Fucose-binding Protein Research Articles

Characterization of the exposed carbohydrates on the surface membrane of adult Schistosoma mansoni by analysis of lectin binding.

The surface architecture of adult male Schistosoma mansoni was explored using a range of lectins with differing carbohydrate specificites. Highest specific binding was achieved with concanavalin A and the agglutinin of molecular weight 60000 from Ricinus communis; the binding of wheat germ agglutinin was mostly non-specific. Small amounts of peanut agglutinin and soybean agglutinin binding were observed and the binding of these lectins was increased by pre-treating the parasite with neuraminidase. The fucose binding protein of Lotus tetragonolobus failed to bind. These results indicate that mannose and/or glucose, galactose, N-acetylglucosamine, N-acetyl-galactosamine and sialic acid are exposed on the surface of the adult male schistosome.

Lotus tetragonolobus fucolectin as a potential model for “MIF-like” modulation of macrophage function: Comparison of the interaction of Lotus fucose binding protein (FBP) and migration inhibitory factor (MIF) with macrophages in the migration inhibition assay

Fucose binding protein (FBP), the fucolectin from Lotus tetragonolobus, was compared with migration inhibitory factor (MIF) for its binding interactions with peritoneal macrophages in the migration inhibition assay and with concanavalin A (Con A) for its mitogenic properties for lymphocytes. FBP was nonmitogenic for guinea pig lymphocytes as demonstrated by its inability to stimulate incorporation of [ 3H]thymidine into TCA insoluble fractions or to induce production of MIF. FBP and MIF inhibited migration of responsive peritoneal macrophages in similar dose-response profiles, whereas refractory macrophages were significantly less responsive to both inhibitors. FBP and MIF were adsorbed correspondingly by responsive macrophages but not by refractory macrophage populations. FBP was bound to peritoneal macrophages during short-term pulse exposure to inhibit macrophage migration in a dose-response fashion similar to that of MIF. Enzymatic treatment of peritoneal macrophages with trypsin, chymotrypsin, or Pronase abrogated their response to both FBP and MIF. l-Fucose (0.1 M) significantly reduced FBP and MIF-mediated migration inhibition while d-fucose and l-rhamnose were ineffective. FBP was also found to augment MIF inhibition of macrophage migration under a variety of experimental conditions. Based on these findings, it is proposed that Lotus fucolectin may provide a useful model for studies on “MIF-like” modulation of macrophage function.

Fertilization in brown algae. III. Preliminary characterization of putative gamete receptors from eggs and sperm of Fucus serratus.

Membrane fractions have been isolated from eggs of Fucus serrratus which inhibit fertilization in a species-specific manner. This activity is destroyed by alpha-fucosidase and alpha-mannosidase. Some 6% of the protein of this membrane fraction binds to Con A-agarose, following SDS solubilization, and when eluted with alpha-methyl mannoside inhibits fertilization when preincubated with sperm, but not eggs. This inhibitory activity is species-specific and destroyed by alpha-fucosidase but not by trypsin. SDS-gel electrophoresis reveals 1 band staining strongly with Coomassie Brilliant Blue G and weakly with the PAS reagent. This major band represents a glycoprotein with an approximate molecular weight of 30 000 Daltons. Membrane fractions from sperm of Fucus serratus solubilized in KC1 yielded a protein-containing fraction, after affinity chromatography on desulphated focoidan-Sepharose. This fraction is 100-fold more effective in inhibiting fertilization after preincubation with eggs than either Con A or fucose-binding protein. It is species-specific and inhibition is reversed when pretreated eggs are washed with fucoidan. Activity is destroyed by heat and trypsin and only one diffuse band is apparent on SDS gels. This stains positively with Coomassie Brilliant Blue G but not with PAS and has a molecular weight of approximately 60 000 Daltons. Tentative calculation of the numbers of putative receptor molecules gives a figure of 2.5 X 10(9) receptors per egg and 1.8 X 10(6) receptors per sperm.

Attachment and short-term maintenance of motility and viability of Entamoeba histolytica in a defined medium.

