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Protein–carbohydrate interactions mediated by lectins have been recognized as key components of innate immunity in vertebrates and invertebrates, not only for recognition of potential pathogens, but also for participating in downstream effector functions, such as their agglutination, immobilization, and complement-mediated opsonization and killing. More recently, lectins have been identified as critical regulators of mammalian adaptive immune responses. Fish are endowed with virtually all components of the mammalian adaptive immunity, and are equipped with a complex lectin repertoire. In this review, we discuss evidence suggesting that: (a) lectin repertoires in teleost fish are highly diversified, and include not only representatives of the lectin families described in mammals, but also members of lectin families described for the first time in fish species; (b) the tissue-specific expression and localization of the diverse lectin repertoires and their molecular partners is consistent with their distinct biological roles in innate and adaptive immunity; (c) although some lectins may bind endogenous ligands, others bind sugars on the surface of potential pathogens; (d) in addition to pathogen recognition and opsonization, some lectins display additional effector roles, such as complement activation and regulation of immune functions; (e) some lectins that recognize exogenous ligands mediate processes unrelated to immunity: they may act as anti-freeze proteins or prevent polyspermia during fertilization.

The mucus produced by many marine organisms is a complex mixture of proteins and polysaccharides forming a weak watery gel. It is essential for vital processes including locomotion, navigation, structural support, heterotrophic feeding and defence against a multitude of environmental stresses, predators, parasites, and pathogens. In the present study we focused on mucus produced by a benthic cnidarian, the sea anemone Actinia equina (Linnaeus, 1758) for preventing burial by excess sedimentation and for protection. We investigated some of the physico-chemical properties of this matrix such as viscosity, osmolarity, electrical conductivity, protein, carbohydrate, and total lipid contents. Some biological activities such as hemolytic, cytotoxic, and antibacterial lysozyme-like activities were also studied. The A. equina mucus is mainly composed by water (96.2% ± 0.3%), whereas its dry weight is made of 24.2% ± 1.3% proteins and 7.8% ± 0.2% carbohydrates, with the smallest and largest components referable to lipids (0.9%) and inorganic matter (67.1%). The A. equina mucus matrix exhibited hemolytic activity on rabbit erythrocytes, cytotoxic activity against the tumor cell line K562 (human erythromyeloblastoid leukemia) and antibacterial lysozyme-like activity. The findings from this study improve the available information on the mucus composition in invertebrates and have implications for future investigations related to exploitation of A. equina and other sea anemones’ mucus as a source of bioactive compounds of high pharmaceutical and biotechnological interest.

a b s t r a c tBased on protein domain structure and organization deduced from mRNA contigs, 15 transcripts of the Toll signaling pathway have been identified in the bivalve, Mytilus galloprovincialis. Identical searches performed on publicly available Mytilus edulis ESTs revealed 11 transcripts, whereas searches performed in genomic and new transcriptome sequences of the Pacific oyster, Crassostrea gigas, identified 21 Toll-related transcripts. The remarkable molecular diversity of TRAF and IKK coding sequences of C. gigas, suggests that the sequence data inferred from Mytilus cDNAs may not be exhaustive. Most of the Toll pathway genes were constitutively and ubiquitously expressed in M. galloprovincialis, although at different levels, and clearly induced after in vivo injection with bacteria. Such over-transcription was more rapid and intense with Gram-negative than with Gram-positive bacteria. Injection of a fungus modulated the transcription of few Toll pathway genes, with the induction levels of TLR/MyD88 complex being always less intense. Purified LPS and b-glucans had marginal effect whereas peptidoglycans were ineffective. At the moment, we found no evidence of an IMD transcript in bivalves. In conclusion, mussels possess a complete Toll pathway which can be triggered either by Gram-positive or Gram-negative bacteria.

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