Metabolic carbohydrate-labelling of glycolipids from mouse splenocytes. Mitogen-stimulated B and T cells show different labelling patterns

ATP-binding cassette transporters mediate differential biosynthesis of glycosphingolipid species

The cytosolic-oriented glucosylceramide (GlcCer) synthase is enigmatic, requiring nascent GlcCer translocation to the luminal Golgi membrane to access glycosphingolipid (GSL) anabolic glycosyltransferases. The mechanism by which GlcCer is flipped remains unclear. To investigate the role of GlcCer-binding partners in this process, we previously made cleavable, biotinylated, photoreactive GlcCer analogs in which the reactive nitrene was closely apposed to the GlcCer head group, while maintaining a C16-acyl chain. GlcCer-binding protein specificity was validated for both photoprobes. Using one probe, XLB, here we identified ATP-binding cassette (ABC) transporters ABCA3, ABCB4, and ABCB10 as unfractionated microsomal GlcCer-binding proteins in DU-145 prostate tumor cells. siRNA knockdown (KD) of these transporters differentially blocked GSL synthesis assessed in toto and via metabolic labeling. KD of ABCA3 reduced acid/neutral GSL levels, but increased those of LacCer, while KD of ABCB4 preferentially reduced neutral GSL levels, and KD of ABCB10 reduced levels of both neutral and acidic GSLs. Depletion of ABCA12, implicated in GlcCer transport, preferentially decreased neutral GSL levels, while ABCB1 KD preferentially reduced gangliosides, but increased neutral GSL Gb3. These results imply that multiple ABC transporters may provide distinct but overlapping GlcCer and LacCer pools within the Golgi lumen for anabolism of different GSL series by metabolic channeling. Differential ABC family member usage may fine-tune GSL biosynthesis depending on cell/tissue type. We conclude that ABC transporters provide a new tool for the regulation of GSL biosynthesis and serve as potential targets to reduce selected GSL species/subsets in diseases in which GSLs are dysregulated.

Neutral glycosphingolipids and gangliosides from spleen T lymphoblasts of genetically different inbred mouse strains

The gangliosides G(M1b), GalNAc-G(M1b) and G(D1alpha) are typical compounds of concanavalin A stimulated splenic T lymphoblasts of CBA/J inbred mice. Their structural characterization has been described in previous studies. The intention of this work was the comparative TLC immunostaining analysis of the glycosphingolipid composition of lectin stimulated splenic T lymphoblasts obtained from six genetically different inbred mouse strains. The strains examined were AKR, BALB/c, C57BL/6, CBA/J, DBA/2 and WHT/Ht, which are commonly used for biochemical and immunological studies. The neutral glycosphingolipid GgOse4Cer, the precursor for G(M1b)-type gangliosides, was expressed by all six strains investigated. AKR, C57BL/6 and DBA/2 showed high and BALB/c, CBA/J and WHT/Ht diminished expression in T lymphoblasts, based on single cell calculation. The gangliosides G(M1b) and GalNAc-G(M1b), elongation products of GgOse4Cer, displayed strain-specific differences in their intensities, which were found to correlate with the intensities of GgOse4Cer expression of the same strains. Concerning sialic acid substitution of gangliosides, G(M1b) and GalNAc-G(M1b) predominantly carry N-acetylneuraminic acid, whereas choleragenoid receptors G(M1a) and Gal-GalNAc-G(M1b), which are also expressed by all six strains, are characterized by dominance of N-glycolylneuraminic acid. Two highly polar gangliosides, designated with X and Y, which have not been previously recognized in murine lymphoid tissue, were detected by positive anti-GalNAc-G(M1b) antibody and choleragenoid binding, respectively. Both gangliosides were restricted to AKR, DBA/2 and C57BL/6 mice. The other three strains BALB/c, CBA/J and WHT/Ht are lacking these structures. In summary, the G(M1b)-type pathway is quite active in all six strains analysed in this study. Strain-specific genetic variations in T lymphoblast gangliosides were observed with the occurrence of gangliosides X and Y. This study and data from other groups strongly indicate for G(M1b)-type gangliosides a functional association with T cell activation and leukocyte mediated reactions.