Organic requirements for attachment to glass, elongation, and motility of Entamoeba histolytica, have been determined. The trophozoite, which has been grown axenically only in highly complex media with reduced oxygen tensions, remains rounded and detached when placed in a Tris-HCl buffered solution containing NaCl, KCl, MgClI, and CaCl2. A maintenance medium in which the amebae could attach to glass, elongate, and remain motile and viable for 12 to 24 h was devised with the addition of cysteine, ascorbic acid, bovine serum albumin, and the vitamin solution of medium NCTC No. 107. Tris-HCl was the most effective buffer tested and the optimal pH was 6.9 to 7.0. Survival, but attachment, of the amebae was decreased at osmolalities ranging between 110 and 180 milliosmoles/kg, whereas both functions were decreased above approximately 260 milliosmoles/kg. Bovine serum albumin, the most effective of the proteins tested, and the vitamin solution helped maintain attachment of some ameba strains, but were not required by other strains. The requirements for cysteine and ascorbic acid were absolute and highly specific. During incubation in the maintenance medium, cell volumes decreased. Sensitivity of the organisms to agglutination by concanavalin A, wheat germ agglutinin, soybean agglutinin and fucose binding protein remained unchanged.

Ultrastructural localization of lectin binding sites on the surface of retinal photoreceptors and pigment epithelium

The ferritin-lectin complexes of Ricinus communis agglutinin (RCA-120), wheat germ agglutinin (WGA), concanavalin A (con A), soybean agglutinin (SBA) and fucose binding protein (FBP) have been used to study the distribution of sugars along the plasma membranes of frog photoreceptor and pigment epithelial cells. The tissues were fixed prior to labeling in order to prevent the lectin-induced rearrangement of binding sites. The plasma membrane of different regions of the rod and cone photoreceptor cells bound each lectin to a different extent. In all cases, the outer segment plasma membrane bound more of the ferritin-lectin complex than did the inner segment plasma membrane. This might reflect the specific differentiation of the outer segment plasma membranes, related to their role in the visual process. The intensity of binding of each lectin to the pigment epithelium plasma membrane was similar to its binding to the rod outer segment plasma membrane. In cone outer segments, where one side of the disk membrane is accessible to the incubation medium, direct binding of lectin to the disk edges, as well as to the plasma membrane, was seen. Cone outer segments bound more of the α-D-N-acetylgalactosamine and D-galactose specific lectin, SBA, than did rod outer segments. No differences were observed in the binding of ferritin-lectin complexes to rod outer segments from dark or light adapted frogs.

Molecular and biosynthetic heterogeneity of fucosyl glycoproteins associated with rat brain synaptic junctions

The composition and biosynthesis of fucosyl glycoproteins present in rat brain synaptic membranes and synaptic junctions were investigated. Reaction with 125I-labelled fucose-binding protein ( Lotus tetragonolobus) following sodium dodecyl sulphate gel electrophoresis identified 6–8 fucosyl glycoproteins in synaptic membranes but only three major high molecular classes ( M r = 180 000, 130 000 and 110 000) in synaptic junctions. Affinity chromatography on concanavalin A-Sepharose resolved each of the synaptic junctional fucosyl glycoproteins into concanavalin A-positive and negative components indicating the presence of at least six high molecular weight fucosyl glycoproteins in synaptic junctions. Following the administration of [ 3H]fucose synaptic membranes, synaptic junctions and post-synaptic densities incorporated isotope, the order of relative specific activities being synaptic membranes > synaptic junctions > post-synaptic densities. Fractionation of [ 3H]fucose-labelled synaptic junctions on concanavalin A-Sepharose revealed a time-dependent increase in the percentage of isotope associated with the concanavalin A-positive glycoproteins. The results demonstrate both molecular and biosynthetic heterogeneity of fucosyl glycoproteins associated with synaptic junctions.

Lipopolysaccharide-derived serotype polysaccharides from Neisseria meningitidis group B.

Three immunologically distinct types of polysaccharides have been isolated by diethylaminoethyl (DEAE) chromatography from the lipopolysaccharide extracts of group B Neisseria meningitidis. All types contain a set of common determinants, as well as distinct ones; all of these determinants are detectable by either immunodiffusion or enzyme-linked immunosorbent assay (ELISA). The polysaccharides elute from a Sepharose 4B column in the range of 2-3 x 10(5) daltons and have isoelectric points from 4.2 to 4.3. Their antigenicity is destroyed by oxidation but is unaffected by neuraminidase, lysozyme, or trypsin. One type of polysaccharide cross-reacts with the Gc2 polysaccharide of Neisseria gonorrhoeae in immunodiffusion systems. Chemical analysis indicates that these polysaccharides contain hexoses, hexosamines, 2-keto-3-deoxyoctonate, ethanolamine, and heptose; analysis of amino acids indicates protein contents of less than 0.05%. In contrast to the lipopolysaccharide from which they are derived, these polysaccharides contain no lipid A and less than 0.5% fatty acids. All three types are precipitated by wheat germ agglutinin but not by concanavalin A or fucose-binding protein. Specific inhibition of this precipitation can be achieved with N-acetyl glucosamine. These antigens may be the bases of a lipopolysaccharide-derived typing system for group B N. meningitidis.

