CD19 has a potential CD77 (globotriaosyl ceramide)-binding site with sequence similarity to verotoxin B-subunits: implications of molecular mimicry for B cell adhesion and enterohemorrhagic Escherichia coli pathogenesis

Establishment of a monoclonal antibody directed against Gb3Cer/CD77: a useful immunochemical reagent for a differentiation marker in Burkitt's lymphoma and germinal centre B cells

A new monoclonal antibody (TU-1) directed against the Gal alpha 1-4Gal beta 1-4Glc residue of the Gb3Cer/CD77 antigen was prepared by the hybridoma technique following immunization of mice with an emulsion composed of monophosphoryl lipid A, trehalose dimycolate, and Gb3Cer isolated from porcine erythrocytes. TU-1 showed reactivity towards Gb3Cer and lyso-Gb3Cer(Gal alpha 1-4Gal beta 1-4Glc beta 1-1'Sph), although the reactivity towards lyso-Gb3Cer was about 10-fold lower than that to Gb3Cer. But it did not react with other structurally-related glycolipids, such as LacCer (Gal beta 1-4Glc beta 1-1'Cer), Gg3Cer, Gg4Cer, Gb4Cer (GalNAc beta 1-3Gal alpha 1-4Gal beta 1-4Glc beta 1-1'Cer), galactosylparagloboside (Gal alpha 1-3Gal beta 1-4GlcNAc beta 1-3Gal beta 1-4Glc beta 1-1'Cer), sulfatide (HSO3-3Gal beta 1-1'Cer), other gangliosides (GM3, GM2, GM1a, GD1a and GT1b), or P1 antigen (Gal alpha 1-4Gal beta 1-4GlcNAc beta 1-3Gal beta 1-4Glc beta 1-1'Cer) among neutral glycolipids prepared from P1 phenotype red blood cells. Furthermore, TU-1 reacted with viable lymphoma cells, such as human Burkitt lymphoma cell line, Daudi, and Epstein-Barr virus (EBV)-transformed B cells by the immunofluorescence method, and also with germinal centre B cells in human tonsil and vessel endothelial cells in human thymus histochemically. These results indicate that TU-1 is a monoclonal antibody directed against Gb3Cer/CD77 antigen and can be utilized as a diagnostic reagent for Burkitt's lymphoma and also for detection of the blood group Pk antigen in glycolipid extracts of erythrocytes.

Intracellular transport and processing of protein toxins produced by enteric bacteria

Bacterial toxins are associated with disease in humans and animals. Toxins can either be preformed in food or produced by bacteria in the intestine. There are two types of toxins: heat-labile protein toxins and heat stabile toxins. Heat labile toxins are produced by Bacillus cereus, Clostridium perfringens, Escherichia coli, and Vibrio cholerae, and heat-stabile enterotoxins consisting of relatively few amino acids are produced by Escherichia coli and acts by activation of guanylate cyclase. Similarly, heat-stabile entero-toxins are also produced by Staphylococcus aureus, a common cause of food poisoning in the United States, and Yersenia enterocolitica. Protein toxins produced by enteric bacteria can intoxicate intestinal cells and can also be taken up from the gut and reach other cells in the body. For example the Shiga-like toxins (vero-toxins) can intoxicate endothelial cells in the kidney and cause kidney failure. Intracellular transport and processing of a few of the protein toxins produced by enteric bacteria, namely Clostridium difficile toxin A and B, cholera toxin and the related heat-labile toxin produced by Escherichia coli, and Shiga toxin and Shiga-like toxins are presented.

