The expression of specific sialyltransferase genes has been shown to be regulated in a cell type-specific manner(1, 2, 3) . In the thymus, the site of maturation and selection of T cells, a number of reports have demonstrated that the pattern of cell-surface sialylation changes as thymocytes mature(4, 5, 6, 7) . The presence or absence of specific sialyloligosaccharides on various types of cells may result from differential expression of sialyltransferases(8, 9, 10) , from differential expression of specific glycoprotein acceptors utilized by these transferases(11) , or from competition among glycosyltransferases for various acceptors(12, 13, 14, 15) .

Our laboratory has demonstrated that, in the human thymus, regulated expression of two glycosyltransferases, both of which modify O-glycans, correlates directly with cell-surface glycosylation phenotype. Expression of the core 2 Gal1, 3GalNAc 1,6GlcNAc-transferase was highest in subcapsular and cortical thymocytes, and the level of enzyme expression correlated precisely with the ability of thymocytes to bind a monoclonal antibody that recognizes core 2 O-glycans created by this enzyme(16) . Similarly, the Gal1,3GalNAc 2,3-sialyltransferase was highly expressed by subcapsular and medullary thymocytes, but not by cortical thymocytes, and expression of this enzyme correlated with the loss of cell-surface binding sites for the plant lectin peanut agglutinin(17) . Sialylation of cell-surface glycoproteins by the Gal1,3GalNAc 2,3-sialyltransferase blocked the oligosaccharide sequence recognized by peanut agglutinin.

Variation in the level of sialylation of N-glycans has been reported among lymphocyte subsets(11, 18) . In the thymus, murine medullary thymocytes have increased binding sites for the 2,6-linked sialic acid-specific lectin CD22, compared with cortical thymocytes (19, 20) . In addition, Lau and co-workers (21) have demonstrated that subsets of B lymphocytes differ in the pattern of expression of ST6N. ()However, little is known about the pattern of expression of sialyltransferases that modify N-glycans in developing T cells.

The addition of sialic acid to cell-surface glycoproteins is potentially an efficient mechanism for modulating cell-cell interactions during thymocyte development. Endogenous lectins such as galectin-1(16, 22) , CD22(23) , CD23(24) , and L-selectin (25) appear to participate in T cell maturation, activation, or trafficking, and each of these lectins recognizes unique oligosaccharide ligands that require (CD22 and L-selectin) or are inhibited by (galectin-1 and CD23) the presence of sialic acid. To characterize the pattern of sialylation of developing thymocytes, we examined human thymocytes for the ability to bind two sialic acid-specific lectins, Sambucus nigra agglutinin (SNA) (26) and Maackia amurensis agglutinin (MAA) (27) , which preferentially bind to 2,6- and 2,3-linked sialic acids, respectively, and compared the pattern of lectin reactivity with the pattern of expression of the relevant sialyltransferase enzymes (28, 29) during thymocyte maturation.

EXPERIMENTAL PROCEDURES

Cells and Tissue Samples

Flow Cytometry

Thymocytes and PBMC (100 µl at 5 10 cells/ml) in 0.01 M sodium phosphate, 0.15 M NaCl, 1% BSA, and 0.01% sodium azide (PBA buffer) were combined with 50 µl of lectin or antibody at the appropriate dilution in PBA buffer and incubated on ice for 60 min. For single-color analysis, cells were washed twice with cold PBA buffer and analyzed directly with conjugated antibodies or were resuspended in 50 µl of PBA buffer containing FITC-labeled avidin (diluted 1:300 in PBA buffer) for SNA and MAA. For two-color analysis, cells were incubated with biotin-conjugated lectin in the first step and then with FITC-labeled avidin in the second step and with the PE-conjugated CD3 reagent in the third step. Control samples containing biotin-labeled BSA or an isotype-matched irrelevant murine antibody were included for each sample. After the final washing, cells were resuspended in PBA buffer containing 1 µg/ml 7-aminoactinomycin D (Calbiochem) to identify nonviable cells. Samples were incubated for 20 min at 4 °C prior to acquisition on a FACScan flow cytometer (Becton Dickinson).

In Situ Hybridization

Sections of thymus (6 µm) on acetylated glass slides were treated with proteinase K and hybridized with the digoxigenin-labeled probes exactly as described(17) . Hybridization was detected by an anti-digoxigenin-alkaline phosphatase conjugate (Boehringer Mannheim), followed by overnight development with the chromogenic substrate nitro blue tetrazolium/5-bromo-4-chloro-3-indolyl phosphate (Bio-Rad). Color development was stopped after 12 h.

Immunohistochemistry

Lectin and Western Blots

RESULTS

The thymus contains T cell precursors at various stages of maturation. To examine changes in the sialylation of N-linked oligosaccharides during thymocyte maturation, we used two sialic acid-specific lectins that have been shown to discriminate between two linkages on N-glycans. Biotinylated MAA and SNA were bound to the surface of freshly isolated human thymocytes, and the cells were analyzed by flow cytometry. As shown in Fig. 1A, the MAA lectin bound to the entire population of thymocytes (solid line). The level of MAA binding to thymocytes was slightly higher than that seen with mature peripheral blood T cells (dotted line).

