Immunocytological and immunochemical analysis on the common acute lymphoblastic leukemia antigen (CALLA): evidence that CALLA on ALL cells and granulocytes are structurally related

Characterization of a Shiga-Toxin 1-Resistant Stock of Vero Cells

Shiga toxins (Stxs, also referred to as verotoxins) were first described as a novel cytotoxic activity against Vero cells. In this study, we report the characterization of an Stx1-resistant (R-) stock of Vero cells. (1) When the susceptibility of R-Vero cells to Stx1 cytotoxicity was compared to that of Stx1-sensitive (S-) Vero cells by methylthiazolyldiphenyl-tetrazolium bromide (MTT) assay, cell viability after 48-hr exposure to 10 pg/ml of Stx1 was greater than 80% and less than 15%, respectively. (2) Although both a binding assay of fluorescence-labeled Stx1 and lipid analysis indicated considerable expression of Gb3Cer, a functional receptor for Stxs, in both Vero cells, anti-Gb3Cer monoclonal antibodies capable of binding to S-Vero cells failed to effectively label R-Vero cells, suggesting a conformational difference in the Gb3Cer expressed on R-Vero cells. (3) The lipid analysis also showed that the R-Vero cells contained significant amounts of Gb4Cer. In addition, introduction of exogenous Gb4Cer into S-Vero cells slightly inhibited Stx1 cytotoxicity, suggesting some correlation between glycosphingolipid composition and Stx1 resistance. (4) Both butyrate treatment and serum depression eliminated the Stx1 resistance of R-Vero cells. (5) The results of the analysis by confocal microscopy suggest a difference in intracellular transport of Stx1 between R-Vero and S-Vero cells. Further study of R-Vero cells may provide a model of Stx1 resistance via distinct intracellular transport of Stx1.

The human CD10 lacking an N-glycan at Asn(628) is deficient in surface expression and neutral endopeptidase activity

BACKGROUND

CD10, also known as neprilysin or enkephalinase exhibiting neutral endopeptidase (NEP) activity, is expressed by B-lineage hematopoietic cells as well as a variety of cells from normal tissues. It cleaves peptides such as cytokines to act for terminating inflammatory responses. Although CD10 molecules of the human pre-B-cell line NALM-6 have 6 consensus N-glycosylation sites, three of them are known to be N-glycosylated by X-ray crystallography.

METHODS

In order to investigate the role of N-glycans in the full expression of NEP activity, we modified N-glycans by treatment of NALM6 cells with various glycosidases or alter each of the consensus N-glycosylation sites by generating site-directed mutagenesis and compared the NEP activities of the sugar-altered CD10 with those of intact CD10.

RESULTS

CD10 of the human B-cell line NALM-6 was dominantly localized in raft microdomains and heterogeneously N-glycosylated. Although neither desialylation nor further degalactosylation caused defective NEP activity, removal of only a small part of N-glycans by treatment with glycopeptidase F under non-denaturing conditions decreased NEP activity completely. All of the three consensus sites of CD10 in HEK293 cells introduced with wild type-CD10 were confirmed to be N-glycosylated. Surface expression of N-glycan at Asn(628)-deleted CD10 by HEK293 cells was greatly decreased as well as it lost entire NEP activities.

CONCLUSIONS

N-glycosylation at Asn(628) is essential not only for NEP activities, but also for surface expression.

GENERAL SIGNIFICANCE

Quality control system does not allow dysfunctional ecto-type proteases to express on plasma membrane.

Characterization of new monoclonal antibodies against porcine lymphocytes: molecular characterization of clone 7G3, an antibody reactive with the constant region of the T-cell receptor δ-chains

A battery of mouse monoclonal antibodies (mAbs) reactive with porcine peripheral blood (PB) leukocytes was generated. Among the mAbs, 6F10 was found to react probably with cluster of differentiation (CD)8 alpha-chain, while 7G3 and 3E12 were found to recognize gammadelta T-cells, as revealed by two-color flow cytometric and immunoprecipitation studies. 7G3 was shown to react with the constant (C) region of the T-cell receptor (TCR) delta-chain by the following facts: (1) 7G3 immunoprecipitated full-length TCR delta-chain protein fused with glutathione S-transferase (GST) produced by Esherichia coli and (2) 7G3 reacted with TCR delta-chain expressing Cos-7 cells transfected with either full-length or N-terminal deleted mutant cDNA, but did not react with Cos-7 cells transfected with C-terminal deleted mutant TCR delta-chain cDNA. All three mAbs produced high-quality immunostaining results on frozen sections, revealing a distinct distribution of gammadelta T-cells and CD8(+) cells. This report precisely characterizes mAbs against porcine TCR for the first time, facilitating molecular biological investigations of the porcine immune system.

