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7 páginas, 5 figuras, 1 tabla. ; Heavy metals are among the main pollutants of the Mediterranean coastal waters where they can harm sublittoral biota. Filter-feeder, long-living invertebrates that remain fixed to the rocky bottom, such as sponges, are good targets tometal contamination studies since theymay be exposed to potential lowlevels of contamination for years. Several molecular and biochemical mechanisms are developed by sponges to counteract the effects of noxious metals. As a result, some of the normal cell functions can be altered. Herewe showthat the main heavy metals that can be found in marine sublittoralwaters (i.e. copper, iron, zinc and manganese) may alter the immune system of sponges by inhibiting the activity of the sponge 2 ,5 -oligoadenylate synthetase (2-5A synthetase), which is an enzyme involved in the immune system of vertebrates. We selected the widespread Mediterranean sponges Geodia cydonium, Crella elegans and Chondrosia reniformis for the study. They exerted a high 2-5A synthetase activity and gave a unique profile of 2 ,5 -oligoadenylate product production. Several metals alter the 2-5A synthetase activity differently, in a species-specific manner. 2-5A synthetases from G. cydonium and C. elegans were inhibited by all the metal ions assayed. However, in C. reniformis, 2-5A synthetase was either activated or inhibited by the same ions depending on their final concentrations. Like in humans, metal contamination may have an effect on the OAS activity and thus it might alter the sponge immune system. However, since the effects are species-specific, 2-5A synthetase cannot be used as general biomarker of metal pollutions. ; This work was supported by the European Union with the Marie Curie Research Training Network, BIOCAPITAL FP6 and by the Spanish Government with the projects INTERGEN, CICYT: CTM2004-05265-C02/MAR and MARMOL, CICYT: CTM2007-66635-CO2. ; Peer reviewed

4 páginas, 1 tabla, 1 figura. ; Sponges [porifera], the most ancient metazoans, contain modules related to the vertebrate immune system, including the 2 0 ,5 0 -oligoadenylate synthetase (OAS). The components of the antiviral 2 0 ,5 0 -oligoadenylate (2–5A) system (OAS, 2 0 -Phosphodiesterase (2 0 -PDE) and RNAse L) of vertebrates have not all been identified in sponges. Here, we demonstrate for the first time that in addition to the OAS activity, sponges possess a 2 0 -PDE activity, which highlights the probable existence of a premature 2–5A system. Indeed, Suberites domuncula and Crella elegans exhibited this 2–5A degrading activity. Upon this finding, two out of three elements forming the 2–5A system have been found in sponges, only a endoribonuclease, RNAse L or similar, has to be found. We suspect the existence of a complex immune system in sponges, besides the self/non-self recognition system and the use of phagocytosis and secondary metabolites against pathogens. ; This work was supported by the European Union with the Marie Curie Research Training Network, BIOCAPITAL FP6 and by the Spanish Government with the project MARMOL, CI-CYT: CTM2007- 66635-CO2. ; Peer reviewed