Invertebrate lectins: I. Occurrence

Purification and structural characterization of lectin with antibacterial and anticancer properties from grubs of hide beetle, Dermestes frischii

Lectins or haemagglutinins are diverse classes of non-immune proteins; they bind to carbohydrates and are abundant in nature. In the present study, a coleopteran lectin from grubs of hide beetle, Dermestes frischii called DFL, was purified by glutaraldehyde (fixative-agent) fixed hen erythrocytes and characterized further for its functional properties. The purified DFL was stable between pH range 5 to 9 and heat-stable up to 50C. It was insensitive to EDTA and did not require any divalent cations. DFL native molecular mass was approximately 69 kDa with three different polypeptide subunits of 33 (pI ~4.4), 22 (pI ~6) and 14 (pI ~4.4) kDa. Haemagglutinating activity of DFL was highly inhibited by N-acetyl-D-glucosamine. DFL partial peptide sequences obtained from peptide mass fingerprinting experiments matched with amino acid sequences of lectins from different organisms confirmed its nature. Biological properties of purified DFL namely antibacterial and bacterial agglutination experiments revealed that DFL have both the effects against laboratory cultures of Aeromonas hydrophila, Enterococcus faecalis, Escherichia coli and habitat bacterial isolates of Staphylococcus cohnii and Bacillus cereus. In addition, the DFL exhibited substantial anticancer properties against HeLa cells. These results concluded that purified DFL could serve as a potent therapeutic agent for various biomedical applications.

Tick lectins: structural and functional properties

Few papers have been published on tick lectins so far, and therefore more data are needed to complete the mosaic of knowledge of their structural and functional properties. Tissue-specific lectin/haemagglutinin activities of both soft and hard ticks have been investigated. Some tick lectins are proteins with binding affinity for sialic acid, various derivatives of hexosamines and different glycoconjugates. Most tick lectin/haemagglutinin activities are blood meal enhanced, and could serve as molecular factors of self/non-self recognition in defence reactions against bacteria or fungi, as well as in pathogen/parasite transmission. Dorin M, the plasma lectin of Ornithodoros moubata, is the first tick lectin purified so far from tick haemolymph, and the first that has been fully characterized. Partial characterization of other tick lectins/haemagglutinins has been performed mainly with respect to their carbohydrate binding specificities and immunochemical features.

Isolation and characterization of Dorin M, a lectin from plasma of the soft tick Ornithodoros moubata

A lectin with high hemagglutinating activity, which we have named Dorin M, was identified in the plasma of the soft tick Ornithodoros moubata. The activity of the plasma lectin could be efficiently inhibited by sialic acid, N-acetyl-D-hexosamines and sialoglycoproteins. Dorin M was purified to homogeneity using two different isolation systems: affinity chromatography on a column of bovine submaxillary mucin conjugated to Sepharose 4B with specific elution by N-acetyl-D-glucosamine and chromatography on Blue-Sepharose followed by anion exchange FPLC on a MonoQ column. The purified lectin is a glycoprotein which, in the native state, forms aggregates with molecular mass of about 640 kDa. Non-reducing SDS PAGE revealed that the lectin consists of two noncovalently bound subunits migrating closely around 37 kDa. Dorin M is a glycoprotein, probably modified by N-type glycosylation. After chemical deglycosylation, only one band of about 32 kDa was detected. Dorin M is the first lectin purified from ticks.

Purification and characterization of a natural agglutinin from the serum of the hermit crab Diogenes affinis

