Effect of crude lipopolysaccharide from Escherichia coli O127:B8 on the amebocyte-producing organ of Biomphalaria glabrata (Mollusca)

Investigation of Immune Responses in Giant African Snail, Achatina immaculata, against a Two-Round Lipopolysaccharide Challenge

As one of the 100 most-threatening invasive alien species, the giant African snail (Achatina immaculata) has successfully invaded and established itself in most areas of southern China. Protection against recurrent pathogen infections is vital to biological invasion. Enhanced immune protection has been previously found in other invertebrates, but not in the unique immune system of the giant African snail. In the present study, the survival rate of the giant African snail was recorded following a second infection with lethal doses of Escherichia coli after a previous first injection using lipopolysaccharide (LPS), and the mechanism of immune enhancement was investigated by examining the cellular and transcriptomic response of the giant African snail after two successive stimuli using LPS. Snails injected first with LPS, sterilized physiologic (0.9%) saline (SPS), phosphate-buffered saline (PBS) or untreated (Blank) were rechallenged at 7d with E. coli (Ec), and were named as LPS + Ec, SPS + Ec, PBS + Ec, Ec, and Blank. The log-rank test shows the survival rate of the LPS + Ec group as significantly higher than that of other control groups after the second injection (p < 0.05). By performing cell counting and BrdU labeling on newly generated circulating hemocytes, we found that the total hemocyte count (THC) and the ratio of BrdU-positive cells to total cells increased significantly after primary stimulation with LPS and that they further increased after the second challenge. Then, caspase-3 of apoptosis protease and two antioxidant enzyme activities (CAT and SOD) increased significantly after infection, and were significantly higher in the second response than they had been in the first round. Moreover, transcriptome analysis results showed that 84 differentially expressed genes (DEGs) were expressed at higher levels in both the resting and activating states after the second immune response compared to the levels observed after the first challenge. Among them, some DEGs, including Toll-like receptor 4 (TLR4) and its downstream signaling molecules, were verified using qRT-PCR and were consistent with the transcriptome assay results. Based on gene expression levels, we proposed that these genes related to the TLR signaling cascade participate in enhanced immune protection. All results provide evidence that enhanced immune protection exists in the giant African snail.

New insights into the Manila clam and PAMPs interaction based on RNA-seq analysis of clam through in vitro challenges with LPS, PGN, and poly(I:C)

Background

Manila clam (Ruditapes philippinarum) is a worldwide commercially important marine bivalve species. In recent years, however, microbial diseases caused high economic losses and have received increasing attention. To understand the molecular basis of the immune response to pathogen-associated molecular patterns (PAMPs) in R. philippinarum, transcriptome libraries of clam hepatopancreas were constructed at 24 h post-injection with Lipopolysaccharide (LPS), peptidoglycan (PGN), and polyinosinic-polycytidylic acid (poly(I:C)) and phosphate-buffered saline (PBS) control by using RNA sequencing technology (RNA-seq).

Results

A total of 832, 839, and 188 differentially expressed genes (DEGs) were found in LPS, PGN, and poly(I:C) challenge group compared with PBS control, respectively. Several immune-related genes and pathways were activated in response to the different PAMPs, suggesting these genes and pathways might specifically participate in the immune response to pathogens. Besides, the analyses provided useful complementary data to compare different PAMPs challenges in vivo. Functional enrichment analysis of DEGs demonstrated that PAMPs responsive signal pathways were related to apoptosis, signal transduction, immune system, and signaling molecules and interaction. Several shared or specific DEGs response to different PAMPs were revealed in R. philippinarum, including pattern recognition receptors (PRRs), antimicrobial peptides (AMPs), interferon-induced proteins (IFI), and some other immune-related genes were found in the present work.