Genetic linkage of familial granulomatous inflammatory arthritis, skin rash, and uveitis to chromosome 16

Blau syndrome (MIM 186580), first described in a large, three-generation kindred, is an autosomal, dominantly inherited disease characterized by multiorgan, tissue-specific inflammation. Its clinical phenotype includes granulomatous arthritis, skin rash, and uveitis and probably represents a subtype of a group of clinical entities referred to as "familial granulomatosis." It is the sole human model with recognizably Mendelian inheritance for a variety of multisystem inflammatory diseases affecting a significant percentage of the population. A genomewide search for the Blau susceptibility locus was undertaken after karyotypic analysis revealed no abnormalities. Sixty-two of the 74-member pedigree were genotyped with dinucleotide-repeat markers. Linkage analysis was performed under a dominant model of inheritance with reduced penetrance. The marker D16S298 gave a maximum LOD score of 3.75 at theta = .04, with two-point analysis. LOD scores for flanking markers were consistent and placed the Blau susceptibility locus within the 16p12-q21 interval.

Aglycone modulation of glycolipid receptor function

The aglycone has been largely ignored in consideration of glycoconjugate function. Evidence is reviewed which suggests that the role of the lipid in glycolipid carbohydrate function may be particularly significant. The lipid moiety can promote or reduce carbohydrate exposure of membrane glycolipids. Theoretical calculation has indicated that the plane of the plasma membrane can restrict the permitted conformations of a given glycolipid oligosaccharide. Thus the lipid moiety may influence the relative conformation of such carbohydrate sequences. Evidence of ceramide regulation of glycolipid function can be found in studies of enzyme substrate specificity, antiglycolipid recognition and bacterial/host cell interactions. Studies of verotoxin binding to its glycolipid receptor globotriaosyl ceramide indicate that modulation of receptor function by glycolipid fatty acid content plays an important role in in vitro binding assays, cell cytotoxicity and intracellular routing.

Activation of B lymphocytes: integrating signals from CD19, CD22 and Fc gamma RIIb1

Three accessory membrane proteins, CD19, CD22 and Fc gamma RIIb1, alter signaling through membrane immunoglobulin of B cells by binding cytosolic proteins containing SH2 domains. Recent biochemical and genetic studies have shown that these receptors enable B cells to amplify responses to certain T-cell-dependent antigens (CD19), to restrict their response to T-cell zones of secondary lymphoid organs (CD22), and to dampen their response to antigens for which IgG is already available (Fc gamma RIIb1).

Two distinct binding sites for globotriaosyl ceramide on verotoxins: identification by molecular modelling and confirmation using deoxy analogues and a new glycolipid receptor for all verotoxins

BACKGROUND

The Escherichia coli verotoxins (VTs) can initiate human vascular disease via the specific recognition of globotriaosyl-ceramide (Gb3) on target endothelial cells. To explore the structural basis for receptor recognition by different VTs we used molecular modelling based on the crystal structure of VT1, mutational data and binding data for deoxy galabiosyl receptors.

RESULTS

We propose a model for the verotoxin 'cleft-site complex' with Gb3. Energy minimizations of Gb3 within the 'cleft site' of verotoxins VT1, VT2, VT2c and VT2e resulted in stable complexes with hydrogen-bonding systems that were in agreement with binding data obtained for mono-deoxy analogues of Gb3. N-deacetylated globoside (aminoGb4), which was found to be a new, efficient receptor for all verotoxins, can be favourably accommodated in the cleft site of the VTs by formation of a salt bridge between the galactosamine and a cluster of aspartates in the site. The model is further extended to explain the binding of globoside by VT2e. Docking data support the possibility of an additional binding site for Gb3 on VT1.

CONCLUSIONS

The proposed models for the complexes of verotoxins with their globoglycolipid receptors are consistent with receptor analogue binding data and explain previously published mutational studies. The results provide a first approach to the design of specific inhibitors of VT-receptor binding.

Mapping of a susceptibility locus for Crohn's disease on chromosome 16

Crohn's disease (CD) and ulcerative colitis are the major forms of chronic inflammatory bowel diseases in the western world, and occur in young adults with an estimated prevalence of more than one per thousand inhabitants. The causes of inflammatory bowel diseases remain unknown, but genetic epidemiology studies suggest that inherited factors may contribute in part to variation in individual susceptibility to Crohn's disease. A genome-wide search performed on two consecutive and independent panels of families with multiple affected members, using a non-parametric two-point sibling-pair linkage method, identified a putative CD-susceptibility locus on chromosome 16 (P less than 0.01 for each panel). The localization was centered around loci D16S409 and D16S419 by using multipoint sibpair analysis (P less than 1.5x10(-5)). This region of the genome contains candidate genes which may be relevant to the pathogenic mechanism of inflammatory bowel diseases.