The T-lymphocyte is the primary cellular target for potentiation of the in vitro T-dependent IgM antibody response by the B subunit of cholera toxin

The B (or binding) subunit of cholera toxin (CTB) was reported previously to potentiate the in vitro T-dependent IgM antibody response by a mechanism independent of the cyclic AMP-generating capacity of the intact toxin. In the present report, experiments were designed to determine the immune cell type mediating potentiation by CTB. Firstly, CTB did not potentiate T-independent antibody responses at concentrations that effectively enhanced T-dependent responses. Secondly, separation/reconstitution studies with splenocytes from CTB- and vehicle-treated mice demonstrated potentiation of T-dependent responses by CTB treatment of either the Sephadex G10 non-adherent population or the T-lymphocyte + macrophage population of cells. Potentiation was not observed by CTB treatment of the plastic adherent population or the B-lymphocyte + macrophage population. The evidence indicates that the T-lymphocyte is the primary cellular target for CTB-induced effects on the T-dependent IgM antibody response. Monosialoganglioside GM1, the putative binding site for CTB, is most likely the site of action for CTB on T-lymphocytes. These studies provide new insight on the mechanism of immunomodulation by cholera toxin, and CTB should provide a useful tool for further understanding the role of gangliosides in cellular immune responses.

Transmembrane signaling by the B subunit of cholera toxin: increased cytoplasmic free calcium in rat lymphocytes

It has previously been shown that the B subunit of cholera toxin, which binds solely to the plasma membrane ganglioside GM1, stimulates the proliferation of rat thymic lymphocytes (Spiegel, S., P. H. Fishman, and R. J. Weber, 1985, Science [Wash. DC], 230:1285-1287). The purpose of this study was to identify which transmembrane signaling system(s) are activated by the B subunit of cholera toxin. We compared the effects of B subunit and concanavalin A (Con A), a potent mitogenic lectin, on a number of second messenger systems that are putative mediators of T cell activation. Changes in the fluorescence of quin2-loaded cells revealed that mitogenic doses of either B subunit or Con A induced rapid and sustained increases in cytoplasmic free Ca2+ ([Ca2+]i). Within 5 min, [Ca2+]i increased from a basal level of 69 +/- 4 to 136 +/- 17 and 185 +/- 24 nM, respectively. The effects of B subunit and Con A were additive and largely dependent on the presence of extracellular Ca2+, though release of Ca2+ from intracellular stores could be detected for Con A, but not B subunit, using indo-1. The B subunit had no effect on either inositol phosphate levels or on the distribution of protein kinase C, indicating that, unlike Con A, the B subunit does not activate phosphoinositide hydrolysis. Fluorimetric measurements on cells loaded with bis(carboxyethyl)-5,6-carboxyfluorescein revealed that Con A induced a rapid cytoplasmic alkalinization via activation of Na+/H+ exchange, whereas B subunit had no effect on intracellular pH. Finally, by monitoring bis-oxonol fluorescence, we found that Con A induced a small hyperpolarization of the membrane potential, whereas B subunit had no acute effect. These data suggest that the biological effects of B subunit are mediated by an increase in [Ca2+]i resulting from a net influx of extracellular Ca2+.

Structural characterization of gangliosides from murine T lymphocytes

Mouse spleen cells were prepared from CBA/J mice, and T lymphocytes were selectively stimulated with the T cell mitogen concanavalin A and further propagated in the presence of the T cell growth factor interleukin-2. The T cells were metabolically labeled with D-[1-14C]galactose and D[1-14C]glucosamine, and the gangliosides were extracted and purified by DEAE-Sepharose column chromatography. Carbohydrate backbone structures of the asialogangliosides, prepared by mild acid hydrolysis, were determined by high-performance liquid chromatography, treatment with exoglycosidases and immunostaining. Monosialylated gangliosides were isolated by gradient elution from DEAE-Sepharose and further separated by preparative high-performance thin-layer chromatography in two solvent systems. Isolated fractions were characterized by preparation of asialogangliosides by mild acid hydrolysis, the action of Vibrio cholerae neuraminidase, and fast-atombombardment mass spectrometry. The following structures were identified: IVNeuAc-GgOse4Cer; IVNeuGc-GgOse4Cer; IVNeuAc-GgOse5Cer; and IVNeu-Gc-GgOse5Cer. The latter two gangliosides were not detected on B lymphoblasts and may be T-cell-specific structures. All gangliosides were heterogeneous in their ceramide moieties, being substituted with C16:0, C24:0, and C24:1 fatty acids. A preliminary study of several other mouse strains showed no strain-specific genetic variations in the T cell gangliosides. The possible role of these gangliosides is discussed.