Development of Novel Monoclonal Antibody 4G8 against Swine Leukocyte Antigen Class I α Chain

A mouse monoclonal antibody (MAb) was generated against swine leukocyte antigen (SLA) class I alpha chain. A newly developed series of MAb clones that react with pan leukocytes were selected and tested by immuno-histochemistry using SLA class I alpha chain expressing Cos-7 cells. Among them, MAb 4G8 was characterized by the following features: (1) 4G8 reacted with Cos-7 cells transfected with SLA class I alpha chain from the d haplotype, (2) 4G8 recognized epitopes that were different from those of commercially available anti-SLA class I MAbs 74-11-10 and PT85A, and (3) 4G8 could be used to immunostain frozen sections of thymus, spleen, lymph node, kidney, and liver tissues with good results.

Diagnostic importance of CD179a/b as markers of precursor B-cell lymphoblastic lymphoma

Surrogate light chains consisting of VpreB (CD179a) and lambda5 (CD179b) are expressed in precursor B cells lacking a complete form of immunoglobulin and are thought to act as substitutes for conventional light chains. Upon differentiation to immature and mature B cells, CD179a/b disappear and are replaced with conventional light chains. Thus, these molecules may be useful as essential markers of precursor B cells. To examine the expression of the surrogate light-chain components CD179a and CD179b in precursor B-cell lymphoblastic lymphoma, we analyzed tissue sections using immunohistochemistry techniques. Among a number of monoclonal antibodies for the surrogate light chains, VpreB8 and SL11 were found to detect CD179a and CD179b, respectively, in acetone-fixed fresh frozen sections. Moreover, we also observed VpreB8 staining in formalin-fixed, paraffin-embedded sections. Using these antibodies, we found that CD179a/b were specifically expressed in precursor B-cell lymphoblastic lymphomas, but not in mature B-cell lymphomas in childhood. Furthermore, other pediatric tumors that must be included in a differential diagnosis of precursor B-cell lymphoblastic lymphoma, including precursor T-cell lymphoblastic lymphoma, extramedullary myeloid tumors, and Ewing sarcoma, were also negative for both CD179a and CD179b. Our data indicate that CD179a and CD179b may be important markers for the immunophenotypic diagnosis of precursor B-cell lymphoblastic lymphomas.

Costimulatory signals distinctively affect CD20- and B-cell-antigen-receptor-mediated apoptosis in Burkitt's lymphoma/leukemia cells

CD20 is a B-cell differentiation antigen and known to induce apoptosis in Burkitt's lymphoma/leukemia (BL) cells upon antibody-mediated crosslinking. We examined the biological effect of CD20 crosslinking on BL cell lines and observed that apoptosis induction is accompanied by activation of multiple caspases, including caspase-8, -9, -3, -2, and -7. Further investigation revealed a clear synergism between apoptosis mediated by CD20 and by B-cell antigen receptor (BCR). Examination of the effect of simultaneous crosslinking of other cell surface molecules with crosslinking of CD20 or BCR on apoptosis induction showed that these molecules had either a synergistic or inhibitory effect on induction of apoptosis. It is worth noting that some molecules had a different effect on CD20- and BCR-mediated apoptosis. Simultaneous crosslinking of the molecules CD10, CD22, CD72, and CD80 inhibited BCR-mediated apoptosis, but enhanced CD20-mediated apoptosis. Further studies revealed that regulation of CD20-induced apoptosis by other costimulatory molecules is achieved by modification of caspase activation. CD20-mediated apoptosis in BL cells may provide not only a model for understanding the mechanism regulating clonal selection of B cells but a new therapeutic strategy for BL patients.

Single-step method for purification of Shiga toxin-1 B subunit using receptor-mediated affinity chromatography by globotriaosylceramide-conjugated octyl sepharose CL-4B

A new single-step purification method for Shiga toxin (Stx) was developed using receptor-mediated affinity chromatography, in which Gb3Cer (globotriaosylceramide) was conjugated to octyl Sepharose CL-4B as a carrier. This method achieves high yield and high purity in a small column on which Gb3Cer has been immobilized at high density. Using this affinity column, the Stx1 B subunit was purified with homogeneity by a one-step procedure from a crude extract of recombinant Stx1 B subunit-producing Escherichia coli. The purified Stx1 B subunit conserved a natural pentamer structure confirmed by gel filtration and sedimentation equilibrium analysis. Furthermore, the purified Stx1 B subunit was able to bind specifically to Gb3Cer expressed on Burkitt's lymphoma cells. This versatile purification method can be used to isolate various types of natural as well as recombinant Stx, facilitating fundamental studies of human diseases caused by this toxin.