Conclusions

This is the first study employing high throughput transcriptomic sequencing to provide valuable genomic resources and investigate Manila clam response to different PAMPs through in vivo challenges with LPS, PGN, and poly(I:C). The results obtained here provide new insights to understanding the immune characteristics of R. philippinarum response to different PAMPs. This information is critical to elucidate the molecular basis of R. philippinarum response to different pathogens invasion, which potentially can be used to develop effective control strategies for different pathogens.

Schistosomiasis from a Snail's Perspective: Advances in Snail Immunity

The snail's immune response is an important determinant of schistosome infection success, acting in concert with host, parasite, and environmental factors. Coordinated by haemocytes and humoral factors, it possesses immunological hallmarks such as pattern recognition receptors, and predicted gastropod-unique factors like the immunoglobulin superfamily domain-containing fibrinogen-related proteins. Investigations into mechanisms that underpin snail-schistosome compatibility have advanced quickly, contributing functional insight to many observational studies. While the snail's immune response is important to continue studying from the perspective of evolutionary immunology, as the foundational determinants of snail-schistosome compatibility continue to be discovered, the possibility of exploiting the snail for schistosomiasis control moves closer into reach. Here, we review the current understanding of immune mechanisms that influence compatibility between Schistosoma mansoni and Biomphalaria glabrata.

Haematopoiesis in molluscs: A review of haemocyte development and function in gastropods, cephalopods and bivalves

Haematopoiesis is a process that is responsible for generating sufficient numbers of blood cells in the circulation and in tissues. It is central to maintenance of homeostasis within an animal, and is critical for defense against infection. While haematopoiesis is common to all animals possessing a circulatory system, the specific mechanisms and ultimate products of haematopoietic events vary greatly. Our understanding of this process in non-vertebrate organisms is primarily derived from those species that serve as developmental and immunological models, with sparse investigations having been carried out in other organisms spanning the metazoa. As research into the regulation of immune and blood cell development advances, we have begun to gain insight into haematopoietic events in a wider array of animals, including the molluscs. What began in the early 1900's as observational studies on the morphological characteristics of circulating immune cells has now advanced to mechanistic investigations of the cytokines, growth factors, receptors, signalling pathways, and patterns of gene expression that regulate molluscan haemocyte development. Emerging is a picture of an incredible diversity of developmental processes and outcomes that parallels the biological diversity observed within the different classes of the phylum Mollusca. However, our understanding of haematopoiesis in molluscs stems primarily from the three most-studied classes, the Gastropoda, Cephalopoda and Bivalvia. While these represent perhaps the molluscs of greatest economic and medical importance, the fact that our information is limited to only 3 of the 9 extant classes in the phylum highlights the need for further investigation in this area. In this review, we summarize the existing literature that defines haematopoiesis and its products in gastropods, cephalopods and bivalves.

Pathogen-associated molecular patterns activate expression of genes involved in cell proliferation, immunity and detoxification in the amebocyte-producing organ of the snail Biomphalaria glabrata

The anterior pericardial wall of the snail Biomphalaria glabrata has been identified as a site of hemocyte production, hence has been named the amebocyte-producing organ (APO). A number of studies have shown that exogenous abiotic and biotic substances, including pathogen associated molecular patterns (PAMPs), are able to stimulate APO mitotic activity and/or enlarge its size, implying a role for the APO in innate immunity. The molecular mechanisms underlying such responses have not yet been explored, in part due to the difficulty in obtaining sufficient APO tissue for gene expression studies. By using a modified RNA extraction technique and microarray technology, we investigated transcriptomic responses of APOs dissected from snails at 24 h post-injection with two bacterial PAMPs, lipopolysaccharide (LPS) and peptidoglycan (PGN), or with fucoidan (FCN), which may mimic fucosyl-rich glycan PAMPs on sporocysts of Schistosoma mansoni. Based upon the number of genes differentially expressed, LPS exhibited the strongest activity, relative to saline-injected controls. A concurrent activation of genes involved in cell proliferation, immune response and detoxification metabolism was observed. A gene encoding checkpoint 1 kinase, a key regulator of mitosis, was highly expressed after stimulation by LPS. Also, seven different aminoacyl-tRNA synthetases that play an essential role in protein synthesis were found to be highly expressed. In addition to stimulating genes involved in cell proliferation, the injected substances, especially LPS, also induced expression of a number of immune-related genes including arginase, peptidoglycan recognition protein short form, tumor necrosis factor receptor, ficolin, calmodulin, bacterial permeability increasing proteins and E3 ubiquitin-protein ligase. Importantly, significant up-regulation was observed in four GiMAP (GTPase of immunity-associated protein) genes, a result which provides the first evidence suggesting an immune role of GiMAP in protostome animals. Moreover, altered expression of genes encoding cytochrome P450, glutathione-S-transferase, multiple drug resistance protein as well as a large number of genes encoding enzymes associated with degradation and detoxification metabolism was elicited in response to the injected substances.

