Brown Ring Disease (BRD), a vibriosis affecting the clam Ruditapes philippinarum, is present on the Atlantic coasts of Western Europe and is considered to be a cold water disease. The present work investigated the effect of temperature on immune response and its relationships with BRD development. Clams maintained at different temperatures (8, 14 and 21°C) were experimentally challenged with the pathogen Vibrio tapetis, the etiologic agent of BRD. Results demonstrated significant effects of temperature on disease development and on hemolymph immune parameters including total and viable hemocyte counts, lysozyme and leucine aminopeptidase activities. Thirty days after challenge, clams maintained at 21°C displayed significantly higher values for all the measured immune parameters in comparison to specimens incubated at 14°C. Improved performance of the immune system was associated with a low BRD prevalence. The recovery process, which occured mainly at 21°C, was associated with high percentages of viable hemocytes and high activities of leucine amino-peptidase and lysozyme. This laboratory study clearly demonstrates that temperature strongly affects BRD development and clam immune response during infection. Favourable immune status at higher temperature may confer upon the clam a better capacity to fight the disease agent, and therefore to recover more easily.KEY WORDS: Immunomodulation · Temperature · Hemocyte · Leucine aminopeptidase · Lysozyme · Disease · Clam · Vibrio Resale or republication not permitted without written consent of the publisherDis Aquat Org 59: [249][250][251][252][253][254][255][256][257][258][259][260][261][262] 2004 tal induction of the disease after V. tapetis challenge performed under standard conditions (14°C, 33 ‰) has shown that physiological functions such as nutrition and the immune defense system are severely affected in diseased clams , Plana 1995, Plana et al. 1996. Generally, at 14°C, the immune response in hemolymph, during the development of BRD, displays a 2-phase pattern: an early induction of cellular and humoral response in hemolymph (total hemocyte counts [THC] and enzymatic activities such as leucine aminopeptidase and lysozyme), followed by an inhibition of these defense parameters (Oubella et al. 1993, Allam et al. 2000b. In severely infected clams, a concomitant increase in THC in the extrapallial fluids is measured suggesting their mobilisation to the site of infection (Oubella et al. 1993, Allam et al. 2000a. Mass mortalities of BRD-infected clams can result from the decline of metabolic activity, sometimes associated with a septicemic invasion of V. tapetis in hemolymph and tissues (Plana et al. 1996, Allam et al. 2002.In marine invertebrates, disease prevalence is controlled by environmental factors (Harvell et al. 1999). In the case of BRD, field studies have suggested the influence of temperature on disease prevalence (Paillard et al. 1997). Along the French Atlantic coast, there is a clear boundary at the Loire river; the observed BRD prevalences...

Environmental chemico-physical factors, pathogens, and biological interactions constantly affect organism physiology and behavior Invertebrates, including bivalve mollusks do not possess acquired immunity. Their defense mechanisms rely oil all innate, non-adaptive immune system employing circulating cells and a large variety of molecular effectors. The mechanisms underlying host defense depend oil the presence of functional proteins in appropriate quantities, within a crucial time window. These proteins arc, encoded by genes whose transcription is tightly coordinated by complex programs of gene expression. Currently, available advanced techniques allow the evaluation of this gene expression, expanding our understanding of the behavior and function of cells and tissues under varying conditions. In particular DNA microarray technology enables measurement of a large predetermined set of known genes or sequences. Expressed sequence tag sequencing from redundant, normalized, subtractive hybridization libraries is a robust method for sampling the protein encoding genes that are expressed within a tissue. The elimination of microorganisms by defense cells is a dynamic process that involves integrating synthesis of granule proteins during differentiation, migration onto sites of infection, phagocytosis and killing of microorganisms, modulation of their effector cells, and finally apoptosis. Understanding how this complex biological process is regulated call best be addressed using a systems biology approach to the stud), of organisms and populations in order to more effectively decipher the continuous challenge between two genomes, i.e., evolving host-pathogen interactions

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Hemocytes represent the most important internal defense mechanism against foreign material in marine bivalve molluscs. Variations in their density were induced in the hemolymph of 2 economically important clam species (Ruditapes philippinarum and R. decussatus) after challenge with a pathogenic bacteria (Vibrio PI) and after starvation. The number of circulating hemocytes increased in both species 72 h post-challenge when compared to control animals. Following 1 wk starvation, a marked reduction of hemocyte density occurred compared to the control values. It is suggested that reversible migration of hemocytes from the tissues to the circulatory compartment or vice versa explains these variations. Consequently, the hemocyte density may be a quantifiable parameter of the immunodefense response of bivalve molluscs to physiological or pathological stress.