Figure 1: Binding of sialic acid-specific lectins differs among T cell subsets. Thymocytes (solid line) and PBMC (dotted line) were stained with biotin-conjugated MAA or SNA (diluted 1:100 in PBA buffer) and FITC-labeled avidin and analyzed by flow cytometry. A, reactivity of thymocytes and PBMC with the MAA lectin, which recognizes SA2,3Gal sequences; B, reactivity of thymocytes and PBMC with SNA, which recognizes SA2,6Gal sequences.

In contrast, when the binding of SNA to thymocytes was examined, two distinct populations of cells were observed (Fig. 1B). The majority of the cells did not bind appreciable levels of SNA, compared with background staining with biotin-labeled BSA (biotin-labeled BSA staining not shown). However, a small population of SNA cells were present. These cells bound the SNA lectin at a level comparable to that observed for peripheral blood T cells (dotted line). These data suggested that expression of the SA2,6Gal sequence was restricted to a discrete subset of thymocytes.

The human thymus can be divided into three major functional and anatomic compartments(33) . The subcapsular cortical cells represent the most recent immigrants from the bone marrow, and they do not express T cell receptor (CD3). The cortical thymocytes are immature cells undergoing T cell receptor gene rearrangement, and they express low levels of cell-surface T cell receptor complex (CD3). The medullary cells are mature cells that are poised to emigrate to the peripheral circulation, and they express high levels of T cell receptor complex (CD3). To relate the level of SNA binding to the stage of thymocyte maturation, we performed dual-color flow cytometric analysis of thymocytes using SNA and CD3 antibody. As shown in Fig. 2A, virtually all of the SNA cells were in the CD3 population, while the majority of the CD3 and CD3 cells bound background levels of SNA, compared with biotin-labeled BSA indicated by the dashed line. These results demonstrated that the mature thymocytes were SNA and that the level of SNA binding to these cells did not change appreciably as the T cells emigrated to the peripheral circulation (see Fig. 1B).

Figure 2: Mature thymocytes bind SNA. A, dual-color analysis of thymocytes with SNA (x axis) and CD3-conjugated PE (y axis) by flow cytometry. Cursors (dashed lines) represent background levels of staining and were set using biotin-labeled BSA and FITC-labeled avidin for the x axis and an isotype-matched PE-conjugated irrelevant murine monoclonal antibody for the y axis. The CD3 cells represent the most mature thymocyte subset and were the only population that stained with SNA. B, treatment of thymocytes with cytokines, which drive T cell maturation and proliferation, results in increased binding of SNA to the cell surface. Freshly isolated thymocytes were cultured for 12 days in medium alone or in medium containing the indicated cytokine. Cells were stained with biotin-conjugated SNA and FITC-labeled avidin and analyzed by flow cytometry. The percent of SNA cells in each sample was as follows: control, 45%; IL-2, 77%; IL-4, 77%; and IL-7, 87%.

To further examine the relationship between SNA binding and thymocyte maturation, we evaluated the ability of specific cytokines, which have been shown to induce maturation or proliferation of thymocytes in vitro, to alter the binding of SNA to the cell surface. Treatment of thymocytes with IL-2(31) , IL-4(34) , and IL-7 (30) results in an increase in the number of CD3 cells in culture, which also express CD45RA, another marker of thymocyte maturation. IL-2 induces proliferation of only the mature CD3 cells; IL-4 induces expression of maturation-associated cell-surface markers with minimal proliferation; and IL-7 induces both proliferation and maturation of thymocytes. To assess the effects of these cytokines on SNA binding, thymocytes were cultured with or without cytokine for 12 days and analyzed for the ability to bind SNA. Treatment with all three cytokines resulted in an increase in the percent of SNA cells (Fig. 2B). These data demonstrate that acquisition of the ability to bind SNA is a marker of thymocyte maturation and may be regulated by specific cytokines during T cell development.

Prior work from our laboratory demonstrated that the level of mRNA encoding the Gal1,3GalNAc 2,3-sialyltransferase and the core 2 GlcNAc-transferase correlated precisely with the expression of the relevant oligosaccharide structure on the thymocyte cell surface(16, 17) . To evaluate the relationship between binding of MAA and SNA and expression of mRNA encoding the relevant sialyltransferases, we performed in situ hybridization experiments with sections of human thymus (Fig. 3). As shown in Fig. 3(B and C), hybridization with an antisense RNA probe for ST3N produced uniform staining of all regions of the thymus. The control section, hybridized with a sense orientation probe, demonstrated negligible background staining (Fig. 3A). The uniform expression throughout the thymus of mRNA encoding ST3N correlated precisely with the pan reactivity of thymocytes with MAA (Fig. 1A).

Figure 3: Expression of mRNA encoding ST3N and ST6N in human thymus. Hybridization of digoxigenin-labeled RNA probes was detected by anti-digoxigenin antibody conjugated to alkaline phosphatase. A, control sense orientation probe for ST3N (magnification 40); B and C, antisense probe for ST3N (magnification 40 and 100, respectively); D, control sense orientation probe for ST6N (magnification 40); E and F, antisense probe for ST6N (magnification 40 and 100, respectively). Uniform staining of all regions of the thymic lobules is seen with both antisense probes. c, cortex; m, medulla.

mRNA encoding ST6N was also present in all regions of the thymus (Fig. 3, E and F), although SNA reactivity was restricted to mature thymocytes. No difference in the level of staining with the antisense probe could be discerned among the three anatomic compartments of the thymus. Control sections, hybridized with a sense orientation probe, showed negligible background reactivity (Fig. 3D). In contrast with the correlation between ST3N mRNA expression and MAA reactivity, the detection of mRNA encoding the ST6N enzyme did not correlate with expression of the relevant oligosaccharide sequence on the thymocyte cell surface.