Membrane glycolipid and phospholipid composition of lipopolysaccharide-responsive and -nonresponsive murine B lymphocytes

Neutral glycolipids, gangliosides, and phospholipids present on membranes of unstimulated or lipopolysaccharide (LPS)-stimulated B cells were analyzed in LPS-responsive C3H/HePAS and LPS-nonresponsive C3H/HeJ mice. In the set of neutral glycolipids, asialo GM1 reacted preferentially with galactose oxidase but was not detectable with monospecific antibodies during immunocytofluorescence analysis. Another, more polar, neutral glycolipid appeared exclusively after stimulation of responsive B cells. Among the membrane gangliosides 1 to 5 that were able to react with galactose oxidase on B cells, ganglioside 3 was not detected in the mutant strain, and its absence was counterbalanced by the presence of a larger amount of ganglioside 1. The biosynthesis of total membrane phospholipids and the balance between phosphatidylethanolamine and phosphatidylcholine were significantly different in the two mouse strains examined and were quantitatively and qualitatively modified during the mitogenic response to LPS.

Glycoconjugates of murine tumor lines with different metastatic capacities. II. Diversity of glycolipid composition

A syngeneic tumor system in DBA/2 mice consisting of a methyl-cholanthrene-induced, weakly metastatic lymphoma, L5178YE (= Eb), its spontaneous strongly metastatic variant, L5178YES (= ESb), and an unrelated, methylcholanthrene-induced, metastasizing tumor, MDAY-D2, were used to study the relationship between metastatic behavior and composition of GSLs. The D-1-14C galactose and D-1-14C glucosamine-labelled neutral GSL and gangliosides of these tumor cells, and additionally ConA-stimulated spleen T cells from normal mice, were analysed by thin-layer chromatography. Unlabelled GSLs of the tumors were also characterized by (HPLC) after perbenzoylation. Results obtained with the radioactively labelled GSLs correlated with those of the HPLC analysis of unlabelled GSLs. All tumors contained neutral GSL of the ganglio-series. Weakly metastatic tumor Eb showed neutral GSL patterns comparable to those from ConA-stimulated spleen cells, whereas strongly metastatic tumors ESb and MDAY-D2 had an enhanced expression of lactosylceramide. Gangliosides of metastatic ESb and MDAY-D2 had a higher degree of polarity than those of weakly metastatic Eb. Eb cells expressed primarily GM1. Metastasizing ESb and MDAY-D2 had significantly higher amounts of GM3, GM2 and GD1a. An unusual ganglioside, IV3GalNAc-GM1, was found in MDAY-D2 cells and ConA blasts. When the extent of label was compared in neutral GSLs and gangliosides, metastasizing ESb and MDAY-D2 were more heavily labelled in the ganglioside fraction (62%, 58%) than Eb (39%). ESb and MDAY-D2 also contained larger amounts of gangliosides than Eb.

Assay for the determination of human carcinoma cells in circulating blood

Methods have been developed in an in vitro system (1) of assessing the number of disseminated tumor cells in peripheral blood and (2) of enriching tumor cells from peripheral blood samples for further characterization. Cells from three human carcinoma lines (E 14, ChaGo, and LEDWiDr) were mixed with leukocytes from normal individuals in various ratios. The proportions of tumor cells were determined by a quantitative assay using 3H-thymidine, 3H-leucine, and 3H-galactose incorporation. Determination of tumor cell proportions with this method was most accurate in the range of 5 X 10(4) to 5 X 10(3) tumor cells mixed with a constant number (5 X 10(5] of lymphocytes. It was possible to separate 75Se-labeled tumor cells from 51Cr-labeled blood leukocytes by centrifugation in isopyknic Percoll density gradients. These cells were mixed at different ratios and subjected to Percoll gradient centrifugation. By this approach as few as 5 X 10(3) tumor cells could by identified in the presence of 5 X 10(7) leukocytes, representing a ratio of 1: 10,000. Percoll centrifugation did not damage the tumor cells. In blood cells from two lung cancer patients with lung metastases the incorporation of 3H-thymidine and 3H-galactose was significantly enhanced compared with that in blood cells from patients with primary lung tumors and in cells from normal individuals. This difference became even more apparent when metabolically-labeled blood cells were subsequently separated by Percoll gradient centrifugation.

