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Ricklin D, Ricklin-Lichtsteiner SK, Markiewski MM, Geisbrecht BV, Lambris JD. Cutting edge: members of the Staphylococcus aureus extracellular fibrinogen-binding protein family inhibit the interaction of C3d with complement receptor 2. THE JOURNAL OF IMMUNOLOGY 2008; 181:7463-7. [PMID: 19017934 DOI: 10.4049/jimmunol.181.11.7463] [Citation(s) in RCA: 50] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/17/2023]
Abstract
Staphylococcus aureus expresses a highly diversified arsenal of immune evasion proteins, many of which target the complement system. The extracellular fibrinogen-binding protein (Efb) and the Efb homologous protein (Ehp) have previously been demonstrated to bind to C3 and inhibit complement activation and amplification. In this study we present the first evidence that Efb and Ehp are also capable of inhibiting the interaction of C3d with complement receptor 2 (CR2), which plays an important role in B cell activation and maturation. The C-terminal domain of Efb efficiently blocked this interaction both in surface plasmon resonance-based competition studies and cellular assays and prevented the CR2-mediated stimulation of B cells. Furthermore, analyses of the available structural data were consistent with a molecular mechanism that reflects both steric and electrostatic effects on the C3d-CR2 interaction. Our study therefore suggests that S. aureus may disrupt both the innate and adaptive immune responses with a single protein module.
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Affiliation(s)
- Daniel Ricklin
- Department of Pathology and Laboratory Medicine, University of Pennsylvania, Philadelphia, PA 19104, USA
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2
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Szakonyi G, Guthridge JM, Li D, Young K, Holers VM, Chen XS. Structure of complement receptor 2 in complex with its C3d ligand. Science 2001; 292:1725-8. [PMID: 11387479 DOI: 10.1126/science.1059118] [Citation(s) in RCA: 126] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/02/2022]
Abstract
Complement receptor 2 (CR2/CD21) is an important receptor that amplifies B lymphocyte activation by bridging the innate and adaptive immune systems. CR2 ligands include complement C3d and Epstein-Barr virus glycoprotein 350/220. We describe the x-ray structure of this CR2 domain in complex with C3d at 2.0 angstroms. The structure reveals extensive main chain interactions between C3d and only one short consensus repeat (SCR) of CR2 and substantial SCR side-side packing. These results provide a detailed understanding of receptor-ligand interactions in this protein family and reveal potential target sites for molecular drug design.
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Affiliation(s)
- G Szakonyi
- Department of Biochemistry and Molecular Genetics, University of Colorado Health Science Center, School of Medicine, Denver, CO 80262, USA
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3
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Mongini PK, Inman JK. Cytokine dependency of human B cell cycle progression elicited by ligands which coengage BCR and the CD21/CD19/CD81 costimulatory complex. Cell Immunol 2001; 207:127-40. [PMID: 11243702 DOI: 10.1006/cimm.2001.1758] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Coengagement of BCR and the C3dg binding CD21/CD19/CD81 costimulatory complex can profoundly reduce the BCR binding threshold for eliciting B cell S phase entry, provided cytokine is present. IL-4 is substantially better than IL-2, IL-13, and TNF-alpha at exhibiting synergy with BCR:CD21 coengaging ligand (anti-IgM:anti-CD21:dextran) in promoting B cell DNA synthesis. Synergy between IL-4 and anti-IgM:anti-CD21:dextran (a) is not explained by the viability-promoting function of IL-4, (b) occurs when the anti-CD21 moiety engages either C3dg binding or non-C3dg binding domains, (c) does not reflect reversal of FcgammaRII-mediated negative regulation, and (d) involves differing temporal requirements for BCR and IL-4R signal transduction during the activation process. The IL-4R signaling pathway appears to synergize directly with the BCR:CD21 signaling pathway(s) in promoting the progression of resting B cells past an early G1 checkpoint, as well as to promote independently the progression of activated B cells past a later G1 to S checkpoint.