A natural agglutinin from the serum of the hermit crab Diogenes affinis was purified to homogeneity by a single-step affinity chromatography using N-acetylglucosamine-coupled Sepharose 6B. The purified serum agglutinin (PSA) showed a strong affinity for rat RBC, and its hemagglutinating (HA) activity was specifically dependent on Ca2+ and reversibly sensitive to EDTA. PSA in active form has a molecular mass estimate of 185 kDa and is composed of four non-identical subunits (51, 49, 42 and 39 kDa) cross-linked by interchain disulfide bonds. The homogeneity of PSA was corroborated by immunodiffusion and immunoelectrophoretic analyses using rabbit antiserum raised against the agglutinin. The antibodies in this antiserum appear to be specific for RBC-binding sites of the agglutinin molecules as revealed by the ability of the antiserum to neutralize HA activities of both whole serum and PSA of D. affinis. In HA-inhibition assays performed with several carbohydrates and glycoproteins, PSA showed a distinct and unique specificity for acetyl group in carbohydrates independently of the presence of this group on C-2 or C-5 and its stereochemical arrangement in the axial or equatorial orientation. Besides, this agglutinin appears to recognize the terminal N- and O- acetyl groups in the oligosaccharide chain of glycoconjugates. The HA activity of D. affinis agglutinin was also susceptible to inhibition by lipopolysaccharides from diverse gram-negative bacteria, which might indicate a significant in vivo role of this humoral agglutinin in the host immune response against bacterial infections.

Isolation and characterization of earthworm hemolysins and agglutinins

Hemolytic activity in coelomic fluid of Eisenia fetida (ECF) is due to three proteins H1, H2, H3 with molecular weights of 46, 43 and 40 kD, respectively. These proteins were isolated by preparative PAGE. H1 and H2 were shown to be stable in SDS and alpha-2-ME whereas H3 splits into two fragments with molecular weights of 18 and 21 kD after SDS treatment. IEF indicates that each protein consists of different isoforms with pIs between 5.1 and 6.2 H3 was demonstrated to be a bifunctional protein that can lyse and agglutinate erythrocytes. At 56 degrees C hemolytic activity of all three proteins was inactivated, but the agglutination activity of H3 was stable. Intracoelomic injection of erythrocytes reduced the number of hemolysins from three to two. Monospecific antisera were raised against the isolated hemolysins H1,2 and 3. The use of these antibodies and of carbohydrates as inhibitors of the biological activity of the molecules demonstrates the close structural relationship of agglutinins and hemolysins in the CF of E. fetida.

Crossreactivity of hemolytic and hemagglutinating proteins in the coelomic fluid of lumbricidae (Annelida)

Oligospecific antisera against the hemolytic and hemagglutinating compounds of the coelomic fluid (CF) of the earthworm species Eisenia fetida, Lumbricus terrestris and Aporrectodea caliginosa were prepared. The proteins were bound to the membranes of erythrocytes and injected into rabbits. By the use of these antisera the following results were obtained: 1) The antisera RaL T and RaAC reached a titer of 1:64,000, the detection limit of RaEF was 1:512,000. RaEF was demonstrated to be oligospecific only against three hemolytic proteins by Western blotting. 2) RaEF is able to inhibit the biological activity not only of hemolysins (E. fetida, A. caliginosa) but also of hemagglutinins (L. terrestris, L. rubellus, D. rubidus). 3) Complex carbohydrates, but not simple sugar compounds, are able to inhibit hemolytic and agglutinating activities in the CF of the investigated species. Fet. and alpha 1ac. GP were demonstrated to be strong inhibitors both of the hemolytic and of the hemagglutinating activity, whereas N-acetylglucosamine was only able to inhibit the hemagglutinating activity. 4) The investigated compounds were shown to crossreact in ELISA experiments. 5) By the use of Western blotting, the crossreacting molecules in the CF of the investigated lumbricid species were identified.

Purification, characterization, and cDNA cloning of a galactose-specific C-type lectin from Drosophila melanogaster

We purified a lectin from a pupal extract of Drosophila melanogaster. This lectin agglutinated trypsinized and glutaraldehyde-fixed bovine red blood cells in the presence of calcium or magnesium. The hapten sugar of this lectin was galactose. The molecular mass of the intact lectin was determined to be 41 kDa, and it comprised 14- and 17-kDa subunits. The 17-kDa subunit was shown to be a glycosylated form of the 14-kDa subunit. Analysis of the cDNA for this lectin revealed that the 14-kDa subunit consists of 163 amino acid residues and contains all residues conserved in various C-type lectins. It was suggested that the Drosophila lectin and Sarcophaga lectin share some properties and function similarly in defense and development, but probably they are not structural homologues.

