Innate and Adaptive Immune Responses of Turbot, Scophthalmus Maximus (L.), Following Experimental Infection with Enteromyxum Scophthalmi (Myxosporea: Myxozoa)

Fish & Shellﬁsh Immunology 21 (2006) 485e500 www.elsevier.com/locate/fsi

Innate and adaptive immune responses of turbot, Scophthalmus maximus (L.), following experimental infection with Enteromyxum scophthalmi (Myxosporea: Myxozoa)

A. Sitja`-Bobadilla a,*, M.J. Redondo a, R. Bermu´dez b, O. Palenzuela a, I. Ferreiro c, A. Riaza c, I. Quiroga b, J.M. Nieto b, P. Alvarez-Pellitero a

a Instituto de Acuicultura de Torre de la Sal, Consejo Superior de Investigaciones Cientı´ficas, Torre de la Sal s/n, 12595 Ribera de Cabanes, Castelloń, Spain b Department of Veterinary Clinical Sciences, School of Veterinary, University of Santiago de Compostela, Lugo, Galicia, Spain c Stolt Sea Farm S.A. Lira, Carnota, La Corunã, Spain Received 16 December 2005; revised 14 February 2006; accepted 15 February 2006 Available online 14 March 2006

Abstract

The innate and adaptive immune responses against Enteromyxum scophthalmi was studied in turbot (Scopthalmus maximus (L.)) experimentally exposed to the parasite by cohabitation. Haematological, histopathological, cellular and humoral factors were de- termined in samples taken from control (CTRL) and recipient (RCPT, na€ıve fish cohabited with donor infected fish) animals at 0, 20, 29, 40 and 43 days post exposure (p.e). Infection was first detected at day 20 p.e. and prevalence reached 100% at 40 days p.e, when first mortalities occurred. A significant reduction in weight and condition factor was found in RCPT, though no significant differences in haematocrit or serum protein levels were detected between CTRL and RCPT. Some immune effectors were clearly activated in RCPT: the percentage of circulating granulocytes was significantly increased, as well as the number of blood cells pos- itive in the respiratory burst assay; leucocyte infiltration in intestine was found mainly on days 20 and 29 p.e.; total serum antipro- teases and a-2-macroglobulin levels were higher in most of the samplings, with significant differences on the last sampling. Other effectors were clearly down regulated in RCPT: haematopoietic depletion appeared in head kidney from day 29 p.e. onwards, and the number of apoptotic cells and MMC increased in head kidney and spleen; the percentage of lymphocytes decreased progres- sively and significantly; a clear, but not statistically significant, drop in serum complement was registered at 40 days p.e.; also, a significant decrease occurred in serum lysozyme at 29 days p.e. No specific antibodies against the parasite were detected in any sampling. Ó 2006 Elsevier Ltd. All rights reserved.

Keywords: Myxozoa; Parasite; Immune response; Experimental infection; Turbot; Aquaculture

* Corresponding author. Tel.: þ34 96 431 9500; fax: þ34 96 431 9509. E-mail address: [email protected] (A. Sitja`-Bobadilla).

1. Introduction

Enteromyxum scophthalmi is a member of a recently created myxozoan genus [1]. This parasite is one of the most significant pathogens in turbot (Scophthalmus maximus L.) aquaculture, producing high mortality [2]. Severely infected fish suffer a progressive destruction of the gut, leading to a cachexy syndrome and death. Direct fish-to-fish transmission (horizontal) [3] favours the rapid spreading of the disease in turbot farms. Myxozoa include more than 1350 species described thus far [4], being responsible for important economic losses in fisheries and aquaculture industry [5e8]. Nevertheless, they still pose important questions about their origin, phylo- genetic relationship and life cycle [9,4,10]. Other scarcely known aspects are the host-parasite relationship and the pathogenic mechanisms. Since there is no effective commercial treatment against myxosporoses, alternative control approaches are urgently needed. Strategies based on the exploitation of the fish immune system are just starting to be considered, as the current knowledge on fish immunity against parasites is much scarcer than that of mammals. A number of investigations have demonstrated that both innate and adaptive immune effectors against parasites exist in teleosts [11e13]. However, research on the immune response against myxosporean parasites is hampered by the lack of in vitro cultures [14] and by the difficulty of developing experimental infection models. Acquired immunity against a few myxosporean species has been demonstrated [7,15e18], including E. scophthalmi [19]. Data on the non-specific immune reaction against myxosporeans are also scarce [20e24], and most of the knowledge is based on histopathological observations. Studies on natural and experimental infections have shown that the progression of the disease due to E. scophthalmi is very fast, and that a short exposure to the parasite can produce 100% prevalence of infection and mortality [25]. Thus, the main objective of the present work was to study the innate and adaptive immune reaction against this myxosporean in relation to the progression of the disease, in order to gain insight into possible tools to control this important myxosporosis. For this purpose, a battery of haematological, histopathological, cellular and humoral factors were measured in turbot experimentally exposed to the parasite.

2. Materials and methods

2.1. Fish and experimental design

Na€ıve turbot (recipients ¼ RCPT) were exposed to the parasite by cohabitation with infected fish (donors) with a procedure similar to that previously described [3,25], with some modifications. It was carried out at the facilities of the Instituto de Acuicultura de Torre de la Sal (IATS) from May to June 2002. Donor fish were initially obtained from a farm located in north-western Spain, suffering serious mortality due to E. scophthalmi. The infection was diagnosed by the typical disease signs and by the presence of parasite spores in intestinal scrapings of some fish. Uninfected RCPT fish were hatched and reared with a flow-through supply of cartridge-filtered (1-mm mesh) and UV-irradiated sea water at a commercial fish farm, and were E. scophthalmi-free. They were sent to the experimental facilities of IATS and became acclimated to experimental conditions for 2 weeks before the beginning of the experiment. Day length and temperature increased over the course of the trial, following natural changes at our latitude (40 50 N; 0 100 E) (Table 1). Water salinity was 37.5&. Duplicate tanks (500 L) for cohabitation contained 22 RCPT and 20 donor fish each (average weight 250 g). Con- trol fish (CTRL) (two tanks of 250 L with 28 fish each, 5 sampled on day 0 p.e.) were kept under the same conditions but unexposed to the infection. The density at the beginning of the cohabitation was similar in both groups (14 kg/m2). All fish were fed a commercial dry pellet at about 1% of body weight daily. Daily mortalities were recorded through- out the experiment. Mortality was calculated as the percentage of dead fish in each period between samplings in respect of the number of fish at the beginning of the considered period. The parasitic status of dead fish was checked by microscopic examination of fresh intestinal scrapings.

2.2. Sampling procedure

An initial sampling of RCPT fish was performed before exposure to the parasite (day 0). CTRL and RCPT fish were randomly sampled at 20, 29, 40 and 43 days post exposure (p.e.), taking the same number of fish from each replicate. Details on the samplings can be found in Table 1. In each sampling, fish were killed by overexposure to MS222 Download English Version: https://daneshyari.com/en/article/2433583

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