Structural, functional, and evolutionary aspects of galectins in aquatic mollusks: From a sweet tooth to the Trojan horse.

Galectins constitute a conserved and widely distributed lectin family characterized by their binding affinity for ß-galactosides and a unique binding site sequence motif in the carbohydrate recognition domain (CRD). In spite of their structural conservation, galectins display a remarkable functional diversity, by participating in developmental processes, cell adhesion and motility, regulation of immune homeostasis, and recognition of glycans on the surface of viruses, bacteria and protozoan parasites. In contrast with mammals, and other vertebrate and invertebrate taxa, the identification and characterization of bona fide galectins in aquatic mollusks has been relatively recent. Most of the studies have focused on the identification and domain organization of galectin-like transcripts or proteins in diverse tissues and cell types, including hemocytes, and their expression upon environmental or infectious challenge. Lectins from the eastern oyster Crassostrea virginica, however, have been characterized in their molecular, structural and functional aspects and some notable features have become apparent in the galectin repertoire of aquatic mollusks. These including less diversified galectin repertoires and different domain organizations relative to those observed in vertebrates, carbohydrate specificity for blood group oligosaccharides, and up regulation of galectin expression by infectious challenge, a feature that supports their proposed role(s) in innate immune responses. Although galectins from some aquatic mollusks have been shown to recognize microbial pathogens and parasites and promote their phagocytosis, they can also selectively bind to phytoplankton components, suggesting that they also participate in uptake and intracellular digestion of microalgae. In addition, the experimental evidence suggests that the protozoan parasite Perkinsus marinus has co-evolved with the oyster host to be selectively recognized by the oyster hemocyte galectins over algal food or bacterial pathogens, thereby subverting the oyster's innate immune/feeding recognition mechanisms to gain entry into the host cells.

A case of double cystic esophageal duplication in VACTERL syndrome: the first case report and a review of the literature.

Background: An esophageal duplication cyst (EDC) is a rare malformation resulting from the embryonic foregut. VACTERL syndrome is a genetic disorder affecting many systems of the human body. We report the first case of VACTERL syndrome associated to asymptomatic double EDC. Case report: A girl with anorectal malformation and rectovestibular fistula, kidney malformation, and various vertebral defects came to our attention at the time of birth. VACTERL disease was diagnosed. She underwent Peña anoplasty at 4 months of life without complications. MRI was conducted at the age of 2. It accidentally showed a double esophageal duplication (12 mm × 35 mm × 10 mm) at the D7-D9 level. We planned a thoracoscopy; previous intraoperative esophagogastroduodenoscopy showed an external compression of the native esophagus. Two duplicated esophageal lesions were removed. The patient made an uneventful recovery and was completely asymptomatic at long-term follow-up. Conclusions: VACTERL syndrome is still a not well-defined disease. Based on the current literature, this is the first case of a double esophageal duplication in a patient affected by VACTERL syndrome. According to us, the thoracoscopic approach of esophageal duplications can be followed by experts. Complete surgical excision is possible even if the cyst shares a common muscular wall with the esophagus. For this reason, we suggest to close the muscular wall by a simple interrupted suture.

Invertebrate recognition protein cross-reacts with an immunoglobulin idiotype.

