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PubMed1996

The Epstein-Barr virus-binding site on CD21 is involved in CD23 binding and interleukin-4-induced IgE and IgG4 production by human B cells.

Human CD21 has previously been described as a receptor for the C3d,g and iC3b proteins of complement, as a receptor for the gp350/220 envelope glycoprotein of the Epstein-Barr virus (EBV) and also as a receptor for inerferon-alpha (IFN-alpha). Structurally, CD21 consists of 15 to 16 short consensus repeats (SCR) of 60 to 75 amino acids followed by a transmembrane domain and an intracytoplasmic region. We reported that CD23, a low-affinity receptor for IgE (Fc epsilon R2), is a new functional ligand for CD21. We recently found that the sites of interaction of CD23 on CD21 are on SCR 5 to 8 and 1-2. The first site is a lectin-sugar type of interaction and the second site is a protein-protein interaction. We report here that amongst the other ligands for CD21 (EBV, C3d,g and IFN-alpha), only EBV is able to inhibit the binding of CD23 to CD21. Furthermore, even a peptide from gp350/220 of EBV known to bind to CD21 is able to decrease CD23 binding to CD21. Since CD23/CD21 pairing is important in the control of IgE production, we tested the effect of the EBV-derived peptide on immunoglobulin production from peripheral blood mononuclear cells and purified tonsillar B cells. Interestingly, the EBV-peptide inhibited IgE and IgG4 production induced by interleukin-4, in a dose-dependent manner. The same results were obtained using either peripheral blood mononuclear cells or purified tonsillar B cells. Another CD21 ligand, C3, did not affect binding of CD23 to CD21 nor the production of IgE and IgG4. This study indicates that blocking CD23 binding to CD21 SCR 2 on human B cells selectively modulates immunoglobulin production.

B-Lymphocytes↗

PubMed1998

B-1-like cells exist in sheep. Characterization of their phenotype and behaviour.

Two populations of B lymphocytes, B-1 (CD5+ and/or CD11b+) and B-2 (CD5- and CD11b-) cells have been described. In mice, which is the species of reference for B-1 and B-2 cell studies, these two subsets present different developmental schemes, phenotypes, antibody repertoires, localization and behaviours. Interestingly, in sheep, B cells rearrange their immunoglobulin (Ig) loci around the neonatal period, similarly to murine B-1 cells. However, the phenotype of the sheep B cells has not been characterized with regards to their developmental pathway. In this report, we show that two sheep B-cell subsets can be distinguished on the basis of CD11b expression. Relative to CD11b- B cells, the CD11b+ B cells frequently co-express CD5, CD11c, higher levels of surface IgM (sIgM), show larger cell size and higher cell-cycling activity, and thus present a B-1-like phenotype. However, unlike murine B-1 cells, sheep B-1 like cells mainly localize in blood, display a higher propensity to spontaneous apoptosis relative to B-2-like cells, and proliferate after sIgM stimulation. Our data show that despite neonatal immunoglobulin loci rearrangements, sheep B cells do not all express a B-1-like phenotype. However, B-1-and B-2-like cells co-exist and present phenotypic and behavioural specificities. Nevertheless, sheep B-1-and B-2-like cells differ from the murine B-1 and B-2 cells in their cell behaviour. These subsets can thus not be considered as true homologues among species.

Animals↗

PubMed2002

Experimental Schistosomiasis japonica in the pig: immunohistology of the hepatic egg granuloma.

Use of the pig as an animal model in schistosomiasis research is increasing, but knowledge of the porcine immune response to schistosome infection is still very limited. We investigated the immunohistology of different maturation stages of the Schistosoma japonicum egg granuloma in pigs. Liver sections from pigs experimentally infected with S.japonicum for 9, 12 or 21 weeks were examined by immunohistochemistry using a three-step streptavidin-biotin-complex/immunoperoxidase method or a two-step alkaline phosphatase-mediated system. All granulomas showed marked expression of major histocompatibility complex (MHC) class II in epithelioid macrophages and were dominated by T lymphocytes, comprising both CD4+ and CD8+ phenotypes, with consistently higher proportions noted for CD8+ cells. B lymphocytes, as identified by expression of CD21, were confined to lymphoid nodular structures primarily associated with mature granulomas. Early and mature granulomas contained numerous immunoglobulin (Ig)G+ plasma cells. Significant differences in immunohistology related to duration of infection were not observed. The results indicate that all stages of the hepatic S.japonicum egg granuloma in the pig manifests MHC class II-dependent CD4+ T cell activity concomitant with infiltration of CD8+ T cells. B cell activity preceding the effector cell stage appears to occur in granuloma-associated lymphoid nodules, whereas antibody, mainly IgG, is produced within the granuloma.