Activation of the caspase cascade during Stx1-induced apoptosis in Burkitt's lymphoma cells

Shiga toxin 1 (Stx1) produced by Escherichia coli has been reported to induce apoptosis in many different cell types, including Burkitt's lymphoma (BL) cells. Since it has been established that the caspases play essential roles as the effector molecules in the apoptotic process in most cases, we examined the kinetics of caspase activation during the process of Stx1-mediated apoptosis of BL cells. Using Ramos BL cells that are highly sensitive to Stx1-mediated cytotoxicity, we observed that multiple caspases, including caspase-3, -7, and -8 were promptly activated following Stx1 treatment, as indicated by both the procaspase cleavages and enhancement of cleavage of the tetrapeptide substrates of the caspases. In addition, the inhibition assay revealed that caspase-8 is located upstream of both caspase-3 and -7, suggesting that Stx1-mediated apoptosis utilizes a similar caspase cascade to that involved in Fas-mediated apoptosis. Neither anti-Fas mAb nor TNF-alpha, however, affected the Stx1-mediated apoptosis of Ramos cells. Although the precise mechanism of Stx1-mediated activation of caspase-8 is still unclear, we have demonstrated that crosslinkage of CD77, a functional receptor for Stx1, with specific antibody is sufficient to induce activation of caspase-8. Our findings should provide new insight into the understanding of the molecular basis of Stx1-mediated cell injury.

Characterization of monoclonal antibodies against mouse and rat platelet glycoprotein V (CD42d)

The mouse- and rat-platelet-specific hamster monoclonal antibody (MAb) 1C2, previously found to react with a thrombin-sensitive 74-kD glycoprotein, was now shown to recognize platelet glycoprotein V (GPV, CD42d). 1C2 reacted with NIH-3T3 cells in which recombinant mouse or rat GPV was expressed. Both 1C2 and 4A5, another mouse-platelet-specific rat MAb, immunoprecipitated GVP, although they recognized different epitopes. Side-by-side comparison confirmed that 1C2 as well as RPM.9, a MAb against rat GPV, recognized the same rat platelet molecule. In a mouse bone marrow culture, 1C2+ megakaryocytes emerged from CD41 (GPIIb)+1C2- megakaryocytes. Because 1C2+ megakaryocytes exhibited higher DNA ploidy distribution than CD41+ cells, GPV likely appears in the late stage of megakaryocyte maturation. This study established 1C2 as a MAb against mouse and rat GPV, namely CD42d, and as useful tool to study rodent megakaryopoiesis.

Globotriaosyl ceramide (CD77/Gb3) in the glycolipid-enriched membrane domain participates in B-cell receptor-mediated apoptosis by regulating lyn kinase activity in human B cells

The role of CD77 expressed on a fraction of germinal center B cells, also known as glycosphyngolipid Gb3, and as a functional receptor for Shiga toxins (Stx) in B-cell receptor (BCR)-mediated apoptosis was investigated. Using Stx1-sensitive Burkitt's lymphoma Ramos cells as an in vitro model of CD77(+) germinal center B cells, intracellular signaling events mediated by either Stx1 or anti-CD77 antibody were examined immunobiochemically and immunocytologically. We observed prompt activation of Lyn and Syk kinases leading to increased binding of these proteins to surface IgM (sIgM) in Ramos cells after Stx1 treatment. We also observed microscopic colocalization of CD77 and sIgM after stimulation with Stx1. Along with the synergism between the cross-linking of CD77 and that of sIgM in their effect on apoptosis induction, it was highly probable that CD77 cross-linking induces activation of the BCR signaling cascade. Analysis using sucrose density gradient centrifugation suggested that Stx1 binding to CD77 induced recruitment and activation of Lyn in the glycolipid-enriched membrane (GEM) fractions. Once activated, however, Lyn seemed to acquire an increased detergent solubility and moved outside of the GEM fractions. This study describes the participation of the GEM domain in BCR-signaling cascade and suggests a possible role of CD77 as a regulator of BCR-induced apoptosis in human B cells.

Functional conservation of platelet glycoprotein V promoter between mouse and human megakaryocytes

OBJECTIVE

In an attempt to clarify the megakaryo-specific regulatory mechanism of GPV gene transcription, we characterized the 5'-flanking region of the mouse GPV gene.