To estimate the minimal structural requirements for cross-reaction of idiotypic determinants, we determined the capacity of monoclonal antibodies specific for the idiotype of the phosphorylcholine (PC)-binding myeloma protein TEPC-15 for cross-reactivities with the PC-binding, acute-phase protein C-reactive protein (CRP) and the hemagglutinin from the horseshoe crab Limulus polyphemus (limulin), which binds sialic acid and PC. Certain monoclonal antibodies (MAb) to the TEPC-15 idiotype showed strong cross-reactions with CRP and limulin when tested by enzyme-linked immunoadsorbent assays. The specificity of the cross-reactivities was confirmed by testing the binding of the reactive anti-TEPC-15 MAb to both CRP and limulin in the presence of p-nitrophenylphosphorylcholine (pNPPC), N-acetylneuraminic acid, and bovine submaxillary mucin. The binding of the MAb to both CRP and limulin was strongly decreased by pNPPC, partially decreased by free PC, and not affected by N-acetylneuraminic acid or bovine submaxillary mucin. Neither CRP nor limulin showed significant overall sequence homology to vertebrate immunoglobulins. However, CRP, limulin, and TEPC-15 variable region heavy chain (VH) shared short stretches of homology (8-10 amino acids) that mapped to a stretch comprised of the second complementarity determining region and third framework region of the TEPC-15 VH. These results might reflect either evolutionary convergence forced upon molecules of diverse evolutionary histories because of steric requirements of binding the same ligand, or a conservation of primitive combining site gene segments in evolution.

Emerging marine diseases--climate links and anthropogenic factors.

Mass mortalities due to disease outbreaks have recently affected major taxa in the oceans. For closely monitored groups like corals and marine mammals, reports of the frequency of epidemics and the number of new diseases have increased recently. A dramatic global increase in the severity of coral bleaching in 1997-98 is coincident with high El Niño temperatures. Such climate-mediated, physiological stresses may compromise host resistance and increase frequency of opportunistic diseases. Where documented, new diseases typically have emerged through host or range shifts of known pathogens. Both climate and human activities may have also accelerated global transport of species, bringing together pathogens and previously unexposed host populations.

F-type lectin from the sea bass (Dicentrarchus labrax): purification, cDNA cloning, tissue expression and localization, and opsonic activity.

Recently described biochemical and structural aspects of fucose-binding lectins from the European eel (Anguilla anguilla) and striped bass (Morone saxatilis) led to the identification of a novel lectin family ("F-type" lectins) characterized by a unique sequence motif and a characteristic structural fold. The F-type fold is shared not only with other members of this lectin family, but also with apparently unrelated proteins ranging from prokaryotes to vertebrates. Here we describe the purification, biochemical and molecular properties, and the opsonic activity of an F-type lectin (DlFBL) isolated from sea bass (Dicentrarchus labrax) serum. DlFBL exhibits two tandemly arranged carbohydrate-recognition domains that display the F-type sequence motif. In situ hybridization and immunohistochemical analysis revealed that DlFBL is specifically expressed and localized in hepatocytes and intestinal cells. Exposure of formalin-killed Escherichia coli to DlFBL enhanced their phagocytosis by D. labrax peritoneal macrophages relative to the unexposed controls, suggesting that DlFBL may function as an opsonin in plasma and intestinal mucus.

Duodenal intraepithelial lymphocytes of children with cow milk allergy preferentially bind the glycan-binding protein galectin-3.

A breakdown in intestinal homeostasis results in inflammatory bowel diseases including coeliac disease and allergy. Galectins, evolutionarily conserved beta-galactoside-binding proteins, can modulate immune-epithelial cell interactions by influencing immune cell fate and cytokine secretion. In this study we investigated the glycosylation signature, as well as the regulated expression of galectin-1 and -3 in human duodenal samples of allergic and non-allergic children. Whereas galectin-1 was predominantly localized in the epithelial compartment (epithelial cells and intraepithelial lymphocytes) and the underlying lamina propria (T cells, macrophages and plasma cells), galectin-3 was mainly expressed by crypt epithelial cells and macrophages in the lamina propria. Remarkably, expression of these galectins was not significantly altered in allergic versus non-allergic patients. Investigation of the glycophenotype of the duodenal inflammatory microenvironment revealed substantial alpha2-6-linked sialic acid bound to galactose in lamina propria plasma cells, macrophages and intraepithelial lymphocytes and significant levels of asialo core 1 O-glycans in CD68+ macrophages and enterocytes. Galectin-1 preferentially bound to neutrophils, plasma cells and enterocytes, while galectin-3 binding sites were mainly distributed on macrophages and intraepithelial lymphocytes. Notably, galectin-3, but not galectin-1 binding, was substantially increased in intraepithelial gut lymphocytes of allergic patients compared to non-allergic subjects, suggesting a potential role of galectin-3-glycan interactions in shaping epithelial-immune cell connections during allergic inflammatory processes.