Fucoidan stimulates cell division in the amebocyte-producing organ of the schistosome-transmitting snail Biomphalaria glabrata

Adult Salvador (schistosome-resistant) strain Biomphalaria glabrata snails were injected with 5 μl of 10 mg/ml solutions of the sulfated polysaccharides λ carageenan, dextran sulfate, fucoidan, and heparin, the nonsulfated polysaccharide laminarin, and the monosaccharides L-fucose and L-galactose, and mitotic activity in the amebocyte-producing organ (APO) was measured in histological sections at 24 h post injection. Among the substances tested, only fucoidan induced elevated mitotic activity. Desulfated fucoidan was not mitogenic, indicating that sulfate groups are required for activity. Schistosome-susceptible M-line snails possessed minimal or no hematopoietic tissue in their APO, which did not respond to fucoidan. Immersion of juvenile Salvador snails in 1 or 10 mg/ml solutions of fucoidan for 3 h did not elevate mitotic activity at 24 h post immersion, suggesting that the external and digestive tract epithelia of B. glabrata are impermeable to this molecule. These results provide support for the hypothesis that fucosylated glycans on the tegument and in excretory-secretory products of sporocysts of Schistosoma mansoni are in part responsible for increased mitotic activity in the APO of B. glabrata infected with this trematode or injected with its extracts.

Activation of an innate immune response in the schistosome-transmitting snail Biomphalaria glabrata by specific bacterial PAMPs

Injection of crude lipopolysaccharide (LPS) from Escherichia coli into the hemocoel of Biomphalaria glabrata stimulates cell proliferation in the amebocyte-producing organ (APO). However, it is not known if mitogenic activity resides in the lipid A or O-polysaccharide component of LPS. Moreover, the possible role of substances that commonly contaminate crude LPS and that are known to stimulate innate immune responses in mammals, e.g., peptidoglycan (PGN), protein, or bacterial DNA, is unclear. Therefore, we tested the effects of the following injected substances on the snail APO: crude LPS, ultrapurified LPS (lacking lipoprotein contamination), two forms of lipid A, (diphosphoryl lipid A and Kdo2-lipid A), O-polysaccharide, Gram negative PGN, both crude and ultrapurified (with and without endotoxin activity, respectively), Gram positive PGN, PGN components Tri-DAP and muramyl dipeptide, and bacterial DNA. Whereas crude LPS, ultrapurified LPS, and crude PGN were mitogenic, ultrapurified PGN was not. Moreover, LPS components, PGN components, and bacterial DNA were inactive. These results suggest that it is the intact LPS molecule which stimulates cell division in the APO.