Fertilization in brown algae. II. Evidence for lectin-sensitive complementary receptors involved in gamete recognition in Fucus serratus.

Fertilization in Fucus serratus is directly proportional to the number of sperm added, saturating at approximately 250 sperm per egg with an apparent Km of 120 sperm per egg. The effect of a range of lectins on fertilization has been tested. Preincubation of gametes with Con A and fucose-binding protein (FBP) inhibited fertilization. At low concentrations this was by specifically binding to eggs; at high concentrations pretreatment of either gametes inhibited fertilization probably due to cytotoxicity. Fertilization was not inhibited by simple sugar haptens, but polysaccharides containing fucosyl or mannosyl residues (yeast mannan, fucoidan, ascophyllan) inhibited fertilization by binding to sperm. Pretreatment of eggs with alpha-fucosidase or alpha-mannosidase was effective in inhibiting fertilization. All the results indirectly demonstrate that fertilization in Fucus serratus is based on an association between fucosyl- and mannosyl-containing ligands on the egg surface and specific carbohydrate-binding receptors on the sperm surface.

Lectin analysis of Trypanosoma congolense bloodstream trypomastigote and culture procyclic surface saccharides by agglutination and electron microscopic technics.

Living, intact bloodstream trypomastigotes and culture procyclic forms of Trypanosoma congolense were tested for aggulination with the lectins concanavalin A (Con A), phytohemagglutinin P (PP), wheat germ agglutinin (WGA), soybean agglutinin (SBA), and fucose binding protein (FBP). Similar experiments were conducted with living bloodstream and culture forms treated with trypsin or dextranase. Parasites were incubated for 30 min at 25 C in various concentrations of each lectin, then examined for agglutination by dark-field microscopy. Control preparations consisted of parasites incubated alone or with 0.5 M of the specific competing sugar, with or without the corresponding lectin. Electron-microscopic localization of lectin binding sites on the surface of intact and dextranase-treated bloodstream and intact culture forms was accomplished with Con A, reacted with horseradish peroxidase (HRP) and then diaminobenzidine (DAB). In addition, FBP and SBA were coupled to HRP, then utilized for the localization of binding saccharides on the surface of bloodstream forms by the DAB technic. Similar studies were conducted with culture procyclics incubated with WGA-, SBA-, PP- or FBP-HRP conjugates and then reacted with DAB. Controls were utilized to confirm the sugar specificity of all positive reactions. Intact living bloodstream forms were agglutinated in a concentration-dependent manner with all the lectins tested. Agglutination levels were scored as Con A greater than FBP greater than WGA = PP = SBA. Sugars resembling alpha-D-mannose, N-acetyl-D-glucosamine, N-acetyl-D-galactosamine, and alpha-L-fucose are evidently present on the surface of the parasites. No agglutination was noted in any control preparations. Identical lectin-induced agglutinations were obtained with trypsin- or dextranase-treated bloodstream forms. Trypsin disrupted but did not entirely remove the surface coat of bloodstream forms, while dextranase did not alter the ultrastructure of the parasites. Con A-, SBA- and FBP-binding saccharides were distributed uniformly on the surface coat of intact bloodstream forms; a similar distribution of Con A receptors was noted also on the surface of dextranase-treated cells. No lectin-binding saccharides were visualized by electron microscopy on any control preparations. Intact, trypsin- or dextranase-treated, procyclics were agglutinated in a concentration-dependent fashion by Con A and WGA, but not by the other lectins tested. Control preparations did not agglutinate and the enzymes did not affect the ultrastructure of the parasites. Con A- and WGA-specifically binding saccharides were uniformly distributed on intact procyclics and control preparations were lectin-negative. Thus, T. congolense procyclics retained surface saccharides resembling alpha-D-mannose and N-acetyl-D-glucosamine but lost sugars resembling N-acetyl-D-galactosamine (or D-galactose) and alpha-L-fucose...

