Flow cytometric analysis of the binding of eleven lectins to human T- and B-cells and to human T- and B-cell lines

Characterization of lectin isolated from Momordica charantia seed as a B cell activator

Lectin isolated from the seeds of Momordica charantia (MCL) is a galactose-specific glycoprotein. To investigate the effects of MCL on cell activation, we analyzed the responses of BALB/c splenocytes, thymocytes, T cells and B cells on MCL stimulation. Proliferation assays showed that MCL selectively stimulates the B cell subset of splenocytes (p<0.05) in a dose and time dependent manner and that this activation proceeds without the involvement of T cells. Flow cytometric analysis revealed that the fluorescein isothiocyanate (FITC)-labeled MCL binds to B cells, which was inhibited by specific sugars, including galactose. Mouse immunoglobulin (Ig) was able to inhibit MCL-induced proliferation of mouse B cells, suggesting MCL stimulates B cell activation via membrane Ig in the B cell surface. Moreover, after 96-h co-culture, MCL triggered splenocytes to produce a large amount of non-specific IgM in culture supernatants (p<0.01). Additionally, MCL was shown to up-regulate the cell activation marker CD86, in a B cell subpopulation distinct from that affected by LPS. These data suggest that MCL is a T cell-independent B cell activator and a polyclonal Ig inducer, and provide further information on the immunomodulatory effect of MCL.

Lectin ligands on human dendritic cells and identification of a peanut agglutinin positive subset in blood

As only a few cell surface markers for dendritic cells (DC) have been identified to date, this study examined the expression of ligands for lectin on different human DC populations. The ability of Concanavalin A (Con A), Wheat Germ Agglutinin (WGA), peanut agglutinin (PNA), and Helix pomatia (HPA) to bind to cell lines and PBMC and DC populations was analyzed by flow cytometry and specificity of binding confirmed using inhibitory and noninhibitory sugars. The cell lines showed non-lineage-restricted binding with Con A and WGA, independent of sialidase treatment. HPA and PNA bound to a restricted number of lines, but showed broad reactivity after sialidase treatment. The peripheral blood mononuclear cells (PBMC) and directly isolated blood DC, activated CD83(+) blood DC, epidermal Langerhans cells (LC), and monocyte-derived DC (Mo-DC) showed strong binding of Con A and WGA, both before and after sialidase treatment. No HPA binding ligands were detected on PBMC populations, including directly isolated blood DC. Following sialidase treatment CD3(+), CD16(+), and a subset of CD19(+) lymphocytes bound HPA. The lectin PNA bound weakly to CD14(+) monocytes and a subpopulation of circulating DC that were HLA-DR(hi)CDw123 Dr(hi)CDw123(dim)/(neg)CD11c(+). The HLA-DR(mod)CDw123(hi)CD11c(neg) subpopulation did not bind PNA. Without sialidase treatment LC expressed both HPA and PNA ligands, but these were either absent on activated CD83(+) blood DC or weakly expressed on Mo-DC. Following sialidase treatment PBMC populations, activated CD83(+) blood DC, and Mo-DC became PNA positive. Thus human DC express several lectin ligands and PNA binding identifies a subset of blood DC. That may reflect discrete changes associated with stages of DC development or functional maturation.

Uvomorulin mediates calcium-dependent aggregation of islet cells, whereas calcium-independent cell adhesion molecules distinguish between islet cell types