Like ST6N mRNA, the ST6N protein was observed in both cortical and medullary thymocytes, as detected by immunohistochemical staining of thymus sections with a polyclonal antibody to ST6N(28) . Fig. 4demonstrates focal cytoplasmic staining of thymocytes in the cortical (panel A) and medullary (panel B) regions. Although the amount of transferase present in the cells cannot be quantified, these results demonstrate that ST6N is translated in both of these anatomic regions, although only medullary cells bind SNA.

Figure 4: Immunohistochemical detection of ST6N in human thymocytes. Immunoreactive material was detected in focal perinuclear patches in both cortical (A) and medullary (B) thymocytes (magnification 400). Scattered stromal cells in both regions also showed reactivity with the antibody. Control sections, incubated with a preimmune rabbit serum, showed no reactivity (C). In situ hybridization with the antisense (D) and sense (E) orientation probes for ST6N is shown at the same magnification.

Given the lack of anatomic correlation between ST6N expression and the ability of thymocytes to bind SNA, we examined separated populations of immature and mature thymocytes for SNA binding and ST6N expression. To avoid cellular activation that is triggered by CD3 binding, we enriched for immature thymocytes by removing the CD5 mature cells and enriched for mature thymocytes by removing immature CD1 cells. In Fig. 5, the CD1-depleted (CD1) thymocytes are enriched for CD3 cells, with an increased number of cells that are CD45RA, compared with the starting material. The CD5-depleted cells (CD5) are primarily CD3 and CD3. In addition, very few CD45RA cells are present in the CD5-depleted subset.

Figure 5: Isolation of immature and mature thymocyte subsets. Freshly isolated thymocytes were incubated with either CD5 or CD1 antibody, and the cells that bound antibody were removed by magnetic bead separation. The remaining cells were assayed for expression of CD3 and CD45RA, a marker of mature thymocytes. The CD5-depleted (CD5) subset is enriched for CD3 and CD3 cells, while the CD1-depleted (CD1) subset is enriched for CD3 cells (upper panels). Dual-color analysis (lower panels) demonstrates that the mature CD1-depleted cells express significantly higher levels of CD45RA than the immature CD5-depleted cells.

To identify SNA-reactive glycoproteins on mature and immature thymocytes, we performed lectin blotting on extracts of CD1- and CD5-depleted cells. As shown in Fig. 6, SNA bound to a prominent band of M = 200,000 in the total thymocyte extract and in the mature CD1-depleted thymocytes, while this band was significantly reduced in the immature CD5-depleted cells. Treatment of the blot with A. ureafaciens sialidase diminished SNA reactivity of this band, indicating that SNA binding of this glycoprotein was sialic acid-dependent. The reactivity of this glycoprotein correlated with the pattern of SNA binding to thymocytes (Fig. 2), suggesting that this molecule was responsible for the selective binding of SNA by mature thymocytes. Probing of the blot with antiserum to ST6N demonstrated immunoreactive material in all three lanes, although the intensity of staining in the CD1- and CD5-depleted lanes was not identical.

Figure 6: SNA binding and ST6N expression in isolated thymocyte subsets. Equal numbers of immature (CD5) and mature (CD1) thymocyte pools as well as total thymocytes (T) were separated by SDS-polyacrylamide gel electrophoresis and analyzed by Western and lectin blotting. The blot was probed with SNA, with monoclonal antibodies to CD45 and CD45R0, and with affinity-purified antiserum to ST6N (2,6ST) and reprobed with SNA after treatment with A. ureafaciens sialidase. The SNA-reactive band that is sialidase-sensitive is indicated by an arrowhead, and the CD45 isoforms are indicated by arrows.

The relative mobility of the SNA-reactive band in extracts of mature CD1-depleted thymocytes suggested that this glycoprotein was an isoform of CD45. CD45, which constitutes 10% of the total cell-surface glycoproteins on T cells, is highly sialylated(35) . In addition, Hart and co-workers (7) have demonstrated that mature thymocytes have fully sialylated CD45, while immature thymocytes can be sialylated by exogenous ST6N enzyme. To determine whether the SNA-reactive band was CD45, we probed the blot with antibodies to CD45. As shown in Fig. 6, CD45 antibody bound primarily to a band of M = 200,000 in the extracts of total thymocytes and mature CD1-depleted cells, with only faint reactivity seen in the lane containing the immature CD5-depleted cell extract. This band migrated slightly above the band detected by an antibody to the 180-kDa CD45R0 isoform, which was present in approximately equal amounts in both the mature and immature populations. These data indicated that SNA was binding to a maturation-specific isoform of CD45, most likely CD45RA(36) . We were unable to detect any reactivity on this blot with the CD45RA-specific antibody 4KB5 (data not shown); however, Fig. 5demonstrates that CD45RA was present primarily in the mature CD1-depleted cells. These results strongly suggest that CD45RA is a glycoprotein counter-receptor for SNA on mature thymocytes.

