Anti-lipopolysaccharide factors in the American lobster Homarus americanus: molecular characterization and transcriptional response to Vibrio fluvialis challenge

Quantification of proteomic profile changes in the hemolymph of crayfish during in vitro coagulation

Hemolymph is the circulatory fluid that fills the body cavity of crustaceans, analogous to blood in vertebrates. Hemolymph coagulation, similar to blood clotting in vertebrates, plays a crucial role in wound healing and innate immune responses. Despite extensive studies on the clotting process in crustaceans, no comparative quantitative analysis of the protein composition of non-clotted and clotted hemolymph in any decapod has been reported. In this study, we used label-free protein quantification with high-resolution mass spectrometry to identify the proteomic profile of hemolymph in crayfish and quantify significant changes in protein abundances between non-clotted and clotted hemolymph. Our analysis identified a total of two-hundred and nineteen proteins in both hemolymph groups. Furthermore, we discussed the potential functions of the top most high and low-abundant proteins in hemolymph proteomic profile. The quantity of most of the proteins was not significantly changed during coagulation between non-clotted and clotted hemolymph, which may indicate that clotting proteins are likely pre-synthesized, allowing for a swift coagulation response to injury. Four proteins still showed abundance differences (p < 0.05, fold change>2), including C-type lectin domain-containing proteins, Laminin A chain, Tropomyosin, and Reverse transcriptase domain-containing proteins. While the first three proteins were down-regulated, the last one was up-regulated. The down-regulation of structural and cytoskeletal proteins may affect the process of hemocyte degranulation needed for coagulation, while the up-regulation of an immune-related protein might be attributed to the phagocytosis ability of viable hemocytes during coagulation.

A novel anti-lipopolysaccharide factor from blue swimmer crab Portunus pelagicus and its cytotoxic effect on the prokaryotic expression host, E. coli on heterologous expression

BACKGROUND

Invertebrates like crabs employ their own immune systems to fight against a number of invasive infections. Anti-lipopolysaccharide factors (ALFs) are an important class of antimicrobial peptides (AMPs) exhibiting binding and neutralizing activities against lipopolysaccharides.

RESULTS

This study identified and characterized a novel homolog of ALF (Pp-ALF) from the blue swimmer crab Portunus pelagicus. Pp-ALF has a 369bp open-reading frame encoding a protein with 123 amino acids. The deduced protein featured an LPS-binding domain and a signal peptide. The predicted tertiary structure of Pp-ALF contains three α helices packed against four β sheets. The deduced amino acid sequence of Pp-ALF had a net positive charge of +10.75 and an isoelectric point of 9.8. Phylogenetic analysis revealed that Pp-ALF has a strong ancestral relationship with crab ALFs.

CONCLUSION

Antibacterial, antiviral, antifungal, anticancer, and antibiofilm activities of Pp-ALF could be revealed by in silico prediction tools. Recombinant expression of Pp-ALF was unsuccessful in the Escherichia coli Rosetta-gami expression system due to the cytotoxic effect of the peptide to the host. The toxic effect of Pp-ALF to the host was displayed by membrane permeabilization and death of the host cells by fluorescent staining with Syto9-Propidium Iodide and CTC-DAPI- FITC.

Immunopathogenesis of hematopoietic tissues in response to Vibrio parahaemolyticus (VPAHPND) infection in Macrobrachium rosenbergii

In crustacean, hemocytes are known as crucial components of crustaceans' innate immunity against pathogens. Drastic hemocytes reduction during infectious disease is apparently related to disease severity and calls for a health status evaluation and aquaculture management. The molecular pathogenesis of hemocytes loss during bacterial infection was elucidated with VP_AHPND challenged in M. rosenbergii. We report herein a correlation between hemocyte loss and the pathogenicity and aggressive immune response in hematopoietic tissues of moribund M. rosenbergii. In this study, adult freshwater prawn was administered an LC₅₀ dose of VP_AHPND; bacterial clearance ensued, and success was reached within 24 h. Hemocytes increased in survival, yet drastically decreased in moribund prawn. Pathological analysis of hematopoietic tissue of moribund prawn showed apparent abnormal signs, including the presence of bacteria, a small number of mitotic cells, cellular swelling, loosening of connective tissue, and karyorrhectic nuclei cells. A significant upregulation of a core apoptotic machinery gene, caspase-3, was detected in hematopoietic tissue of moribund shrimp, but not in those of Escherichia coli DH5α (non-pathogenic bacteria) and VP_AHPND survival prawn. The highest level was found in the moribund group, which confirms the occurrence of apoptosis in this hematopoietic tissue. Further, our results suggest that hematopoietic tissue damage may arise from inflammation triggered by an aggressive immune response. Immune activation was indicated by the comparison of immune-related gene expression between controls, E. coli (DH5α)-infected (non-pathogenic), and VP_AHPND-infected survival groups with moribund prawn. RT-PCR revealed a significant upregulation of all genes in hematopoietic tissues and hemocytes within 6-12 h and declined by 24 h. This evident related to the almost VP_AHPND are clearance in survival and E. coli (DH5α) challenged group in contrast with drastic high expression was determined in moribund group. We conclude that a reduction of renewing circulating hemocytes in fatally VP_AHPND-infected prawn was caused by an acute self-destructive immune response by hematopoietic cells.

American lobster postlarvae alter gene regulation in response to ocean warming and acidification

Anthropogenic carbon emissions released into the atmosphere is driving rapid, concurrent increases in temperature and acidity across the world's oceans. Disentangling the interactive effects of warming and acidification on vulnerable life stages is important to our understanding of responses of marine species to climate change. This study evaluates the interactive effects of these stressors on the acute response of gene expression of postlarval American lobster (Homarus americanus), a species whose geographic range is warming and acidifying faster than most of the world's oceans. In the context of our experiment, we found two especially noteworthy results: First, although physiological end points have consistently been shown to be more responsive to warming in similar experimental designs, our study found gene regulation to be considerably more responsive to elevated pCO2. Furthermore, the combined effect of both stressors on gene regulation was significantly greater than either stressor alone. Using a full factorial experimental design, lobsters were raised in control and elevated pCO2 concentrations (400 ppm and 1,200 ppm) and temperatures (16°C and 19°C). A transcriptome was assembled from an identified 414,517 unique transcripts. Overall, 1,108 transcripts were differentially expressed across treatments, several of which were related to stress response and shell formation. When temperature alone was elevated (19°C), larvae downregulated genes related to cuticle development; when pCO2 alone was elevated (1,200 ppm), larvae upregulated chitinase as well as genes related to stress response and immune function. The joint effects of end-century stressors (19°C, 1,200 ppm) resulted in the upregulation of those same genes, as well as cellulase, the downregulation of calcified cuticle proteins, and a greater upregulation of genes related to immune response and function. These results indicate that changes in gene expression in larval lobster provide a mechanism to respond to stressors resulting from a rapidly changing environment.