Animals↗

PubMed2002

Relationship between reactive nitrogen intermediates and total immunoglobulin E, soluble CD21 and soluble CD23: comparison between cerebral malaria and nonsevere malaria.

To search for evidence of a protective role of the CD23/NO pathway against cerebral malaria, concentrations of reactive nitrogen intermediates (RNI) and sCD21, total immunoglobulin (Ig)E and sCD23 were compared between 17 cases of cerebral malaria and 33 controls. The geometric mean of sCD23 concentration was higher among cerebral malaria cases than among controls (optical density 2643/1495, P = 0.01). The ratio between sCD21 and sCD23 was significantly lower in cerebral malaria cases than in controls (0.67 +/- 0.02 versus 0.77 +/- 0.02, respectively, P = 0.009). Multiple linear regression analysis showed that, among cerebral malaria cases, there was a clear correlation between RNI and both IgE (P = 0.007) and sCD21 (P < 0.0001). Among controls, there was a strong negative correlation between RNI and sCD23 concentrations (r = -0.61, P < 0.0001). However, multivariate analysis unmasked the fact that, in controls, there was also a positive correlation between RNI and IgE (P = 0.045). Logistic regression showed that increased RNI concentrations were associated with a cerebral malaria adjusted odds ratio of 1.05 per unit increase [95% confidence interval (CI) 1.006-1.1, P = 0.02] and that an increased ratio between sCD21 and sCD23 was associated with protection from cerebral malaria (adjusted OR = 0.00001 per unit increase (95% CI 0-0.03, P = 0.005). These different immunological profiles suggest that, among controls, the CD23/NO pathway was chronically stimulated whereas, in cerebral malaria, its stimulation was acute, which could explain why some patients developed cerebral malaria and others did not.

Animals↗

PubMed1999

Low responsiveness to immunization with immunoglobulin E/antigen and immunoglobulin G/antigen complexes in H-2Ab mice.

Immunoglobulin (Ig)E and IgG antibodies specific for 2,4, 6-trinitrophenyl (TNP) are able to enhance the carrier-specific antibody response to TNP-conjugated soluble proteins such as bovine serum albumin (BSA). We have recently reported that mice carrying the MHC class II Ab molecule are low responders to immunization with IgE/antigen complexes and now show that H-2Ab mice are also low responders to IgG/antigen complexes. In addition, we found that spleen cells from naive low- and high-responder mice captured IgE/antigen complexes exclusively on B cells, and that the binding was completely inhibited by monoclonal antibodies (MoAbs) against the low-affinity receptor for IgE (FcepsilonRII or CD23). The IgG/antigen complexes were targeted both to B cells and macrophages. The binding of IgG/antigen to B cells primarily seemed to be dependent on the low-affinity receptor for IgG (FcgammaRII or CD32), although some influence of complement receptor 2 (CR2 or CD21) was seen. Capture of IgG/antigen complexes on macrophages was partially blocked by MoAbs against FcgammaRII/III. There was no difference in expression of FcepsilonRII, FcgammaRII/III, CR1, CR2, and CR3 between low- and high-responder strains, thus excluding low levels of these FcRs and CRs as a reason for low responsiveness in H-2Ab mice.

Animals↗

PubMed1980

Transfer of Epstein-Barr virus receptors to receptor-negative cells permits virus penetration and antigen expression.

Epstein-Barr virus (EBV) receptors were implanted into the membranes of receptor-negative cells, using Sendai virus envelopes as vehicles. The presence of the receptors in the target cell membrane was demonstrated by monitoring the fate of radioiodinated donor membranes. Receptors could be detected for at least 36 hr after implantation. [3H]Thymidine-labeled EBV bound efficiently to receptor-implanted cells but not to control cells. Binding was inhibited by an excess of nonlabeled virus. Of the [3H]thymidine-labeled EBV DNA, 50-75% was found inside the receptor-implanted, EBV-exposed cells 24 hr after the infection. The viral genome was functionally active in B lymphocyte-derived cell lines of human, murine, and baboon origin; in T lymphocyte-derived lines of human and murine origin; in mouse fibroblasts; and in freshly explanted mouse lymphocytes, as shown by the expression of EBV-determined nuclear, early, and viral capsid antigens.

