acid phosphatase activity and containing apoptotic cells from tail tissue degeneration. After metamorphosis, in the filter-feeding oozoid stage, nephrocytes involved in nitrogen catabolism finally appeared. In both the subendostylar sinus and the peripheral blind-sac vessels (ampullae), clusters of haemoblasts were recognisable, some of which showed incipient specialisations, considering the hypothesis of the presence of putative niches of haemolymph stem cells.

Early life microbial exposures shape the Crassostrea gigas immune system for lifelong and intergenerational disease protection

BACKGROUND

The interaction of organisms with their surrounding microbial communities influences many biological processes, a notable example of which is the shaping of the immune system in early life. In the Pacific oyster, Crassostrea gigas, the role of the environmental microbial community on immune system maturation - and, importantly, protection from infectious disease - is still an open question.

RESULTS

Here, we demonstrate that early life microbial exposure durably improves oyster survival when challenged with the pathogen causing Pacific oyster mortality syndrome (POMS), both in the exposed generation and in the subsequent one. Combining microbiota, transcriptomic, genetic, and epigenetic analyses, we show that the microbial exposure induced changes in epigenetic marks and a reprogramming of immune gene expression leading to long-term and intergenerational immune protection against POMS.

CONCLUSIONS

We anticipate that this protection likely extends to additional pathogens and may prove to be an important new strategy for safeguarding oyster aquaculture efforts from infectious disease. tag the videobyte/videoabstract in this section Video Abstract.

Immune priming in Armadillidiumvulgare against Salmonellaenterica: direct or indirect costs on life history traits?

Invertebrate immune priming is defined as an enhanced protection against secondary pathogenic infections when individuals have been previously exposed to the same or a different pathogen. Immune priming can be energetically costly for individuals, thus impacting trade-offs between life-history traits, like reproduction, growth, and lifetime. Here, the reproductive cost(s) and senescence patterns of immune priming against S.enterica in the common woodlouse A.vulgare (Crustacea, Isopoda) were investigated. Four different groups of females were used that either (1) have never been injected (control), (2) were injected twice with S.enterica (7 days between infections), (3) were firstly injected with LB-broth, then with S.enterica, and (4) females injected only once with S.enterica. All females were allowed to breed with one non-infected male and were observed for eight months. Then, the number of clutches produced, the time taken to produce the clutch(es), the number of offspring in each clutch, the senescence biomarkers of females, and parameters of their haemocytes were compared. The result was that immune priming did not significantly impact reproductive abilities, senescence patterns, and haemocyte parameters of female A.vulgare, but had an indirect effect through body weight. The lighter immune primed females took less time to produce the first clutch, which contained less offspring, but they were more likely to produce a second clutch. The opposite effects were observed in the heavier immune primed females. By highlighting that immune priming was not as costly as expected in A.vulgare, these results provide new insights into the adaptive nature of this immune process.

The antiviral role of NF-κB-mediated immune responses and their antagonism by viruses in insects

The antiviral role of innate immune responses mediated by the NF-κB family of transcription factors is well established in vertebrates but was for a long time less clear in insects. Insects encode two canonical NF-κB pathways, the Toll and Imd ('immunodeficiency') pathways, which are best characterised for their role in antibacterial and antifungal defence. An increasing body of evidence has also implicated NF-κB-mediated innate immunity in antiviral responses against some, but not all, viruses. Specific pattern recognition receptors (PRRs) and molecular events leading to NF-κB activation by viral pathogen-associated molecular patterns (PAMPs) have been elucidated for a number of viruses and insect species. Particularly interesting are recent findings indicating that the cyclic GMP-AMP synthase (cGAS)-stimulator of interferon genes (STING) pathway detects viral RNA to activate NF-κB-regulated gene expression. We summarise the literature on virus-NF-κB pathway interactions across the class Insecta, with a focus on the dipterans Drosophila melanogaster and Aedes aegypti. We discuss potential reasons for differences observed between different virus-host combinations, and highlight similarities and differences between cGAS-STING signalling in insects versus vertebrates. Finally, we summarise the increasing number of known molecular mechanisms by which viruses antagonise NF-κB responses, which suggest that NF-κB-mediated immunity exerts strong evolutionary pressures on viruses. These developments in our understanding of insect antiviral immunity have relevance to the large number of insect species that impact on humans through their transmission of human, livestock and plant diseases, exploitation as biotechnology platforms, and role as parasites, pollinators, livestock and pests.

Symbiont-mediated immune priming in animals through an evolutionary lens

Protective symbionts can defend hosts from parasites through several mechanisms, from direct interference to modulating host immunity, with subsequent effects on host and parasite fitness. While research on symbiont-mediated immune priming (SMIP) has focused on ecological impacts and agriculturally important organisms, the evolutionary implications of SMIP are less clear. Here, we review recent advances made in elucidating the ecological and molecular mechanisms by which SMIP occurs. We draw on current works to discuss the potential for this phenomenon to drive host, parasite, and symbiont evolution. We also suggest approaches that can be used to address questions regarding the impact of immune priming on host-microbe dynamics and population structures. Finally, due to the transient nature of some symbionts involved in SMIP, we discuss what it means to be a protective symbiont from ecological and evolutionary perspectives and how such interactions can affect long-term persistence of the symbiosis.