Anti-lipopolysaccharide Factor from Crucifix Crab Charybdis feriatus, Cf-ALF2: Molecular Cloning and Functional Characterization of the Recombinant Peptide

Antilipopolysaccharide factors (ALFs) are important effectors of innate immunity in crustaceans with broad spectrum antimicrobial activity. Present study deals with the molecular and functional characterization of a 98-amino acid ALF isoform from, crucifix crab, Charybdis feriatus termed as Cf-ALF2. The ALF isoform Cf-ALF2 exhibits characteristic features of an AMP including a cationic net charge of + 9 and a total hydrophobic ratio of 34%. Recombinant peptide rCf-ALF2 showed remarkable antimicrobial activity against Gram-negative and Gram-positive bacteria especially against Staphylococcus aureus (minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) of 5 µM) and Escherichia coli (MIC 10 µM and MBC 20 µM). Using scanning electron microscopy, bacterial membrane blebbing, disruption, and cell content leakage were observed in peptide treated E. coli. The recombinant peptide was found to be non-hemolytic and non-cytotoxic in NCI-H460 cell line at the highest tested concentration (20 µM). Thus, this study identified a novel isoform of ALF from C. feriatus and revealed the potent antimicrobial property of the recombinant peptide Cf-ALF2 and the future prospects of using the peptide for therapeutic applications in the future.

Characterization of a Lymphoid Organ Specific Anti-lipopolysaccharide Factor From Shrimp Reveals Structure-Activity Relationship of the LPS-Binding Domain

Anti-lipopolysaccharide factor (ALF) is a kind of important antimicrobial peptides with broad-spectrum antimicrobial activities. The LPS-binding domain (LBD) contributes to the major antimicrobial activity of ALF. However, LBDs from different ALFs share low sequence similarity. The general character of LBDs needs to be elucidated to understand the molecular mechanism of their function and facilitate LBD-original drug design. Here we identified a lymphoid organ specifically expressed ALF, designated as FcALF8, from the Chinese shrimp Fenneropenaeus chinensis. The synthetic LBD peptide of FcALF8 (LBD8) showed strong antibacterial activities to the pathogenic Vibrio, such as Vibrio alginolyticus, Vibrio harveyi, and Photobacterium damselae with a MIC value of 0.5–1, 1–2, and 1–2 μM, respectively. FcALF8 knock-down using dsRNA led to significant increase of the viable bacteria in the lymphoid organ and hepatopancreas of shrimp upon V. harveyi infection. On the contrary, the proliferation of V. harveyi in the shrimp lymphoid organ and hepatopancreas significantly decreased after infected by LBD8 pre-incubated V. harveyi. Sequence alignments showed that the LBDs from 39 ALFs shared only two identical cysteine residues. However, 17 of the total 22 LBD residues showed high similarity when the amino acids were classified into hydrophobic and hydrophilic ones. A further activity analysis on modified LBD8 peptides showed that the antibacterial activity of LBD8 was lost after linearization and apparently weakened after changing the amino acid property at certain positions. The data indicated that the disulfide bond and amino acid property contributed to the conservation of the functional domain. To the best of our knowledge, this is the first identified ALFs specifically expressed in the lymphoid organ of shrimp with strong antibacterial activity. The present data will give creative instructions for the design of LBD-originated antimicrobial agents.

Development of novel antimicrobial peptides derived from anti-lipopolysaccharide factor of the swimming crab, Portunus trituberculatus

Anti-lipopolysaccharide factors (ALFs) are a representative host defense protein in crustaceans. In this study, we successfully developed two novel antimicrobial peptides (AMPs), named crab-ALF2A and crab-ALF6A, which contain changes to the amino acid sequences of the lipopolysaccharide binding domain and signal peptide, respectively, of the ALF of the swimming crab Portunus trituberculatus. The crab-ALF2A peptide showed potent antimicrobial activity against the Gram-positive bacteria Bacillus cereus, Staphylococcus aureus, and Streptococcus iniae (minimal effective concentration [MEC] 1.51-1.93 μg/mL) and the Gram-negative bacteria Pseudomonas aeruginosa and Escherichia coli (MEC 1.87-1.98 μg/mL), with maximal bactericidal activity at a peptide concentration of 5 μg/mL. The crab-ALF6A peptide also showed potent antimicrobial activity against B. cereus, S. aureus, and S. iniae (MEC 1.49-2.3 μg/mL) and P. aeruginosa and E. coli (MEC 1.72-1.19 μg/mL) at a peptide concentration of 5 μg/mL. Notably, the crab-ALF2A and crab-ALF6A peptides exhibited strong activity against Candida albicans (MECs of 2.11 and 1.95 μg/mL, respectively). These activities were stable following heat treatment. Moreover, the effect of crab-ALF2A and crab-ALF6A peptide treatment on microbe cell morphology was confirmed by scanning electron microscopy. Membrane disruption and damage, and the leakage of cytoplasmic content were clearly observed. A downsizing peptide approach illustrated that the hexapeptide ALF6A8 (RVLLRL) was the shortest peptide showing significant antimicrobial activity. Our approach allows for the generation of novel antimicrobial peptides in a cost effective manner as potential next-generation antibiotics.

Multiple Isoforms of Anti-Lipopolysaccharide Factors and Their Antimicrobial Functions in the Ridgetail Prawn Exopalaemon carinicauda

As a kind of antimicrobial peptides (AMP) in crustacean, anti-lipopolysaccharide factors (ALFs) have broad spectrum antimicrobial activities. In the present study, we identified four ALF genes, EcALF2-5, from the ridgetail prawn Exopalaemon carinicauda. Tissue distribution analysis showed that EcALF2 and EcALF4 transcripts were mainly located in gill, epidermis, and stomach, while EcALF3 and EcALF5 were mainly in hemocytes. Peptides corresponding to the LPS binding domain (LBD) of EcALFs were synthesized for analyzing their antimicrobial activities. Minimal inhibitory concentration (MIC) analysis showed that the synthetic LBD peptides of EcALF3 and EcALF4 could inhibit the growth of Gram-positive and Gram-negative bacteria, while the synthetic LBD peptides of EcALF2 and EcALF5 showed antibacterial activity against Vibrio. Incubation of white spot syndrome virus (WSSV) with the synthetic LBD peptides of EcALF3, EcALF4, and EcALF5 could reduce the in vivo viral copy number in WSSV-infected prawns. After silencing of EcALFs, Vibrio exhibited a rapid proliferation in the hepatopancreas of the prawn. The present data showed the important function of different EcALFs in modulating the in vivo bacterial and viral propagation in E. carinicauda. This study will provide new clues into the disease control in aquaculture.

