Receptors For Soybean Agglutinin Research Articles

Differential redistribution of lectin receptor classes on clonal rat myotubes and myoblasts.

To evaluate the relative mobilities of cell surface glycoconjugates during myogenesis we have studied the redistribution of fluorescein-conjugated plant lectins on L6 rat myogenic cells. Previous experiments had demonstrated that the receptors for the lectins soybean agglutinin (SBA), wheat germ agglutinin, concanavalin A and Lens culinaris agglutinin all were relatively uniformly distributed on both myoblasts and myotubes, and that SBA receptors were capable of rapid redistribution on myotubes but not myoblasts at 4 degrees C (Sawyer & Akeson, 1983). Here we show that when SBA-labelled myoblasts are incubated at 37 degrees C, or for extended times at 4 degrees C, the lectin aggregates as on myotubes. So it appears that SBA-binding components show a quantitative rather than qualitative change in their mobility during L6 differentiation. In addition, the redistribution of the three other lectins on myoblasts and myotubes was either less prominent (i.e. showing fewer apparent surface clusters) or occurred less rapidly than with SBA. None of these three lectins showed striking differences in mobility between myoblasts and myotubes. Thus, it appears that SBA binds to a subset of surface glycoconjugates that is relatively highly mobile, and that this mobility is specifically enhanced with differentiation.

In vitro activation of bone marrow-derived T- and non-T-cell subsets by α-fetoprotein

α-Fetoprotein (AFP) is a major serum glycoprotein during embryonic and early postnatal life. A number of diverse biologic functions have been attributed to AFP, including osmotic and carrier function and immunosuppressive activity. In this study we demonstrate that AFP selectively stimulates in vitro proliferation of two distinct subsets of adult murine bone marrow cells. One population of AFP-reactive bone marrow cells expresses surface receptors for soybean agglutinin (SBA) lectin. SBA + bone marrow cells are resistant to cytotoxic pretreatment with T-cell-specific antisera and are not retained on Ig-anti-Ig affinity columns. The absence of conventional T- and B-cell markers, coupled with the presence of SBA receptors, suggests that AFP-activated non-T bone marrow cells may belong to an immature set of B lymphocytes. A second population of AFP-responsive bone marrow cells expresses the Thy-1 + Lyt1 +2 − phenotype characteristic of conventional mature adult T helper cells. The potential physiological relevance of the mitogenic effects of AFP on bone marrow cells with respect to immunoregulatory processes in the fetal/newborn environments is discussed.

Lectin separation of nonlymphoid suppressor cells induced by total lymphoid irradiation.

Suppression of the mixed lymphocyte reaction (MLR) exerted by splenocytes derived from mice treated with fractionated total lymphoid irradiation (TLI, 200 rds x 8) was analyzed by various criteria in order to characterize the phenotype of the cell type(s) responsible for suppression. TLI-induced suppressor cells could not be eliminated by removal of cells bearing surface immunoglobulin, Thy-1, Lyt-2 and TL, and thus could not be ascribed to lymphocytes of the B or T cell lineage. Suppressor cells were large, and nonadherent to nylon wool, Sephadex G-10 and plastic surfaces. Suppressor activity of TLI splenocytes was predominantly located in fractions of cells bearing receptors for soybean agglutinin (SBA), peanut agglutinin (PNA) or both lectins. SBA+, PNA+, sequentially agglutinated (SBA followed by PNA) SBA+PNA+ and (PNA followed by SBA) PNA+SBA+ suppressor cells were radioresistant upon exposure to 1000 rds in vitro. Cells bearing the receptor for PNA but lacking that for SBA (PNA+SBA-) had sharply reduced suppressor activity. However, a radiosensitive PNA- suppressor cell subset was also documented in the spleen of TLI-treated mice. Thus, suppressor cells could best be physically separated from nonsuppressors by the SBA lectin. SBA+ suppressor cells were found, by scatter analysis, to include the population of large cells characteristic of TLI splenocytes, whereas SBA- cells were much smaller and almost exclusively devoid of suppressive capacity. The PNA receptor was found to further dissect the SBA+ suppressor cells into two distinct subpopulations: radioresistant SBA+PNA+ cells and radiosensitive SBA+PNA- cells. In summary, we suggest here the presence of at least two suppressive populations induced by TLI: radioresistant SBA+, PNA+, SBA+PNA+ or PNA+SBA+ cells, and radiosensitive PNA- and SBA+PNA- cells. Similar subsets of MLR suppressor cells can be isolated from normal bone marrow cells and splenocytes of nude mice, suggesting that suppression is mediated by large, immature, nonlymphoid cells which might migrate from shielded bone marrow compartments into the spleen of TLI-treated mice.