Studies on fertilization in the ascidians: II. Lectin binding to the gametes of ciona intestinalis

In the present work we have compared the binding of fluorescein-conjugated lectins (concanavalin A (ConA), wheat germ agglutinin (WGA), fucose binding protein (FBP) and soybean agglutinin (SBA)) to the sperm surface and to the egg and its envelopes of Ciona intestinalis. Only WGA is bound to the follicle cells: yet this lectin has no binding sites on the sperm surface. Both ConA and FBP are bound by the chorion, the oolemma and the sperm surface. However, while ConA reacts only with the sperm head, FBP is bound both to the head and to the flagellum. Experiments on the effect of ConA and FBP on the fertilization reaction have been carried out. The role of the lectin-binding sites that are shared by the surfaces of both gametes is discussed in connection with the nature of the sperm-binding sites.

Lectin-mediated agglutination of amphibian embryonic cells.

Dissociated blastula cells of Xenopus laevis are agglutinated with wheat germ agglutinin (WGA), Ricinus communis agglutinin (RCA), concanavalin A (Con A) and, to a lesser extent with soya bean agglutinin (SBA). They are not agglutinated with fucose-binding protein. Neuraminidase treatment of cells enhances their agglutinability with RCA and SBA, but has no effect on Con A- and WGA-mediated agglutinability. Treatment of cells with procaine, or xylocaine, has no effect on the cells' agglutinability or on the extrusion of lobopodia. Treatment with colchicine or cytochalasin B either separately or simultaneously has no effect on lectin-mediated agglutinability. Cells treated with cytochalasin B or colchicine and cytochalasin B simultaneously lack lobopodial extensions, while colchicine alone has no effect on these structures. Phenothiazine tranquillizers inhibit agglutination mediated by all of the above mentioned lectins. Lobopodial extensions are absent in cells treated with these compounds. Glutaraldehyde fixation inhibits RCA and WGA mediated agglutinability and reduces the Con A-mediated agglutinability. Results suggest that in this system microtubules and microfilaments are not involved in lectin-mediated agglutination.

Leishmania donovani: Surface membrane carbohydrates of promastigotes

Cloned promastigote forms of Leishmania donovani, a human protozoan pathogen, were agglutinated specifically with the plant lectins concanavalin A (Con A), fucose binding protein, phytohemagglutinin-M and -P, soybean agglutinin (SBA), and wheat germ agglutinin (WGA). Cell agglutination with lectins was inhibited, and reversed in the presence of specific lectin-binding monosaccharides. Promastigotes also were agglutinated by viable influenza virions. Neuraminidasetreated cells were not agglutinated by the virions. Cells were agglutinated randomly with all lectins and the influenza virions suggesting a uniform distribution in the promastigote cell surface of the lectin and influenza virion-binding saccharide ligands. Both living and glutaraldehyde-fixed cells gave similar agglutination results with the various lectins and influenza virus. Promastigotes were also agglutinated with low concentrations of cationized ferritin indicative of a negative surface charge. Noncationized ferritin did not induce cell agglutination. Living L. donovani promastigotes were also specifically adsorbed onto the surface of Con A-Sepharose beads but not onto heat-denatured Con A-Sepharose or Sepharose 4B. No cell adsorption to Con A-Sepharose was observed in controls treated with α-methyl- D-mannoside. The lectin-binding kinetics of the cell surface α- D-mannose receptor ligand was assessed using 3H-labeIed Con A. At saturation, 2.78–4.86 × 10 −4 μmole of [ 3H]Con A were bound per 10 8 promastigotes with a mean of 3.73 × 10 −4 μmole/10 8 cells. Membrane receptor sites sterically available for binding [ 3H]Con A were calculated from kinetic data, and ranged from 1.67–2.93 × 10 6 sites/cell with a mean of 2.24 × 10 6 ligand sites/promastigote. Cell-surface-bound Con A was visualized at the ultrastructure level with an iron-dextran (Fe-Dex) conjugate. The dense Fe-Dex particles were distributed randomly on the pellicular and flagellar membrane outer lamina. Con A bound at the cell surface was also visualized using horseradish peroxidase (HRPO) and diaminobenzidine (DAB) coupled reactions. Dense Con A-HRPO-DAB reaction product was deposited uniformly on the cell pellicular and flagellar membranes. SBA and WGA were chemically conjugated to HRPO and these were used in DAB coupled reactions with the L. donovani promastigotes. The fine structure cell surface localization and distribution of these HRPO-conjugated lectins was similar to that obtained with the Con A-HRPO-DAB preparations. Influenza virions visualized at the fine structure level were bound randomly to the outer lamina of the cell pellicular and flagellar membranes. At the ultrastructure level, cationized ferritin was uniformly distributed over the entire cell surface. The cumulative results demonstrate that ligands similar or identical to α- d-mannose, N-acetylgalactosamine, N-acetylglucosamine, α- l-fucose, and an N-acetylated neuraminic acid are constituents of the L. donovani pellicular and flagellar membranes. These carbohydrates probably represent terminal moieties of cell membrane structural and functional glycoproteins. Further, the polyanionic carbohydrates impart a net negative charge to the L. donovani surface membrane.