Chitovibrin: a chitin-binding lectin from Vibrio parahemolyticus

A novel 134 kDa, calcium-independent chitin-binding lectin, 'chitovibrin', is secreted by the marine bacterium Vibrio parahemolyticus, inducible with chitin or chitin-oligomers. Chitovibrin shows no apparent enzymatic activity but exhibits a strong affinity for chitin and chito-oligomers > dp9. The protein has an isoelectric pH of 3.6, shows thermal tolerance, binds chitin with an optimum at pH 6 and is active in 0-4 M NaCl. Chitovibrin appears to be completely different from other reported Vibrio lectins and may function to bind V. parahemolyticus to chitin substrates, or to capture or sequester chito-oligomers. It may be a member of a large group of recently described proteins in Vibrios related to a complex chitinoclastic (chitinivorous) system.

A lipopolysaccharide-binding hemagglutinin with specificity for acetylated aminosugars in the serum of the hermit crab Diogenes affinis (Henderson)

A naturally occurring hemagglutinin was detected in the serum of the hermit crab Diogenes affinis, and its erythrocyte (RBC) binding activities, physicochemical properties, and carbohydrate binding specificity were characterized. Both the hemagglutination profile and the pattern of cross-reactivity of the serum with different RBC types in cross-adsorption tests suggested a strong affinity of the serum agglutinin for rat RBC. Further analysis revealed that the agglutinin was specifically dependent on Ca2+ for its hemagglutinating activity and reversibly sensitive to EDTA. The activity was found to be stable between pH 6.0 and 7.5, heat-labile, and completely precipitable by ammonium sulphate or TCA, suggesting the proteinaceous nature of the serum agglutinin. In hemagglutination-inhibition assays, the serum agglutinin of D. affinis showed a distinct and unique specificity for acetyl group-containing carbohydrates and glycoprotein. Furthermore, the hemagglutinating activity of the serum agglutinin was also inhibited by lipopolysaccharide from Salmonella abortus equi, which might indicate a significant role of humoral agglutinin in the immune response of crustaceans against bacterial infection.

Characterization of a natural hemagglutinin in the serum of a freshwater crab Parathelphusa hydrodromus (Herbst)

A naturally occurring hemagglutinin (HA) was detected in the serum of the freshwater crab Parathelphusa hydrodromus using mammalian erythrocytes (RBC) as indicator cells. The serum gave the highest HA titer with rabbit RBC. In cross adsorption tests, this RBC type completely adsorbed all HA activities from serum. An analysis of the physico-chemical properties of HA showed it to be specifically dependent on the presence of Ca2+ for its activity, irreversibly sensitive to EDTA, stable between pH 7.5 and 10.0, and heat-labile. Further studies demonstrated that the HA is proteinaceous as it was precipitable by conventional deproteinizing agents, and susceptible to the action of proteases and 2-mercaptoethanol. HA-inhibition assays performed with 44 carbohydrates revealed that the serum HA was specific for non-reducing terminal glucose with alpha 1-2 glycosidic linkage. Thus this agglutinin appears to be unique among all the known crustacean agglutinins.

A novel role of Periplaneta lectin as an opsonin to recognize 2-keto-3-deoxy octonate residues of bacterial lipopolysaccharides

1. Periplaneta lectin of the American cockroach was shown to have affinity to bacterial lipopolysaccharides (LPS) of chemotypes Rb-Re, but not to lipid A. 2. 2-Keto-3-deoxy octonate (KDO) was the most effective sugar so far tested for inhibition of the hemagglutinating activity of Periplaneta lectin. 3. Periplaneta lectin was suggested to participate in the clearance of bacteria injected into the abdominal cavity of the cockroach.