Carbohydrate structure in tumor immunity

Researchers have endeavored to define surface alterations associated with neoplasia for at least 25 years. In comparisons of normal tissues with animal and human tumors, cultured cells before and after transformation with oncogenic agents, tumorigenic and nontumorigenic transformed cells, metastatic and nonmetastatic tumor cells, high- and low-metastatic variants, and tumor cells before and after induction of differentiation to a less malignant phenotype, a consistent finding has been some form of alteration in surface carbohydrate structures. These changes in glycolipids, glycoproteins and glycosaminoglycans are reviewed, and their structures are illustrated. Both nucleotide sugar biosynthesis and glycosyltransferase changes have been associated with these alterations. In some cases, alterations in transformed cells were related to growth, rather than transformation. In others, the altered glycoconjugates are truly tumor-associated. There is evidence that cell surface glycoconjugates may function in growth control. Altered carbohydrate structures could also serve as receptors for growth promoting factors and be directly responsible for altered growth control. Recent studies with monoclonal antibodies indicate that the vast majority of antibodies recognizing tumor-associated antigens are detecting altered carbohydrate structures. Mechanisms by which the immune system can recognize these carbohydrate structures are considered, and immune recognition of tumor-associated carbohydrate structural alterations is explored. A number of these hypotheses relating to alterations in glycosylation, growth control, and tumor immunity deserve further investigation.

The glycosphingolipid globoside as a serological marker on cytolytic T lymphocyte precursors and alloantigen-responsive proliferating T lymphocytes in murine spleen

Biochemical analyses of murine lymphocytes have shown that the glycosphingolipid globoside (Glo) is present exclusively on alloantigen-stimulated murine T lymphocytes (Gruner, K. R., Van Eijk, R. V. W. and Mühlradt, P. F., Biochemistry 1981. 20: 4518). An anti-Glo antibody has now been raised in rabbits immunized with purified antigen. Most activity was recovered in the IgM fraction. The specificity of the antibody was ascertained in an enzyme-linked immunosorbent assay with purified glycosphingolipids bound to the solid phase. In antibody-dependent complement lysis experiments the anti-Glo eliminated about 20% of nylon wool-nonadherent splenic T cells of CBA/J mice. To determine the functional identity of these Glo+ cells, the effects of Glo+ cell elimination on mitogen stimulation with concanavalin A and lipopolysaccharide, as well as the effects on the mixed lymphocyte culture (MLC) reaction and cell-mediated lympholysis with mitomycin-treated DBA/2 splenocytes as stimulator cells were studied. Whereas lipopolysaccharide stimulation was not affected by elimination of Glo+ cells, there was a slight inhibitory effect on the concanavalin A stimulation, and a severe inhibition of the MLC reaction and the generation of H-2d-specific cytolytic T lymphocytes. Addition of interleukin 2 increased the MLC reaction, but interleukin 2-saturated cultures were also severely inhibited by anti-Glo and complement treatment. Combined treatment with anti-Glo and anti-Lyt-1 or anti-Lyt-2 antibodies, and determination of cytolytic T lymphocyte precursor frequencies in limiting dilution cultures after Glo+ cell elimination showed that a large proportion of T cells proliferating in a primary MLC are Lyt-1+,2+,3+Glo+, whereas in secondary MLC they are Lyt-1+,2-,3-,Glo+. Fifty % of the cytolytic T lymphocyte precursors in primary as well as secondary MLC are Glo+. The Glo marker is lost upon differentiation to cytolytic T lymphocyte effector cells. It is discussed herein that Glo is a marker for alloantigen-stimulated precursor T lymphocytes of both helper and cytolytic T cells.

Glycoconjugates of murine tumor lines with different metastatic capacities. I. Differences in fucose utilization and in glycoprotein patterns