Animals↗

PubMed1984

Epstein-Barr virus receptor of human B lymphocytes is the C3d receptor CR2.

Identity of the Epstein-Barr virus (EBV) receptor with the complement receptor type 2 (CR2) was established in three sets of experiments using the monoclonal antibodies, HB-5 and anti-B2, which recognize a Mr 145,000 B-lymphocyte membrane protein that is CR2. First, the rank order for binding of fluoresceinated EBV to four lymphoblastoid cell lines (SB, JY, Raji, and Molt-4) was identical to the rank order for binding of HB-5 and anti-B2 by analytical flow cytometry. Second, pretreatment of cells with HB-5 followed by treatment with goat F(ab')2 fragments to mouse IgG blocked binding of fluoresceinated EBV on SB, a B-lymphoblastoid cell line. Virus attachment was not inhibited by HB-5 alone, second antibody alone, rabbit anti-C3b receptor, or UPC10 (an irrelevant monoclonal antibody). Third, transfer of CR2 from SB to protein A-bearing Staphylococcus aureus particles, to which HB-5 had been absorbed, conferred on them the specific ability to bind 125I-labeled EBV. We conclude that CR2 is the EBV receptor of human B lymphocytes.

Antibodies, Monoclonal↗

PubMed1985

gp140, the C3d receptor of human B lymphocytes, is also the Epstein-Barr virus receptor.

The relationship between gp140, the membrane C3d receptor (CR2) of human B lymphocytes, and the Epstein-Barr virus receptor (EBVR) was analyzed by using the polyclonal anti-gp140, previously prepared by immunizing rabbits with highly purified gp140 (isolated by some of us) from CR2/EBVR-positive Raji cells. Polyclonal anti-gp72, a C3-binding membrane component, not related to the EBVR but also expressed on the Raji cell surface, was used as a control. Binding of rabbit IgG and EBV on cells was assessed by using immunofluorescence techniques with analysis by flow cytofluorometry. A semiquantitative bioassay was also used to measure the EBV binding. Polyclonal monospecific anti-gp140 IgG inhibits directly the binding of EBV to Raji cells at the same concentration that inhibits the binding of EC3d on cells, whereas a 35 times higher concentration of anti-gp72 IgG or preimmune serum IgG does not. Anti-gp140 IgG treatment also inhibits the induction of EBV-determined nuclear antigen in normal tonsil B lymphocytes or in EBV-negative Ramos cells, whereas high concentrations of anti-gp72 IgG or preimmune serum IgG have no effect. These data strongly suggest that gp140, the CR2 of human B lymphocytes, is also the EBVR.

B-Lymphocytes↗

PubMed1986

Identification of a partial cDNA clone for the C3d/Epstein-Barr virus receptor of human B lymphocytes: homology with the receptor for fragments C3b and C4b of the third and fourth components of complement.

Human complement receptor type 2 (CR2) is the B-lymphocyte receptor both for the C3d fragment of the third component of complement and for the Epstein-Barr virus. Amino acid sequence analysis of tryptic peptides of CR2 revealed a strong degree of homology with the human C3b/C4b receptor, CR1. This homology suggested that CR1 gene sequences could be used to detect the CR2 sequences at conditions of low-stringency hybridization. Upon screening a human tonsillar cDNA library with CR1 cDNA sequences, two clones were identified that hybridized at low, but not at high, stringency. Redundant oligonucleotides specific for CR2 sequences were synthesized and used to establish that the two cDNA clones weakly hybridizing with the CR1 cDNA contained CR2 sequences. One of these CR2 cDNA clones hybridized to oligonucleotides derived from two distinct CR2 tryptic peptides, whereas the other, smaller cDNA clone hybridized to oligonucleotides derived from only one of the CR2 peptides. Nucleotide sequence analysis of the CR2 cDNA confirmed that the site of oligonucleotide hybridization was identical to that predicted from the peptide sequence, including flanking sequences not included within the oligonucleotide probes. The CR2-specific cDNA sequences identified a poly(A)+ RNA species of 5 kilobases in RNA extracted from human B cells but did not hybridize to any RNA obtained from the CR2-negative T-cell line HSB-2, thus confirming the appropriate size and tissue-specific distribution for the CR2 mRNA. The striking peptide sequence homology between CR2 and CR1 and the cross-hybridization of the CR2 cDNA with the CR1-specific sequences allow the placement of CR2 in a recently defined gene family of C3- and C4-binding proteins consisting of CR1, C4-binding protein, factor H, and now, CR2.