Recent Advances in Antibacterial and Antiendotoxic Peptides or Proteins from Marine Resources

Infectious diseases caused by Gram-negative bacteria and sepsis induced by lipopolysaccharide (LPS) pose a major threat to humans and animals and cause millions of deaths each year. Marine organisms are a valuable resource library of bioactive products with huge medicinal potential. Among them, antibacterial and antiendotoxic peptides or proteins, which are composed of metabolically tolerable residues, are present in many marine species, including marine vertebrates, invertebrates and microorganisms. A lot of studies have reported that these marine peptides and proteins or their derivatives exhibit potent antibacterial activity and antiendotoxic activity in vitro and in vivo. However, their categories, heterologous expression in microorganisms, physicochemical factors affecting peptide or protein interactions with bacterial LPS and LPS-neutralizing mechanism are not well known. In this review, we highlight the characteristics and anti-infective activity of bifunctional peptides or proteins from marine resources as well as the challenges and strategies for further study.

A novel anti-lipopolysaccharide factor SpALF6 in mud crab Scylla paramamosain exhibiting different antimicrobial activity from its single amino acid mutant

In crustaceans, anti-lipopolysaccharide factors (ALFs) are important immune effectors that have sequence diversity and exhibit broad antimicrobial activities. In this study, we characterized a novel ALF homolog SpALF6 from mud crab Scylla paramamosain and its variant SpALF6-V, which was generated by mutations of two amino acids (H46 to R and A110 to P) due to the presence of two single nucleotide polymorphisms (SNPs). SpALF6 was an anionic peptide with isoelectric point (pI) 6.79, whereas SpALF6-V was a cationic protein with pI 7.98. These two proteins shared a common lipopolysaccharide (LPS)-binding domain (LBD) with pI 6.05. SpALF6 was expressed mainly in hemocytes and up-regulated by Vibrio parahaemolyticus or Staphylococcus aureus challenge, indicating that SpALF6 may participate in the antibacterial immune responses. To investigate the likely functional differences between SpALF6 and SpALF6-V and elucidate the underlying mechanisms, a single amino acid mutant SpALF6-M (from H46 to R, outside but very close to LBD), which had the same pI as SpALF6-V, was harvested by a fusion PCR. Then, both SpALF6 and SpALF6-M were overexpressed and purified to test antimicrobial activity and binding activity to microbial cells or polysaccharides. SpALF6-M exhibited more potent antimicrobial and cell-binding activity on Gram-positive bacteria and fungi than SpALF6. Furthermore, SpALF6-M possessed stronger lipoteichoic acid (LTA)-binding activity than SpALF6, demonstrating that this particular positively charged amino acid outside but close to LBD contributed to the increase in SpALF6-M antibacterial activity. In addition, SpALF6 LBD peptide and its biotin-labeled form were synthesized in this study. Results showed that this anionic LBD peptide itself did not exhibit any significant antimicrobial activity against 10 kinds of microorganisms but it possessed strong binding activity to LPS, LTA, and peptidoglycan. These findings suggested that this anionic LBD was still an important active center and required collaboration with some particular positively charged amino acids outside LBD to exhibit antibacterial activity. Thus, SpALF6-M antimicrobial activity was increased by the mutation of H46 to R instead of A110 to P, which did not change the protein charge, suggesting that SpALF6-V may have more potent antimicrobial activity than SpALF6 and play more important roles in antibacterial immunity. This study provided a new insight into the mechanisms of how ALF amino acid sequence diversity resulted in their functional divergence.

Newly identified PcToll4 regulates antimicrobial peptide expression in intestine of red swamp crayfish Procambarus clarkii

Tolls or Toll-like receptors (TLRs) have an essential role in initiating innate immune responses against pathogens. In this study, a novel Toll gene, PcToll4, was first identified from the intestinal transcriptome of the freshwater crayfish, Procambarus clarkii. The PcToll4 cDNA is 4849bp long with a 3036bp open reading frame that encodes a 1011-amino acid protein. PcToll4 contains a signal peptide, 13 LRR domains, 3 LRR TYP domains, 2 LRR CT domains, an LRR NT domain, a transmembrane region, and a TIR domain. Quantitative RT-PCR analysis revealed that PcToll4 mRNA was detected in all tested tissues, and the expression of PcToll4 in the intestine was significantly upregulated after white spot syndrome virus (WSSV) challenge. Overexpression of PcToll4 in Drosophila Schneider 2 (S2) cells activates the antimicrobial peptides (AMPs) of Drosophila, including metchnikowin, drosomycin, attacin A, and shrimp Penaeidin-4. Results of RNA interference by siRNA also showed that PcToll4 regulates the expressions of 5 anti-lipopolysaccharide factors (ALFs) in the intestine of crayfish. Our findings suggest that PcToll4 is important for the innate immune responses of P. clarkii because this gene regulates the expressions of AMPs against WSSV.

Molecular Characterization and Phylogenetic Analysis of Novel Isoform of Anti-lipopolysaccharide Factor from the Mantis Shrimp, Miyakea nepa

Anti-lipopolysaccharide factor (ALF) is a cationic anti-microbial peptide representing humoral defence system exhibiting a diverse spectrum of activity against microbial pathogens, including gram-negative and gram-positive bacteria, fungi, parasites and viruses. In this study, we identified and characterized a novel ALF homologue (MnALF) encoding cDNA sequence from the haemocytes of stomatopod mantis shrimp Miyakea nepa. The deduced peptide of MnALF encoded for a 123-amino acid peptide with a 25-residue signal peptide containing selenocysteine followed by a highly cationic mature peptide comprised of a putative LPS-binding domain flanked by two cysteine residues. BLAST analysis of MnALF showed that it exhibits identity to crustacean and limulid ALFs. The mature peptide of MnALF has a net charge of +7 and predicted molecular weight of 10.998 kDa with a theoretical isoelectric point (pI) of 9.93. Spatial structure of MnALF comprises three α-helices packed against a four-stranded β-sheet of which two were linked by a disulphide bond to form an amphipathic loop similar to the structure of Penaeus monodon, ALF-Pm3. All these features suggest that MnALF could play an imperative role in the innate defence mechanism of M. nepa. To our knowledge, this study accounts for the first report of an anti-microbial peptide from the order stomatopoda.

