The role of lectins in blood group serology

Structure-function and application of plant lectins in disease biology and immunity

Lectins are proteins with a high degree of stereospecificity to recognize various sugar structures and form reversible linkages upon interaction with glyco-conjugate complexes. These are abundantly found in plants, animals and many other species and are known to agglutinate various blood groups of erythrocytes. Further, due to the unique carbohydrate recognition property, lectins have been extensively used in many biological functions that make use of protein-carbohydrate recognition like detection, isolation and characterization of glycoconjugates, histochemistry of cells and tissues, tumor cell recognition and many more. In this review, we have summarized the immunomodulatory effects of plant lectins and their effects against diseases, including antimicrobial action. We found that many plant lectins mediate its microbicidal activity by triggering host immune responses that result in the release of several cytokines followed by activation of effector mechanism. Moreover, certain lectins also enhance the phagocytic activity of macrophages during microbial infections. Lectins along with heat killed microbes can act as vaccine to provide long term protection from deadly microbes. Hence, lectin based therapy can be used as a better substitute to fight microbial diseases efficiently in future.

Glycan binding profile of a fucolectin-related protein (FRP) encoded by the SP2159 gene of Streptococcus pneumoniae

The recombinant fucolectin-related protein (FRP) of unknown function, encoded by the SP2159 gene of Streptococcus pneumoniae, was expressed in E. coli. In this study, its glycan-recognition epitopes and their binding potencies were examined by enzyme-linked lectinosorbent and inhibition assays. The results indicate that FRP reacted strongly with human blood group ABH and l-Fucα1→2-active glycotopes and in their polyvalent (super) forms. When expressed by mass relative potency, the binding affinities of FRP to poly-l-Fucα1→glycotopes were about 5.0 × 10⁵ folds higher than that of the mono-l-Fucα1→glycotope form. This unique binding property of FRP can be used as a special tool to differentiate complex forms of l-Fucα1→2 and other forms of glycotopes.

Bauhinia purprea agglutinin-modified liposomes for human prostate cancer treatment

Bauhinia purprea agglutinin (BPA) is a well‐known lectin that recognizes galactosyl glycoproteins and glycolipids. In the present study, we firstly found that BPA bound to human prostate cancer specimens but not to normal prostate ones. Therefore, we sought to develop BPA‐PEG‐modified liposomes (BPA‐PEG‐LP) encapsulating anticancer drugs for the treatment of prostate cancer. We examined the tumor targetability of BPA‐PEG‐LP with human prostate cancer DU145 cells, and observed that fluorescently labeled BPA‐PEG‐LP dominantly associated with the cells via the interaction between liposome‐surface BPA and cell‐surface galactosyl molecules. We also observed that BPA‐PEG‐LP accumulated in the prostate cancer tissue after the i.v. injection to DU145 solid cancer‐bearing mice, and strongly bound to the cancer cells. In a therapeutic study, DU145 solid cancer‐bearing mice were i.v. injected thrice with BPA‐PEG‐LP encapsulating doxorubicin (BPA‐PEG‐LPDOX, 2 mg/kg/day as the DOX dosage) or PEG‐modified liposomes encapsulating DOX (PEG‐LPDOX). As a result, BPA‐PEG‐LPDOX significantly suppressed the growth of the DU145 cancer cells, whereas PEG‐LPDOX at the same dosage as DOX showed little anti‐cancer effect. The present study suggested that BPA‐PEG‐LP could be a useful drug carrier for the treatment of human prostate cancers.

Medicinal Applications of Plant Lectins

Plant lectins are a unique group of proteins and glycoproteins with potent biological activity and have received widespread attention for many years. They can be found in wheat, corn, tomatoes, peanuts, kidney beans, bananas, peas, lentils, soybeans, mushrooms, tubers, seeds, mistletoe and potatoes among many others. Due to their ability to bind reversibly with specific carbohydrate structures and their abundant availability, plant lectins have commonly been used as a molecular tool in various disciplines of biology and medicine. Whilst once thought of being a dietary toxin, the focus on plant lectins has since shifted to understanding the useful properties of these lectins and utilizing them in medicinal applications to advance human health. This chapter reviews the current and potential applications of plant lectins in various areas of medically related research.