Detection, isolation and characterization of multiple lectins from the haemolymph of the cockroach Blaberus discoidalis

Three agglutinins (lectins), designated BDL1, BDL2 and BDL3, were identified in the haemolymph of the cockroach Blaberus discoidalis by erythrocyte cross-adsorption and sugar inhibition tests. With the use of (NH4)2SO4 fractionation, anion-exchange and affinity chromatography, BDL1 and BDL2 have been purified to homogeneity, and BDL3 has been partially purified to three bands on SDS/PAGE. BDL1 has a molecular-mass estimate of 390 kDa by gel filtration and approx. 158 kDa by SDS/PAGE under non-reducing conditions, further reduced to subunits of 36 kDa under reducing conditions. BDL2 has a molecular mass of approx. 140 kDa and is composed of subunits of 67 kDa which can be further reduced to identical subunits of 23 kDa. Isoelectric focusing in agarose gels revealed that BDL1 and BDL2 both focused as single bands at pH 6.0 and pH 5.2 respectively. The purified forms of BDL1 and BDL2 were stained by the periodic acid/Schiff's reagent showing that both lectins are glycoproteins. In addition, BDL1 was deglycosylated by endo-beta-N-acetylglucosaminidase H. Immunological tests showed that these three lectins are not structurally related. All three lectins bind galactose but have different specificities for binding other sugars and for a range of vertebrate erythrocytes. BDL1 is specifically inhibited by D-(+)-glucose, D-(+)-mannose and N-acetyl-D-mannosamine, but not by N-acetyl-D-glucosamine, and BDL2 is inhibited by N-acetyl-D-glucosamine, but not by D-(+)-glucose, D-(+)-mannose or N-acetyl-D-mannosamine. BDL3 is strongly inhibited by N-acetyl-D-galactosamine, but not by any of the other above-mentioned sugars. Erythrocyte specificities showed that BDL1 is more specific for rabbit than mouse erythrocytes, whereas BDL2 and BDL3 are more specific for mouse than rabbit erythrocytes. The haemagglutinating activities of both the serum and isolated lectins are Ca(2+)-dependent. Localization of BDL1 and BDL2 with fluorescein isothiocyanate-labelled antibodies showed that both lectins are associated with the granules and other areas of the cytoplasm of all blood cell types.

Agglutinins from aquatic insects--tumor cell agglutination activity

Agglutinins were identified in whole body extracts of aquatic insects by means of murine tumor cell agglutination, using sarcoma 180 ascites, Ehrlich, and MM-46 cells. Screening revealed agglutinins in 5 of 10 of the larvae tested, and in 2 of 6 of the water-dwelling adult insects; Gerris paludum insularis and Gyrinus japonicus. Only the agglutinin from adult G. paludum also agglutinated human erythrocytes. An ascites tumor was converted into a solid form in vivo after administration of G. paludum agglutinin. The observation that these aquatic insect agglutinins preferentially agglutinate tumor cells has considerable implications in terms of anti-tumor effects such as inhibition of cell proliferation and metastasis.

Agglutination of bacteria and erythrocytes by serum from six species of marine molluscs

Lectins have been implicated as recognition molecules in the invertebrate immune response, yet their capacity to recognize (agglutinate and/or opsonize) potentially invasive microorganisms is largely unknown. In this study, sera from six species of marine molluscs (oyster, clam, octopus, squid, cuttlefish, and sea hare) were found to agglutinate 64 of 94 bacterial isolates (15 genera, 36 species) and seven types of vertebrate erythrocytes. Oyster, clam, and octopus sera agglutinated the greatest number of bacterial isolates and oyster serum exhibited the highest intensity and titer of agglutination. Agglutination was isolate dependent, implying high lectin specificity. Titers were highly variable for wild populations of oysters and sea hares and relatively constant for F4-generation cuttlefish reared in aquaculture systems. Simultaneous agglutination of specific bacterial isolates indicated conservation of lectin specificity between oyster and clam sera (bivalves) and between squid and cuttlefish sera (cephalopods).