De novo transcriptome assembly for the lobster Homarus americanus and characterization of differential gene expression across nervous system tissues

BACKGROUND

The American lobster, Homarus americanus, is an important species as an economically valuable fishery, a key member in marine ecosystems, and a well-studied model for central pattern generation, the neural networks that control rhythmic motor patterns. Despite multi-faceted scientific interest in this species, currently our genetic resources for the lobster are limited. In this study, we de novo assemble a transcriptome for Homarus americanus using central nervous system (CNS), muscle, and hybrid neurosecretory tissues and compare gene expression across these tissue types. In particular, we focus our analysis on genes relevant to central pattern generation and the identity of the neurons in a neural network, which is defined by combinations of genes distinguishing the neuronal behavior and phenotype, including ion channels, neurotransmitters, neuromodulators, receptors, transcription factors, and other gene products.

RESULTS

Using samples from the central nervous system (brain, abdominal ganglia), abdominal muscle, and heart (cardiac ganglia, pericardial organs, muscle), we used RNA-Seq to characterize gene expression patterns across tissues types. We also compared control tissues with those challenged with the neuropeptide proctolin in vivo. Our transcriptome generated 34,813 transcripts with known protein annotations. Of these, 5,000-10,000 of annotated transcripts were significantly differentially expressed (DE) across tissue types. We found 421 transcripts for ion channels and identified receptors and/or proteins for over 20 different neurotransmitters and neuromodulators. Results indicated tissue-specific expression of select neuromodulator (allostatin, myomodulin, octopamine, nitric oxide) and neurotransmitter (glutamate, acetylcholine) pathways. We also identify differential expression of ion channel families, including kainite family glutamate receptors, inward-rectifying K(+) (IRK) channels, and transient receptor potential (TRP) A family channels, across central pattern generating tissues.

CONCLUSIONS

Our transcriptome-wide profiles of the rhythmic pattern generating abdominal and cardiac nervous systems in Homarus americanus reveal candidates for neuronal features that drive the production of motor output in these systems.

Identification of five anti-lipopolysaccharide factors in oriental river prawn, Macrobrachium nipponense

Anti-lipopolysaccharide factors (ALFs) are a group of antimicrobial peptides (AMPs) with broad-spectrum antimicrobial activities and antiviral activities mainly found in crustaceans and horseshoe crabs. In the present study, we identified 5 ALF expression sequence tags (ESTs) through analysis of the established M. nipponense transcriptome, and cloned their full-length cDNA sequences using rapid amplification of cDNA ends (RACE) method. The 5 ALFs were designated as MnALF1-5, and all of them showed high similarity with their Macrobrachium rosenbergii homologs in the phylogenetic analyses, especially in LPS binding domains. In healthy adult prawns, we found the highest expression of MnALF2 and MnALF4 in haemocytes, and the highest expression of MnALF4 and MnALF3 in intestine. Some isoforms of MnALF were down-regulated but the majority was up-regulated in different prawn tissues upon Aeromonas hydrophila challenge. To conform the expected antimicrobial activities harbored in MnALFs' LPS binding domains, we used a synthesized peptide cMnALF24 that corresponds to the LPS binding domain of MnALF2 as a representative molecule for the antibacterial activity test, and found that cMnALF24 possessed strong and broad-spectrum antibacterial activity against Gram positive and Gram negative bacteria, but no inhibition activity against fungi; Meanwhile, in the hemolytic test, cMnALF24 showed weak hemolysis activities (around 10%) to the rabbit red blood cells at concentrations of 0.67-33.50 μM. This study provides insights into understanding the antibacterial function of ALFs in the innate immunity of freshwater prawn, and reports a peptide that can be a potential drug candidate with good efficacy against bacterial infection and low toxicity to host cells.

A new group of anti-lipopolysaccharide factors from Marsupenaeus japonicus functions in antibacterial response

Anti-lipopolysaccharide factors (ALFs) are a group of critical effector molecules with a broad spectrum of antimicrobial activities in crustaceans. Four groups of ALFs (A, B, C, and D) have been identified in peneaid shrimp. In the study, we identified a new group of ALFs (designated as MjALF-E) from Marsupenaeus japonicus. This new group (group E) included MjALF-E1 and E2. MjALF-E1 was highly expressed in hemocytes, heart, and intestine, whereas E2 was highly expressed in gills, stomach, and intestine. Expressions of both MjALF-E1 and E2 were upregulated by bacterial challenge. Synthesized LPS-binding domain peptides of MjALF-E1 and E2 strongly bind to bacterial cell wall components lipopolysaccharide (LPS) and peptidoglycan (PGN). The recombinant rMjALF-E2 showed relatively weak binding activity to LPS and PGN. Both synthesized peptides and rMjALF-E2 exhibited antimicrobial activity against Gram-negative bacteria, whereas rMjALF-E2 could promote the clearance of bacteria in vivo. After knockdown of MjALF-E2 and infection with Vibrio anguillarum, shrimp showed high and rapid mortality compared with GFPi shrimp. These results suggest that MjALF-Es serves a protective function against bacterial infection in shrimp.

Characterization and functional classification of American lobster (Homarus americanus) immune factor transcripts

The American lobster (Homarus americanus) is the most important commercially exploited marine species in Canada. Very little is known about the H. americanus molecular humoral immune response or how to determine if a seemingly healthy lobster is infected with a pathogen. The goal of this work is to characterize several important H. americanus immune genes as well as highlight and classify hundreds of others into functional immune groups. The protein sequence of H. americanus acute phase serum amyloid protein A (SAA) was found to be similar to that of vertebrate SAA, and is likely a good clinical marker for immune activation in lobsters and some crustaceans. Additionally, only one gene, Trypsin 1b, was found to be differentially regulated during bacterial, microparasitic and viral challenges in lobster and is likely critical for the activation of the H. americanus immune response. Bioinformatic analysis was used to functionally annotate, 263 H. americanus immune genes and identify the few shared patterns of differential gene expression in lobsters in response to bacterial, parasitic and viral challenge. Many of the described immune genes are biomarker candidates which could be used as clinical indicators for lobster health and disease. Biomarkers can facilitate early detection of pathogens, or anthropomorphic stressors, so that mitigation strategies can be developed in order to prevent the devastating economic losses that have occurred in Southern New England, USA. This work is contributes to further our understanding of how the lobster immune system works and how it can be used to maintain the health and sustainability of the overall American lobster fishery.