Humoral and cell membrane-associated lectins from invertebrates and lower chordates: specificity, molecular characterization and their structural relationships with putative recognition molecules from vertebrates.

Based on their carbohydrate-binding properties and their ubiquitous presence in pro- and eukaryotes, recognition functions have been hypothesized for many humoral and tissue lectins. In this review three main topics relevant to the possible biological roles and evolution of invertebrate and chordate lectins are discussed. They include the broad carbohydrate-binding spectrum of lectins from chelicerata, the distribution and specificity of cell membrane-associated lectins in mollusks and the serological and biochemical characterization of lectins from tunicates and their structural relationships with putative non-self recognition molecules from vertebrates.

Inhibition of in vitro replication of the oyster parasite Perkinsus marinus by the natural iron chelators transferrin, lactoferrin, and desferrioxamine.

The mammalian iron-binding proteins transferrin and lactoferrin, the bactericidal peptide lactoferricin B, and the bacterial siderophore desferrioxamine were tested for their ability to inhibit the in vitro replication of the oyster parasite Perkinsus marinus. All three chelators were effective in reducing the parasite proliferation in a dose-dependent manner. Lactoferricin B, a peptide of lactoferrin that exhibits bactericidal properties unrelated to iron chelation, had no inhibitory activity on the parasite. When the chelators were partially or completely saturated with the appropriate iron equivalents, their inhibitory effects on the parasite proliferation were diminished or abolished accordingly, confirming that this activity was related to the chelator's capacity for iron sequestration. Our results indicate that the parasite has a strong requirement for soluble iron and its growth rates are correlated with iron availability. We propose that excess iron accumulation in the host Crassostrea virginica promotes parasite proliferation. P. marinus may avoid oxidative damage that would compromise its intracellular survival by exhaustion the host's intracellular selected iron pools required for superoxide and hydroxyl radical production.

Innate immunity in the Aegean: ancient pathways for today's survival.

A workshop on innate immunity that took place this past autumn in Fira, Santorini, as part of the Aegean Conferences, provided tantalizing evidence about the early origin and evolutionary conservation of humoral and cellular components of innate immunity from sponges, flies and sea squirts to man, uncovered mechanistic aspects of its fundamental role in defense against disease, as well as the serious consequences of misdirected responses, and revealed the untapped potential of novel therapeutic approaches.

The specificity of Centruroides sculpturatus Ewing (Arizona lethal scorpion) hemolymph agglutinins.

C. sculpturatus sera agglutinate human erythrocytes independently of the ABO blood group, enzyme treatment, incubation temperature or sex of the scorpions. Tested with human lymphocytes and reptile and bird erythrocytes, C. sculpturatus serum reacts like an anti-sialic acid agglutinin. With leukemic lymphocytes, titers are higher than with normal lymphocytes. Mammalian erythrocytes show characteristic agglutination patterns for C. sculpturatus for Limulus polyphemus (horseshoe crab) that suggest different receptors for agglutinins of both species. Cross absorption and elution experiments indicate the presence of at least two specific agglutinins in C. sculpturatus serum. Agglutination is inhibited by N-acetylneuraminic acid and N-glycolyneuraminic acid, for all erythrocytes tested. Calcium is required for optimal activity of C. sculpturatus agglutinins. C. sculpturatus agglutinating activity is destroyed at 65% degrees C for 20 minutes. Titers are decreased by 2-mercaptoethanol, and more so after alkylation with iodoacetic acid suggesting that disulfide bonds are present in C. sculpturatus agglutinin molecules.

Sialic acid binding lectins in the serum of American spiders of the genus Aphonopelma.