Chemical biology of the sugar code

A high-density coding system is essential to allow cells to communicate efficiently and swiftly through complex surface interactions. All the structural requirements for forming a wide array of signals with a system of minimal size are met by oligomers of carbohydrates. These molecules surpass amino acids and nucleotides by far in information-storing capacity and serve as ligands in biorecognition processes for the transfer of information. The results of work aiming to reveal the intricate ways in which oligosaccharide determinants of cellular glycoconjugates interact with tissue lectins and thereby trigger multifarious cellular responses (e.g. in adhesion or growth regulation) are teaching amazing lessons about the range of finely tuned activities involved. The ability of enzymes to generate an enormous diversity of biochemical signals is matched by receptor proteins (lectins), which are equally elaborate. The multiformity of lectins ensures accurate signal decoding and transmission. The exquisite refinement of both sides of the protein-carbohydrate recognition system turns the structural complexity of glycans--a demanding but essentially mastered problem for analytical chemistry--into a biochemical virtue. The emerging medical importance of protein-carbohydrate recognition, for example in combating infection and the spread of tumors or in targeting drugs, also explains why this interaction system is no longer below industrial radarscopes. Our review sketches the concept of the sugar code, with a solid description of the historical background. We also place emphasis on a distinctive feature of the code, that is, the potential of a carbohydrate ligand to adopt various defined shapes, each with its own particular ligand properties (differential conformer selection). Proper consideration of the structure and shape of the ligand enables us to envision the chemical design of potent binding partners for a target (in lectin-mediated drug delivery) or ways to block lectins of medical importance (in infection, tumor spread, or inflammation).

Lectinochemical studies on the affinity of Anguilla anguilla agglutinin for mammalian glycotopes

Anguilla anguilla agglutinin (AAA) is a fucose-specific lectin found in the serum of the fresh water eel. It is suggested to be associated with innate immunity by recognizing disease-associated cell surface glycans, and has been widely used as a reagent in hematology and glycobiology. In order to gain a better understanding of AAA for further applications, it is necessary to elucidate its binding profile with mammalian glycotopes. We, therefore, analyzed the detailed carbohydrate specificity of AAA by enzyme-linked lectinosorbent assay (ELLSA) with our extended glycan/ligand collection and lectin-glycan inhibition assay. Among the glycans tested, AAA reacted well with nearly all human blood group Ah (GalNAcalpha1-->3[LFucalpha1-->2]Gal), Bh (Galalpha1-->3[LFucalpha1-->2]Gal), H LFucalpha1-->2Gal) and Leb (Fucalpha1-->2Galbeta1-->3[Fucalpha1-->4]GlcNAc) active glycoproteins (gps), but not with blood group Lea (Galbeta1-->3[Fucalpha1-->4]GlcNAc) substances, suggesting that residues and optimal density of alpha1-2 linked LFuc to Gal at the non-reducing end of glycoprotein ligands are essential for lectin-carbohydrate interactions. Blood group precursors, Galbeta1-3GalNAc (T), GalNAcalpha1-Ser/Thr (Tn) containing glycoproteins and N-linked plasma gps, gave only negligible affinity. Among the mammalian glycotopes tested, Ah, Bh and H determinants were the best, being about 5 to 6.7 times more active than LFuc, but were weaker than p-nitrophenylalphaFuc indicating that hydrophobic environment surrounding the LFuc moiety enhance the reactivity. The hierarchy of potency of oligo- and monosaccharides can be ranked as follows: p-nitrophenyl-alphaFuc > Ah, Bh and H > LFuc > LFucalpha1-->2Galbeta1-->4Glc (2'-FL) and Galbeta1-->4[LFucalpha1-->3]Glc (3'-FL), while LNDFH I (Leb hexa-), Lea, Lex (Galbeta1-->4[Fucalpha1-->3]GlcNAc), and LDFT (gluco-analogue of Ley) were inactive. From the present observations, it can be concluded that the combining site of AAA should be a small cavity-type capable of recognizing mainly H/crypto H and of binding to specific polyvalent ABH and Leb glycotopes.

Multiplicity, structures, and endocrine and exocrine natures of eel fucose-binding lectins

Lectins, a group of proteins that bind to cell surface carbohydrates and play important roles in innate immunity, are widely used experimentally to distinguish cell types and to induce cell proliferation. Eel serum lectins have been useful as anti-H hemagglutinins and also in lectin histochemistry as fucose-binding lectins (fucolectins), but their structures have not been determined. Here we report the primary structures and the sites of synthesis of eel fucolectins. Eel serum fucolectins were separated by two-dimensional gel electrophoresis and sequenced. cDNA cloning, based on the amino acid sequence information, and Northern blot analysis indicated that 1) the fucose-binding lectins are secretory proteins and have unique structures among the lectins, exhibiting only weak similarities to frog pentraxin, horseshoe crab tachylectin-4, and fly fw protein; 2) there are at least seven closely related members; and 3) their messages are abundantly expressed in the liver and in significant levels in the gill and intestine. The lectin-producing hepatic cells were identified by immunostaining; in the gill, exocrine mucous cells were stained, suggesting that serum fucolectins derive from the liver. Using primary culture of eel hepatocytes, the message levels were shown to be increased by lipopolysaccharide, suggesting a role for fucolectins in host defense. SDS-polyacrylamide gel electrophoresis analysis showed that eel fucolectins have a SDS-resistant tetrameric structure consisting of two disulfide-linked dimers.