The role of biophysical parameters in the antilipopolysaccharide activities of antimicrobial peptides from marine fish

Numerous antimicrobial peptides (AMPs) from marine fish have been identified, isolated and characterized. These peptides act as host defense molecules that exert antimicrobial effects by targeting the lipopolysaccharide (LPS) of Gram-negative bacteria. The LPS-AMP interactions are driven by the biophysical properties of AMPs. In this review, therefore, we will focus on the physiochemical properties of AMPs; that is, the contributions made by their sequences, net charge, hydrophobicity and amphipathicity to their mechanism of action. Moreover, the interactions between LPS and fish AMPs and the structure of fish AMPs with LPS bound will also be discussed. A better understanding of the biophysical properties will be useful in the design of AMPs effective against septic shock and multidrug-resistant bacterial strains, including those that commonly produce wound infections.

SpALF4: a newly identified anti-lipopolysaccharide factor from the mud crab Scylla paramamosain with broad spectrum antimicrobial activity

Anti-lipopolysaccharide factors (ALFs) are antimicrobial peptides with binding and neutralizing activities to lipopolysaccharide (LPS) in crustaceans. This study identified and characterized a novel ALF homolog (SpALF4) from the mud crab Scylla paramamosain. The complete cDNA of SpALF4 had 756 bp with a 381 bp open reading frame encoding a protein with 126 aa. The deduced protein contained a signal peptide and a LPS-binding domain. SpALF4 shared the highest identity with PtALF5 at amino acid level but exhibited low similarity with most of other crustacean ALFs. Furthermore, different from the previously identified three SpALF homologs and most of other ALFs, SpALF4 had a low isoelectric point (pI) for the mature peptide and the LPS-binding domain with the values of 6.93 and 6.74, respectively. These results indicate that SpALF4 may be a unique ALF homolog with special biological function in the mud crab. Similar to the spatial structure of ALFPm3, SpALF4 contains three α-helices packed against a four-strand β-sheet, and an amphipathic loop formed by a disulphide bond between two conserved cysteine residues in LPS-binding domain. SpALF4, mainly distributed in hemocytes, could be upregulated by Vibrio harveyi, Staphylococcus aureus, or white spot syndrome virus. Recombinant SpALF4 could inhibit the growth of Gram-negative bacteria (V. harveyi, Vibrio anguillarum, Vibrio alginolyticus, Aeromonas hydrophila, Pseudomonas putida), Gram-positive bacteria (S. aureus and Bacillus megaterium), and a fungus Candida albicans to varying degrees. Further study showed that it could also bind to all the aforementioned microorganisms except S. aureus. These results demonstrate that SpALF4 is a unique ALF homolog with potent antimicrobial activity against bacteria and fungi. This characteristic suggests SpALF4 plays an essential function in immune defense against pathogen invasion in mud crab.

Transcriptome analysis on Chinese shrimp Fenneropenaeus chinensis during WSSV acute infection

Previous studies have discovered a lot of immune-related genes responding to white spot syndrome virus (WSSV) infection in crustacean. However, little information is available in relation to underlying mechanisms of host responses during the WSSV acute infection stage in naturally infected shrimp. In this study, we employed next-generation sequencing and bioinformatic techniques to observe the transcriptome differences of the shrimp between latent infection stage and acute infection stage. A total of 64,188,426 Illumina reads, including 31,685,758 reads from the latent infection group and 32,502,668 reads from the acute infection group, were generated and assembled into 46,676 unigenes (mean length: 676 bp; range: 200-15,094 bp). Approximately 24,000 peptides were predicted and classified based on homology searches, gene ontology, clusters of orthologous groups of proteins, and biological pathway mapping. Among which, 805 differentially expressed genes were identified and categorized into 11 groups based on their possible function. Genes in the Toll and IMD pathways, the Ras-activated endocytosis process, the RNA interference pathway, anti-lipopolysaccharide factors and many other genes, were found to be activated in shrimp from latent infection stage to acute infection stage. The anti-bacterially proPO-activating cascade was firstly uncovered to be probably participated in antiviral process. These genes contain not only members playing function in host defense against WSSV, but also genes utilized by WSSV for its rapid proliferation. In addition, the transcriptome data provides detail information for identifying novel genes in absence of the genome database of shrimp.

Molecular cloning, genomic structure and antimicrobial activity of PtALF7, a unique isoform of anti-lipopolysaccharide factor from the swimming crab Portunus trituberculatus

Anti-lipopolysaccharide factors (ALFs), as the potent antimicrobial peptides, are becoming predominant candidates for potential therapeutic agents of bacterial and viral diseases. In this study, a unique isoform of ALF (PtALF7) was identified from hemocytes cDNA library of the swimming crab Portunus trituberculatus. The PtALF7 cDNA contained an open reading frame (ORF) of 372 bp encoding 123 amino acids. The deduced peptide of PtALF7 shared high similarity with our previously reported PtALF1-3 but low with PtALF4-6. The PtALF7 gene consisted of three exons interrupted by two introns, and was clearly transcribed from different genomic loci compared with other PtALF isoforms. Totally 128 SNPs including 12 in coding region and 116 in noncoding region were detected in PtALF7 gene by direct sequencing of 20 samples. The mRNA expression of PtALF7 transcript was primarily observed in hemocytes followed by gill and eyestalk, but barely detectable in hepatopancreas. After challenge with Vibrio alginolyticus, a main pathogen causing high mortality in P. trituberculatus, the PtALF7 transcript in hemocytes showed a clear time-dependent response expression pattern with obvious decrease at 6 h and significant increase at 24 h. The recombinant PtALF7 protein exhibited antimicrobial activity against the test Gram-negative and Gram-positive bacteria, but did not inhibit the growth of fungus Pichia pastoris. These results together indicate a potential involvement for PtALF7 in the innate immune response of P. trituberculatus.

