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Lectins play relevant roles in the innate immunity of invertebrates. From the haemolymph of the prawn Macrobrachium americanum Spence Bate, 1868 we purified by affinity chromatography a lectin (MaL) composed of three subunits (86.6, 66.2 and 42.7 kDa), as identified by SDS-PAGE. It is mainly composed of Gly, Ser and Arg, and Ala, Glx and Lys in a minor proportion; it lacks Trp, Cys and carbohydrates. MaL agglutinated mainly rat erythrocytes, rabbit or mouse erythrocytes were agglutinated with lower capacity; whereas erythrocytes from human or other species were not agglutinated. It is specific for N-acetyl-neuraminic acid (sialic acid), N-acetyl-d-glucosamine and N-acetyl-d-galactosamine; sialylated fetuin and bovine submaxillary mucin are also powerful inhibitors of the lectin’s activity. After physical daily manipulation of prawns for 7 days, the lectin concentration and the specific activity (haemagglutinating activity/protein concentration) increased more than four-fold over the control group (those animals that had not been manipulated until bleeding), suggesting that increased lectin concentration and activity after manipulation could be considered as markers of stress.

article i nfo A 66-kDa lectin (OmA) was purified from the serum of the Yucatan peninsula endemic octopus (Octopus maya) by a single step affinity chromatography on glutaraldehyde-fixed stroma from rat erythrocytes. OmA corresponds to 0.8% of the total circulating protein in the hemolymph; it is composed of three equal subunits of 22 kDa each, and 7.4% of linked carbohydrates. The amino acids' composition indicated that agglutinin contained mainly aspartic and glutamic acids, and cysteine and methionine were identified in minor proportion. OmA agglutinates mainly rat, guinea pig, and rabbit erythrocytes, and this activity is partially inhibited by galactosamine, melobiose, galacturonic acid, mannose, and methyl α and β galactosides. Hemagglutinating activity is not dependent on divalent cations, such as Ca 2+ ,M g 2+ ,o r Mn 2+ . The OmA subunits showed no identity for any lectin in databases but partial identity with the type A hemocyanin from Octopus dolfleini hemolymph; the main similarities are related to tyrosinase domains and copper A and B sites that conform to the oxygen-binding site of hemocyanin.

Article history:Received 6 February 2008Received in revised form 19 March 2009Accepted 19 March 2009Keywords:HemocyaninReceptorLectinCrustaceanLitopenaeus setiferusOxidative burstN-acetylated carbohydratesReactive oxygen intermediates Inordertoidentifythespecificroleofhumorallectinsincrustaceans'immuneresponse,weevaluatedtheeffectofthe 291 kDa hemocyanin-like lectin from Litopenaeus setiferus (LsL) on its own hemocytes. LsL binds 5.6% ofcirculatingnon-activatedhemocytes,butisabletorecognize85%oftotaladhered(activated)hemocytes,showingfilipodiaandpseudopodia,inducingtheproductionofreactiveoxygenintermediates(ROIs)inatime-anddose-dependent manner (100 ng/10 5 cells/20 min). This effect was inhibited specifically by N-acetylated sugars(NeuAc, GalNAc or GlcNAc), as well as by superoxide dismutase (SOD), acetylsalicylic, and mefenamic acid. Inhemocytes, LsL also induced higher ROIs production than Zymozan (pN0.05). The receptor for LsL in thehemocytesmembraneisaglycoproteinof61and52kDapersubunit,asdeterminedbywesternblot.Ourresultssuggest that LsL participates in the activation of oxidative immune responses of granularhemocytes induced byNADPH and other oxidative pathways through a specific membrane receptor.© 2009 Elsevier B.V. All rights reserved.

Crustacean aquaculture represents a major industry in tropical developing countries. As a result of high culture densities and increasing extension of aquaculture farms, the presence of diseases has also increased, inducing economic losses. Invertebrates, which lack adaptive immune systems, have developed defense systems that respond against antigens on the surface of potential pathogens. The defense mechanisms of crustaceans depend completely on the innate immune system that is activated when pathogen-associated molecular patterns are recognized by soluble or by cell surface host proteins, such as lectins, antimicrobial, clotting, and pattern recognition proteins, which, in turn, activate cellular or humoral effector mechanisms to destroy invading pathogens. This work is aimed at presenting the main characteristics of the crustacean proteins that participate in immune defense by specific recognition of carbohydrate containing molecules, i.e. glycans, glycolipids, glycoproteins, peptidoglycans, or lipopolysaccharides from Gram-negative and Gram-positive bacteria, viruses, or fungi. We review some basic aspects of crustacean effector defense processes, like agglutination, encapsulation, phagocytosis, clottable proteins, and bactericidal activity, induced by these carbohydrate-driven recognition patterns.

We determined the cross-reactivity of a monoclonal antibody against the Macrobrachium rosenbergii lectin with proteins in the hemolymph from Procambarus clarkii (Pc), Procambarus americanus (Pa), Litopenaeus setiferus (Ls), and Pseudothelphusa americana (Psa). Crustaceans' hemolymph agglutinated erythrocytes from rat, mouse, guinea pig, and rabbit. Decapods' hemolymph hemagglutinating activity was inhibited by N-acetylated carbohydrates as well as by antibodies. Western blot assays indicated that the antibodies recognized two main proteins of 97.5 and 80.9 kDa in all hemolymphs studied; moreover, ELISA assays indicated that, in PSa, 7.2% of total proteins showed crossreactivity with antibodies in Pa, Pc, and Lc hemolymphs represented 4.2, 3.1%, and 2.5%, respectively. Our results suggested that antibodies recognize the lectin active site in the crustacean species tested; we propose the use of antibodies as an immunological marker for lectin identification and quantification among crustaceans.

A 291-kDa lectin (LsL) was purified from the hemolymph of the white shrimp Litopenaeus setiferus by affinity chromatography on glutaraldehyde-fixed stroma from rabbit erythrocytes. LsL is a heterotetramer of two 80-kDa and two 52-kDa subunits, with no covalently-liked carbohydrate, and mainly composed by aspartic and glutamic acids, glycine and alanine, with relatively lower methionine and cysteine contents. Edman degradation indicated that the NH2-terminal of the 80-kDa subunit is composed DASNAQKQHDVNFLL, whereas the NH2-terminal of the 52-kDa subunit is blocked. The peptide mass fingerprint of LsL was predicted from tryptic peptides from each subunit by MALDI-TOF, and revealed that each subunit showed 23 and 22%, respectively, homology with the hemocyanin precursor from Litopenaeus vannamei. Circular dichroism analysis revealed beta sheet and alpha helix contents of 52.7 and 6.1%, respectively. LsL agglutinate at higher titers guinea pig, murine, and rabbit erythrocytes its activity is divalent cation-dependent. N-acetylated sugars, such as GlcNAc, GalNAc, and NeuAc, were the most effective inhibitors of the LsL hemagglutinating activity. Sialylated O-glycosylated proteins, such as bovine submaxillary gland mucin, human IgA, and fetuin, showed stronger inhibitory activity than sialylated N-glycosylated proteins, such as human orosomucoid, IgG, transferrin, and lactoferrin. Desialylation of erythrocytes or inhibitory glycoproteins abolished their capacity to bind LsL, confirming the relevance of sialic acid in LsL-ligand interactions.