Inhibitory effect of halocyamine, an antimicrobial substance from ascidian hemocytes, on the growth of fish viruses and marine bacteria

Halocyamine A, an antimicrobial substance isolated from hemocytes of the solitary ascidian Halocynthia roretzi, inhibited in vitro the growth of fish RNA viruses (infectious hematopoietic necrosis virus and infectious pancreatic necrosis virus). Pretreatment of RNA virus with halocyamine A reduced the infectivity of the virus toward host cells. The growth of marine bacteria, Achromobacter aquamarinus and Pseudomonas perfectomarinus, was also inhibited by halocyamine A but that of Alteromonas putrefaciens and Vibrio anguillarum was not. These results suggest that halocyamine may have a role in the defense mechanisms of H. roretzi against marine viruses and bacteria.

Sialic acid binding lectins

The literature contains several reviews on lectins in general, covering mainly those from plants and invertebrates. However, the sialic acid binding lectins have not been reviewed so far. Considering the importance of sialic acids in cell sociology, lectins which specifically recognize terminal sialic acid residues are potentially useful as analytical tools in studying the biological functions of sialoglycoconjugates. These lectins, along with monoclonal antibodies raised against sialoglycoconjugates, have been used in the detection, affinity purification, cytochemical localization and quantitation of such glycoconjugates. In this review the main emphasis has been placed on the occurrence, general purification procedures, macromolecular properties, sugar specificities and applications of these lectins.

Seasonally occurring lectins from the bryozoan Bugula neritina

Two different lectins (termed BnA-I and BnA-II) with distinct carbohydrate specificities were identified and subsequently isolated from the marine bryozoan Bugula neritina. BnA-I hemagglutinating activity was inhibited by N-acetylated hexosamines, their polymers, and glycoproteins rich in these moieties. BnA-II-induced hemagglutination was not blocked by any simple sugars but could be inhibited by several complex glycoproteins (e.g., thyroglobulin and orosomucoid). Both lectins required the presence of Ca(+)+ for reactivity and were purified by affinity chromatographic procedures. Purified BnA-I was determined to have a native molecular weight of 240 Kd and appeared to be a hexameric homopolymer while BnA-II was shown to be a 65-70 Kd monomer. Both lectins showed seasonality in expression, BnA-I appearing in animal extracts prepared in the spring and fall while BnA-II was expressed only during the summer and winter.

Comparative analysis of agglutinins from hemolymph and albumin gland of Helix pomatia

The hemolymph of Helix pomatia contains a weak agglutinating activity. This lectin concentration was calculated to be about 1.8 micrograms.ml-1. Among the different red blood cells tested, pronase-treated sheep erythrocytes were found to be the most suitable indicator cells. Their agglutination could be inhibited by GalNAc and GlcNAc. The serum agglutinin was isolated by affinity chromatography using Sephadex G-200 as the matrix. It exhibited a single band in discontinuous PAGE. In the presence of SDS, subunits of 27,000 daltons were obtained which, after addition of 2-mercaptoethanol, partly dissociated into 13,000-dalton subunits. The biochemical properties observed were compared with those of the well-known blood group A-specific lectin from the albumin gland of H. pomatia.

Purification and some properties of a lectin from the hemolymph of Periplaneta americana (American cockroach)

A lectin showing specificity for human A-type red blood cells was purified to homogeneity from the hemolymph of the American cockroach Periplaneta americana by affinity chromatography on bovine submaxillary gland mucin. This lectin was a huge molecule with molecular mass of about 1500 kDa, with a single subunit of 30-kDa protein, and required Ca2+ for expression of lectin activity. Electron microscopic examination showed that these molecules were rods with helical structure with an average length of 50.5 nm and width of 10 nm. The molecule was suggested to contain tandemly aligned basic units of 10 nm length.