Multiple lectins were detected in the serum of three American species of the genus Aphonopelma (A. chalcodes, A. cochise and A. chiricawa) through tests of agglutination and crossed absorption with a panel of untreated and enzyme treated of vertebrate erythrocytes. Hemagglutination-inhibition experiments showed that a fraction of A. chalcodes serum lectins bind sialic acids and sialoconjugates although other related carbohydrates as N-acetyl-D-glucosamine and 2-keto-3-deoxyoctonate also are recognized. Results of these studies extend our observations about the presence of sialoconjugate binding lectins in members of the Chelicerata to species from the Order Araneae. At the present time the Chelicerata (horseshoe crabs, scorpions, whip scorpions and spiders), would constitute the only group of high taxonomic rank which includes species that exhibit certain common patterns in the specificity of their humoral lectins.

Serological characterization of humoral lectins from the freshwater prawn Macrobrachium rosenbergii.

We have detected and partially characterized multiple lectins present in the serum of the freshwater prawn Macrobrachium rosenbergii. Since agglutination of erythrocytes (RBC) is not abolished by treatment with Vibrio cholerae neuraminidase (VCN), Macrobrachium shows an agglutination pattern different from that of other sialic acid-specific lectins such as Limulus polyphemus lectin. However, after absorption with primate and bird VCN-treated RBC, Macrobrachium serum exhibits high titers with untreated and pronase-treated RBC and no agglutination of VCN-treated RBC, suggesting a typical sialic acid specific lectin agglutination profile. Hemagglutination-inhibition tests indicate that sialic acid containing compounds are the best inhibitors for Macrobrachium lectins. Subterminal sugars and type of linkage are probably important for the lectin binding since bovine submaxillary mucin (containing mainly terminal NANA-alpha-2 6-GalNAc-) is a better inhibitor than fetuin (containing mainly terminal NANA-alpha-2 leads to 3-Gal-) and colominic acid (-NANA-alpha-2 leads to 8-NANA-) is a weak inhibitor.

A comparative study on the specificity of Androctonus australis (Saharan scorpion) and Limulus polyphemus (horseshoe crab) agglutinins.

The specificities of Limulus polyphemus and Androctonus australis sera were compared by agglutination and agglutination-inhibition micromethods with human untreated and enzyme-treated peripheral blood cells (erythrocytes, normal lymphocytes and chronic lymphocytic leukemia lymphocytes). Androctonus sera give higher titers than Limulus sera with erythrocytes and lymphocytes. Both sera show more avidity for leukemic than for normal lymphocytes. Limulus sera fail to agglutinate neuraminidase-treated cells but Androctonus sera react with untreated and neuraminidase-treated erythrocytes at the same degree. Sialyl-lactose is the best inhibitor for Androctonus sera, followed by N-acetylneuraminic and N-glycolylneuraminic acids, glucuronic and galacturonic acids, N-acetyl-D-glucosamine and N-acetyl-D-galactosamine. The amounts of inhibitor required depend upon the particular cell and enzyme treatment: agglutination of neuraminidase-treated erythrocytes by Androctonus is inhibited by lower concentrations of the same compounds that inhibit untreated erythrocytes agglutination. Results suggest that although Limulus and Androctonus have specificity for sialic acid containing compounds, on the cell surface, the Limulus receptors might be different from Androctonus receptors.

C-type lectins and galectins mediate innate and adaptive immune functions: their roles in the complement activation pathway.