CD40 and B cell antigen receptor dual triggering of resting B lymphocytes turns on a partial germinal center phenotype

Phenotypic alterations occur when resting human B lymphocytes become germinal center (GC) cells. These include the induction of surface CD38, CD95 (FAS/APO-1), and carboxy-peptidase-M (CPM), a recently described GC marker. However, the factors that govern the in vivo induction of these surface molecules on B cells remain unknown. Here, we purified resting (CD38-) human B lymphocytes from tonsils in an attempt to establish culture conditions resulting in the induction of these three GC markers. We show that interferon (IFN) alpha or IFN-gamma, as well as antibodies against the B cell antigen receptor (BCR), could induce CD38 on resting B lymphocytes, a phenomenon further enhanced by CD40 stimulation. Concomitantly, CD95 was upregulated by CD40 ligation and, to a lesser extent, by IFN-gamma. By contrast, CPM expression could be upregulated only through BCR triggering. This CPM induction was specifically enhanced by CD19 or CD40 ligation. CD40 + BCR stimulation of resting B cells with CD40 ligand-transfected fibroblastic cells in the presence of cross-linked anti-BCR monoclonal antibodies resulted in the coexpression of CD38, CD95, and CPM. As GC cells, these cells also expressed CD71, CD80 (B7.1), and CD86 (B7.2), but not CD24. However, CD10+ or CD44- B cells could not be detected in these culture conditions, suggesting that yet other signals are required for the induction of these GC markers. Consistent with a GC phenotype, CD40 + BCR-stimulated cells exhibited reduced viability when cultured for 20 h in the absence of stimulus. These results first demonstrate that cotriggering of resting B cells through BCR and CD40 induces both phenotypic and functional GC features. They also show that IFN and CD19 triggering of resting B cells specifically modulate the expression of GC markers.

Engaging CD19 or target of an antiproliferative antibody 1 on human B lymphocytes induces binding of B cells to the interfollicular stroma of human tonsils via integrin alpha 4/beta 1 and fibronectin

Adhesion of B lymphocytes within the different compartments of secondary lymphoid organs is essential for the function of the humoral immune response. It is not currently known how the temporary immobilization of B cells in distinct areas of this complex microenvironment is regulated. The present study aimed at defining B cell antigens that initiate binding of B cells to human tonsil sections in situ. Engaging the B cell antigens CD19 and target of an antiproliferative antibody 1 (TAPA-1) with monoclonal antibodies induced adhesion of these B cells to the interfollicular stroma. This binding occurred through the integrin alpha 4 beta 1 on the B cell surface and via the extracellular matrix protein fibronectin expressed in the interfollicular compartment of the tonsil. Signaling through either antigen, CD19 or TAPA-1, depended on tyrosine kinases. Binding induced by engaging CD19 required an intact cytoskeleton, whereas TAPA-1-transmitted adhesion did not. We suggest that CD19 and TAPA-1 have a novel and unique function by regulating an alpha 4 beta 1/fibronectin-mediated binding of B cells to the interfollicular stroma of lymphoid tissues.

Specific binding of Fyn and phosphatidylinositol 3-kinase to the B cell surface glycoprotein CD19 through their src homology 2 domains

