Shrimp Molecular Responses to Viral Pathogens

Abstract

From almost negligible amounts in 1970, the quantity of cultivated shrimp (∼3 million metric tons in 2007) has risen to approach that of the capture fishery and it constitutes a vital source of export income for many countries. Despite this success, viral diseases along the way have caused billions of dollars of losses for shrimp farmers. Desire to reduce the losses to white spot syndrome virus in particular, has stimulated much research since 2000 on the shrimp response to viral pathogens at the molecular level. The objective of the work is to develop novel, practical methods for improved disease control. This review covers the background and limitations of the current work, baseline studies and studies on humoral responses, on binding between shrimp and viral structural proteins and on intracellular responses. It also includes discussion of several important phenomena (i.e., the quasi immune response, viral co-infections, viral sequences in the shrimp genome and persistent viral infections) for which little or no molecular information is currently available, but is much needed.

Addendum

Because a year has passed since submission of the original version of our review, a number of papers in press at the time have been published and we have been able to update these citations with volume and page numbers. However, many other relevant papers were published in 2009–2010 that were unaware of at the time of writing the manuscript. Thus, we have prepared this brief addendum to present a selection of them in order of the headings in our review.

First we would like to cite three reviews, one on antiviral immunity in crustaceans that appeared after we had submitted our manuscript (Liu et al. 2009b), another on functional genomic and proteomic studies on immunity in P. vannamei (Robalino et al. 2009b) and another on sequence analysis of Kazal-type proteinase inhibitors in crustaceans (Cerenius et al. 2010). There have also been two notable global studies on gene expression response, one to yellow head virus (YHV) in P. monodon (Prapavorarat et al. 2010) and one to white spot syndrome virus (WSSV) in naïve and previously challenged P. vannamei (García et al 2009). With respect to binding with viral structural proteins, there has been an additional publication on interaction of P. monodon chitin-binding protein (PmCBP) with VP53A and other WSSV envelope proteins (Chen et al. 2009). This included results on a protective affect against mortality from WSSV by administration of recombinant VP53A and on immunoreactivity of a protein from P. vannamei to PmCBP antibody. In another report, VP28 was shown to bind to shrimp heat-shock cognate protein 70 (Hsc70) in the cytoplasm of hemocytes in a manner dependent on ATP and on Hsc70 concentration (Xu et al. 2009).

With respect to pattern recognition molecules, a very exciting development was the discovery in shrimp of a unique homologue of the Down syndrome cell adhesion molecule (Dscam) gene in P. vannamei (Chou et al. 2009). Dscam is a member of the immunoglobulin super-family that can be generated in thousands of variable forms by alternative splicing of exons. Its invertebrate homologues were initially studied in the context of specific axonal guidance in the developing nervous system, but later studies suggested that it might play a role in adaptive immunity. Other publications focused on aspects of the ProPO pathway (Kong et al. 2009; Ma et al. 2010) and on the Toll pathway (Labreuche et al. 2009; Li et al. 2009; Shi et al. 2009; Wang et al. 2010). There were two publications on antioxidant enzymes (Lin et al. 2010; Ren et al. 2009a, b) and three on lectins (Wang et al. 2009a, b; Zhang et al. 2009a, b; Zhao et al. 2009).

In terms of miscellaneous molecules, an acyl-CoA-binding protein (FcACBP) and a fatty acid binding protein (FcFABP) from the Chinese white shrimp P. (Fenneropenaeus) chinensis were both reported to be up-regulated after WSSV challenge (Ren et al. 2009a, b). A receptor for activated protein kinase C1 (Pm-RACK1) from P. monodon was reported to be upreglated upon WSSV challenge and to interact with WSSV nonstructural protein VP9 (Tonganunt et al. 2009). A Centaurin-α1 like GTPase-activating protein (GAP) of ADP-ribosylation factor (ARF6) was found to be up-regulated in WSSV sensitive shrimp, but not in WSSV resistant shrimp (Wang et al. 2009a, b). In a related study, an ARF from P. (Marsupenaeus) japonicus was also reported to be up-regulated upon WSSV challenge (Zhang et al. 2010). Finally, there have been conflicting reports on the occurrence of an interferon-like protein in P. japonicas and on its role in response to WSSV infection (Barracco and Rosa 2009; Mai et al. 2009; Mai 2009; Rosa and Barracco 2008).