In recent years, a 'new' pathway for complement activation mediated by the mannose-binding lectin (MBL) has been described as a key mechanism for the mammalian acute phase response to infection. This complement activation pathway is initiated by a non-self recognition step: the binding of a humoral C-type lectin [mannose-binding lectin (MBL)] to microbial surfaces bearing 'foreign' carbohydrate determinants. The recognition factor, MBL, is associated with a serine protease [MBL-associated serine protease (MASP)] which, upon MBL binding to the microbial ligand, activates the complement component C3, leading to either (a) phagocytosis of the opsonized target via the complement receptor, or (b) humoral cell killing via assembly of the membrane attack complex. Galectins (formerly known as S-type lectins) modulate activity of the complement receptor 3 (CR3), the macrophage membrane receptor for complement components C3b and iC3b, downstream products of the MBL pathway which are covalently bound to 'target cells. Galectins also mediate macrophage- and dendrocyte-adhesion to lymphocytes activated by signaling through another C-type lectin, the L-selectin, leading to immunoglobulin-mediated responses. Thus, the functional interplay of MBL, galectins and L-selectin in the acute phase response neutralizes the microbial challenge, and lead to further adaptive immunity. Although the observation of various components of the lectin pathway in different invertebrate species demonstrates the high conservation and ancient roots of the components of innate immunity, there has previously been no evidence supporting the possibility that the integral lectin-mediated complement activation pathway is present in invertebrates. We now have evidence for the coexistence of homologs of all the pathway's key components (MBL, MASP, C3, and galectin) in the protochordate Clavelina picta, suggesting the lectin-mediated pathway of complement activation preceded the immunoglobulin pathway in evolution. Therefore, despite being 'new' to the textbooks, experimental evidence indicates that this pathway is ancient, and has been conserved intact throughout its evolution.

Molecular analysis of the lymphocyte membrane.

Methods for the molecular analysis of lymphocyte membranes are reviewed briefly, and wherever possible presented in a manner relevant to comparative studies. The specific areas reviewed include the bulk isolation of lymphocyte membranes, the use of radioisotopes to covalently label lymphocyte membrane molecules, the use of lectins to characterize membrane glycoconjugates, and our current understanding of lymphocyte membrane immunoglobulins.

Classification and identification of Pfiesteria and Pfiesteria-like species.

Dinoflagellates can be classified both botanically and zoologically; however, they are typically put in the botanical division Pyrrhophyta. As a group they appear most related to the protistan ciliates and apicomplexans at the ultrastructure level. Within the Pyrrhophyta are both unarmored and armored forms of the dominant, motile flagellated stage. Unarmored dinoflagellates do not have thecal or wall plates arranged in specific series, whereas armored species have plates that vary in thickness but are specific in number and arrangement. In armored dinoflagellates, the plate pattern and tabulation is a diagnostic character at the family, subfamily, and even genus levels. In most cases, the molecular characterization of dinoflagellates confirms the taxonomy on the basis of external morphology; this has been demonstrated for several groups. Together, both genetic and morphological criteria are becoming increasingly important for the characterization, separation, and identification of dinoflagellates species. Pfiesteria and Pfiesteria-like species are thinly armored forms with motile dinospore stages characterized by their distinct plate formulae. Pfiesteria piscicida is the best-known member of the genus; however, there is at least one other species. Other genetically and morphologically related genera, now grouped under the common names of "Lucy," "Shepherd's crook," and cryptoperidiniopsoid, are being studied and described in separate works. All these other heterotrophic dinoflagellate groups, many of which are thought to be benign, co-occur in estuarine waters where Pfiesteria has been found.

Galectin-1 from bovine spleen: biochemical characterization, carbohydrate specificity and tissue-specific isoform profiles.