Amino Acid Sequence↗

PubMed1987

Molecular cloning of the cDNA encoding the Epstein-Barr virus/C3d receptor (complement receptor type 2) of human B lymphocytes.

Complementary DNA clones for complement receptor type 2 (CR2), the B-lymphocyte membrane protein that serves as the receptor for Epstein-Barr virus and the C3d complement fragment, were obtained by screening a lambda gt11 library generated from Raji B lymphoblastoid cell mRNA. A 4.2-kilobase (kb) clone, representing the entire coding sequence of the protein plus untranslated 5' and 3' nucleotide sequences was obtained and sequenced. The 4.2-kb clone, which contains all but about 500 base pairs (bp) of the 5' untranslated region of the full-length CR2 mRNA, consists of 63 bp of 5' untranslated nucleotide sequence followed successively by a start codon, a 20-amino acid hydrophobic signal peptide, 1005 amino acids having a repeating motif, a 28-amino acid probable transmembrane domain, and a 34-amino acid cytoplasmic tail. The deduced amino acid sequence of the protein indicates that the extracellular domain consists entirely of 16 tandemly arranged repeating elements, each 60-75 amino acids in length, which are identified by multiple conserved residues. This repeating motif also occurs in the C3b/C4b receptor, several complement proteins, and a number of noncomplement proteins. In CR2, the 16 repeats occur in four clusters of four repeats each. Approximately 10% of the deduced amino acid sequence, including the amino and carboxyl termini, was confirmed by amino acid sequencing of tryptic peptides derived from purified CR2. The nucleotide and derived amino acid sequence of CR2 and related studies are presented here.

Amino Acid Sequence↗

PubMed1990

Ligation of membrane immunoglobulin leads to inactivation of the signal-transducing ability of membrane immunoglobulin, CD19, CD21, and B-cell gp95.

We have examined the ability of membrane immunoglobulin-binding ligands to desensitize several human B-cell surface molecules that normally transduce signals leading to Ca2+ mobilization. Ligation of membrane IgM or IgD leads to heterologous desensitization of the reciprocal receptor in Epstein-Barr virus-transformed B-cell lines and peripheral blood B cells, as evidenced by a failure of cells to mobilize in response to receptor ligation. Under these conditions CD19, CD21, and B-cell gp95 ligation also did not lead to normal Ca2+ mobilization, indicating that these transducers are also desensitized. The desensitization does not reflect receptor modulation from the cell surface or reduced accessibility to ligand and is long lived, lasting greater than 16 hr. Finally, data that indicate that desensitized cells remain responsive to the G protein activating agent AIF4-, as measured by Ca2+ mobilization, suggest that desensitization reflects uncoupling of these receptors from G proteins that are intermediaries in their transduction of signals. We hypothesize that the molecular target of desensitization may be a recently described membrane immunoglobulin-associated and inducibly tyrosine-phosphorylated protein complex that may function as a master transducer in B cells, analogous to CD3 in T cells.

Aluminum↗

PubMed2000

Increased expression of CD23 in rheumatoid synovitis.

OBJECTIVE: Soluble (s)CD23 is a potent macrophage stimulator. High levels of this molecule have been reported in rheumatoid arthritis (RA) serum. We investigated the expression of CD23 and its ligands in rheumatoid synovial fluid and cells. METHODS: Levels of sCD23, and cellular expression of CD23 and its ligands CD21, CD11b, and CD11c were measured in synovial fluid (SF) of RA patients and in blood of RA patients and controls. RESULTS: SF contained higher levels of sCD23 than either rheumatoid or normal sera (median 4.8, 3.16,and 1.13 ng/ml respectively, p <0.01). Synovial CD23 was found to be expressed principally on macrophages. While little CD21 expression was detected, CD11b and CD11c were both expressed at high levels, particularly on macrophages. CONCLUSIONS: Soluble CD23 is present in high levels in RA synovial fluid. Macrophages appear to be the principal source. Macrophages also express ligands for sCD23, and may therefore also be the targets of this potent pro-inflammatory molecule.

