Extraction of the carbohydrate-defined class of Ia antigens from murine spleen cells and serum

A quantitative analysis of H-2 linked effects on hepatic ganglioside composition

We have conducted a quantitative analysis of the gangliosides extracted from brain, spleen, thymus, and liver tissue of 8-week-old male mice from H-2 congenic mouse strains on the B10 background, using high performance thin-layer chromatography (HPTLC). An analysis of variance of replicate samples of liver from strains B10, B10.A, and B10.G revealed that the time of sample and colony of origin were not sources of significant variance but that for N-glycolylated gangliosides GM2, GM1, and GD1a, the differences detected between strains were significant. Particularly important were the differences for GM1: the values of 0.0% for B10, 19.0% for B10.A, and 36.0% for B10.G were each significantly different from the others (P less than 0.0005). Further studies with liver tissue from B10/A H-2 recombinant strains also revealed three significantly different levels of GD1a: less than or equal to 4.0% [B10, B10.A (3R), B10.A (5R), B10.A (18R)], 11.0% (B10.A), and 33% [B10.A (1R), B10.A (2R), B10.A (4R)]. Our findings support prior studies which indicate that a gene linked to the H-2 complex affects hepatic GM2 galactosyltransferase activity. However, they also indicate that the current model, which classifies all strains as possessing either an allele for "high" enzyme activity or a single alternative allele for "low" enzyme activity, is probably oversimplified, since at least three levels of enzyme activity appear to exist as stable phenotypic markers. Moreover, the current model cannot readily account for the three different levels of GD1a observed with B10/A H-2 recombinants. Alternative models are proposed, including the novel suggestion that a distinct H-2 linked gene may affect hepatic GM1 sialyltransferase activity. These findings demonstrate that further study of H-2 linked genes affecting the activities of glycosyltransferases is indicated.

Simple sugars inhibit proliferation of human T lymphocytes in autologous and allogeneic mixed lymphocyte reactions

Several oligo- and monosaccharides were studied for their capacity to modulate lymphocyte proliferation in human allogeneic and autologous mixed lymphocyte reactions (MLR). A defined subset of sugars showed a marked inhibitory effect on lymphocyte proliferative response in the majority of the allogeneic MLR combinations studied. The inhibitory effect disappeared when sugars were added to allogeneic MLR 96 hr after the beginning of culture. These sugars also showed a significant inhibitory power on autologous MLR, performed by using T- and non-T-enriched lymphocytes from the same donor. The reported data suggest that carbohydrate determinants are involved in the proliferative response of human lymphocytes in both autologous and allogeneic MLR.

Potentiating and suppressive IgE-binding factors are expressed by a single cloned gene

We have investigated expression of an IgE-binding factor (IgE-BF) cDNA in both COS-7 monkey kidney cells and Chinese hamster ovary cells. Transient expression of the IgE-BF clone in either cell type yielded IgE-BF, which potentiated an in vitro IgE response and had an affinity for lentil lectin. In contrast, when the transient expression experiments were carried out in the presence of tunicamycin, the factors no longer bound to lentil lectin. Moreover, IgE-BF expressed under these conditions suppressed an in vitro IgE response. IgE-BF lacking affinity for lentil lectin and suppressing the IgE response also resulted from transient expression of the IgE-BF gene in the presence of glycosylation inhibiting factor, a phospholipase inhibitory protein. Thus, IgE-BF that either potentiate or suppress the IgE response can be expressed from a single cloned gene; the difference in biological activities appears to be determined principally by the type of glycosylation of the common polypeptide chain. Previous work showed that IgE-BF bears an antigenic determinant recognized by the anti-Ia monoclonal antibody OX3. IgE-BF produced in the presence of tunicamycin, and IgE-BF expressed from a mutant cDNA lacking one of two carbohydrate-attachment sites, lacked the OX3 determinant. Thus, the OX3 determinant on IgE-BF appears to be associated with a site of N-linked glycosylation.

Glycolipid-dependent interaction between human migration-inhibitory factor and mononuclear phagocytes

It has been previously established in the guinea pig that the response of peritoneal macrophages to migration inhibitory factor (MIF) is enhanced by a macrophage glycolipid and that gangliosides reversibly bind MIF. This suggests that glycolipids function as cell surface receptors for MIF. In this report, it is demonstrated that the response of human peripheral blood monocytes to human MIF is augmented by preincubation of these cells with glycolipid-enriched material extracted from the human macrophage-like cell line U937 or human peripheral blood monocytes and with a purified glycolipid from guinea pig peritoneal macrophages. In addition, a mixed ganglioside preparation from bovine brain shows the same effect. In contrast, the pure gangliosides, GM1 and GD1a, and glycolipids from the HL-60 cell line, which is a MIF-unresponsive cell line, were not able to enhance the response to human MIF. The specificity of enhancement by particular glycolipids could not be attributed to an increased uptake of only enhancing glycolipids since there was no significant difference between the association of monocytes with radioactive liposomes containing biologically active or inactive glycolipids. Pronase treatment did not affect the enhancing activity of the U937 glycolipid-enriched material. Incubation of cells with glycolipids results in enhancement only if done at 37 degrees C and not at 4 degrees C. Therefore, the association of lipid with the monocyte surface appears to be dependent on temperature. Further evidence for the receptor nature of these enhancing glycolipids is provided by experiments involving affinity purification experiments. Coupling of bovine brain mixed gangliosides to agarose resulted in a matrix capable of reversibly binding MIF. GD1a-agarose was inactive in this respect.