CD19 is a B cell surface protein capable of forming non-covalent molecular complexes with a number of other B cell surface proteins including the CD21/CD81/Leu-13 complex as well as with surface immunoglobulin. CD19 tyrosine phosphorylation increases after B cell activation, and is proposed to play a role in signal transduction through its cytoplasmic domain, which contains nine tyrosine residues. Several second messenger proteins have been shown to immunoprecipitate with CD19, including p59 Fyn (Fyn), p59 Lyn (Lyn) and phosphatidylinositol-3 kinase (PI-3 kinase). These associations are predicted to occur via the src-homology 2 (SH2) domains of the second messenger proteins. Two of the cytoplasmic tyrosines in the CD19 cytoplasmic region contain the consensus binding sequence for the PI-3 kinase SH2 domain (YPO4-X-X-M). However, the reported consensus binding sequence for the Fyn and Lyn SH2 domains (YPO4-X-X-I/L) is not found in CD19. We investigated the capacity of CD19 cytoplasmic tyrosines to bind both Fyn and PI-3 kinase SH2-domain fusion proteins. In activated B cells, both Fyn and PI-3 kinase SH2-domain fusion proteins precipitate CD19. Using synthetic tyrosine-phosphorylated peptides comprising each of the CD19 cytoplasmic tyrosines and surrounding amino acids, we investigated the ability of the Fyn SH2 and PI-3 kinase SH2 fusion proteins to bind to the different CD19 cytoplasmic phosphotyrosine peptides. ELISA revealed that the two CD19 cytoplasmic tyrosine residues contained within the Y-X-X-M sequences (Y484 and Y515) bound preferentially to the PI-3 kinase SH2-domain fusion proteins. Two different tyrosines (Y405 and Y445) bound preferentially to the Fyn SH2-domain fusion protein via a novel sequence, Y-E-N-D/E, different from that previously reported for the Fyn SH2 domain. In precipitation studies, peptide Y484 was able to compete with tyrosine phosphorylated CD19 specifically for binding to the PI-3 kinase SH2 domain fusion proteins, while peptides Y405 and Y445 were able to compete specifically for binding to the Fyn SH2 domain fusion proteins. These results indicate that CD19 may be capable of binding both Fyn and PI-3 kinase concurrently, suggesting a mechanism for CD19 signal transduction, in which binding of PI-3 kinase to the Fyn SH3 domain results in activation of PI-3 kinase.

The bacterial colicin active against tumor cells in vitro and in vivo is verotoxin 1

We have identified verotoxin 1 (VT1) as the active component within an antineoplastic bacteriocin preparation from Escherichia coli HSC10 studied over two decades. Recombinant VT1 can simulate the toxicity of anticancer proteins (ACP), and the antineoplastic activity of ACP (and VT1) was abrogated by treatment with anti-VT1 antibody. Similarly, VT1 mimics the protective effect of ACP in a murine metastatic fibrosarcoma model. Prior immunization with VT1 B subunit prevents the effect of VT1 or ACP in this model. The activity of ACP against a variety of human ovarian cell lines was mimicked by VT1, and multidrug-resistant variants were significantly hypersensitive. Primary ovarian tumors and metastases contain elevated levels of globotriaosylceramide compared with normal ovaries, and overlay of frozen tumor sections showed selective VT binding to tumor tissue and the lumen of invading blood vessels. Our contention that VT1 could provide an additional approach to the management of certain human neoplasms is discussed.

Decreased incorporation of D-glucosamine into glycosphingolipids of intact Familial Dysautonomia lymphoblasts

Familial Dysautonomia (FD) is an autosomal recessive Ashkenazi Jewish genetic disease, of unknown etiology, involving deficits in both autonomic and sensory functions. Previously, we found statistically significant increases in globotriaosylceramide (Gb3) in FD fibroblasts and lymphoblasts, and a decrease in ganglioside levels. FD fibroblasts exhibited pleiomorphic changes at the light microscopy level, suggestive of changes in the plasma membrane. We described an increase in Gb3 on the surface of synchronized cells at the G1/S boundary of the cell cycle, based on Gb3-verotoxin (derived from E. coli) interactions. Using D-glucosamine-1-14C as an in vitro precursor, we herein report a marked decrease in the rate of incorporation of D-glucosamine into the sialic acid and the N-acetylgalacto/glucosamine moieties of gangliosides and neutral glycosphingolipids in intact FD compared to control lymphoblasts. The total ganglioside content of FD cells (primarily GM3, measured as incorporation of 3H from NaB3H4) was also decreased. These data indicate differences in the turnover of sialic acid and N-acetylated sugar constituents in FD vs normal cells.