A newly identified anti-lipopolysaccharide factor from the swimming crab Portunus trituberculatus with broad spectrum antimicrobial activity

Anti-lipopolysaccharide factors (ALFs), exhibiting binding and neutralizing activities to lipopolysaccharide (LPS), are the potent antimicrobial peptides of innate immunity in crustaceans. In this study, a unique isoform of ALF (PtALF6) was identified from eyestalk cDNA library of the swimming crab Portunus trituberculatus. The full-length cDNA of PtALF6 was 669 bp encoding 115 amino acids, relatively short to other known ALFs. The deduced peptide of PtALF6 was conserved; it contained the signal peptide and LPS-binding domain, especially the two conserved cysteine residues at both ends of the domain. Predicted tertiary structures of PtALF6 containing four β-strands and three α-helices were similar to that described in Limulus polyphemus. The genomic fragment of PtALF6 contained three exons separated by two introns. Unlike most ALFs expressed in hemocytes, PtALF6 transcript was predominantly detected in gill with 14.05-fold higher than that in hemocytes. After challenge with Vibrio alginolyticus, the temporal expression level of PtALF6 transcript in hemocytes showed a clear time-dependent response expression pattern with two significant peaks at 12 h and 32 h post-injection. The recombinant PtALF6 protein revealed antimicrobial activity against the test Gram-negative and Gram-positive bacteria, but did not inhibit the growth of fungus Pichia pastoris. These results together indicate that PtALF6 is a potential antimicrobial protein against Gram-negative and Gram-positive bacteria infection, and may play an important role in innate immune response of P. trituberculatus.

Three different anti-lipopolysaccharide factors identified from giant freshwater prawn, Macrobrachium rosenbergii

Anti-lipopolysaccharide factor (ALF) is a type of basic protein and an important antimicrobial peptide that can bind and neutralize lipopolysaccharides (LPS). This protein shows a broad spectrum of antimicrobial activity. In this study, three forms of ALF designated as MrALF5, MrALF6, and MrALF7 were identified from giant freshwater prawn, Macrobrachium rosenbergii. MrALF5, MrALF6, and MrALF7 genes encode 133, 121, and 120 amino acids of the corresponding proteins, respectively. All these ALF proteins contain LPS-binding domain with two conserved cysteine residues. The genomic sequences of MrALF5 and MrALF7 were amplified. The genomic structures of MrALF5 and MrALF7 comprise three exons interrupted by two introns. Phylogenetic analysis showed that MrALF5, MrALF6, and MrALF7 were clustered into clade II. Evolutionary analysis showed that ALF genes from M. rosenbergii may suffer a rapid evolution. MrALF5 was expressed mainly in the hepatopancreas, gills, and heart. MrALF6 was mainly distributed in the intestine and hepatopancreas. The highest expression level of MrALF7 was detected in the hepatopancreas. MrALF6, as well as MrALF7, was downregulated by Escherichia coli challenge, and all three ALF genes were upregulated by Vibrio or white spot syndrome virus challenge. MrALF6 was also upregulated by Staphylococcus aureus challenge. In summary, the three isoforms of ALF genes may participate in the innate immune response against bacteria and virus infecting the giant fresh water prawn.

Molecular cloning, expression pattern and antimicrobial activity of a new isoform of anti-lipopolysaccharide factor from the swimming crab Portunus trituberculatus

A new isoform of anti-lipopolysaccharide factor (PtALF5) was cloned from eyestalk cDNA library of swimming crab Portunus trituberculatus. The full-length cDNA of PtALF5 was 1045 bp encoding 120 amino acids. PtALF5 shared lower amino acid similarity with other ALFs, yet it contained the conserved LPS-binding domain and was clearly member of the ALF family. The genomic fragment of PtALF5 contained two exons separated by one intron. Several tandem repeats were found in intron. The mRNA transcript of PtALF5 was predominantly expressed in the hemocytes but barely detectable in muscle. After challenge with Vibrio alginolyticus, a main pathogen causing high mortality in P. trituberculatus, the PtALF5 transcript in hemocytes showed a clear time-dependent response expression pattern with obvious decrease at 6 h and significant increase at 24 h. The recombinant PtALF5 protein revealed antimicrobial activity against Gram-negative bacteria V. alginolyticus and Pseudomonas aeruginosa, but did not inhibit the growth of the tested Gram-positive bacteria and fungus. These results together suggest that PtALF5 is a potent antibacterial protein against Gram-negative bacteria infection, and might function as a promising therapeutic agent in disease control of crab aquaculture.

Time-course recovery of estrogen-responsive genes of a cichlid fish exposed to waterborne octylphenol

The aim of this study was to describe the time-course of estrogen-induced gene expression, corresponding plasma protein detection and histological alterations after cessation of octylphenol (OP) exposure of Cichlasoma dimerus, to test differential responses of biomarkers suitable for environmental monitoring. Male fish were exposed to a nominal concentration of 150 μg/L OP for 28 days, and later transferred to OP-free water aquaria for 1, 3, 7, 14, 21 or 28 days. Blood and mucus samples were obtained in order to analyze vitellogenin (VTG) and zona pellucida (ZP) proteins by Western blot; liver samples were used for gene expression and to assess tissue damage and further recovery of all the analyzed endpoints. Partial sequences of C. dimerus VTG and Na⁺/K⁺-ATPase were obtained. Comparison with VTGs of several teleosts supports that the partial sequence obtained for C. dimerus belongs to VTGAb type. ZP and VTG expression was highly up-regulated by OP. Immunoreactive (ir-) bands of 62, 52 and 50 kDa for ZP and 140, 103, 75 and 64 kDa for VTG, were detected after 28 days of OP exposure in plasma and mucus samples. After transfer of treated fish to clean water, ZP ir-bands in plasma disappeared rapidly (day 3), while VTG ir-bands decreased gradually; no ir-bands were detected on day 28 of recovery. Similarly, ZPB transcripts abruptly returned to background levels (day 3), earlier than for ZPC (day 7) or VTG (day 14). Liver from OP treated fish showed tissue disarrangement, eccentric and euchromatic hepatocytes nuclei and intense perinuclear basophilia. After the recovery period, these changes were still evident though less pronounced, accounting for irreversibility of tissue damage or the requirement for a longer period of depuration. The present results confirm that for biochemical and molecular biomarkers, such as induction of female proteins in male fish exposed to OP, complete recovery is achieved after adequate time of depuration (28 days). Male ZPB expression reflects a recent exposure to estrogenic contaminants, while VTG may reveal past exposures. The combination of biomarkers with different temporal responses such as C. dimerus ZP and VTG provides a more comprehensive interpretation of pollution status.