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Affiliation(s)
- P K Mongini
- Department of Rheumatology, Hospital for Joint Diseases, New York, New York 10003, USA
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4
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Prodinger WM. Complement receptor type two (CR2,CR21): a target for influencing the humoral immune response and antigen-trapping. Immunol Res 1999; 20:187-94. [PMID: 10741859 DOI: 10.1007/bf02790402] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
Abstract
Cellular receptors for complement C3 fragments deposited on antigens are important bricks in the wall defending against microbial pathogens. The part of complement receptor type 2 (CR2; CD21) deals with enhancing humoral immune responses and with long-term trapping of C3d-coated antigen by follicular dendritic cells. CR2 is also pivotal for Epstein-Barr virus (EBV) infection. Here, the current understanding, how CR2 interacts with its ligands C3d, EBV, and CD23 is summarized. The potential to target CR2 for clinical therapy or immunization purposes are discussed.
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Affiliation(s)
- W M Prodinger
- Institut für Hygiene, University of Innsbruck, Austria.
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5
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Prodinger WM, Schwendinger MG, Schoch J, Köchle M, Larcher C, Dierich MP. Characterization of C3dg Binding to a Recess Formed Between Short Consensus Repeats 1 and 2 of Complement Receptor Type 2 (CR2; CD21). THE JOURNAL OF IMMUNOLOGY 1998. [DOI: 10.4049/jimmunol.161.9.4604] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/01/2023]
Abstract
Abstract
To allow for a better characterization of the ligand binding structures of human complement receptor type 2 (CR2; CD21), we have established an IgG1 κ mouse mAb, FE8, that interferes efficiently with binding of C3dg and EBV to CR2. In contrast to mAb OKB7, the only well-characterized mAb with similar specificity, mAb FE8 blocked binding of soluble C3dg or particles carrying multiple copies of surface-bound C3dg to CR2 or induced complete removal of these ligands from the receptor. In vitro EBV infection of B lymphocytes, on the other hand, was abrogated by mAbs FE8 and OKB7 with similar dose-response characteristics. As FE8 was shown to recognize a discontinuous epitope, a series of overlapping peptides derived from SCR1 and -2 and immobilized on cellulose was screened with FE8. The results suggest that up to five discontinuous sequences contributed to the epitope. The sequence 63-EYFNKYS-69, located between the two SCR units, reacted most intensively. Two other sequences, 16-YYSTPI-21 and 105-NGNKSVWCQANN-116, are located between Cys1 and Cys2 of SCR1 and around Cys3 of SCR2, respectively. Based on the solution structure for two factor H SCRs, a three-dimensional model of SCR1 and -2 was generated. The FE8 binding peptide sequences were located in relative proximity to each other, bounding the recess formed between SCR1 and -2. This potential of mAb FE8 is currently unique and may be exploited for interfering with conditions of unwanted recognition of C3dg-coated structures by the immune system.
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Affiliation(s)
| | | | - Jürgen Schoch
- Institut für Hygiene, University of Innsbruck, Innsbruck, Austria
| | - Maria Köchle
- Institut für Hygiene, University of Innsbruck, Innsbruck, Austria
| | - Clara Larcher
- Institut für Hygiene, University of Innsbruck, Innsbruck, Austria
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6
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Martin DR, Yuryev A, Kalli KR, Fearon DT, Ahearn JM. Determination of the structural basis for selective binding of Epstein-Barr virus to human complement receptor type 2. J Exp Med 1991; 174:1299-311. [PMID: 1660522 PMCID: PMC2119041 DOI: 10.1084/jem.174.6.1299] [Citation(s) in RCA: 64] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022] Open
Abstract
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.