Arthritis, Rheumatoid↗

PubMed1988

Structure of the human B lymphocyte receptor for C3d and the Epstein-Barr virus and relatedness to other members of the family of C3/C4 binding proteins.

Human complement receptor type 2 (CR2) is the B lymphocyte receptor for C3d and the Epstein-Barr virus. This protein is also a member of a family of C3b/C4b binding proteins that regulate complement activation, comprise tandemly repeated 60-75 amino acid sequences, and whose genes map to band q32 on chromosome 1. Overlapping cDNA clones encoding the entire human CR2 protein have been isolated from a human tonsillar cDNA library. The derived amino acid sequence of 1,032 residues encodes a peptide of 112,716 mol wt. A signal peptide was identified, followed by 15 copies of the short consensus repeat (SCR) structure common to the C3/C4 binding protein family. The entire extracellular portion of the protein comprised SCRs, thus, the ligand binding sites both for C3d and the EBV protein gp350/220 are positioned within this structure. Immediately following the final SCR was a transmembrane sequence of 24 amino acids and a cytoplasmic region of 34 amino acids. One of five cDNA clones isolated contained an additional SCR, providing evidence for alternative mRNA splicing or gene products of different human alleles. The CR2 cDNAs were used to isolate CR2-specific genomic phage. The entire CR2 coding sequences were found within 20 kb of human DNA. Analysis of the CR2 cDNA sequence indicated that CR2 contained internally homologous regions and suggested that CR2 arose by duplication of a primordial gene sequence encoding four SCRs. Comparison of the CR2 peptide sequence with those of other members of the gene family has identified many regions highly homologous with human CR1, fewer with C4bp and decay accelerating factor, and very few with factor H, and suggested that CR2 and CR1 arose by duplication of the same ancestral gene sequence. The homology between CR2 and CR1 extended to the transmembrane and cytoplasmic regions, suggesting that these sequences were derived from a common membrane-bound precursor.

Amino Acid Sequence↗

PubMed1991

Determination of the structural basis for selective binding of Epstein-Barr virus to human complement receptor type 2.

Epstein-Barr virus (EBV) is an oncogenic herpesvirus that selectively infects and immortalizes human B lymphocytes. One determinant of this narrow tropism is human CR2, the only viral receptor within the superfamily of proteins that contain short consensus repeats (SCRs). Human CR2 serves as a receptor for both C3dg and the gp350/220 glycoprotein of EBV, and binds the monoclonal antibody (mAb) OKB7, which blocks binding of both ligands to the receptor. In contrast, although murine CR2 is capable of binding human C3dg and this interaction can be blocked with the mAb 7G6, it does not bind OKB7 or EBV. We have determined the structural basis for absolute specificity of EBV for human CR2 through characterization of a panel of 24 human-murine chimeric receptors, all of which bind human C3dg. The results indicate that preferential binding of EBV to human CR2 is not due to unique amino acids that are capable of binding the virus, but reflects a distinct receptor conformation that can be achieved in murine CR2 with single amino acid substitutions in two discontinuous regions of the primary structure: replacement of proline at position 15 with the corresponding serine from human CR2, and elimination of a potential N-linked glycosylation site between SCR-1 and SCR-2. Furthermore, species-specific binding of EBV, OKB7, and 7G6 can all be manipulated through substitutions among residues 8-15, suggesting that this octapeptide is part of a structural determinant that is critical for binding of both viral and natural ligands to CR2.

Amino Acid Sequence↗

PubMed1992

Characterization of an Epstein-Barr virus receptor on human epithelial cells.