Selected biochemical properties, including the charge heterodispersity profile and carbohydrate specificity, of bovine galectin-1 were determined in detail. The lectin was purified through an improved purification protocol that yielded 35-40 mg/kg of wet tissue with a specific activity of 1.7-2 x 10(4) mg-1.ml. The galectin is a homodimer of approximately 14.5 kDa subunits with E(280)mg/ml of 0.65 ml.mg-1.cm-1. When stored in the presence of its carbohydrate ligand, the lectin's binding activity remained stable in a non-reducing environment even at room temperature. The optimal pH for binding to the ligand was 6.5-8.0. The overall carbohydrate specificity of the bovine galectin-1 isolated from spleen is similar to that of the galectin isolated from heart and to other mammalian galectins that exhibit "conserved" (Type I) carbohydrate recognition domains (CRDs) [Ahmed, H. and Vasta, G.R. (1994) Glycobiology 4, 545-549], but differs from those from Xenopus laevis and rat intestine domain I. The fluorescence of 4-methylumbelliferyl alpha-D-galactopyranoside was quenched on binding to bovine spleen galectin-1. Scatchard plots of data obtained at 5, 15, and 30 degrees C showed that the galectin has two sugar exothermic binding sites with association constants of 3.4 x 10(5), 1.0 x 10(5), and 0.3 x 10(5), respectively. Chemical modification studies indicated that histidine, tryptophan, carboxylic acid, and arginine, but not lysine or tyrosine, are involved in the binding to the carbohydrate ligand. On isoelectric focusing, the spleen galectin-1 appeared as six isoforms ranging from pI4.56-4.88 with main components at pI 4.63 (34.0%), 4.73 (42.6%), and 4.88 (16.6%). The galectin-1 isolated from heart yielded a quali- and quantitatively different profile with four isoforms ranging from pI 4.53-4.73, those with pIs of 4.56, 4.63, and 4.73 being common to the spleen homolog. Edman degradation of selected peptides purified from the spleen galectin-1 digest revealed amino acid sequences identical to those obtained for the heart galectin-1. This suggests that although point mutations in the subunit primary structure may not be the likely source of isolectins, as observed for X. laevis, tissue-specific co- or post-translational modifications may be the possible cause of the differences in the galectin isoform profile between bovine spleen and heart.

Animal lectins as self/non-self recognition molecules. Biochemical and genetic approaches to understanding their biological roles and evolution.

In recent years, the significant contributions from molecular research studies on animal lectins have elucidated structural aspects and provided clues not only to their evolution but also to their multiple biological functions. The experimental evidence has suggested that distinct, and probably unrelated, groups of molecules are included under the term "lectin." Within the invertebrate taxa, major groups of lectins can be identified: One group would include lectins that show significant homology to membrane-integrated or soluble vertebrate C-type lectins. The second would include those beta-galactosyl-specific lectins homologous to the S-type vertebrate lectins. The third group would be constituted by lectins that show homology to vertebrate pentraxins that exhibit lectin-like properties, such as C-reactive protein and serum amyloid P. Finally, there are examples that do not exhibit similarities to any of the aforementioned categories. Moreover, the vast majority of invertebrate lectins described so far cannot yet be placed in one or another group because of the lack of information regarding their primary structure. (See Table 1.) Animal lectins do not express a recombinatorial diversity like that of antibodies, but a limited diversity in recognition capabilities would be accomplished by the occurrence of multiple lectins with distinct specificities, the presence of more than one binding site, specific for different carbohydrates in a single molecule, and by certain "flexibility" of the binding sites that would allow the recognition of a range of structurally related carbohydrates. In order to identify the lectins' "natural" ligands, we have investigated the interactions between those proteins and the putative endogenous or exogenous glycosylated substances or cells that may be relevant to their biological function. Results from these studies, together with information on the biochemical properties of invertebrate and vertebrate lectins, including their structural relationships with other vertebrate recognition molecules, are discussed.

Protectins in Argentine mollusks: immunological and immunochemical aspects.

Protectins and agglutinins in several organs, fluids and spawn from Argentine terrestrial and fresh-water gastropod species were examined. Differences or analogies with vertebrate immunoglobulin serological behaviour are summarized. Individual or group variability and the evolutionary meaning of the reproductive system-linked and the Ca++ ion-linked protectins are discussed.

Neonatal diaphragmatic hemangioma.

The first neonatal case of a hemangioma of the diaphragm in a neonate is reported. After 25 months the patient is well with no signs of recurrence. Diaphragmatic tumors should be considered in the differential diagnosis of neonatal thoracic masses.