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Affiliation(s)
- D R Martin
- Graduate Program in Immunology, Johns Hopkins University School of Medicine, Baltimore, Maryland 21205
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7
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Affiliation(s)
- R S Larson
- Center for Blood Research, Harvard Medical School, Boston, MA 02115
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8
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Nemerow GR, Moore MD, Cooper NR. Structure and function of the B-lymphocyte Epstein-Barr virus/C3d receptor. Adv Cancer Res 1990; 54:273-300. [PMID: 2136962 DOI: 10.1016/s0065-230x(08)60814-3] [Citation(s) in RCA: 19] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022]
MESH Headings
- Animals
- Antigens, Differentiation, B-Lymphocyte/analysis
- Antigens, Differentiation, B-Lymphocyte/genetics
- Antigens, Differentiation, B-Lymphocyte/physiology
- Antigens, Viral/metabolism
- B-Lymphocytes/immunology
- Complement Activation
- Complement C3d/metabolism
- Humans
- Infant
- Lymphocyte Activation
- Multigene Family
- Receptors, Complement/analysis
- Receptors, Complement/genetics
- Receptors, Complement/physiology
- Receptors, Complement 3d
- Structure-Activity Relationship
- Viral Matrix Proteins
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Affiliation(s)
- G R Nemerow
- Research Institute of Scripps Clinic, Department of Immunology, La Jolla, California 92037
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9
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Fearon DT, Ahearn JM. Complement receptor type 1 (C3b/C4b receptor; CD35) and complement receptor type 2 (C3d/Epstein-Barr virus receptor; CD21). Curr Top Microbiol Immunol 1990; 153:83-98. [PMID: 2153507 DOI: 10.1007/978-3-642-74977-3_5] [Citation(s) in RCA: 22] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022]
MESH Headings
- Amino Acid Sequence
- Animals
- Antigens, Differentiation, B-Lymphocyte/biosynthesis
- Antigens, Differentiation, B-Lymphocyte/immunology
- Complement C3b/metabolism
- Complement C3d/metabolism
- Herpesvirus 4, Human/metabolism
- Humans
- Molecular Sequence Data
- Receptors, Complement/biosynthesis
- Receptors, Complement/immunology
- Receptors, Complement 3b
- Receptors, Complement 3d
- Sequence Homology, Nucleic Acid
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Affiliation(s)
- D T Fearon
- Department of Medicine, Johns Hopkins University School of Medicine, Baltimore, MD 21205
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10
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Lowell CA, Klickstein LB, Carter RH, Mitchell JA, Fearon DT, Ahearn JM. Mapping of the Epstein-Barr virus and C3dg binding sites to a common domain on complement receptor type 2. J Exp Med 1989; 170:1931-46. [PMID: 2479703 PMCID: PMC2189535 DOI: 10.1084/jem.170.6.1931] [Citation(s) in RCA: 116] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023] Open
Abstract
Complement receptor type 2 (CR2;CD21), a member of the superfamily of proteins containing short consensus repeats (SCRs), is the B cell receptor for both the gp350/220 envelope protein of Epstein-Barr virus (EBV), and for the C3dg protein of complement. By analysis of CR2 deletion mutants and chimeras formed with CR1 (CD35) we determined that of the 15 SCRs in CR2, the NH2-terminal two SCRs are necessary and sufficient to bind both gp350/220 and C3dg with affinities equivalent to those of the wild-type receptor. The epitope for OKB-7, a mAb that blocks binding of both EBV and C3dg and shares with these ligands B cell-activating capabilities, also requires both SCR-1 and SCR-2, whereas mAbs lacking these functions bind to other SCRs. Thus, EBV, a polyclonal activator of B cells, has selected a site that is proximate or identical to the natural ligand binding site in CR2, perhaps reflecting the relative immutability of that site as well as its signal transducing function.
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Affiliation(s)
- C A Lowell
- Department of Medicine, Johns Hopkins University School of Medicine, Baltimore, Maryland 21205
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11
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Kubicka U, Olszewski WL, Maldyk J, Wierzbicki Z, Orkiszewska A. Normal human immune peritoneal cells: phenotypic characteristics. Immunobiology 1989; 180:80-92. [PMID: 2696725 DOI: 10.1016/s0171-2985(89)80032-4] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/02/2023]
Abstract
Normal human peritoneal cells (PC) collected from patients with calculous cholecystitis without clinically detectable inflammatory changes were characterized morphologically, histochemically and phenotypically by means of monoclonal antibodies. The PC consisted of 45% of monocytes/macrophages (M718 + cells). Thirty-five per cent of PC were esterase-positive and 23% acid phosphatase positive. Forty-five per cent of PC adhered to glass surface. In the lymphocyte population, 2% of CD22 B lymphocytes (M738 +) and 42% CD2 T lymphocytes (M720+) were found. CD4/CD8 ratio was 0.4. There were 8% of Leu7 + cells. The PC did not reveal interleukin 2 (OKT26a +) and transferrin receptors (OKT9 +) on their surface. No blast cells were detected in the PC suspension. Approximately 49% of the PC expressed Ia antigens (OKIa1 +). Two per cent of S100 positive dendritic cells (Z311 +) were found. Peritoneal fluid contained 9% of granulocytes, mostly neutrophils. Two per cent of PC were free mesothelial cells (M717 +). We conclude that human peritoneal cavity contains a cell population significantly differing from that which is present in peripheral blood, which strongly suggests a non-random cell accumulation in the peritoneum. Lack of any activated cells indicates that under normal conditions the peritoneum lavage fluid contains a steady-state population. We conclude that the normal peritoneal fluid cells represent a heterogeneous population capable of reacting to various antigens entering the cavity from the gut.