DISCUSSION

We have examined the pattern of expression in the human thymus of four glycosyltransferase enzymes, the Gal1, 3GalNAc 2,3-sialyltransferase(17) , the core 2 Gal1,3GalNAc 1,6GlcNAc-transferase(16) , and ST3N and ST6N (Fig. 1Fig. 2Fig. 3). Comparison of the pattern of mRNA expression and the relevant cell-surface glycotype is shown in Table 1. Two conclusions can be drawn from these data. First, the tight control of cell-surface glycosylation in the thymus suggests that specific oligosaccharide sequences participate in distinct functions during thymocyte development. It is striking that, for the four transferases examined, four different patterns of expression were observed. Second, the level of expression of mRNA encoding a particular enzyme does not always correlate with the amount of the relevant oligosaccharide sequence on the cell surface. For the Gal1,3GalNAc 2,3-sialyltransferase, the core 2 Gal1,3GalNAc 1,6GlcNAc-transferase, and ST3N, lectin and monoclonal antibody binding studies demonstrated that specific oligosaccharide sequences were always detected in thymocyte subsets that expressed the cognate transferase mRNA. However, although mRNA encoding ST6N was detected throughout the thymic lobule (Fig. 3), only mature cells bound SNA (Fig. 2A). We detected SNA binding to thymocytes by flow cytometry since histochemical staining of the thymus with SNA revealed staining of stromal structures as well as thymocytes, so that the reactivity of thymocyte subsets was difficult to ascertain by lectin histochemistry (data not shown).

The reactivity of CD3 medullary thymocytes with SNA resembles that found with CD22, a B lymphocyte lectin that recognizes 2,6-linked sialic acid (37) and that can bind to 2,6-linked sialic acid on CD45(23) . The reactivity of CD22 with murine medullary thymocytes suggested that expression of the ST6N enzyme might be limited to mature thymocytes in medulla(19, 20) . However, in situ hybridization, immunohistochemical analyses, and Western blotting (Fig. 3, Fig. 4, and Fig. 6, respectively) demonstrated that the ST6N mRNA and protein were present in both cortical (SNA) and medullary (SNA) thymocytes, suggesting that expression of SA2,6Gal sequences on T cell glycoproteins may be regulated at additional points downstream of enzyme transcription and translation. This same lack of correlation between expression of the ST6N enzyme and SNA reactivity in various cell types has been recently described in human and rat tissues(38) , indicating that the thymus is not unique in this respect.

A number of factors may contribute to differential glycosylation of cell-surface glycoproteins in different cellular subsets. One possibility is that either the donor or acceptor substrate is limiting. In the thymus, it is unlikely that the donor substrate for the ST6N enzyme, CMP-SA, is limiting since subcapsular and cortical thymocytes synthesize the SA2,3Gal sequence detected by MAA. However, specific glycoprotein acceptor substrates preferentially utilized by ST6N may be expressed only in the mature thymocyte population. A number of studies have demonstrated preferential glycosylation of potential acceptor substrates by different transferases(11, 13, 39, 40) . In T cells, Kobata and co-workers (41) found differences in the pattern of sialylation of CD45 and CD11a/CD18; N-glycans on CD45 had exclusively SA2,6Gal sequences (although isoforms were not separated in this study), while N-glycans of CD11a/CD18 had SA2,3Gal sequences. Our results suggest that CD45RA is a preferred acceptor substrate for ST6N in the thymus and that the increased binding of SNA to mature thymocytes results from the dramatic increase in CD45RA expression that accompanies thymocyte maturation(36) .

Another factor that could contribute to differential glycosylation among various cellular subsets is differential expression of enzyme isoforms, as has been shown for ST6N in B lymphoblastoid cell lines (21) . In our in situ hybridization experiments, we used full-length RNA probes to detect mRNA expression in thymus sections (Fig. 3). Thus, we cannot determine whether specific splice variants of the ST6N mRNA were synthesized in the different thymic regions. Future experiments will address whether T cell subsets, like B cell subsets, express different ST6N isoforms.

This study reinforces the observation that differences in glycosyltransferase expression and glycoprotein glycosylation may be found among subsets of cells within a single organ as well as between organs(16, 17) . Prior studies that examined expression of sialyltransferase mRNA in the thymus (3) or cell-surface glycosylation of thymocytes (7, 42, 43) may not have accounted for the relative contribution of different subsets of thymocytes to the total pool of material analyzed. Since the three major subsets of cells found within the thymus have significant phenotypic and functional differences(33) , dissection of these subsets may be important when considering the role of specific oligosaccharides during T cell development.

The coordinated expression of glycosyltransferases and their cognate oligosaccharide sequences on the T cell surface may be critical for proper thymocyte maturation. We have recently found that galectin-1, expressed on thymic epithelial cells, mediated binding of immature T cells to the thymic stroma(16) . Galectin-1 induces apoptosis of immature thymocytes, ()and galectin-1 binding and apoptosis are blocked by antibodies to CD45(16, 44) . Galectin-1 binding to lactosamine, the preferred oligosaccharide ligand, is negatively modulated by the presence of SA2,6Gal sequences on the termini of the oligosaccharide chains(22) . We found that galectin-1 preferentially bound to CD3 and CD3 thymocytes(16) , the subsets that did not bind SNA (Fig. 2A and Table 1). Thus, the ability of thymocyte subsets to bind galectin-1 and the susceptibility of these cells to galectin-1-induced apoptosis may be modulated by the expression of specific oligosaccharide sequences on the cell surface.