Since various experimental findings point towards an important role of cell surface carbohydrates - in particular sialic acid - in cancer metastasis, the rationale of this study was to look for possible differences in carbohydrate metabolism and glycoprotein expression in well-defined related tumor lines of different metastatic capacity. The tumor lines analyzed were L5178Y E (= Eb), a low-metastasizing, methylcholanthrene-induced lymphoma of a DBA/2 mouse, and L5178Y ES (= ESb), a spontaneous high-metastatic variant thereof. A non-related, highly metastasizing tumor, MDAY-D2, and ConA-stimulated spleen cells were included in the study. These cell lines were compared for incorporation rates of various labelled carbohydrates and for glycoprotein patterns in SDS-polyacrylamide gels. Marked differences were observed in the incorporation of 3H-fucose, while the incorporation of 3H-galactose and 3H-mannose was similar in the different cell lines studied. Only the metastatic variant ESb incorporated 3H-fucose at a rate similar to that of ConA-stimulated T-cell blasts. Eb cells did not incorporate 3H-fucose while MDAY-D2 had a significantly lower 3H-fucose incorporation rate. Separation and purification of the intracellular products of 3H-fucose by gel filtration and high-voltage electrophoresis revealed in Eb cells a block in the synthesis of fucosylated glycoproteins at the step of the fucose-I-P-guanylyltransferase. No apparent defect in the fucose pathway was detectable in MDAY-D2 cells. An Eb----ESb shifted cell line regained the ability to incorporate 3H-fucose. All tumors displayed unique glycoprotein patterns in SDS-PAGE. Labelling with 3H-mannose revealed the most distinct bands, while labelling with 3H-galactose gave fewer and broader bands. Although clonal instability of metastasizing tumor variants has been frequently reported, subclones of Eb and ESb showed characteristics similar to those of the original cell lines with regard to metastatic capacity, fucose metabolism and glycoprotein expression. These results will be discussed in relation to differences in fucose metabolism and in surface expression of fucose as observed in other tumor systems consisting of high- and low-metastatic lines.

Positive selection of mouse B and T lymphocytes and analysis of isolated populations by flow cytometry

Mouse spleen cells were separated into Ig+ and Ig- populations by positive selection using petri plates coated with rabbit anti-mouse immunoglobulin. The Ig- cells were subsequently incubated with mouse monoclonal alloantisera to Thy1.2 prior to a second positive selection. The adherent populations were characterized as B (Ig+) or T (Thy1.2+) lymphocytes on the basis of surface immunofluorescence and mitogen-induced proliferation. Analysis of the 2 isolated populations by flow cytometry showed that B and T lymphocytes could be distinguished by their forward light scatter as well as their fluorescence after incubation with fluorescein diacetate.

Comparative study on ganglioside compositions of various rabbit tissues. Tissue-specificity in ganglioside molecular species of rabbit thymus

Ganglioside compositions of various organs of rabbit (NIBS strain, male, 10 months old) were studied. Organs examined contained lipid-bound sialic acid at various concentrations but the amounts in extraneural tissues were less than one-fifth of that in brain. The gangliosides of various tissues were analyzed by ganglioside-mapping and by isolating individual components and determining their structures chemically or enzymatically. According to their backbone asialocarbohydrate chain, the major gangliosides of various tissues were classified into three groups: (1) lactose and ganglio-N-triose (lung, stomach, liver, intestine, kidney, testis and muscle); (2) ganglio-N-tetraose (brain); (3) lacto-N-neotetraose (thymus). 70% of all thymus gangliosides had a lacto-N-neotetraose backbone, which was tissue-specific. In marked contrast to the case in other tissues, in thymus N-glycoloylneuraminic acid constituted 90% of the total lipid-bound sialic acid, and all molecular species of thymus gangliosides contained N-glycoloylneuraminic acid. Palmitic acid was a major fatty acid of thymus gangliosides. Distinct differences were found in the fatty acid compositions of gangliosides with longer carbohydrate chains in various tissues.

Carbohydrate-labelled glycoproteins as markers of human lymphocyte subsets stimulated with mitogen and alloantigen

Human lymphocytes from thymus, spleen, and blood were stimulated by concanavalin A, phytohemagglutinin or pokeweed mitogen to incorporate radioactive thymidine and various carbohydrates. Peripheral-blood lymphocytes were also activated by alloantigen in a mixed lymphocyte reaction. Incorporation of thymidine and carbohydrates was parallel in stimulated cells. Carbohydrate-labelled cells were extracted with Triton X-100 buffer and the extracts subjected to sodium dodecylsulfate/polyacrylamide gel electrophoresis and subsequent autoradiography. From a comparison of the resulting glycoprotein patterns the following conclusions could be drawn. (a) The same population of thymocytes responds to all three mitogens. (b) Pokeweed-mitogen-stimulated blood lymphocytes are similar to this mitogen-responsive thymocyte population. (c) The glycoprotein pattern of pokeweed-mitogen-responsive spleen cells shows two characteristic glycoproteins, GP 50 and GP 78, and resembles that of murine B cells. (d) Whereas concanavalin A and phytohemagglutinin activate identical subpopulations of T cells in the spleen, this is not the case in the blood. (e) Concanavalin-A-activated and alloantigen-activated blood lymphocytes express a glycoprotein GP 185 which is not found on phytohemagglutinin-responsive cells. (f) The kinetic relationship during alloantigen stimulation in a mixed lymphocyte reaction between the appearance of glycoprotein GP 185 and subsequent maximal killing activity in an assay using release of 51Cr makes it likely that glycoprotein GP 185 is a marker for cytotoxic T lymphocytes.