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Affiliation(s)
- U Kubicka
- Department for Surgical Research and Transplantation, Polish Academy of Sciences, Warsaw
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12
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Rask R, Rasmussen JM, Jepsen HH, Svehag SE. Enhanced binding of immune complexes processed by erythrocyte CR1 (CD 35) receptors to purified CR2 (CD 21) receptors from tonsillar mononuclear cells. APMIS 1989; 97:374-80. [PMID: 2524204 DOI: 10.1111/j.1699-0463.1989.tb00803.x] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023]
Abstract
The binding of immune complexes (IC) opsonized by serum complement (C) and IC processed by CR1 (CD 35) receptors on human erythrocytes (E) to purified CR2 (CD 21) receptors was compared. Soluble CR2 was prepared from tonsillar mononuclear cells and purified by antibody affinity chromatography. Solid phase CR2 as well as CR2 subjected to PAGE and blotted onto nitro-cellulose membranes bound 125I-labelled BSA anti-BSA IC which had been opsonized by C and processed by CR1 up to ten times more efficiently than IC reacted with serum only. Radiolabelled monomeric C3d also bound to solid phase CR2. The binding of IC to purified and solid phase bound CR2 could be inhibited by anti-CR2 antibodies or by preincubation of the IC with polyclonal antibodies reacting with C3d or C3b/iC3b. Thus, both C3dg and iC3b appeared to mediate binding of IC to CR2. Preincubation of solid phase CR2 with purified monomeric C3d did not inhibit the subsequent binding of E-CR1 processed IC. The data indicate that E-CR1 have an important role in generating IC which bind effectively to CR2 receptors on B lymphocytes.
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Affiliation(s)
- R Rask
- Institute of Medical Microbiology, Odense University, Denmark
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13
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Clark EA, Ledbetter JA. Structure, function, and genetics of human B cell-associated surface molecules. Adv Cancer Res 1989; 52:81-149. [PMID: 2662716 DOI: 10.1016/s0065-230x(08)60211-0] [Citation(s) in RCA: 43] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/02/2023]
Affiliation(s)
- E A Clark
- Department of Microbiology, University of Washington, Seattle 98195
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14
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Ahearn JM, Fearon DT. Structure and function of the complement receptors, CR1 (CD35) and CR2 (CD21). Adv Immunol 1989; 46:183-219. [PMID: 2551147 DOI: 10.1016/s0065-2776(08)60654-9] [Citation(s) in RCA: 346] [Impact Index Per Article: 9.9] [Reference Citation Analysis] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023]
MESH Headings
- Amino Acid Sequence
- Animals
- Antigens, Differentiation, B-Lymphocyte/genetics
- Antigens, Differentiation, B-Lymphocyte/metabolism
- Antigens, Differentiation, B-Lymphocyte/physiology
- B-Lymphocytes/immunology
- B-Lymphocytes/metabolism
- Cell Differentiation
- Cloning, Molecular
- Complement Activation
- Complement C3/metabolism
- Complement C3b/metabolism
- Complement C3d
- Endocytosis
- Herpesvirus 4, Human/metabolism
- Humans
- Mice
- Molecular Sequence Data
- Protein Conformation
- Receptors, Complement/genetics
- Receptors, Complement/metabolism
- Receptors, Complement/physiology
- Receptors, Complement 3b
- Receptors, Complement 3d
- Receptors, Virus/metabolism
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Affiliation(s)
- J M Ahearn
- Department of Medicine, Johns Hopkins University School of Medicine, Baltimore, Maryland
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15
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Poletti A, Manconi R, De Paoli P. Double labeling immunohistologic and flow cytometric analysis of human B cells with particular reference to Leu-8 expression. Hum Pathol 1988; 19:1001-7. [PMID: 3262082 DOI: 10.1016/s0046-8177(88)80077-7] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/04/2023]
Abstract
