The scope of the crustacean immune system for disease control

The culture or wild capture of marine and freshwater shellfish, including crustaceans, is without doubt a key source of protein for a burgeoning world population. Historically the expansion of aquaculture has, however, been accompanied by the increased incidence of economically significant diseases, most notably of viral and bacterial origin. Since the late 1970s great progress has been made in our understanding of the generalized protostome innate immune system. Distinct pathways, pathogen receptor proteins and effector molecules have since been identified that are not ancestral or homologous to those of the deuterostomes, including vertebrates. Within the past decade progress has accelerated with the rapid characterisation of new classes of recognition proteins, immune effectors and regulatory pathways. This paper provides a broad overview of our current understanding of invertebrate immunology, taking the crustacean decapod immune system as its focus. Recent developments in the field are described briefly and their implications and potential considered. These advances offer fundamental new insights in our efforts to understand disease in cultured populations and also to develop knowledge of environmental effects on host/pathogen interactions within a fishery context. Of course, challenges do remain, including the lack of an immortal cell line and the limited publically-available genomic resources. These are considered in this review as priorities for future research effort. With the continued application of more insightful technologies, coupled with associated investment, it is expected that the speed at which some of these issues are resolved will accelerate

Crustins: enigmatic WAP domain-containing antibacterial proteins from crustaceans

Crustins are antibacterial proteins of ca. 7�14 kDa with a characteristic four-disulphide core-containing whey acidic protein (WAP) domain, expressed by the circulating haemocytes of crustaceans. Over 50 crustin sequences have been now reported from a variety of decapods, including crabs, lobsters, shrimp and crayfish. Three main types seem to occur but all possess a signal sequence at the amino terminus and a WAP domain at the carboxyl end. Differences between types lie in the structure of the central region. Those crustins purified as the native protein or expressed recombinantly all kill Gram-positive bacteria, and gene studies have shown that they are constitutively expressed, often at high levels, but show no consistent patterns of change in expression following injection ofbacteria. This variable response to infection is enigmatic but indicates that these proteins could perform additional functions, perhaps as immune regulators in recovery from wounding, trauma or physiological stress

White spot syndrome virus: an overview on an emergent concern

Viruses are ubiquitous and extremely abundant in the marine environment. One of such marine viruses, the white spot syndrome virus (WSSV), has emerged globally as one of the most prevalent, widespread and lethal for shrimp populations. However, at present there is no treatment available to interfere with the unrestrained occurrence and spread of the disease. The recent progress in molecular biology techniques has made it possible to obtain information on the factors, mechanisms and strategies used by this virus to infect and replicate in susceptible host cells. Yet, further research is still required to fully understand the basic nature of WSSV, its exact life cycle and mode of infection. This information will expand our knowledge and may contribute to developing effective prophylactic or therapeutic measures. This review provides a state-of-the-art overview of the topic, and emphasizes the current progress and future direction for the development of WSSV control strategies

Bacteria-Induced Dscam Isoforms of the Crustacean, Pacifastacus leniusculus

The Down syndrome cell adhesion molecule, also known as Dscam, is a member of the immunoglobulin super family. Dscam plays an essential function in neuronal wiring and appears to be involved in innate immune reactions in insects. The deduced amino acid sequence of Dscam in the crustacean Pacifastacus leniusculus (PlDscam), encodes 9(Ig)-4(FNIII)-(Ig)-2(FNIII)-TM and it has variable regions in the N-terminal half of Ig2 and Ig3 and the complete Ig7 and in the transmembrane domain. The cytoplasmic tail can generate multiple isoforms. PlDscam can generate more than 22,000 different unique isoforms. Bacteria and LPS injection enhanced the expression of PlDscam, but no response in expression occurred after a white spot syndrome virus (WSSV) infection or injection with peptidoglycans. Furthermore, PlDscam silencing did not have any effect on the replication of the WSSV. Bacterial specific isoforms of PlDscam were shown to have a specific binding property to each tested bacteria, E. coli or S. aureus. The bacteria specific isoforms of PlDscam were shown to be associated with bacterial clearance and phagocytosis in crayfish

Immunity in Society: Diverse Solutions to Common Problems

How do social animals, from insects to humans, limit the spread of disease by deploying community-level responses to pathogens? Active immunization of healthy ants by infected ants is one intriguing example

Urochordate Histoincompatible Interactions Activate Vertebrate-Like Coagulation System Components