Red blood cell polyagglutination: clinical aspects

Polyagglutination is the term applied to red blood cells (RBCs) that are agglutinated by almost all samples of human sera from adults but not by autologous serum or sera of newborns. The polyagglutinable state may be transient or persistent. Transient polyagglutinability results from the exposure of normally cryptic antigens by bacterial enzymatic activity during the course of an infectious process. RBCs are polyagglutinable because most sera from adults contain agglutinins for the exposed antigens. This type of polyagglutination can often be reproduced in vitro with bacterial culture fluids or isolated enzymes. Persistent polyagglutination may be a consequence of somatic mutation leading to a cellular lineage characterized by an enzyme deficiency that results in exposure of a normally cryptic antigen, Tn. Most human sera contain anti-Tn. Tn polyagglutination is regularly accompanied by leukopenia and thrombocytopenia and has been associated with leukemia. Other forms of persistent polyagglutination are due to the inheritance of rare blood groups or are associated with a hematologic dyscrasia.

A comparison of the Aplysia lectin anti-I specificity with human anti-I and several other I-detecting lectins

BACKGROUND

Lectins displaying blood group specificity are important for blood group typing and antigen recognition. Their use in blood banks is especially widespread in situations where there is a shortage of specific antisera. This report describes the efficiency of Aplysia gonad lectin as a reliable reagent for the detection of I antigen, which is common on adult human cells but reduced in fetal, newborn, and rare adult red cells.

STUDY DESIGN AND METHODS

The selective hemagglutinating activity of the Aplysia lectin was compared with that of human anti-I and several I-reactive lectins, including two plant lectins, one galactophilic microbial lectin, and bovine spleen galectin.

RESULTS

The comparison has revealed that Aplysia gonad lectin, like human anti-I, strongly agglutinates and adsorbs to adult I-positive red cells, differentiating between them and fetal or rare I-negative adult red cells (although with less of a difference). In contrast to the plant and microbial lectins examined, its I-affinity does not depend on the presence of ABH or P system antigens and it clearly detects higher I antigen expression in Oh red cells. The hemagglutinating activity of Aplysia lectin as that of all the I-detecting proteins is enhanced at 4 degrees C, but unlike the human anti-I Aplysia lectin-induced hemagglutination is stable at room temperature.

CONCLUSIONS

The Aplysia lectin is a reliable anti-I reagent, which strongly agglutinates I-positive adult human red cells irrespective of their ABH or P system antigens. This lectin is usable at room temperature.

Cold-induced augmentation of I blood group antigen interactions with galactophilic lectins

The I antigen appears on human cells in the postnatal period, by addition of N-acetyllactosamine (beta 1-6) branching to the fetal i antigen structure, which is specified by linear oligo N-acetyllactosamine (beta 1-3) chain. Concurrently with the I antigen appearance on adult human erythrocytes most human sera exhibit low levels of anti-I agglutinins. These antibodies induce hemagglutination mainly at low temperatures (4 degrees C) and scantly at body temperature. Therefore they were named "cold agglutinins". We have used these antibodies and several hemagglutinating galactophilic animal, plant, and microbial lectins that also react with the I antigen, to study whether the cold-favored agglutination of the I antigen-bearing cells is a peculiar property of the anti-I antibodies or a special trait of that antigen. It has been found that the interactions of all of the examined lectins, irrespective of their source, with the adult human erythrocytes significantly increased at 4 degrees C, in contrast to those of the same cells with diverse I-insensitive antibodies and lectins, which were significantly higher at room temperature.

Erythrina lectins detect the H/HI blood groups

The lectin purified from Erythrina corallodendron seeds which binds N-acetyllactosamine greater than N-acetyl-D-galactosamine greater than alpha and beta galactosides greater than D-galactose was examined for its ABO(H) blood group specificity. It has been shown that this lectin causes the strongest hemagglutination of O(H) and weakest of Oh(Bombay) red blood cells, and interacts with the H antigen in association with the I antigen. The reactions of Erythrina corallodendron and Erythrina indica lectins (which are similar in sugar specificity) with erythrocytes of different ABO(H) and Ii blood groups (the I bloods were all from adults and the i from either cord or adult bloods) revealed the following order of activity: O(H)I greater than A2 I greater than O(H)i adult greater than A2BI greater than BI greater than O(H)i cord greater than A1I greater than A1i adult greater than Bi cord greater than A1BI greater than Ai cord greater than ABi cord greater than OhI. The Erythrina indica lectin showed a lower differentiation between the agglutination of O(H) and Oh erythrocytes. Both Erythrina lectins exhibited H/HI blood group preference but were not inhibited by the saliva from ABO(H) "secretors". Thus they may be classified with the Cytisus sessilifolius, Lotus tetragonolobus and Laburnum alpinum lectins which are inhibited by lactose but not by H blood group substances in secretions.