T cell mitogenicity of a novel beta-D-galactoside-specific lectin from the beetle, Allomyrina dichotoma (allo A)

We examined the lymphocyte mitogenicity of a novel beta-D-galactoside-specific lectin from the beetle Allomyrina dichotoma, named allo A. Allo A was mitogenic to spleen cells of various strains of mice and rats and to human peripheral blood lymphocytes. When the selectivity of mitogenicity to T or B lymphocytes was examined with mouse spleen cells, allo A was selectively mitogenic to T-enriched spleen cells, which indicates that allo A is a T cell mitogen. Thymocytes from non-treated mice hardly responded to allo A, while those from cortisone-treated mice did to a great extent, indicating that allo A is mitogenic to mature thymocytes. The lymphocyte activation with allo A was inhibited by lactose, but not by melibiose, N-acetyl-D-glucosamine, or methyl-alpha-D-mannoside, which suggests that cell surface molecules containing beta-D-galactosyl residues are of importance in the structure of allo A receptors on the cell surface.

Further characterization of the cold agglutinin from the snail Achatina fulica

The cold agglutinin from the albumin gland of the snail Achatina fulica was purified to homogeneity by using sheep gastric mucin-Sepharose 4B as affinity column followed by gel filtration on Bio-Gel P-300. The homogeneity was checked by alkaline gel electrophoresis, immunodiffusion and immunoelectrophoresis. The purified cold agglutinin is a glycoprotein of native M2 220,000 consisting of three non-covalently bound subunits of Mr 84,000, 74,000 and 62,000 and having a pI value of 4.5. The predominant amino acids are aspartic acid and glutamic acid (or amides) and serine, which account for 39% of the residues. About 3% of the residues are half-cystine. The lectin is a glycoprotein with about 30.7% carbohydrate, the most abundant sugars being galactose, N-acetylgalactosamine and N-acetylglucosamine. Mannose, xylose and fucose are also present. The inhibition of agglutination of human umbilical-cord erythrocytes by the cold agglutinin is specific for methyl beta-D-galactoside and also for glycolipids present on cord erythrocytes. The c.d. data show only negative ellipticity values in the far-u.v. region for the protein at various concentrations and temperatures and also in the presence of the hapten lactose (at different concentrations), indicating the presence of a random-coil conformation in the agglutinin that varies according to temperature.

Carbohydrate-binding specificity of silkworm lectin

The binding specificity of a lectin from the hemolymph of silkworm larvae was examined quantitatively by taking advantage of the fluorospectrophotometric properties of the lectin. On excitation at 280 nm, the lectin fraction gave a fluorescence-emission spectrum centered at 336 nm, which was attributable to tryptophan residues. The fluorescence could be completely quenched by the addition of specific saccharides. The affinity constants of the silkworm lectin with specific saccharides were calculated from the changes in intensities of fluorescence-difference spectra induced by the saccharides. The silkworm lectin had the highest affinity for dermatan sulfate and hyaluronic acid, followed by protuberic acid, heparin, and chondroitin sulfate A. Among monosaccharides tested, only D-glucuronic acid and N-acetyl-neuraminic acid induced weak but significant quenching, and their affinity constants were found to be low. These results indicate that the silkworm lectin has a strong affinity for carboxyl groups, especially alpha-L-iduronic acid residues, in the saccharides. In most cases, sulfate groups on the saccharides interfere with the specific interactions.

A single step purification of a sialic acid binding lectin (AchatininH) from Achatina fulica snail

A sialic acid binding lectin, AchatininH, was purified in single step from the hemolymph of the land snail, Achatina fulica, by the affinity chromatography on sheep submaxillary mucin coupled to Sepharose 4B. The yield of the lectin was found to be 3 mg from 100 ml of hemolymph. The homogeneity of the lectin was established by alkaline gel electrophoresis, immunodiffusion, immunoelectrophoresis and analytical isoelectrophoresis. The molecular weight of the native protein was 242,000, having identical subunits of Mr 15,000. The lectin agglutinated rabbit erythrocytes in the presence of Ca2+. The inhibition study clearly suggests that the binding site of the lectin recognizes sialic acid as the immunodominant sugar. This was further confirmed by the observation that there was a marked decrease of agglutinating activity of the lectin with neuraminidase treated rabbit erythrocytes and asialofetuin was unable to inhibit the activity of AchatininH. Among the inhibitors used the glycoconjugate containing alpha 2----6 linkages of N-acetylneuraminic acid with subterminal galactopyranose or 2-acetamido-2-deoxy-galactopyranose residue was found to be better inhibitor than that containing alpha 2----3 linkages of N-acetyl neuraminic acid. Besides that sialoglycoprotein containing both N and O type of glycosidic linkages plays an important role in binding with the lectin. Fetuin was found to be the best inhibitor.