The colonial ascidian Botryllus schlosseri expresses a unique allorecognition system. When two histoincompatible Botryllus colonies come into direct contact, they develop an inflammatory-like rejection response. A surprising high number of vertebrates' coagulation genes and coagulation-related domains were disclosed in a cDNA library of differentially expressed sequence tags (ESTs), prepared for this allorejection process. Serine proteases, especially from the trypsin family, were highly represented among Botryllus library ortholgues and its “molecular function” gene ontology analysis. These, together with the built-up clot-like lesions in the interaction area, led us to further test whether a vertebrate-like clotting system participates in Botryllus innate immunity. Three morphologically distinct clot types (points of rejection; POR) were followed. We demonstrated the specific expression of nine coagulation orthologue transcripts in Botryllus rejection processes and effects of the anti-coagulant heparin on POR formation and heartbeats. In situ hybridization of fibrinogen and von Willebrand factor orthologues elucidated enhanced expression patterns specific to histoincompatible reactions as well as common expressions not augmented by innate immunity. Immunohistochemistry for fibrinogen revealed, in naïve and immune challenged colonies alike, specific antibody binding to a small population of Botryllus compartment cells. Altogether, molecular, physiological and morphological outcomes suggest the involvement of vertebrates-like coagulation elements in urochordate immunity, not assigned with vasculature injury

Sigma E Regulators Control Hemolytic Activity and Virulence in a Shrimp Pathogenic Vibrio harveyi

Members of the genus Vibrio are important marine and aquaculture pathogens. Hemolytic activity has been identified as a virulence factor in many pathogenic vibrios including V. cholerae, V. parahaemolyticus, V. alginolyticus, V. harveyi and V. vulnificus. We have used transposon mutagenesis to identify genes involved in the hemolytic activity of shrimp-pathogenic V. harveyi strain PSU3316. Out of 1,764 mutants screened, five mutants showed reduced hemolytic activity on sheep blood agar and exhibited virulence attenuation in shrimp (Litopenaeus vannamei). Mutants were identified by comparing transposon junction sequences to a draft of assembly of the PSU3316 genome. Surprisingly none of the disrupted open reading frames or gene neighborhoods contained genes annotated as hemolysins. The gene encoding RseB, a negative regulator of the sigma factor (σE), was interrupted in 2 out of 5 transposon mutants, in addition, the transcription factor CytR, a threonine synthetase, and an efflux-associated cytoplasmic protein were also identified. Knockout mutations introduced into the rpoE operon at the rseB gene exhibited low hemolytic activity in sheep blood agar, and were 3-to 7-fold attenuated for colonization in shrimp. Comparison of whole cell extracted proteins in the rseB mutant (PSU4030) to the wild-type by 2-D gel electrophoresis revealed 6 differentially expressed proteins, including two down-regulated porins (OmpC-like and OmpN) and an upregulated protease (DegQ) which have been associated with σE in other organisms. Our study is the first report linking hemolytic activity to the σE regulators in pathogenic Vibrio species and suggests expression of this virulence-linked phenotype is governed by multiple regulatory pathways within the V. harveyi

Advances in dissecting mosquito innate immune responses to arbovirus infection

Arthropod-borne viruses – arboviruses – are a significant threat to public health. Whilst there is considerable knowledge about arbovirus interactions with vertebrate immunity, relatively little is known about how vectors such as mosquitoes control arbovirus infections. In this review, we discuss novel findings in the field of mosquito antiviral responses to arboviruses, in particular RNA interference, the up-and-coming field of general immune-signalling pathways, and cell death/apoptosis

Immunity of an Alternative Host Can Be Overcome by Higher Densities of Its Parasitoids Palmistichus elaeisis and Trichospilus diatraeae

Interactions of the parasitoids Palmistichus elaeisis Delvare & LaSalle and Trichospilus diatraeae Cherian & Margabandhu (Hymenoptera: Eulophidae) with its alternative host Anticarsia gemmatalis (Hübner) (Lepidoptera: Noctuidae) affect the success or failure of the mass production of these parasitoids for use in integrated pest management programs. The aim of this study was to evaluate changes in the cellular defense and encapsulation ability of A. gemmatalis pupae against P. elaeisis or T. diatraeae in adult parasitoid densities of 1, 3, 5, 7, 9, 11 or 13 parasitoids/pupae. We evaluated the total quantity of circulating hemocytes and the encapsulation rate versus density. Increasing parasitoid density reduced the total number of hemocytes in the hemolymph and the encapsulation rate by parasitized pupae. Furthermore, densities of P. elaeisis above 5 parasitoids/pupae caused higher reduction in total hemocyte numbers. The encapsulation rate fell with increasing parasitoid density. However, parasitic invasion by both species induced generally similar responses. The reduction in defensive capacity of A. gemmatalis is related to the adjustment of the density of these parasitoids to their development in this host. Thus, the role of the density of P. elaeisis or T. diatraeae by pupa is induced suppression of cellular defense and encapsulation of the host, even without them possesses a co-evolutionary history. Furthermore, these findings can predict the success of P. elaeisis and T. diatraeae in the control of insect pests through the use of immunology as a tool for evaluation of natural enemies