The regulation of glycoprotein glycosylation has recently been the subject of intense investigation. Determining the pattern of expression of specific oligosaccharide sequences by normal and neoplastic tissues is relevant to the study of carbohydrate-mediated adhesion in inflammation and metastasis(25) . In addition, manipulation of glycosylation in tissue culture systems is of interest in the production of recombinant glycoproteins, where glycosylation may affect the activity, stability, or immunogenicity of the material(45, 46, 47, 48) . While expression of cDNA encoding a glycosyltransferase in specific cell lines may result in the production of the predicted product(12, 15, 49) , a number of factors, such as enzyme subcellular localization, competition among endogenous and exogenous enzymes for the same acceptors, and availability of acceptor substrates(13, 39, 50, 51, 52) , may affect the pattern of oligosaccharide structures synthesized by the cell.

FOOTNOTES

*

This work was supported in part by grants from the Leukemia Research Foundation (to L. G. B.) and by National Institutes of Health Grants AI-07126 (to N. L. P.), HD-29341 (to C. U.), and CA-16042 (to the Jonsson Comprehensive Cancer Center). The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore by hereby marked ``advertisement'' in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.

§

To whom correspondence and reprint requests should be addressed: Dept. of Pathology and Laboratory Medicine, UCLA School of Medicine, 10833 LeConte Ave., Los Angeles, CA 90024-1732. Tel.: 310-206-5985; Fax: 310-206-0657.

()

The abbreviations used are: ST6N, Gal1,4GlcNAc 2,6-sialyltransferase; ST3N, Gal1,3/4GlcNAc 2,3-sialyltransferase; SNA, S. nigra agglutinin; MAA, M. amurensis agglutinin; PBMC, peripheral blood mononuclear cells; IL, interleukin; PE, phycoerythrin; FITC, fluorescein isothiocyanate; BSA, bovine serum albumin; SA, sialic acid.

()