A bacterial-induced lectin which triggers hemocyte coagulation in Manduca sexta

An inducible hemagglutinin termed M13, was purified from M. sexta hemolymph. M13 is a glucose-specific lectin which in addition to erythrocyte agglutination, can activate dedifferentiation of various hemocytes into a filamentous coagulation network. When lectin activity was inhibited with glucose or antiserum, neither erythrocyte agglutination or hemocyte coagulation occurred. When M13 was boiled or trypsin treated, hemocyte activation was lost, but erythrocyte agglutination remained. Hence M13 activity appears to be bimodal, possessing both a lectin activity and a hemocyte-coagulating activity.

Galactose-specific lectin in the hemolymph of solitary ascidian, Halocynthia roretzi. Molecular, binding and functional properties

Galactose-specific lectin isolated from the hemolymph of solitary ascidian, Halocynthia roretzi, has been further characterized. The hemagglutinating activity of the lectin is Ca2+-dependent. The lectin has a large molecular form as revealed by gel-permeation chromatography, sedimentation equilibrium and velocity measurement, and electron microscopic observation. The lectin is adsorbed to columns of blue-Sepharose and phenyl-Sepharose, and eluted with ethylene glycol, not with lactose or high concentration of NaCl. The lectin shows a stimulatory effect on the superoxide anion production by guinea-pig polymorphonuclear leukocytes, and the effect is inhibited, among various sugars, most strongly by melibiose.

Purification and characterization of the gonad lectin of Aplysia depilans

Extracts of gonads and fertilized eggs of Aplysia depilans contain a D-galacturonic and D-galactose-binding lectin. This lectin reacts strongly with rabbit and human erythrocytes independent of ABO blood groups, weakly with dog, mouse, rat, and chick erythrocytes and not at all or very weakly with sheep erythrocytes. Purification of the gonad lectin was easily achieved, with a high yield, by heating to 70 degrees C, precipitation with ammonium sulfate and affinity chromatography on Sepharose 4B. The purified lectin was found to be a glucoprotein of molecular mass around 55-60 kDa; it stimulates mitogenesis of human peripheral lymphocytes.

Naturally occurring agglutinins against trypanosomatid flagellates in the haemolymph of insects

In vitro studies of the behaviour of the trypanosomatid flagellates Trypanosoma brucei and Leishmania hertigi in the presence of cell-free haemolymph of locusts, Schistocerca gregaria and cockroaches, Periplaneta americana revealed the presence of parasite agglutinins. The range of normal values of agglutination titres was 2(-4) to 2(-13). Physico-chemical treatment of haemolymph indicated that these agglutinins are protein or glycoprotein in nature and are only partially affected by heat treatment below 65 degrees C, at which temperature incubation of haemolymph for 30 min abrogated all agglutination. Agglutination was not dependent on the presence of Ca2+ or Mg2+. Prior injection of locusts and cockroaches with T. brucei and L. hertigi significantly increased agglutinin titres between Days 4 and 6 in cockroaches (P less than 0.05) and from Days 2 to 4 when L. hertigi was inoculated into locusts. The induced differences in titres observed in locusts infected with T. brucei were not significant. Lysozyme levels were significantly increased after inoculation of T. brucei into cockroaches compared with placebo-inoculated and uninoculated controls. L. hertigi inoculation produced significant increases in lysozyme levels compared with controls between Days 1 and 7 in locusts and 3 to 6 in cockroaches. These studies indicate that, at least in easily manipulated model systems, induced responses to intrahaemocoelic inoculation to trypanosomes and Leishmania can occur. As far as we are aware this is the first report of an induced response of an insect to such important parasites. The possibility that induced responses in natural vector to this parasites occurs requires investigation.