Structural and functional diversity of the lectin repertoire in teleost fish: Relevance to innate and adaptive immunity

Abstract

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.

Evolution and Immune Function of Fish Lectins

“…[15][16][17] The available genomes of tetraodontid pufferfish (Takifugu rubripes and T. nigroviridis) (www.genoscope.com), zebrafish (Danio rerio) (www.sanger.ac.uk), and medaka (Oryzias latipes) (www.ensamble.org) are expanding this view even further. 17,20 …”

“…The ligand of fish RBL is the glycosphingolipid globotriaosylceramide (Gb3), which is abundant in membrane lipid rafts. 17,21,36 The RBL CRD appeared early in metazoan evolution and it is found in a variety of proteins, with different domain architecture, To protect the rights of the author(s) and publisher we inform you that this PDF is an uncorrected proof for internal business use only by the author(s), editor(s), reviewer(s), Elsevier and typesetter TNQ Books and Journals Pvt Ltd. It is not allowed to publish this proof online or in print.…”

“…17 In addition, recent studies on teleost fish have identified novel families of lectins, some of them with members present in other vertebrate and invertebrate taxa. 1,17 This lectin diversity is greatly amplified by the presence of isoforms with differences in sugar specificity and recognition ability. [15][16][17] The available genomes of tetraodontid pufferfish (Takifugu rubripes and T. nigroviridis) (www.genoscope.com), zebrafish (Danio rerio) (www.sanger.ac.uk), and medaka (Oryzias latipes) (www.ensamble.org) are expanding this view even further.…”

“…26 Several fish species have proved to be useful model organisms for gaining insight into structural, functional, and evolutionary aspects of lectin immunobiology. 17,27 For example, based on the identification of a novel CRD sequence motif 20 and a unique structural fold, 28 the FTL family was identified both in prokaryotes and in fluids and tissues of invertebrates and vertebrates. [29][30][31][32][33][34] …”

“…Members of most lectin families described in mammals, including CTLs, XTLs, and galectins have been isolated from fish serum, skin mucus, and other tissues. [17][18][19][20] Furthermore, some lectin families unique to fish, such as the RBLs have also been identified in eggs and embryos 21 but are also present in the serum. 22 Lectins can exert opsonic activity 7,9,23 or enhance respiratory burst and bactericidal activity of phagocytic cells.…”