MATERIALS AND METHODS

The promotor activity of a -481/+22 5'-fragment of the mouse GPV gene was examined in normal mouse bone marrow cells (BMC) and various human cell lines using two distinct reporter gene assay systems, luciferase and green fluorescence protein (GFP).

RESULTS

When a DNA construct consisting of this fragment and a GFP reporter gene were transiently expressed in thrombopoietin-supported mouse BMC culture, GFP was identified only in megakaryocytes. The same construct expressed high levels of GFP in the human megakaryocytic Dami line. When assessed by dual luciferase assay, the full -481/+22 fragment could drive variable promoter activity in human as well as mouse megakaryocytic lines but did not work in non-megakaryocytic cells. Sufficient transcriptional activation of this fragment was restricted to the cells expressing apparent GPV mRNA. A deletion and point mutation study indicated that GATA and Ets motifs, typical cis-acting elements for platelet-specific genes, located of -75 and -46, respectively, were essential for promoter function.

CONCLUSION

The GPV promoter has the general characteristics found in platelet-specific genes, and the mechanism for megakaryocyte-specific, maturation-dependent regulation of GPV gene transcription is highly conserved between mouse and human. Analysis of GPV transcription mechanism utilizing human lines as well as BMC should provide new information on the final maturational process of megakaryocytes.

Characteristic expression of Hck in human B-cell precursors

OBJECTIVE

To identify molecules involved in signaling for early B-cell development, we investigated the expression of signal transduction-related proteins in B-cell progenitors.

MATERIALS AND METHODS

[corrected] Normal as well as leukemic B-cell progenitors were examined by immunoblotting and immunofluorescence study.

RESULTS

[corrected] In a survey of the expression of a broad range of signal transduction molecules, the Src-family protein tyrosine kinases were found to be differentially expressed in early B-cell differentiation. [corrected] Analysis of freshly prepared precursor-B acute lymphoblastic leukemia cells and B-lineage cell lines showed Hck and Lyn are major Src-family protein tyrosine kinases expressed in this type of leukemic blasts. [corrected] However, heterogeneity of Hck and Lyn expression was found in these cells, and precursor-B acute lymphoblastic leukemia cells subsequently were classified according to the expression pattern of Hck and Lyn as Hck/Lyn dual-negative, Hck-predominant, Hck/Lyn dual-positive, and Lyn-predominant. Further studies on normal B-lineage cells indicated that the Src-family protein tyrosine kinases are expressed sequentially in a differentiation-dependent fashion during B-cell ontogeny and that the predominant expression of Hck is a common feature in B-cell progenitors, whereas Lyn expression is more significant in mature B cells.

CONCLUSIONS

Although the biologic significance remains unknown, sequential expression of Src-family protein tyrosine kinases should play a role in regulation of early B-cell differentiation.

The detection of Shiga toxins in the kidney of a patient with hemolytic uremic syndrome

Infection of Shiga toxin (Stx)-producing Escherichia coli induces hemolytic uremic syndrome (HUS) in 10 to 15% of cases in infants and young children. Although the endothelial cell damage induced by Stx is widely believed to be a primary event of renal dysfunction in HUS, the precise mechanism remains to be elucidated. We were able to examine the kidney obtained at autopsy of a child who died after HUS associated with Stx-producing Escherichia coli O157:H7 infection, and immunohistochemistry indicated the deposition of Stxl and Stx2 in a portion of the distal tubular epithelia. To our knowledge, this is the first report to show the presence of Stx in human tissue of a patient with HUS, and the results obtained in this study provide evidence that Stx indeed migrates into the kidney and binds to renal tubules during Stx-producing Escherichia coli infection.

Verotoxins induce apoptosis in human renal tubular epithelium derived cells

Apoptosis mediated by verotoxins (VTs) has been identified in a renal carcinoma cell line, ACHN cells, which are an in vitro model of renal tubular epithelial cells. ACHN cells express the renal tubular marker CD24 as well as globotriaosyl ceramide/CD77, the receptor for VTs. VT binding to the ACHN cell surface was confirmed by positive staining with antibodies to the VTs. Treatment of ACHN cells with VTs induced prompt growth inhibition and cell death, and fragmentation of the genomic DNA in cells, typical of apoptosis, was observed. The expression of apoptotic antigen 7A6 detected by APO2.7 antibody in ACHN cells further supports the occurrence of apoptosis as a result of VT treatment. Cycloheximide enhanced VT-mediated apoptosis of ACHN cells, suggesting a strong correlation between the inhibition of protein synthesis and VT-mediated apoptosis. Moreover, tumor necrosis factor-alpha had a synergistic effect on VT-mediated apoptosis in ACHN cells. Considering the above evidence together with the clinical evidence showing the presence of apoptosis in the renal epithelium of a HUS patient, our results suggest a VT-induced apoptotic mechanism in normal renal tubular epithelium that may contribute to the pathogenesis of hemolytic uremic syndrome.