N. L. Perillo and L. G. Baum, unpublished data.

ACKNOWLEDGEMENTS

REFERENCES

1. Paulson, J. C., and Colley, K. J. (1989) J. Biol. Chem. 264, 17615-17618 [Free Full Text]
2. O'Hanlon, T. P., Lau, K. M., Wang, X., and Lau, J. T. Y. (1989) J. Biol. Chem. 264, 17389-17394 [Abstract/Free Full Text]
3. Kitigawa, H., and Paulson, J. C. (1994) J. Biol. Chem. 269, 17872-17878 [Abstract/Free Full Text]
4. Despont, J. P., Abel, C. A., and Grey, H. M. (1975) Cell. Immunol. 17, 487-494 [CrossRef][Medline] [Order article via Infotrieve]
5. Reisner, Y., Linker-Israeli, M., and Sharon, N. (1976) Cell. Immunol. 25, 129-134 [CrossRef][Medline] [Order article via Infotrieve]
6. Akashi, M., Takaku, F., Nojiri, H., Miura, Y., Yashitaka, N., and Saito, M. (1988) Blood 72, 469-479 [Abstract/Free Full Text]
7. Whiteheart, S. W., McLenithan, J. C., and Hart, G. W. (1990) Cell. Immunol. 125, 337-353 [CrossRef][Medline] [Order article via Infotrieve]
8. Keppler, O. T., Moldenhauer, G., Oppenlander, M., Schwartz-Albiez, R., Berger, E. G., Funderrud, S., and Pawlita, M. (1992) Eur. J. Immunol. 22, 2777-2781 [Medline] [Order article via Infotrieve]
9. Sasaki, K., Watanabe, E., Kawashima, K., Sekine, S., Dohi, T., Oshima, M., Hanai, N., Nishi, T., and Hasegawa, M. (1993) J. Biol. Chem. 268, 22782-22787 [Abstract/Free Full Text]
10. Hanasaki, K., Varki, A., Stamenkovic, I., and Bevilacqua, M. (1994) J. Biol. Chem. 269, 10637-10643 [Abstract/Free Full Text]
11. Dahms, N. M., and Hart, G. W. (1986) J. Biol. Chem. 261, 13186-13196 [Abstract/Free Full Text]
12. Lee, E. U., Roth, J., and Paulson, J. C. (1989) J. Biol. Chem. 264, 13848-13855 [Abstract/Free Full Text]
13. Smith, D. F., Larsen, R. D., Mattox, S., Lowe, J. B., and Cummings, R. D. (1990) J. Biol. Chem. 265, 6225-6234 [Abstract/Free Full Text]
14. Do, K. Y., Fregien, N., Pierce, M., and Cummings, R. D. (1994) J. Biol. Chem. 269, 23456-23464 [Abstract/Free Full Text]
15. Bierhuizen, M. F. A., and Fukuda, M. (1992) Proc. Natl. Acad. Sci. U. S. A. 89, 9326-9330 [Abstract/Free Full Text]
16. Baum, L. G., Pang, M., Perillo, N. P., Wu, T., Delegeane, A., Uittenbogaart, C. H., Fukuda, M., and Seilhamer, J. J. (1995) J. Exp. Med. 181, 877-887 [Abstract/Free Full Text]
17. Gillespie, W., Paulson, J. C., Kelm, S., Pang, M., and Baum, L. G. (1993) J. Biol. Chem. 268, 3801-3804 [Abstract/Free Full Text]
18. Ohta, T., Kitamura, K., Maizel, A., and Takeda, A. (1994) Biochem. Biophys. Res. Commun. 200, 1283-1289 [CrossRef][Medline] [Order article via Infotrieve]
19. Sgroi, D., and Stamenkovic, I. (1994) Scand. J. Immunol. 39, 433-438 [CrossRef][Medline] [Order article via Infotrieve]
20. Sjoberg, E. R., Powell, L. D., Klein, A., and Varki, A. (1994) J. Cell Biol. 126, 549-562 [Abstract/Free Full Text]
21. Wang, X., Vertino, A., Eddy, R. L., Byers, M. G., Jani-Sait, S. N., Shows, T. B., and Lau, J. T. Y. (1993) J. Biol. Chem. 268, 4355-4361 [Abstract/Free Full Text]
22. Hughes, R. C. (1992) Curr. Opin. Struct. Biol. 2, 687-692 [CrossRef]
23. Sgroi, D., Koretzky, G. A., and Stamenkovic, I. (1995) Proc. Natl. Acad. Sci. U. S. A. 92, 4026-4030 [Abstract/Free Full Text]
24. Kijimoto-Ochiai, S., and Uede, T. (1995) Glycobiology 5, 443-448 [Abstract/Free Full Text]
25. Varki, A. (1994) Proc. Natl. Acad. Sci. U. S. A. 91, 7390-7397 [Abstract/Free Full Text]
26. Shibuya, N., Goldstein, I. J., Broekhaert, W. F., Nsimbe-Lubaki, M., Peeters, B., and Peumans, W. J. (1987) J. Biol. Chem. 262, 1596-1601 [Abstract/Free Full Text]
27. Wang, W. C., and Cummings, R. D. (1988) J. Biol. Chem. 263, 4576-4585 [Abstract/Free Full Text]
28. Weinstein, J., Lee, E. U., McEntee, K., Lai, P., and Paulson, J. C. (1987) J. Biol. Chem. 262, 17735-17743 [Abstract/Free Full Text]
29. Wen, D., Livingston, B. D., Medzihradszky, K. F., Kelm, S., Burlingame, A. L., and Paulson, J. C. (1992) J. Biol. Chem. 267, 21011-21019 [Abstract/Free Full Text]
30. Vollger, L. W., and Uittenbogaart, C. H. (1993) Cytokine 5, 157-168 [CrossRef][Medline] [Order article via Infotrieve]
31. Ueno, Y., Hays, E., Hultin, L., and Uittenbogaart, C. H. (1989) Cell. Immunol. 124, 239-251 [CrossRef][Medline] [Order article via Infotrieve]
32. Taatjes, D. J., Roth, J., Weinstein, J., and Paulson, J. C. (1988) J. Biol. Chem. 263, 6302-6309 [Abstract/Free Full Text]
33. Boyd, R. L., and Hugo, P. (1991) Immunol. Today 12, 71-79 [CrossRef][Medline] [Order article via Infotrieve]
34. Uittenbogaart, C. H., Higashitani, S., Schmid, I., Vollger, L. W., Boone, T., and Clement, L. T. (1990) Int. Immunol. 2, 1179-1187 [Abstract/Free Full Text]
35. Trowbridge, I. S., and Thomas, M. L. (1994) Annu. Rev. Immunol. 12, 85-116 [CrossRef][Medline] [Order article via Infotrieve]
36. Terstappen, L. W. M. M., Huang, S., and Picker, L. J. (1992) Blood 79, 666-677 [Abstract/Free Full Text]
37. Powell, L. D., and Varki, A. (1994) J. Biol. Chem. 269, 10628-10636 [Abstract/Free Full Text]
38. Kaneko, Y., Yamamoto, H., Colley, K. J., and Moskal, J. R. (1995) J. Histochem. Cytochem. 43, 945-954 [Abstract]
39. Goelz, S., Kumar, R., Potvin, B., Sundram, S., Brickelmaier, M., and Stanley, P. (1994) J. Biol. Chem. 269, 1033-1040 [Abstract/Free Full Text]
40. Verostek, M. F., and Trimble, R. B. (1995) Glycobiology 5, 671-681 [Abstract/Free Full Text]
41. Sato, T., Furukawa, K., Autero, M., Gahmberg, C. G., and Kobata, A. (1993) Biochemistry 32, 12694-12704 [CrossRef][Medline] [Order article via Infotrieve]
42. Fox, R. I., Heuniken, M., Fong, S., Behar, S., Royston, I., Singhal, S. K., and Thompson, L. (1983) J. Immunol. 131, 762-767 [Abstract]
43. Iwamori, M., Kawaguchi, T., and Nagai, Y. (1989) J. Biochem. (Tokyo) 105, 723-727
44. Perillo, N. L., Pace, K. E., Seilhamer, J. J., and Baum, L. G. (1995) Nature 378, 736-739 [CrossRef][Medline] [Order article via Infotrieve]
45. Borrebaech, C. A. K., Malmborg, A. C., and Ohlin, M. (1993) Immunol. Today 14, 477-479 [CrossRef][Medline] [Order article via Infotrieve]
46. Galili, U. (1993) Immunol. Today 14, 480-482 [CrossRef][Medline] [Order article via Infotrieve]
47. Cumming, D. A. (1991) Glycobiology 1, 115-130 [Abstract/Free Full Text]
48. Stanley, P. (1992) Glycobiology 2, 99-107 [Free Full Text]
49. Lowe, J. B. (1991) Semin. Cell Biol. 2, 289-307 [Medline] [Order article via Infotrieve]
50. Kumar, R., Potvin, B., Muller, W. A., and Stanley, P. (1991) J. Biol. Chem. 266, 21777-21783 [Abstract/Free Full Text]
51. Lowe, J. B., Kukowska-Latallo, J. F., Nair, R. P., Larsen, R. D., Marks, R. M., Macher, B. A., Kelly, R. J., and Ernst, L. K. (1991) J. Biol. Chem. 266, 17467-17477 [Abstract/Free Full Text]
52. Sawada, R., Lowe, J. B., and Fukuda, M. (1993) J. Biol. Chem. 268, 12675-12681 [Abstract/Free Full Text]