Epstein-Barr virus (EBV) adsorption to human B lymphocytes is mediated by the viral envelope glycoprotein, gp350/220, which binds to the cell surface protein, CD21, also known as the CR2 complement receptor. Human epithelial cells also express an EBV receptor. A candidate surface molecule of 195 kD has previously been identified on an epithelial cell line and explanted epithelial tissue by reactivity with the CD21 specific monoclonal antibody (mAb), HB-5a. In experiments to further characterize the epithelial cell EBV receptor, we have found that two human epithelial cell lines, RHEK-1 and HeLa, specifically bind intact EB virions. A 145-kD protein, similar in size to B lymphocyte CD21, was specifically precipitated from surface iodinated RHEK-1 cells using the HB-5a mAb, or using purified soluble gp350/220 coupled to agarose beads. The previously identified 195-kD protein did not bind to gp350/220 or react with two other anti-CD21 mAbs. CD21 homologous RNA, similar in size to the B lymphocyte CD21 mRNA, was detected in both RHEK-1 and HeLa cells. The nucleotide sequence of the epithelial cell cDNA was identical to B lymphocyte CD21. The longest clone differs from previously reported CD21 cDNAs in having additional 5' untranslated sequence. Polymerase chain reaction amplification of RHEK-1- or B lymphoblastoid-derived cDNA verified that most CD21 transcripts are initiated at least 30-50 nucleotides upstream of the previously reported mRNA cap site. These experiments demonstrate that human epithelial cells can express CD21, and that CD21 is likely to mediate EBV adsorption to epithelial cells.

Antigens, CD↗

PubMed1993

Human B cell precursors proliferate and express CD23 after CD40 ligation.

The CD40 surface membrane molecule plays an important role in the activation of mature human B cells, but its role in earlier stages of B lineage development is unknown. Here, we have investigated the effects of triggering the CD40 antigen on B cell precursors (BCP) by crosslinking with anti-CD40 antibody presented by Fc gamma-receptor type II-transfected murine Ltk- cells (CD40 system). CD10+ surface immunoglobulin negative (sIg-) BCP, freshly isolated from fetal bone marrow or precultured on stromal cells, proliferated in the CD40 system. This effect required the presence of IL-3, which acted as a specific cosignal among a panel of cytokines examined. The association of IL-10 and IL-7 potentiated the observed IL-3 and CD40-dependent BCP proliferation, demonstrating that IL-10 can act on early B lineage cells. CD40-dependent activation of fetal BCP did not favor maturation to sIg+ B cells, but resulted in the induction of high levels of surface membrane CD23. The emerging CD23+ BCP lacked sIg and CD10, and represented an important proportion of the cycling cells in the CD40-dependent cultures. Taken together, our data demonstrate that stimulation of the CD40 antigen induces expression of the CD23 gene, and regulates cell proliferation during normal human B cell ontogeny.

Animals↗

PubMed1997

Epstein-Barr virus binding to CD21 activates the initial viral promoter via NF-kappaB induction.

Epstein-Barr virus (EBV), an oncogenic human herpesvirus, binds to and infects normal human B lymphocytes via CD21, the CR2 complement receptor. Studies of the mechanisms that enable EBV to infect nonactivated, noncycling B cells provide compelling evidence for a sequence of events in which EBV binding to CD21 on purified resting human B cells rapidly activates the NF-kappaB transcription factor, which, in turn, binds to and mediates transcriptional activation of Wp, the initial viral latent gene promoter. Thus, EBV binding to its cellular receptor on resting B cells triggers an NF-kappaB-dependent intracellular signaling pathway which is required for infection.

Aspirin↗

PubMed2002

B lymphocyte memory: role of stromal cell complement and FcgammaRIIB receptors.

To dissect the influence of CD21/CD35 and FcgammaRIIB in antigen retention and humoral memory, we used an adoptive transfer model in which antigen-primed B and T lymphocytes were given to sublethally irradiated wild-type mice or mice deficient in CD21/CD35 (Cr2(-/-)) or FcgammaRIIB receptors (FcgammaRIIB(-/-)). Cr2(-/-) chimeras showed impaired memory as characterized by a decrease in antibody titer, reduced frequency of antibody secreting cells, an absence of affinity maturation, and significantly reduced recall response. The impaired memory in Cr2(-/-) chimeras corresponded with the reduced frequency of antigen-specific memory B cells. Interestingly, FcgammaRIIB(-/-) chimeras showed a differential phenotype with impaired splenic but normal bone marrow responses. These data suggest that CD21/CD35 on stroma, including follicular dendritic cells, is critical to the maintenance of long-term B lymphocyte memory.

Animals↗