Molecular characterization of three crustin genes in the morotoge shrimp, Pandalopsis japonica

Crustins are among the most important antimicrobial peptides (AMPs) found in decapod crustaceans. They are small cationic AMPs (5-7 kDa) characterized by a proline-rich amino-terminal domain and a cysteine-rich carboxyl-terminal domain. Here, the first 3 crustin-like cDNAs (Pj-crus Ia, Ib, and II) were identified from the morotoge shrimp, Pandalopsis japonica. The full-length cDNAs of Pj-crus Ia, Ib, and II consisted of 1135, 580, and 700 nucleotides and encoded putative proteins containing 109, 119, and 186 amino acids residues, respectively. All 3 identified Pj-crus sequences exhibited the conserved domain organization for crustins, including a signal sequence, a cysteine-containing region, a glycine-rich region, and a whey-acidic protein (WAP) domain. Amino acid sequence comparisons and phylogenetic analysis revealed that the Pj-crus Ia and Ib belong to type I crustins (e.g., carcinin), which have been mostly identified from Brachyura and Astacidea, whereas Pj-crus II was classified as belonging to the type II crustins, which are mainly found in Dendrobranchiata. An analysis of the organization of these 3 Pj-crus genes revealed that the splicing site within the WAP domain may be an important key for classifying types I and II crustin family members. The tissue distribution profile results showed that the Pj-crus I genes were expressed in a tissue-specific manner but that the Pj-crus II gene was expressed ubiquitously, suggesting that these crustins may play different roles in various tissues or under different physiological conditions. The bacterial challenge results suggested that the Pj-crus genes may be transcriptionally influenced by different bacterial types. This comparative study of various crustin family members will help extend the knowledge on the crustacean innate immune response, which will provide important basic information for controlling shrimp immunity against various pathogens.

A new anti-lipopolysaccharide factor isoform (PtALF4) from the swimming crab Portunus trituberculatus exhibited structural and functional diversity of ALFs

Anti-lipopolysaccharide factors (ALFs) are the potent antimicrobial peptides that can bind and neutralize lipopolysaccharide (LPS). In this study, a new isoform of the ALF homologs (PtALF4) was cloned from eyestalk cDNA library of swimming crab Portunus trituberculatus. PtALF4 shared lower amino acid similarity with other ALFs, yet it contained the conserved LPS-binding domain and was clearly member of the ALF family. The genomic sequence of PtALF4 consisted of three exons interrupted by two introns. Several tandem repeats were found in both introns. Unlike most ALFs expressed in hemocytes, PtALF4 transcript was predominantly detected in eyestalk. After challenge with Vibrio alginolyticus, the temporal expression level of PtALF4 transcript in hemocytes showed a clear time-dependent response expression pattern with two significant peaks. The recombinant proteins of PtALF1, PtALF3 and PtALF4 revealed different antimicrobial activities against bacteria or fungus. These results together suggest that PtALF isoforms might be potent immune effectors to provide multiple protective functions against invading bacteria or fungus in P. trituberculatus.

Cationic antimicrobial peptides in penaeid shrimp

Penaeid shrimp aquaculture has been consistently affected worldwide by devastating diseases that cause a severe loss in production. To fight a variety of harmful microbes in the surrounding environment, particularly at high densities (of which intensive farming represents an extreme example), shrimps have evolved and use a diverse array of antimicrobial peptides (AMPs) as part of an important first-line response of the host defense system. Cationic AMPs in penaeid shrimps composed of penaeidins, crustins, and anti-lipopolysaccharide factors are comprised of multiple classes or isoforms and possess antibacterial and antifungal activities against different strains of bacteria and fungi. Shrimp AMPs are primarily expressed in circulating hemocytes, which is the main site of the immune response, and hemocytes expressing AMPs probably migrate to infection sites to fight against pathogen invasion. Indeed, most AMPs are produced as early as the nauplii developmental stage to protect shrimp larvae from infections. In this review, we discuss the sequence diversity, expression, gene structure, and antimicrobial activities of cationic AMPs in penaeid shrimps. The information available on antimicrobial activities indicates that these shrimp AMPs have potential therapeutic applications in the control of disease problems in aquaculture.

Multiple isoforms of immune-related genes from hemocytes and eyestalk cDNA libraries of swimming crab Portunus trituberculatus

Expressed sequence tags (ESTs) analysis has been shown to be an efficient approach not only for gene discovery, but also for gene expression profiles performance. Two full-length enriched cDNA libraries were constructed from hemocytes and eyestalk of Portunus trituberculatus, respectively, and randomly sequenced to collect genomic information and identify genes involved in immune defense response. A total of 99 unigenes including 64 unigenes (6.00% of 1066 unigenes) in hemocytes library and 35 unigens (6.86% of 510 unigenes) in eyestalk library are identified to be immune genes. These genes are categorized into six classes, viz. antimicrobial peptides, redox proteins, melanization related proteins, chaperone proteins, clottable proteins and other immune factors. The content and category of immune genes in eyestalk library indicate eyestalk might have unrecognized role in crab immunity. Five immune genes containing multiple protein isoforms are identified and characterized, including anti-lipopolysaccharide factor (PtALF1-7), crustin (PtCrustin1-3), thioredoxin (PtTrx1-2), clip domain serine proteinase (PtcSP1-5) and kazal-type proteinase inhibitor (PtKPI1-4). Sequence alignment and phylogenetic analysis reveal PtALF1-7 contain two conserved cysteine residues and might be encoded by multiple genomic loci. PtCrustin1-3 share the consensus cysteine motif and are considered as Type I crustins. PtTrx1 possesses the critical structural cysteine residue C⁷³ of Trx-1, while PtTrx2 has the N-terminal mitochondrial translocation signal of Trx-2. Sequence analysis shows PtcSP1-5 contain one clip domain and one partial SP catalytic triad domain. PtKPI1-4 present one typical Kazal domain consisting of six conserved cysteine residues. Some protein isoforms are tissue-specific, which might suggest they have different origins and perform diverse functions. Except PtALF1-3 and PtCrustin1, the other isoformes in this study are firstly identified from P. trituberculatus. Especially, PtTrx2 are firstly identified from crustaceans. Our research will provide useful genomic information of P. trituberculatus and be helpful in understanding the molecular mechanisms of crab immunity.

