Similar to what was observed in our present study, differential expression of TNF-α isoforms was demonstrated after stimulation with LPS or stimulation of the hemoparasite Trypanoplasma borreli, with a predominant rise in TNF-α2 (Zou et al., 2002; Bridle et al., 2006). Rainbow trout infected with the

protozoan parasites Tetracapsuloides brysalmonae ABT-199 in vivo (the causative agent of proliferative kidney disease) and Neoparamoeba sp. (causative agent of amoebic gill disease) also displayed an increased expression of TNF-α2 relative to TNF-α1. In contrast, stimulation by IHN virus (causative agent of infectious hematopoietic necrosis) by the protozoan Ichthyophthirius multifiliis (‘white spot’ disease) or by the monogenean parasite Gyrodactylus derjavini

(skin fluke) induced an increase in the expression of the TNF-α1 isoform at a higher magnitude than that of the TNF-α2 isoform. KU-57788 in vivo Thus, the differential expression of TNF-α isoforms is apparently dependent on the species of pathogen or stimulus, the tissue sampled and the species of fish studied (Purcell et al., 2004; Bridle et al., 2006), and the results obtained here probably reflect the interaction of S. iniae EPS with different cell types, including granulocytes and nongranulocytes present in the blood and organs. Indeed, the use of an in vivo system may help to preserve the integrity of cellular interactions, as well as the effect of lymphocyte-derived factors on proinflammatory cytokine production and,

similarly to other studies, ensues in elevated cytokine levels (O’Dwyer et al., 2006; Bozza et al., 2007). The role of EPS in S. iniae pathogenesis is poorly understood. There is evidence, however, that the interaction between the immune system and the EPS produced by this pathogen play an important role in both the development of the disease and protection against the pathogen (Eyngor et al., 2008). Not surprisingly, it is now revealed that EPS is also a key molecule in S. iniae pathogenesis; the failure to control the inflammatory cascade following MG-132 cost EPS administration is accompanied by a considerable increase in the secretion of proinflammatory cytokines that are likely to be at the origin of clinical manifestations and poor outcome, both of which are typical of septic shock. Indeed, several inflammatory and infectious diseases are associated with the overproduction of proinflammatory cytokines and chemokines, and the recruitment and activation of different leukocyte populations are a hallmark of acute inflammation (Saukkonen et al., 1990; Welbourn & Young, 1992). These cytokines are believed to mediate responses associated with clinical deterioration, multiorgan system failure and death from septic shock (Waage et al., 1991; Anderson et al., 1992; Bone et al., 1992; Beutler & Grau, 1993; Bone, 1993; Casey et al.