Cell surface saccharides of Trypanosoma lewis i. II. Lectin-mediated agglutination and fine-structure cytochemical detection of lectin-binding sites.

Bloodstream (BSF) and culture forms (CF) of Trypanosoma lewisi were specifically agglutinated with the plant lectins concanavalin A (Con A), soybean agglutinin (SBA), wheat germ agglutinin (WGA), and fucose-binding protein (FBP). Lectin-mediated cell agglutination was inhibited, and reversed in the presence of specific lectin-binding saccharides. Cells were agglutinated randomly with all lectins suggesting a uniform distribution in the trypanosome cell surface of the lectin-binding saccharide ligands. The BSF and CF were not agglutinated with phytohaemagglutinin-M, phytohaemagglutinin-P, or influenza virions. Living trypsinized BSF, which lacked a surface coat, gave agglutination results with the lectins identical to those obtained with living intact BSF. Glutaraldehyde- or formalin-fixed intact and trypsinized BSF gave results similar to those obtained with living cells and SBA, WGA, and FBP. However, intact, fixed BSF gave much lower agglutination levels with Con A than trypsinized-fixed, living intact, or living trypsinized BSF cells. Intact and trypsinized living and fixed CF gave identical agglutination results with each of the lectins. Living and fixed cells treated extensively with the glycoside hydrolases alpha-amylase, dextranase, and neuraminidase gave results with the lectins identical to those obtained with untreated cells. Con A bound at the cell surface was visualized with an iron-dextran (Fe-Dex) conjugate. Dense iron marker particles were distributed randomly in the intact BSF surface coat. The Con A-bound Fe-Dex marker was present on the pellicular and flagellar membrane outer lamina of trypsinized BSF and intact CF cells. Horseradish peroxidase (HRPO)-diaminobenzidine (DAB) coupled reactions also were used to visualize surface-bound Con A. Dense Con A-HRPO-DAB deposits were present uniformly in the BSF surface coat, and on the membranes of trypsinized BSF and intact CF trypanosomes. SBA and WGA were conjugated to HRPO and these used in DAB-coupled reactions at the ultrastructure level. Results obtained with the HRPO-conjugated lectins were similar in surface localization and distribution to those obtained with the Con A-HRPO-DAB preparations. Treatment of BSF and CF with the several glycoside hydrolases produced no apparent enhanced or reduced reactivity for the lectins in any of the fine-structure cytochemistry experiments. The cumulative results indicate that ligands similar or identical to alpha-D-mannose, N-acetylgalactosamine, and N-acetylglucosamine, and alpha-L-fucose are constituents in the extracellular surface coat matrix of T. lewisi BSF. Similar conclusions also pertain to the pellicular and flagellar membrane ligands of the BSF and CF cells. Moreover, results obtained with the glycoside hydrolases and influenza virions suggest that the T. lewisi cell surface ligands are not associated directly with repetitively bonded alpha-I,4- and alpha-I,6-D-glucans or sialic acid moieties.

The Cell Surface of Trypanosoma musculi Bloodstream Forms. II. Lectin and Immunologic Studies*