Rat islets of Langerhans are organized as a core of B-cells surrounded by non-B-cells. It is believed that cell type segregation during histogenesis is the result of the differential expression of cell adhesion molecules (CAMs). Since we have previously shown that in contrast to non-B-cells, homotypic adhesion of pancreatic B-cells is dependent on the presence of Ca2+, the possibility exists that Ca(2+)-dependent CAMs (cadherins) might be in part responsible for islet topography. We now demonstrate that after selective removal of Ca(2+)-independent CAMs from the surface of islet cells by mild trypsin/Ca2+ digestion (TC-treatment), there is no significant difference in homotypic adhesion between sorted B- and non-B-cells in the presence of calcium, suggesting an identical deployment of cadherins. Flow cytometric analysis reveals high levels of uvomorulin on both B- and non-B-cells, without any difference between the two populations. On a "1 to 100" scale, B-cell aggregation in the presence of Ca2+ was decreased by anti-uvomorulin Fab fragments from 67 +/- 4 to 25 +/- 3 (mean +/- SEM, n = 4, P less than 0.01). This level is not different from the degree of B-cell aggregation seen in the presence of 0.5 mM EDTA (22 +/- 2). Aggregation of non-B-cells was only slightly decreased by anti-uvomorulin Fab fragments (from 69 +/- 3 to 52 +/- 4). However, after TC-treatment, homotypic cell aggregation of both B- and non-B-cells was completely inhibited by anti-uvomorulin Fab fragments. Thus, uvomorulin appears to be the only functional cadherin on islet cells, and cell type aggregation properties diverge only by virtue of higher levels of Ca(2+)-independent CAMs on non-B-cells. Fab fragments with the property of perturbing islet cell aggregation in the absence but not in the presence of calcium also prevented pseudoislet organization in vitro, suggesting that Ca(2+)-independent CAMs play the major role in islet cell type segregation. In conclusion, the results show that uvomorulin is responsible for the Ca(2+)-dependent aggregation of islet cells and suggest that the cellular organization within islets or pseudoislets results from the different level of Ca(2+)-independent CAMs on islet cell types.

Differences in aggregation properties and levels of the neural cell adhesion molecule (NCAM) between islet cell types

Cells within rat islets of Langerhans are typically organized as a core of B-cells, surrounded by the other cell types. When mixed in culture, primary islet cells and insulinoma (RIN2A) cells form aggregates where B-cells are centrally located, surrounded by non-B-cells, while RIN-cells segregate as the outermost layer. To gain insight into the molecular basis underlying this nonrandom cellular organization, the aggregation properties of the three cell populations were studied. Isolated islet cells were separated into B-cells and non-B-cells by autofluorescence-activated cell sorting (FACS). In a short-term aggregation assay, primary B-cell aggregation in the absence of calcium was only 19 +/- 3.7%, compared to the 67 +/- 2.9% seen in the presence of calcium (mean +/- SEM; P less than 0.001; n = 7). By contrast, non-B-cell aggregation and RIN cell aggregation in the absence of calcium (62 +/- 2 and 66 +/- 2%, respectively) were only slightly less than with calcium (70 +/- 3 and 76 +/- 3%). The surface density of the Ca2(+)-independent neural CAM (NCAM) was therefore measured by flow cytometry and found to be 2.64 +/- 0.82-fold higher in non-B-cells, compared to that in B-cells (P less than 0.01; n = 3). Even higher levels were found on RIN cells. In the three cell types, NCAM-140 was the only molecular form detected by immunoblotting. In conclusion, differences in the calcium dependency of aggregation and in the levels of NCAM are demonstrated among islet B-cells, non-B-cells, and RIN cells. Because cell-cell adhesion is crucial for the maintenance of adult tissue, these aggregation specificities might contribute to the concentric segregation of islet cell types in culture and to the nonrandom distribution of cells within rat islets.

Binding of mitogenic plant lectins to human lymphocytes. Flow cytometric analysis

Several plant lectins, such as phytohaemagglutinin (PHA), pokeweed mitogen (PWM), concanavalin A (ConA), Maclura pumifera (MPA) and Pisum sativum agglutinin (PSA), are potent mitogens for human lymphocytes. The pattern of activation induced, however, is not uniform for all mitogenic lectins. The different biological effects following lectin activation of human lymphocytes might be due at least in part to a differential binding of the various lectins to lymphocyte subsets. We have therefore studied the binding of five mitogenic plant lectins, namely PHA, PWM, ConA, MPA and PSA to three major human lymphocyte subsets as defined by anti-CD4, anti-CD8 and anti-CD16 monoclonal antibodies. Dual colour, flow cytometric analysis employing PE-conjugated monoclonal antibodies and FITC-conjugated lectins revealed that all subsets uniformly show high binding of PHA, whereas two different populations, one high binding and the other low binding, can be detected with PWM, ConA, MPA and PSA.