Lack of CD54 expression and mutation of p53 gene relate to the prognosis of childhood Burkitt's lymphoma

Expression of the intercellular adhesion molecule-1 (CD54) as well as the mutations of p53 gene were studied in childhood Burkitt's lymphoma (BL). Expression of CD54 was identified in 6 of 15 fresh BL cases. Mutations of p53 gene, analyzed by polymerase chain reaction-single stranded chain polymorphism followed by sequencing, were found in 5 of 14 cases examined. Interestingly, all the cases with p53 mutation were CD54 negative. This high frequency of p53 mutation in the CD54 negative group prompted us to analyze the clinical features of these cases. Six of 15 cases died within 21 months after initiation of therapy and five of these were CD54 negative. In addition, four of these had p53 mutation. These results suggest that the lack of CD54 by BL cells may provide the background for the mutation of p53 gene to occur which could result in the transformation to a more aggressive phenotype.

Characterization of the common acute lymphoblastic leukaemia antigen (CD10) as an activation molecule on mature human B cells

Distinct expression pattern of CD10 molecules during B cell activation was analysed using in vivo and in vitro systems. By two-colour flowcytometrical analysis, CD10 was found to be expressed at a specific stage of in vivo activating B cells. The expression of CD10 during B cell activation appeared to be unique from that of other activation-related B cell antigens including L29, MA6, OKT9 and OKT10. Although the expression of CD10 was associated with that of the activation-related B cell antigens, CD10+ B cells could be separated in the distinct fractions to those expressing other activation-related B cell antigens when fractionated by cell gravity. In particular, certain CD10+ B cells were detected positive for the resting B cell antigen, L30. In vitro studies revealed that CD10+ B cells arose from CD10- B cells at an early step of B cell activation, and disappeared lately when activated by Staphylococcus aureus Cowan I. Collectively, CD10 was an antigen transiently expressed at an early phase of B cell activation process. Expression of CD10 and other antigens on Burkitt's lymphomas (15 cases) was studied next. All cases were CD10+, and 87% (13 cases) were also L30+. In addition, six of CD10+ L30+ cases were L29+. This observation suggested that Burkitt's lymphomas were phenotypically similar to the B cells at an early phase of activation, those expressing CD10 and L30, simultaneously. The present study has dissected a precise expression pattern of CD10 on mature B cell activation in vitro and in vivo, and could be implicated for the histogenesis of one of the poorly characterized B cell lymphoma, namely Burkitt's lymphoma.

Human yolk-sac tumor antigen 2G10: biochemical characterization and significance as a serum antigen

The biochemical characterization of human yolk-sac tumor (YST) antigen 2G10, detected by monoclonal antibody (MAb) M912-2G10, was studied. Previous results indicated that glycolipids having a non-reducing terminal N-acetyllactosamine structure were the epitope of 2G10 on human erythrocytes. In this study, the glycoprotein nature of 2G10 on the infantile embryonal carcinoma line, MTE, was investigated. 2G10 activity, measured by a new enzyme-linked immunosorbent assay (2G10-ELISA), was recovered in residual fractions of MTE from which glycolipids were removed. Chromatographically, 3H-galactose-labelled 2G10 on MTE had a molecular weight (mw) of about 580 kDa, which decreased after pronase or alkaline-borohydride treatment. Our results indicate the glycoprotein nature of 2G10 on MTE. Furthermore, 2G10, both on erythrocytes and on MTE, was sensitive to galactosidase but not to neuraminidase and fucosidase, suggesting that terminal galactose is involved in the antigenic structure. It was also found by 2G10-ELISA that 2G10 sheds from tumor cells. Shedding occurs in nude mice transplanted with MTE as well as in patients with germ-cell tumors (GCTs). The serum level of 2G10 in non-tumor patients was low, but high levels were detected in patients with YSTs and with GCTs having YST components. Immunohistochemically, the presence of 2G10-positive YST components was shown in patients who had high serum levels of 2G10. Sera from other urogenital and childhood solid tumors did not have elevated 2G10. The mw of shed 2G10 was lower than that of 2G10 on the cell surfaces. Our results clearly indicate the usefulness of serum 2G10 as a tumor marker for GCTs having YST components.