Surface Galactolipids of Wheat Protoplasts as Receptors for Soybean Agglutinin and Their Possible Relevance to Host-Parasite Interaction

Soybean agglutinin, a lectin specific for N-acetyl-d-galactosamine and d-galactose, was previously shown to agglutinate wheat leaf protoplasts (Larkin 1978 Plant Physiol 61: 626-629). We investigated the receptors for soybean agglutinin on the plasma membrane of these protoplasts. After treatment of the protoplasts with galactose oxidase, they were no longer agglutinated by the lectin, whereas upon reduction of the galactose oxidase-treated protoplasts with sodium borohydride the susceptibility to agglutination was restored. Analysis of the glycolipids of protoplasts surface labeled by the galactose oxidase-borotritide method, revealed that the radioactivity was mainly present in monogalactosyldiglyceride and digalactosyldiglyceride. The same galactolipids were identified as the only receptors for soybean agglutinin by direct binding of the (125)I-labeled lectin to a thin layer chromatogram of the glycolipids of wheat leaf protoplasts.

Redistribution of cell surface receptors induced by cell-cell contact.

Cell surface lectin receptors underwent rapid redistribution after embryonic Xenopus myotomal muscle cells were manipulated into contact in culture. Soybean agglutinin (SBA) receptors became highly concentrated at the contact area and concanavalin A (Con A) and ricin receptors were depleted at the same region. The accumulation of SBA receptors was greatly reduced by the presence of SBA specific sugars in the incubating medium, by precontact binding of SBA to the surface and by lowering the temperature, but it was unaffected by prolonged treatments with metabolic inhibitors. It is culture-age dependent: older cultures showed a markedly reduced extent of accumulation, and the high accumulation resulting from contact made in younger cultures disappeared with time in culture. These findings are consistent with the notion that specific molecular interaction between the contacting surfaces results in a redistribution of preexisting rapidly diffusing surface receptors. In support of this notion, ligand-free SBA and Con A receptors were shown to be laterally mobile in the membrane, and at least a subpopulation of the SBA receptors contains physically distinct molecules from the Con A receptors. We suggest that such contact-induced redistribution of various surface components may play a role in the interaction between embryonic cells.

Allogeneic hemopoietic stem cell transplantation using mouse spleen cells fractionated by lectins: in vitro study of cell fractions.

Mouse spleen cells sequentially agglutinated by soybean agglutinin (SBA) and peanut agglutinin (PNA) previously had been shown to be sufficiently depleted of graft-versus-host activity to allow reconstitution of lethally irradiated allogeneic recipient mice. We have now tested the extent of T-cell depletion in this cell fraction by various in vitro assays, including cytotoxicity testing with anti-Thy-1 antiserum, mitogenic response to the T-cell mitogens concanavalin A and phytohemagglutinin and allogeneic responsiveness in the mixed lymphocytes culture assay. By these criteria the SBA+, PNA+ spleen fraction, used previously in the in vivo experiments, was found to possess about 1% T-cell contamination. The slight contamination with T cells previously found in the singly agglutinated SBA fraction can be removed by a second fractionation with SBA, thus eliminating the possibility that a minor T-cell subpopulation bears receptors for SBA. Finally, we demonstrated that the twice-agglutinated fraction, by SBA and PNA or by SBA alone, contains a significant number of prothymocytes, thereby indicating that mouse prothymocytes bear receptors for both SBA and PNA. The implication of these findings to bone marrow transplantation in humans is discussed.