Epigenetic modification in neurons of the mollusc Pomacea canaliculata after immune challenge

In human and rodents, the transcriptional response of neurons to stress is related to epigenetic modifications of both DNA and histone proteins. To assess the suitability of simple invertebrate models in studying the basic mechanisms of stress-related epigenetic modifications, we analyzed epigenetic modifications in neurons of the freshwater snail Pomacea canaliculata after the injection of Escherichia coli-derived lipopolysaccharide (LPS). The phospho-acetylation of histone H3, together with the induction of stress-related factors, c-Fos and HSP70, were evaluated in large and small neurons of the pedal ganglia of sham- and LPS-injected snails. Immunocytochemical investigations showed that after LPS injection, the immunopositivity towards phospho (Ser10)-acetyl (Lys14)-histone H3 and c-Fos increases in the nuclei of small gangliar neurons. Western blot analysis confirmed a significant increase of phospho (Ser10)-acetyl (Lys14)-histone H3 in nuclear extracts from 2h LPS-injected animals. c-Fos protein levels were significantly augmented 6h after LPS injection. Immunocytochemistry and western blot indicated that no changes occurred in HSP70 distribution and protein levels. To our knowledge this is the first demonstration of epigenetic changes in molluscan neurons after an immune challenge and indicate the gastropod P. canaliculata as a suitable model for evolutionary and translational studies on stress-related epigenetic modifications.

Dermal exposure to immunostimulants induces changes in activity and proliferation of coelomocytes of Eisenia andrei

Due to the specific habitat conditions in which they live, earthworms are constantly exposed to pathogens. Consequently, they have evolved various immuno-defense mechanisms, including cellular (coelomocytes) and humoral responses, which may help to eliminate deleterious micro-organisms but also repair and/or protect host cells and tissues. Similar to mammalian phagocytes, coelomocytes can kill ingested pathogens with reactive oxygen species (ROS) and nitric oxide. In the present work, we studied the effects of the dermal exposure of Eisenia andrei earthworms to different immuno-stimulants: phorbol-12-myristate-13-acetate (PMA), lipopolysaccharide (LPS) or concanavalin A (ConA). After 3 days of treatment with all immuno-stimulants, decreased numbers and changed composition of the coelomocytes were observed. The immuno-stimulants also induced numerous changes in bactericidal activity, including ROS production. Furthermore, all stimulants increased cell proliferation while only LPS-treatment significantly elevated apoptosis of coelomocytes. These results demonstrate that in vivo treatment of earthworms with immuno-stimulants induces various changes in their coelomocyte response.

Differential expression analysis of nuclear oligomerization domain proteins NOD1 and NOD2 in orange-spotted grouper (Epinephelus coioides)

Nucleotide-binding oligomerization domain-containing proteins-1 and -2 (NOD1 and NOD2) are members of the NOD-like receptors (NLRs) family. They are both cytoplasmic receptors, and sense microbial infections/danger molecules to induce host innate immune response. In this study, the full-length ORF sequences of NOD1 and NOD2 were cloned, and the putative amino acid sequences were identified in orange-spotted grouper (Epinephelus coioides). The complete open reading frame (ORF) of grouper NOD1 contained 2823 bp encoding a 940 amino acid protein. Grouper NOD2 cDNA contained a 2967 bp ORF, encoding a protein of 988 amino acid residues. Both grouper NOD1 and NOD2 had similar domains to human and fish counterparts. Phylogenetic tree analysis showed that grouper NOD1 clustered with grass carp, zebrafish and channel catfish, while NOD2 was most closely related to fugu. Expression patterns of grouper NOD1 and NOD2 were next studied. NOD1 had the highest level of expression in skin while NOD2 in trunk kidney. Post Vibrio alginolyticus (strain EcGS020401), lipopolysaccharide (LPS) or PolyI:C challenges, gene expression of grouper NOD1 and NOD2 was stimulated to different extents. NOD1 showed a significant enhancement after LPS stimulation, but NOD2 increased more significantly after PolyI:C invasion, indicating that NOD1 and NOD2 may exert different effects on the eradication of bacteria and virus. The adaptor protein RIP-like-interacting CLARP kinase (RICK) and downstream molecule interleukin-8 (IL-8) were also induced at different levels after stimulation, which indicated that NOD1 and NOD2 signal transduction was involved in grouper innate immune protection against bacterial and viral infections.