Evidence from a carbohydrate incorporation assay for direct activation of bone marrow myelopoietic precursor cells by bacterial cell wall constitutents

The stimulation of incorporation of [3H]galactose into membrane glycoconjugates, measured in a precipitation test, was used as a criterion for activation of bone marrow cells. In this assay, purified bacterial lipopolysaccharide, lipoprotein, and murein monomer and dimer fragments all activated rat bone marrow cells in vitro. The response was dose dependent, followed a defined time course, and was not serum dependent. O-Acetylated murein dimer fragments from Proteus mirabilis were much less active than their unsubstituted counterparts, indicating a structural specificity for murein activation. Removal of adherent and phagocytizing cells from the marrow suspensions did not alter these results. The labeled, activated cells constituted a distinct population of buoyant density 1.064 to 1.069 g/cm3 when centrifuged on a continuous gradient of Percoll. Enrichment of the target cell population was achieved by a combination of adherent cell removal and discontinuous density gradient centrifugation to remove granulocytes and erythropoietic cells. It was concluded that a population of myelopoietic precursors could be activated by direct contact with bacterial cell wall constituents. The stimulation of galactose incorporation was not coupled to active deoxyribonucleic acid synthesis in the marrow cells. Thus, the activation was interpreted as an induction of differentiation rather than a mitotic event.

Lipid fluidity and membrane protein monitoring using 1,6-diphenyl-1,3,5-hexatriene

Experiments have been designed to challenge the use of stedy-state fluorescence polarizaiton with 1,6-diphenyl-1,3,5-hexatriene as an evaluator of the fluidity of cell plasma membranes. We used paraffinic systems, of defined structure and composition (liquid paraffin, soap bilayers and phospholipid liposomes--with and without incorporated proteins), to demonstrate that corresponding polarizaiton values cannot be interpreted in terms of the overall fluidity of the labeled medium. In homogeneous structured paraffinic media (lipid bilayers), knowledge of the location of the probe is essential for a consistent interpretation of the observed fluorescence polarization. Due to the highly polarizable electronic structure of the diphenylhexatriene molecule, the presence of heterogeneities with potential sites for interaction (e.g., C18-coated Si particles, albumin molecules, etc.) can lead to relatively high polarization values, even in isotropic media. In cellular systems, translocation experiments from labeled cells to added proteins show a rather localized peripheral distribution of the probe as well as its high affinity for hydrophobic sites of proteins. This and other arguments presented here suggest that although cellular polarization values represent an intricate average over all labeled hydrophobic regions of the cell (phospholipid bilayers, membrane proteins, etc.), these values might reflect, to a large extent, interactions of the probe with proteins from the inner periphery of the cell.

Mitogenic effects of partially purified interleukin 2 on thymocyte subpopulations and spleen t cells of the mouse

Partially purified interleukin 2 (IL-2) promotes proliferation of mouse spleen T, but not B cells, and of peanut-agglutinin-negative (PNA-), and cortisone-resistant "mature" thymocytes, but not of PNA+ "immature" thymocytes. Within the cortisone-resistant thymocyte population, IL-2-responsive cells were found in the blast cell fraction. Proliferation was measured by [3H] thymidine incorporation and subsequent increase in viable cells. The mitogenic effect of IL-2 could not be inhibited by 50 mM methyl-alpha-D-mannoside which excludes contaminating concanavalin A (Con A) as a cause of mitogenicity. The relative increase in viable cells in IL-2 vs. control cultures was abrogated by 1.5 mM hydroxyurea. A possible effect of IL-2 on cell survival is thus ruled out. IL-2, when acting as comitogen with Con A, affected only PNA- and cortisone-resistant thymocytes. These cells also showed high intrinsic IL-2 release when stimulated with Con A such that a comitogenic effect of externally added IL-2 was only seen at low cell concentrations. PNA+ thymocytes could neither be induced to release IL-2 nor did these cells become Con A-responsive under the influence of IL-2, thereby excluding an IL-2-mediated maturation.