Distribution of cell surface saccharides on pancreatic cells. II. Lectin-labeling patterns on mature guinea pig and rat pancreatic cells.

The surface saccharide composition of collagenase-dispersed pancreatic cells from adult guinea pig and rat glands was examined by using eight lectins and their ferritin conjugates: Concanavalin A (ConA); Lens culinaris (LCL); Lotus tetragonolobus (LTL); Ricinus communis agglutinins I and II (RCA I, RCA II); Soybean agglutinin (SBA); Ulex europeus lectin (UEL); and wheat germ agglutinin (WGA). Binding studies of iodinated lectins and lectin-ferritin conjugates both revealed one population of saturable, high-affinity receptor sites on the total cell population (approximately 95% acinar cells). Electron microscopy, however, revealed differences in lectin-ferritin binding to the plasmalemma of acinar, centroacinar, and endocrine cells. Whereas acinar cells bound heavily all lectin conjugates, endocrine and centroacinar cells were densely labeled only by ConA, LCL, WGA, and RCA I, and possessed few receptors for LTL, UEL, and SBA. Endocrine and centroacinar cells could be differentiated from each other by using RCA II, which binds to centroacinar cells but not to endocrine cells. Some RCA II receptors appeared to be glycolipids because they were extracted by ethanol and chloroform-methanol in contrast to WGA receptors which resisted solvent treatment but were partly removed by papain digestion. RCA I receptors were affected by neither treatment. The apparent absence of receptors for SBA on endocrine and centroacinar cells, and for RCA II on endocrine cells, was reversed by neuraminidase digestion, which suggested masking of lectin receptors by sialic acid. The absence of LTL and UEL receptors on endocrine and centroacinar cells was not reversed by neuraminidase. We suggest that the differential lectin-binding patterns observed on acinar, centroacinar, and endocrine cells from the adult pancreas surface-carbohydrate-developmental programs expressed during morphogenesis and cytodifferentiation of the gland.

Ultrastructural and lectin binding changes during the formation of the animal dimple in oocytes of Discoglossus pictus (Anura)

In Discoglossus pictus eggs, the animal dimple is the only place where fertilization can occur. The carbohydrate composition of the dimple membrane was investigated using fluorescent-labeled lectins. Receptors for soybean agglutinin (SBA) and wheat germ agglutinin (WGA) are specifically localized on the dimple walls, whereas fucose-like residues are only present at the bottom of the dimple. This lectin binding pattern is transient since it only appears when the dimple is completely formed and disappears immediately after fertilization. The formation of the dimple requires an increase in surface. Our ultrastructural studies suggest that membrane growth occurs through the insertion of vesicles into the plasma membrane. We hypothesize that the lectin-binding glycocomponents that we observed are inserted along with the vesicles which fuse into the membrane. These vesicles most probably originate from the annulate lamellae and cisternal stacks present in full-grown oocytes. The possibility that the surface features of the dimple, such as the microvilli, the complex glycocalyx, and particulary the neutral carbohydrate residues (fucose-like), might favor sperm-egg fusion is discussed.

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In Discoglossus pictus eggs, the animal dimple is the only place where fertilization can occur. The carbohydrate composition of the dimple membrane was investigated using fluorescent-labeled lectins. Receptors for soybean agglutinin (SBA) and wheat germ agglutinin (WGA) are specifically localized on the dimple walls, whereas fucose-like residues are only present at the bottom of the dimple. This lectin binding pattern is transient since it only appears when the dimple is completely formed and disappears immediately after fertilization. The formation of the dimple requires an increase in surface. Our ultrastructural studies suggest that membrane growth occurs through the insertion of vesicles into the plasma membrane. We hypothesize that the lectin-binding glycocomponents that we observed are inserted along with the vesicles which fuse into the membrane. These vesicles most probably originate from the annulate lamellae and cisternal stacks present in full-grown oocytes. The possibility that the surface features of the dimple, such as the microvilli, the complex glycocalyx, and particulary the neutral carbohydrate residues (fucose-like), might favor sperm-egg fusion is discussed.