Living Trypanosoma musculi bloodstream trypomastigotes were agglutinated specifically with concanavalin A (ConA), wheat germ agglutinin (WGA), soybean agglutinin (SBA), and fucose-binding protein (FBP). The agglutination with these lectins of living cells from which the coat was removed by trypsinization was the same as with intact trypanosomes. Glutaraldehyde or formalin fixation did not affect the results with regard to agglutination with WGA, SBA, and FBP, but lower agglutination with ConA was observed upon fixation. By using a dense iron-dextran marker many fewer ConA marker particles were localized at the fine structural level in the intact than in trypsin-treated trypanosomes. On the basis of the results obtained by agglutination and electron microscopy, it is likely that fixation cross-links intact surface-coat components associated with the ConA binding sites. It is evident from the studies in which lectins were employed that ligands containing alpha-D-mannose, N-acetylglucosamine, N-acetylgalactosamine, and alpha-L-fucose are randomly distributed in the outer surface of the pellicular and flagellar membranes of T. musculi trypomastigotes. Results obtained with alpha-amylase- and dextranase-treated trypanosomes suggested that lectin-binding sugar ligands in the cell surface were not directly associated with alpha-1,4 or repetitive alpha-1,6 glucan-bonded polysaccharide moieties. Similar conclusions can be drawn on the basis of neuraminidase treatment with regard to N-acetylated neuraminic acids. After thorough washing, intact, but not trypsin-treated trypomastigotes were agglutinated specifically with antisera against whole mouse serum and against mouse IgG. Evidently, adsorbed constituents of mouse serum are regular components of the T. musculi surface coat. After incubation in dilute whole mouse serum or in mouse IgG solutions, also the trypsinized cells were agglutinated by the 2 antisera. No such results were obtained with trypsinized cells incubated in serum-free buffers. It was concluded that mouse serum proteins were readily readsorbed on, and firmly bound to the trypsinized cells' surfaces. Specific agglutinations were obtained with trypsinized cells after incubation in dilute rat, rabbit, bovine, and human sera and in solutions of rat and rabbit IgG in reactions with the corresponding antisera. It seems, therefore, that the host serum proteins are adsorbed nonspecifically to the cell surface of trypsinized T. musculi bloodstream forms. When examined by electron microscopy, the intact trypomastigotes were covered by an ununiform, slightly granular, fibrillar extracellular coat, applied to the entire outer lamina of the pellicular and flagellar membranes. No indication of such a coat was noted in the trypsinized organisms. Flocculent surface coat-like matrix could, however, be discerned in cells which, after trypsinization, were incubated in various sera.

Comparison of early embryonic and differentiating cell surfaces: Interaction of lectins with plasma membrane components

1. 1. Cells of the unincubated as well as those of primitive streak chick blastoderm, which are preparing for or are involved in morphogenetic movements, are agglutinated by wheat germ agglutinin, Ricinus communis agglutinin and concanavalin A, but not by fucose-binding protein. 2. 2. Agglutination of these cells with soybean agglutinin occurs only after neuraminidase treatment, while that induced by concanavalin A, wheat germ and Ricinus communis agglutinins is not affected. 3. 3. Trypsin treatment of blastoderm cells had no effect on lectin-mediated agglutination. 4. 4. In contrast, cells derived from 10- and 12-day differentiating chick liver were agglutinated by wheat germ agglutinin only after trypsinization. 5. 5. Mechanically dissociated embryonic liver cells, which are not agglutinated, more 3H-labelled wheat germ agglutinin per cell than trypsinized cells, suggesting that during differentiation there may be a spatial reorganization of wheat germ agglutinin receptors within the plasma membrane. 6. 6. Membranes isolated from the above cell types were examined by analytical polyacrylamide gel isoelectric focusing and, in combination with affinity chromatography using wheat germ agglutinin conjugated to agarose, membrane material in the differentiating liver membrane, which binds to this lectin, was identified.

The effect of lectins on the migration of lymphocytes in vivo

The aim of the present study was to determine whether the cell-surface structures involved in the migration of lymphocytes to lymphoid organs are related to the structures on lymphocytes which interact with plant lectins. Cells from the spleen, lymph nodes, thymus, and bone marrow of A and C3H mice strains were labeled with 51Cr, exposed in vitro to various concentrations of lectins, and injected intravenously to syngeneic recipients. Exposure of lymphocytes of various sources to Con A inhibited their migration to lymph nodes to a significantly greater extent than their migration to the spleen. Various concentrations of PHA inhibited the migration of lymphocytes to the spleen and lymph nodes to a similar degree. The migration of thymus cells was affected by lower concentrations of either Con A or PHA than the migration of the other cell types. Fucose-binding protein and wheat germ agglutinin failed to affect lymphocyte migration. The inhibitory effect of Con A could be abrogated by α-methyl-mannopyranoside added either simultaneously with Con A or following exposure of the cells to Con A. In contrast, the inhibitory effect of PHA could not be abolished by the addition of N-acetyl-galactosamine. Secondary transfer experiments with lymphocytes localizing in the spleen and lymph nodes of primary hosts indicate that Con A does not eliminate a subpopulation of lymph-node-seeking lymphocytes, but rather interferes specifically with the process involved in the localization of lymphocytes to lymph nodes.