Three isoforms of anti-lipopolysaccharide factor identified from eyestalk cDNA library of swimming crab Portunus trituberculatus

Anti-lipopolysaccharide factors (ALFs), as the potent antimicrobial peptides, can bind and neutralize lipopolysaccharide (LPS) and exhibit broad spectrum antimicrobial activities. In this study, three isoforms of the ALF homologues (PtesALF1-3) were identified from eyestalk cDNA library of swimming crab Portunus trituberculatus. The full-length cDNA sequences of PtesALF1, 2 and 3 were 1138, 1052 and 1057 bp encoding 92, 108 and 123 amino acids, respectively. PtesALF1-3 contained two conserved cysteine residues and shared high similarity with other reported ALFs. Predicted tertiary structures of PtesALF2 and 3 containing four β-strands and three α-helix were similar to that described in Limulus polyphemus, while PtesALF1 had only one α-helix in its spatial structure. Sequence analysis revealed PtesALF1-3 were encoded by the same genomic locus and generated by alternative splicing of the pre-mRNA. Totally 89 SNPs including 18 in coding region and 71 in noncoding region were detected by direct sequencing of 30 genomic samples. The mRNA expression of PtesALF1 and PtesALF1-3 transcripts was mainly detected in haemocytes but showed different expression pattern in other tissues including hepatopancreas, gill, eyestalk and muscle. After challenge with Vibrio alginolyticus, the temporal expression level of PtesALF1-3 transcripts in haemocytes showed a clear time-dependent response expression pattern with two peaks within the experimental period of 32 h, while PtesALF1 was up-regulated only once with obvious decrease at 6 h and significant increase at 24 h. These results suggest that the PtesALF isoforms have different tissue specificity and might provide multiple protective functions against invading bacteria in P. trituberculatus.

Cationic antimicrobial peptides in penaeid shrimp

Penaeid shrimp aquaculture has been consistently affected worldwide by devastating diseases that cause a severe loss in production. To fight a variety of harmful microbes in the surrounding environment, particularly at high densities (of which intensive farming represents an extreme example), shrimps have evolved and use a diverse array of antimicrobial peptides (AMPs) as part of an important first-line response of the host defense system. Cationic AMPs in penaeid shrimps composed of penaeidins, crustins, and anti-lipopolysaccharide factors are comprised of multiple classes or isoforms and possess antibacterial and antifungal activities against different strains of bacteria and fungi. Shrimp AMPs are primarily expressed in circulating hemocytes, which is the main site of the immune response, and hemocytes expressing AMPs probably migrate to infection sites to fight against pathogen invasion. Indeed, most AMPs are produced as early as the nauplii developmental stage to protect shrimp larvae from infections. In this review, we discuss the sequence diversity, expression, gene structure, and antimicrobial activities of cationic AMPs in penaeid shrimps. The information available on antimicrobial activities indicates that these shrimp AMPs have potential therapeutic applications in the control of disease problems in aquaculture.

The second anti-lipopolysaccharide factor (EsALF-2) with antimicrobial activity from Eriocheir sinensis

The anti-lipopolysaccharide factor (ALF) is a small basic protein that can bind and neutralize lipopolysaccharide (LPS), mediating degranulation and activation of an intracellular coagulation cascade. In the present study, cDNA of the second Eriocheir sinensis ALF (designated as EsALF-2) was cloned and the full-length cDNA of EsALF-2 was of 724bp, consisting of an open reading frame (ORF) of 363bp encoding a polypeptide of 120 amino acids. The deduced amino acid of EsALF-2 shared 82% similarity with EsALF-1 from E. sinensis and about 53-65% similarity with ALFs from other crustaceans. The potential tertiary structures of EsALF-1 and EsALF-2 contained two highly conserved-cysteine residues to define the LPS binding site, but the N-terminal of EsALF-1 formed a single additional alpha-helix compared to EsALF-2, implying that EsALF-1 and EsALF-2 might represent different biological functions in E. sinensis. The mRNA transcript of EsALF-2 was detected in all examined tissues of healthy crabs, including haemocytes, hepatopancreas, gill, muscle, heart and gonad, which suggested that EsALF-2 could be a multifunctional molecule for the host immune defense responses and thereby provided systemic protection against pathogens. The mRNA expression of EsALF-2 was up-regulated after Listonella anguillarum and Pichia pastoris challenge and the recombinant protein of EsALF-2 showed antimicrobial activity against L. anguillarum and P. pastoris, indicating that EsALF-2 was involved in the immune defense responses in Chinese mitten crab against L. anguillarum and P. pastoris. These results together indicated that there were abundant and diverse ALFs in E. sinensis with various biological functions and these ALFs would provide candidate promising therapeutic or prophylactic agents in health management and diseases control of crab aquaculture.

Conventional and unconventional antimicrobials from fish, marine invertebrates and micro-algae

All eukaryotic organisms, single-celled or multi-cellular, produce a diverse array of natural anti-infective agents that, in addition to conventional antimicrobial peptides, also include proteins and other molecules often not regarded as part of the innate defences. Examples range from histones, fatty acids, and other structural components of cells to pigments and regulatory proteins. These probably represent very ancient defence factors that have been re-used in new ways during evolution. This review discusses the nature, biological role in host protection and potential biotechnological uses of some of these compounds, focusing on those from fish, marine invertebrates and marine micro-algae.

Role of anti-lipopolysaccharide factor from the black tiger shrimp, Penaeus monodon, in protection from white spot syndrome virus infection

The anti-lipopolysaccharide factor (ALF) from the black tiger shrimp, Penaeus monodon, has been shown previously to exhibit a broad spectrum of activity against various strains of bacteria and fungi. Herein, the recombinant ALFPm3 (rALFPm3) protein was examined for its role in the defence against white spot syndrome virus (WSSV) infection in haematopoietic (Hpt) cell cultures of the freshwater crayfish, Pacifastacus leniusculus, as well as in live P. monodon shrimps. Incubation of Hpt cell cultures with a mixture of WSSV and rALFPm3 resulted in a dose-dependent decrease in VP28 gene expression levels, compared with those incubated with WSSV alone, with an rALFPm3 IC50 value lower than 2.5 μM. However, pre-treatment of Hpt cells with 5 μM rALFPm3 showed no induced protection against subsequent WSSV infection, whereas the synthetic crayfish ALF peptide could protect cells at a higher concentration (10 μM). The in vivo role of ALFPm3 was examined by injection of P. monodon with WSSV pre-treated with rALFPm3 protein. The results clearly showed that rALFPm3 was able to reduce WSSV propagation and prolong the survival of shrimps.