Gangliosides of calf thymus and of normal and leukemic bovine lymphocytes

The gangliosides of calf thymus and of lymphocytes from blood, lymph nodes, lymph and spleen of normal and leukemic cows were investigated in an attempt to determine whether there exists a relation between the ganglioside composition and the maturity of the lymphocytes. With all normal peripheral lymphocytes studied the largely prevailing (up to 97%) ganglioside component was found to be N-glycoloylneuraminosyllactosylceramide. The ganglioside spectrum of calf thymus was much more complex and included at least six different components. By thin-layer chromatography, methylation analysis and neuraminidase treatment they were identified as N-glycoloylneuraminosyl and N-acetylneuraminosyl lactosylceramides, N-glycoloylneuraminosylneolactotetraosylceramide, di-(N-glycoloylneuraminosyl), di-(N-acetylneuraminosyl) lactosylceramides and N-glycoloylneuraminosyl-N-acetylneuraminosyllactosylceramide. The ganglioside spectra of leukemic peripheral lymphocytes were different from those of normal peripheral lymphocytes and resembled the ganglioside profile of the thymus. The data obtained indicate that, in the normal animal, the development of thymocytes into mature peripheral lymphocytes is accompanied by loss of disialosyl-gangliosides and sialosylneolactotetraosylceramide. It is concluded that both the structure and the composition of the lymphocyte ganglioside become more simple during maturation and ageing of the lymphocyte.

Studies on glycosphingolipid biosynthesis by lectin-stimulated human lymphocytes

1. Human peripheral lymphocytes, normal and stimulated by phytohemagglutinin or concanavalin A. were investigated with respect to their ability to biosynthesize neutral and acidic glycosphingolipids from D-[U-14C]glucose, D-[U-14C]galactose and D-[U-14C]glucosamine as precursors. 2. Galactose and glucosamie are taken up selectively, in the presence of excessive glucose concentrations. Labeling of total neutral glycosphingolipids from D-[U-14]galactose in normal cells decreases after the first 6 h while in stimulated cells there is a fourfold and a sevenfold increase after 6 and 12 h of incubation respectively. Under similar conditions stimulation with concanavalin A gives a fourfold increase after 12 h of incubation. 3. Analysis of individual glycosphingolipids biosynthesized from [U-14C]galactose shows that lactosylceramide is the major radioactive neutral glycosphingolipid and that stimulation by phytohemagglutinin yields an almost sevenfold and 13-fold increase in the radioactivity incorporated within 6 and 12 h of incubation respectively. Glucosylceramide shows about an eightfold increase, globotetraosylceramide a threefold increase and globotriaosylceramide a fourfold increase. The rate of incorporation into glucosylceramide of stimulated lymphocytes declines after 6 h of incubation, accompanied by a concomitant increase of incorporation into lactosylceramide. 4. At 12 h of incubation the ratios of radioactivities incorporated into neutral glycosphingolipids of phytohemagglutinin-stimulated cells compared to normal cells were 1.0 for D-[U-14C]glucose 7.0 for D-[U-14C]galactose and 2.5 for D-[U-14C]glucosamine. Respective ratios for lactosylceramide are 1.0 for [U-14C]glucose and 13.0 for [U-14C]galactose. These differences did not arise from changes of the uptake of the glycosyl precursor by the cell due to stimulation. 5. Incorporation of D-[U-14C]galactose into II3-N-acetylneuraminosyllactosylceramide by cells stimulated by phytohemagglutinin and concanavalin A is enhanced 14-times and 15-times respectively. With [U-14C]glucosamine as precursor, this increase in the labeling is much more impressive, 80-fold after 12 h of incubation by the phytohemagglutinin-stimulated lymphocytes. Neuraminidase treatment and gas radiochromatographic analysis of the labeled compound derived from [U-14C]-galactose as precursor indicate that 89% of the radioactivity was incorporated into the glucosyl and galactosyl moieties, in a ratio 1:1. With [U-14C]glucosamine as precursor, a selective labeling of the sialyl moiety of the II3-N-acetylneuraminosyllactosylceramide was indicated. 6. The pattern of complex gangliosides (more complex than II3-N-acetylneuraminosyllactosylceramide) which are biosynthesized after phytohemagglutinin stimulation of the cells, show no significant differences when compared to the patterns obtained from normal cells.