Previous results have shown that human lymphocyte subpopulations are heterogeneous as to Leu-8 expression. In the present study, we performed a heretofore unreported immunohistologic analysis and flow cytometric double labeling investigation focused on Leu-8+ and Leu-8- human B cells, with special reference to their expression of other B cell lineage antigens (Leu-14, B1, OKB7 or B2, OKB2, BA-1, BA-2, IgD, and IgM) or of a functional marker of cell proliferation (Ki-67). Immunohistologic analysis was performed on frozen sections of nine normal or reactive lymph node and tonsil biopsy specimens tested with either single or paired antibodies, the latter procedure (double labeling) being directed at revealing positively subtracted Leu-8+ or Leu-8- cells expressing a given marker depending on the antibody staining sequence used. Dual flow cytometry with paired antibodies was performed on cell suspensions from four normal or reactive lymph nodes and tonsils. As to the follicular district, immunohistologic analysis suggests that germinal center (proliferating) B lymphocytes, identifiable in cell suspension as Leu-8-B1+ and representing 80% of the B1+ cells, are Leu-8- and Leu-14+, BA-2+, OKB7+, and IgM+, being rarely IgD+. Most lymphocytes located in the mantle zone (resting cells), identifiable in cell suspension as Leu-8+B1+ and representing the remaining 20% of the B1+ cells, are Leu-8+, Leu-14+. OKB7+, OKB2+, BA-1+, IgD+, and IgM+. Furthermore, from our results, there is indirect evidence to support the existence of a Leu-8+BA-2+ lymphocyte subset located in the mantle zone. Immunohistologic study of four lymph nodes by Leu-8 and Ki-67 antibody (that recognizes a nuclear, cell proliferation-associated antigen absent only in the Go phase of the cell cycle) showed that these markers are mutually exclusive and added further evidence that Leu-8 antigen is a marker of resting lymphocytes.
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Affiliation(s)
- A Poletti
- Division of Pathology, Centro di Riferimento Oncologico, Aviano, Italy
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16
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Barel M, Vazquez A, Charriaut C, Aufredou MT, Galanaud P, Frade R. gp 140, the C3d/EBV receptor (CR2), is phosphorylated upon in vitro activation of human peripheral B lymphocytes. FEBS Lett 1986; 197:353-6. [PMID: 2936622 DOI: 10.1016/0014-5793(86)80356-8] [Citation(s) in RCA: 31] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/03/2023]
Abstract
gp 140, the C3d/EBV receptor (CR2), is a specific marker of human B lymphocytes. Very recent data suggest that CR2 is a membrane site involved in early B cell activation. These properties of CR2 led us to analyze the molecular events associated with gp 140. We analyzed whether in some conditions of B lymphocyte activation, CR2 could be phosphorylated. We have found that when highly enriched peripheral B cells were cultured for 48 h with anti-mu Ab and/or SAC, in order to provide an optimal activating signal, phosphorylation of the CR2 was induced.
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17
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Tedder TF, Weis JJ, Clement LT, Fearon DT, Cooper MD. The role of receptors for complement in the induction of polyclonal B-cell proliferation and differentiation. J Clin Immunol 1986; 6:65-73. [PMID: 3485654 DOI: 10.1007/bf00915366] [Citation(s) in RCA: 29] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/06/2023]
Abstract
A panel of monoclonal antibodies and ligands that bind to the CR1 or CR2 complement receptors of B cells has been used to investigate the role of these membrane molecules in regulating B-cell proliferation and differentiation. When CR2 was modulated from the surface of B cells by treatment with the HB-5 antibody and a secondary goat anti-mouse immunoglobulin antibody, Epstein-Barr virus-induced polyclonal B-cell proliferation and immunoglobulin production were inhibited by 83 and 90%, respectively. In contrast, modulation of other cell surface molecules, HB-2, B1, and the C3b receptor (CR1), or pretreatment of B cells with C3d,g (a CR2 ligand) or HB-5 antibody, alone minimally inhibited these responses. Neither the HB-5 antibody C3d,g, nor a monoclonal antibody (YZ-1) reactive with CR1 induced resting B cells to proliferate, nor did they alter anti-mu antibody-induced proliferation. Similarly, treatment with C3d,g or with the HB-5 or YZ-1 antibodies did not induce B cells to secrete immunoglobulin or affect pokeweed mitogen-induced plasma-cell formation. Whereas CR2 appears to be the functionally relevant receptor for Epstein-Barr virus on B cells, the effects of ligand interactions with CR1 and CR2 on normal B-cell proliferation or differentiation remain unidentified.
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