Fluorescein Isothiocyanate-Labeled Lectin Analysis of the Surface of the Nitrogen-Fixing Bacterium Azospirillum brasilense by Flow Cytometry

The cell surface of Azospirillum brasilense was probed by using fluorescein isothiocyanate (FITC)-labeled lectins, with binding determined by fluorescence-activated flow cytometry. Cells from nitrogen-fixing or ammonium-assimilating cultures reacted similarly to FITC-labeled lectins, with lectin binding in the following order: Griffonia simplicifolia II agglutinin > Griffonia simplicifolia I agglutinin > Triticum vulgaris agglutinin > Glycine max agglutinin > Canavalia ensiformis agglutinin > Limax flavus agglutinin > Lotus tetragonolobus agglutinin. The fluorescence intensity of cells labeled with FITC-labeled G. simplicifolia I, C. ensiformis, T. vulgaris , and G. max agglutinins was influenced by lectin concentration. Flow cytometry measurements of lectin binding to cells was consistent with measurements of agglutination resulting from lectin-cell interaction. Capsules surrounding nitrogen-fixing and ammonium-assimilating cells were readily demonstrated by light and transmission electron microscopies.

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.

Lectins as markers for eosinophilic leukocytes

Lectin from Griffonia simplicifolia (GSA-I) and soybean (SBA) are reliable markers for human eosinophils. In this study we have shown that fluorochrome labeled GSA-I and SBA can be used for specific labeling of eosinophils in paraffin embedded tissue sections, in peripheral blood smears and in cell suspensions prepared for flow cytometry. These two lectins are useful diagnostic reagents which could be applied for further characterization of cytoplasmic components selectively found in human eosinophils.

Griffonia simplicifolia I isolectin as a functionally monovalent probe for use in flow cytometry

The inherent tendency of lectins to agglutinate cells has limited their use as reagents for the detection of carbohydrate groups on cell surfaces by flow cytometry. In the current study, we demonstrate a method for the use of a fluoresceinated tetrameric isolectin (Griffonia simplicifolia I-A3B, FITC-GS I-A3B) as a functionally monovalent, nonagglutinating probe in flow cytometry. This isolectin contains three A subunits and one B subunit. Both types of subunits bind alpha-D-galactopyranosyl (alpha-D-galp-) end groups with similar affinities; however, the A subunits have a 1,000-fold greater affinity for N-Acetyl-D-galactosamine (GalNAc) than does the B subunit. The addition of low (1-2 mM) concentrations of GalNAc to the FITC-GS I-A3B isolectin results in blockage of the three A subunits without significantly affecting the B subunit; this yields a functionally monovalent probe for the detection of cell surface alpha-D-Galp end groups. This approach has been used to examine two types of cells: Ehrlich ascites tumor cells and rat alveolar macrophages, both of which are known to express cell surface alpha-D-Galp end groups. Lectin binding, as determined by number of positive cells and fluorescence intensity, was dependent upon concentration of the lectin and haptenic sugar. Specificity of the staining was demonstrated by the ability of methyl alpha-D-galactopyranoside (Met alpha-D-Galp) to abolish the binding of the lectin to the cells. Elimination of both GalNAc and Met alpha-D-Galp from the staining solution resulted in agglutination of the cells, indicating that the A subunits were active in the absence of GalNAc.

Progressive muscular dystrophy (Duchenne): biochemical studies by flow-cytometry

The peanut lectin (PNL) receptor density of the cell membrane and several metabolic parameters of cultured fibroblasts of normal human individuals and of patients with muscular dystrophy were measured by simultaneous two and three parameter flow cytometry. The PNL-receptor density was significantly decreased on muscular dystrophy fibroblasts (between 20.7 and 33.6%) as compared to normal fibroblasts. The cell volume, the esterase activity, the intracellular pH, and the percentage of proliferating cells of both types of fibroblasts were not significantly altered. The mean cell volume of different fibroblast cultures varied between 2500 and 6000 micron 3. The concentration of the intracellular esterase activity of fibroblasts was low (0.169 relative units) as compared to lymphocytes and granulocytes of the peripheral blood (1.56 and 2.17 relative units). The fibroblasts had an acidic intracellular pH of 6.52 while lymphocytes and granulocytes had basic pH values of 7.30 and 7.17. Some of the fibroblasts were in the S + G2/M phase of the cell cycle (20%). The study shows that the measurement of biochemical parameters of vital and fixed single fibroblasts by flow-cytometry is of great interest for the recognition of differences between normal individuals and muscular dystrophy patients.