CiteULike

Complore

Connotea

Del.icio.us

Digg

Reddit

Technorati

This article has been cited by other articles:

				J. Zeng, H. M. Joo, B. Rajini, J. P. Wrammert, M. Y. Sangster, and T. M. Onami The Generation of Influenza-Specific Humoral Responses Is Impaired in ST6Gal I-Deficient Mice J. Immunol., April 15, 2009; 182(8): 4721 - 4727. [Abstract] [Full Text] [PDF]

				S. Rifat, T. J. Kang, D. Mann, L. Zhang, A. C. Puche, N. M. Stamatos, S. E. Goldblum, R. Brossmer, and A. S. Cross Expression of sialyltransferase activity on intact human neutrophils J. Leukoc. Biol., October 1, 2008; 84(4): 1075 - 1081. [Abstract] [Full Text] [PDF]

				J. H Marino, C. Tan, B. Davis, E.-S. Han, M. Hickey, R. Naukam, A. Taylor, K. S Miller, C J. Van De Wiele, and T K. Teague Disruption of thymopoiesis in ST6Gal I-deficient mice Glycobiology, September 1, 2008; 18(9): 719 - 726. [Abstract] [Full Text] [PDF]

				S. D. Liu, C. C. Whiting, T. Tomassian, M. Pang, S. J. Bissel, L. G. Baum, V. V. Mossine, F. Poirier, M. E. Huflejt, and M. C. Miceli Endogenous galectin-1 enforces class I-restricted TCR functional fate decisions in thymocytes Blood, July 1, 2008; 112(1): 120 - 130. [Abstract] [Full Text] [PDF]

				M. V. Tribulatti, J. Mucci, V. Cattaneo, F. Aguero, T. Gilmartin, S. R. Head, and O. Campetella Galectin-8 Induces Apoptosis in the CD4highCD8high Thymocyte Subpopulation Glycobiology, December 1, 2007; 17(12): 1404 - 1412. [Abstract] [Full Text] [PDF]

				J. D. Hernandez, J. Klein, S. J. Van Dyken, J. D. Marth, and L. G. Baum T-cell activation results in microheterogeneous changes in glycosylation of CD45 Int. Immunol., July 2, 2007; (2007) dxm053v1. [Abstract] [Full Text] [PDF]

				Y. Naito, H. Takematsu, S. Koyama, S. Miyake, H. Yamamoto, R. Fujinawa, M. Sugai, Y. Okuno, G. Tsujimoto, T. Yamaji, et al. Germinal Center Marker GL7 Probes Activation-Dependent Repression of N-Glycolylneuraminic Acid, a Sialic Acid Species Involved in the Negative Modulation of B-Cell Activation Mol. Cell. Biol., April 15, 2007; 27(8): 3008 - 3022. [Abstract] [Full Text] [PDF]

				P. V. Cabrera, M. Amano, J. Mitoma, J. Chan, J. Said, M. Fukuda, and L. G. Baum Haploinsufficiency of C2GnT-I glycosyltransferase renders T lymphoma cells resistant to cell death Blood, October 1, 2006; 108(7): 2399 - 2406. [Abstract] [Full Text] [PDF]

				E. Ish-Shalom, A. Gargir, S. Andre, Z. Borovsky, Z. Ochanuna, H.-J. Gabius, M. L. Tykocinski, and J. Rachmilewitz {alpha}2,6-Sialylation promotes binding of placental protein 14 via its Ca2+-dependent lectin activity: insights into differential effects on CD45RO and CD45RA T cells Glycobiology, March 1, 2006; 16(3): 173 - 183. [Abstract] [Full Text] [PDF]

				A. H. Merry, R. J. C. Gilbert, D. A. Shore, L. Royle, O. Miroshnychenko, M. Vuong, M. R. Wormald, D. J. Harvey, R. A. Dwek, B. J. Classon, et al. O-Glycan Sialylation and the Structure of the Stalk-like Region of the T Cell Co-receptor CD8 J. Biol. Chem., July 11, 2003; 278(29): 27119 - 27128. [Abstract] [Full Text] [PDF]

				M. Amano, M. Galvan, J. He, and L. G. Baum The ST6Gal I Sialyltransferase Selectively Modifies N-Glycans on CD45 to Negatively Regulate Galectin-1-induced CD45 Clustering, Phosphatase Modulation, and T Cell Death J. Biol. Chem., February 21, 2003; 278(9): 7469 - 7475. [Abstract] [Full Text] [PDF]