Hematopoietic subpopulations express cross-reactive, lineage-specific molecules detected by monoclonal antibody

The molecular specificity of a rat anti-mouse monoclonal antibody for cell surface antigens expressed by T- and B-lymphocyte subsets, erythrocytes and polymorphonuclear neutrophils (PMN) was determined. The antibody reacts with B-lymphocyte-associated molecules which migrated as a sharp 48,000 mol. wt band on SDS-PAGE. The antibody reacts with heterogeneous thymocyte and PMN molecules with a predominant mol. wt of 52,000. The same antibody reacts with heat-stable, amphipathic, organic-solvent-soluble erythrocyte molecules of mol. wt 35,000-40,000 present in Folch upper-phase ganglioside fractions, and evidence is presented that the determinant is protein-defined. Thus, a single monoclonal reagent which recognizes distinct, lineage-specific cell surface proteins on erythroid, lymphoid and myeloid elements may be used to probe not only the characteristic patterns of development of these hematopoietic subsets, but also the biochemical functions of the protein antigens themselves. In the case of B- and T-lymphocytes, such functions may extend to involvement in ligand-induced maturation and repertoire selection.

The receptor function of galactosyltransferase during cellular interactions

The molecular mechanisms that underly cellular interactions during development are still poorly understood. There is reason to believe that complex glycoconjugates participate in cellular interactions by binding to specific cell surface receptors. One class of carbohydrate binding proteins that could serve as receptors during cellular interactions are the glycosyltransferases. Glycosyltransferases have been detected on a variety of cell surfaces, and evidence suggests that they may participate during cellular interactions by binding their specific carbohydrate substrates on adjacent cells or in extracellular matrix (see Refs. 1-4 for review). This review will focus on the receptor function of galactosyltransferase, in particular, during fertilization, embryonic cell adhesion and migration, limb bud morphogenesis, immune recognition and growth control. In many of these systems, the galactosyltransferase substrate has been characterized as a novel, large molecular weight glycoconjugate composed of repeating N-acetyllactosamine residues. The function of surface galactosyltransferase during cellular interactions has been examined with genetic and biochemical probes, including the T/t-complex morphogenetic mutants, enzyme inhibitors, enzyme modifiers, and competitive substrates. Collectively, these studies suggest that in the mouse, surface galactosyltransferase is under the genetic control of the T/t-complex, and participates in multiple cellular interactions during development by binding to its specific lactosaminoglycan substrate.

Demonstration of carbohydrate- and protein determined Ia antigens by monoclonal antibodies

Ten monoclonal alloantibodies were examined by submitting each antibody to five independent tests in order to determine whether they reacted primarily with the glycoprotein or glycolipid class of Ia antigens. The tests employed were as follows: (1) the ability to participate an Ia-like protein from the cell surface as detected by SDS-PAGE; (2) inhibition by protein-Ia extracts free of CHO-Ia; (3) inhibition by CHO-Ia extracts free of protein-Ia; (4) neuraminidase sensitivity of the antigen and (5) inhibition by simple sugars. Using these tests, three of the ten monoclonal antibodies were shown to recognize a CHO-Ia antigen while seven recognized the protein class of Ia antigens. The three CHO-Ia-specific monoclonal antibodies recognized Ia specificities 2, 9 and 17. Monoclonal antibodies recognizing protein-defined Ia.2 and 17 specificities were also characterized. These results imply that some Ia specificities, as defined by genetic testing, can occur both as carbohydrate-defined and protein-defined determinants.--Sugar inhibition studies showed that CHO-Ia.2 has D-glucosamine as its immunodominant sugar while CHO-Ia.17 shows preference for a beta-linked galactose. Furthermore, studies with neuraminidase demonstrated that sialic acid plays a role in the antigenic determinants of CHO-Ia.9 and CHO-Ia.17. Finally, it is noteworthy that CHO-Ia.2, the private specificity of the k haplotype, appears to be expressed only on cells and not in serum. These studies clearly demonstrate the existence of the two Ia antigen classes and emphasize the complexity of the murine I region.