Studies of lectin binding to the human cervix uteri: I. Normal cervix

Lectins of Bauhinia purpurea (BPA), Canavalin ensiformis (Con A), Griffonia simplicifolia I (GS I), Griffonia simplicifolia II (GS II), Maclura pomifera (MPA), Arachis hypogaea (PNA), Glycine max (SBA), Ulex europaeus I (UEA I) and Triticum vulgaris (WGA) were used to evaluate cell surface carbohydrates in formalin-fixed paraffin-embedded tissue sections of normal human cervix uteri. Consistent patterns of staining of the squamous epithelium were obtained in all 30 cases with BPA, GS II, MPA, PNA, SBA and WGA. A variable distribution of lectin binding was seen in squamous epithelium with Con A, GS I and UEA I. The patterns of GS I and GS II binding reflected squamous epithelial maturation. Columnar epithelium did not stain with GS II, stained variably with Con A, and stained consistently with the remaining seven lectins in all cases. No association between lectin binding and blood group or phase of the menstrual cycle was found. These findings may be used as a baseline for evaluation of lectin binding in both preinvasive and invasive lesions of the cervix uteri.

The application of lectins to the characterization and isolation of mammalian cell populations

Mammalian cells invariably contain a vast array of glycosylated moieties, both inside the cell and on the cell surface. There is an increasing awareness of the utility of these carbohydrates in delineating the phenotype or function of many populations of cells. To this end lectins are extremely useful reagents. Lectins are carbohydrate-binding proteins and glycoproteins of non-immune origin derived from numerous plants and animals. A wide variety of lectins with many distinct carbohydrate specificities have been isolated. Historically the most common laboratory techniques utilizing lectins have been agglutination, mitogen stimulation, and fluorescence techniques. Recent advances in the development and conjugation procedure for labels and matrices have led to the creation of numerous novel lectin-based assays. Lectins are currently used not only to identify cells with specified carbohydrate groups, but also to quantitate the carbohydrate groups or to isolate the carbohydrate-bearing cells or structures.

Adhesivity and rigidity of erythrocyte membrane in relation to wheat germ agglutinin binding

Binding of the plant lectin wheat germ agglutinin (WGA) to erythrocyte membranes causes membrane rigidification. One of our objectives has been to directly measure the effects of WGA binding on membrane rigidity and to relate rigidification to the kinetics and levels of WGA binding. Our other objective has been to measure the strength of adhesion and mechanics of cell separation for erythrocytes bound together by WGA. The erythrocyte membrane rigidity was measured on single cells by micropipette aspiration. The slope of the suction pressure-length data for entry into the pipette provided the measure of the membrane extensional modulus. Data were collected for cells equilibrated with WGA solutions in the range of concentrations of 0.01- 10 micrograms/ml. Erythrocyte-erythrocyte adherence properties were studied by micropipette separation of two-cell aggregates. First, a "test" cell was selected from a WGA solution by aspiration into a small micropipette, then transferred to a separate chamber that contained erythrocytes in WGA-free buffer. Here, a second cell was aspirated with another pipette and maneuvered into close proximity of the test cell surface, and adhesive contact was produced. The flaccid cell was separated from the test cell surface in steps at which the force of attachment was derived from the pipette suction pressure and cell geometry. In addition, we measured the time-dependent binding and release of fluorescently labeled WGA to single erythrocytes with a laser microfluorometry system. The results showed that the stiffening of the erythrocyte membrane and binding of fluorescently labeled WGA to the membrane surface followed the same concentration and time dependencies. The threshold concentration for membrane stiffening was at approximately 0.1 microgram/ml where the time course to reach equilibrium was close to 1 h. The maximal stiffening (almost 30-fold over the normal membrane elastic modulus) occurred in concentrations greater than 2 micrograms/ml where the time to reach equilibrium took less than 1 min. The WGA binding also altered the normal elastic membrane behavior into an inelastic, plastic-like response which indicated that mechanical extension of the membrane caused an increase in cross-linking within the surface plane. Similar to the stiffening effect, we observed that the membrane adhesivity of cells equilibrated with WGA solutions greatly increased with concentration greater than 0.1 microgram/ml.(ABSTRACT TRUNCATED AT 400 WORDS)