				A. R. Todeschini, M. F. Girard, J.-M. Wieruszeski, M. P. Nunes, G. A. DosReis, L. Mendonca-Previato, and J. O. Previato trans-Sialidase from Trypanosoma cruzi Binds Host T-lymphocytes in a Lectin Manner J. Biol. Chem., November 22, 2002; 277(48): 45962 - 45968. [Abstract] [Full Text] [PDF]

				J. D. Hernandez and L. G. Baum Ah, sweet mystery of death! Galectins and control of cell fate Glycobiology, October 1, 2002; 12(10): 127R - 136R. [Abstract] [Full Text] [PDF]

				T. M. Onami, M.-Y. Lin, D. M. Page, S. A. Reynolds, C. D. Katayama, J. D. Marth, T. Irimura, A. Varki, N. Varki, and S. M. Hedrick Generation of Mice Deficient for Macrophage Galactose- and N-Acetylgalactosamine-Specific Lectin: Limited Role in Lymphoid and Erythroid Homeostasis and Evidence for Multiple Lectins Mol. Cell. Biol., July 15, 2002; 22(14): 5173 - 5181. [Abstract] [Full Text] [PDF]

				A. R. Todeschini, M. P. Nunes, R. S. Pires, M. F. Lopes, J. O. Previato, L. Mendonca-Previato, and G. A. DosReis Costimulation of Host T Lymphocytes by a Trypanosomal trans-Sialidase: Involvement of CD43 Signaling J. Immunol., May 15, 2002; 168(10): 5192 - 5198. [Abstract] [Full Text] [PDF]

				J. Mucci, A. Hidalgo, E. Mocetti, P. F. Argibay, M. S. Leguizamon, and O. Campetella Thymocyte depletion in Trypanosoma cruzi infection is mediated by trans-sialidase-induced apoptosis on nurse cells complex PNAS, March 19, 2002; 99(6): 3896 - 3901. [Abstract] [Full Text] [PDF]

				A. Taniguchi, I. Yoshikawa,, and K. Matsumoto Genomic structure and transcriptional regulation of human Gal{beta}1,3GalNAc {{alpha}}2,3-sialyltransferase (hST3Gal I) gene Glycobiology, March 1, 2001; 11(3): 241 - 247. [Abstract] [Full Text] [PDF]

				D. H. Chung, K. Natarajan, L. F. Boyd, J. Tormo, R. A. Mariuzza, W. M. Yokoyama, and D. H. Margulies Mapping the Ligand of the NK Inhibitory Receptor Ly49A on Living Cells J. Immunol., December 15, 2000; 165(12): 6922 - 6932. [Abstract] [Full Text] [PDF]

				M. Fabbi, J. Geginat, M. Tiso, D. Ramarli, D. Parent, A. Bargellesi, and E. Remold-O'Donnell 8B4/20, A Private CD43 Epitope on Developing Human Thymocytes, Is Involved in Thymocyte Maturation J. Immunol., December 1, 1999; 163(11): 5964 - 5970. [Abstract] [Full Text] [PDF]

				K. E. Pace, C. Lee, P. L. Stewart, and L. G. Baum Restricted Receptor Segregation into Membrane Microdomains Occurs on Human T Cells During Apoptosis Induced by Galectin-1 J. Immunol., October 1, 1999; 163(7): 3801 - 3811. [Abstract] [Full Text] [PDF]

				O. T. Keppler, S. Hinderlich, J. Langner, R. Schwartz-Albiez, W. Reutter, and M. Pawlita UDP-GlcNAc 2-Epimerase: A Regulator of Cell Surface Sialylation Science, May 21, 1999; 284(5418): 1372 - 1376. [Abstract] [Full Text]

				N. Razi and A. Varki Masking and unmasking of the sialic acid-binding lectin activity of CD22 (Siglec-2) on B lymphocytes PNAS, June 23, 1998; 95(13): 7469 - 7474. [Abstract] [Full Text] [PDF]

				M. Krishna and A. Varki 9-O-Acetylation of Sialomucins: A Novel Marker of Murine CD4 T Cells that Is Regulated during Maturation and Activation J. Exp. Med., June 2, 1997; 185(11): 1997 - 2013. [Abstract] [Full Text] [PDF]

				J. Ma, R. Qian, F. M. Rausa III, and K. J. Colley Two Naturally Occurring alpha 2,6-Sialyltransferase Forms with a Single Amino Acid Change in the Catalytic Domain Differ in Their Catalytic Activity and Proteolytic Processing J. Biol. Chem., January 3, 1997; 272(1): 672 - 679. [Abstract] [Full Text] [PDF]

				M. Galvan, S. Tsuboi, M. Fukuda, and L. G. Baum Expression of a Specific Glycosyltransferase Enzyme Regulates T Cell Death Mediated by Galectin-1 J. Biol. Chem., May 26, 2000; 275(22): 16730 - 16737. [Abstract] [Full Text] [PDF]

This Article Abstract Full Text (PDF) Submit a Letter to Editor Alert me when this article is cited Alert me when eLetters are posted Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Request Permissions Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Baum, L. G. Articles by Uittenbogaart, C. Search for Related Content PubMed PubMed Citation Articles by Baum, L. G. Articles by Uittenbogaart, C. Social Bookmarking                      What's this?