Epstein-Barr virus nuclear antigen 2 specifically induces expression of the B-cell activation antigen CD23

Purification and characterization of the Epstein-Barr virus nuclear antigen 2 using monoclonal antipeptide antibodies

The Epstein-Barr virus (EBV) nuclear antigen 2 (EBNA-2) is the only one of the EBNA proteins to have been implicated as an EBV-encoded transforming protein. More detailed studies of this protein have been hampered by the lack of EBNA-2-specific monoclonal antibodies (MAbs) and of purified protein. To overcome these problems, we isolated 5 hybridomas producing MAbs reactive with an 18 residue synthetic peptide corresponding to the carboxyterminus of EBNA-2. Four of the 5 MAbs were specifically reactive with EBNA-2 in its denatured form on immunoblots. The 5th antibody (115E) was reactive with the native form of EBNA-2. By using a one-step immunoaffinity purification method with 115E cross-linked to protein-A-Sepharose, we purified EBNA-2 to homogeneity, i.e., more than 1,200-fold, from Burkitt lymphoma cell extracts. A major 32-kDa associated protein and a less abundant 17-kDa protein were co-purified with EBNA-2. Immunoprecipitation with 115E from 35S-methionine-labelled cell extracts showed that the 32-kDa protein co-precipitated with EBNA-2 from EBV-positive cells, but was not detectable in immunoprecipitates of EBV-negative cells. When the immunoprecipitates or the purified proteins were immunoblotted with EBV-immune sera, only EBNA-2 was reactive, indicating that the associated proteins are of cellular origin. Immunoprecipitation of cells labelled with 32P-orthophosphate showed that EBNA-2, but not the associated proteins, is a phosphoprotein. The expression level of EBNA-2 varied between different EBV-carrying cell lines, as measured by a 2-site ELISA based on antibody 115E. In indirect immunofluorescence, the 115E MAb gave an EBNA-2-specific characteristic granular staining pattern. These characteristics of EBNA-2 resemble those of other viral transforming proteins.

Epstein-Barr virus latent infection membrane protein alters the human B-lymphocyte phenotype: deletion of the amino terminus abolishes activity

A latent infection membrane protein (LMP) encoded by the Epstein-Barr virus (EBV) genome in latently infected, growth-transformed lymphocytes alters the phenotype of a human EBV-negative B-lymphoma cell line (Louckes) when introduced by gene transfer. These LMP-expressing cells exhibit increased homotypic adhesion due to increased expression of the adhesion molecules LFA-1 and ICAM-1. Increased homotypic adhesion could foster B-cell growth by facilitating autocrine growth factor effects. LFA-3 expression is also induced. The induction of LFA-3 and ICAM-1 results in increased heterotypic adhesion to T lymphocytes. This could result in more effective T-cell immune surveillance. Since LMP is expressed in EBV-transformed lymphocytes and has been demonstrated to transform rodent fibroblasts in vitro, a wide range of possible effects on B-lymphoma cell growth were assayed. In the Louckes B-lymphoma cell line, EBV LMP causes increased cell size, acid production, plasma membrane ruffling, and villous projections. Although cell proliferation rate was not greatly affected, the steady-state intracellular free calcium level, transforming growth factor beta responsiveness, and expression of the lymphocyte activation markers (CD23 and transferrin receptor) were increased. Thus, LMP appears to be a mediator of EBV effects on B-cell transformation. In transfected lymphoma cells, LMP localizes to patches at the cell periphery and associates with the cytoskeleton as it does in EBV-transformed B lymphocytes or in rodent fibroblasts. A partially deleted form of LMP (D1LMP) does not aggregate in patches or associate with the cytoskeleton and had little effect on B-cell growth. Thus, cytoskeletal association may be integral to LMP activity.

Induction of interleukin-4-dependent IgE synthesis and interleukin-5-dependent eosinophil differentiation by supernatants of a human helper T-cell clone

The human alloreactive T-cell clone A1 produces interleukin (IL)-4, IL-5, and granulocyte macrophage-colony stimulating factor (GM-CSF), but not IL-2 or interferon-gamma (IFN-gamma), as assessed by probing for mRNA transcripts, immunoassays, or bioassays. Supernatants from clone A1 induced IgE synthesis by normal human peripheral blood mononuclear cells. IL-4 was shown to be necessary and sufficient for the induction of IgE by clone A1 supernatants. In contrast, IgE induction by clone A1 supernatants and recombinant (r) IL-4 was inhibited by IFN-gamma. This suggests that the absence of IFN-gamma from the IL-4-containing A1 supernatants was important for their IgE-inducing ability. Supernatants from clone A1 could also specifically induce the growth of cord blood cell progenitors and their differentiation into eosinophils but not into basophils. rIL-5, but not rIL-4 or rGM-CSF, also induced eosinophil maturation. These data suggest that IL-5 secreted by clone A1 was responsible for its ability to induce eosinophil differentiation. The implications of the concomitant production of IL-4 and IL-5 by a single T-cell clone are discussed.

Epstein-Barr virus-specific cytotoxic T-cell recognition of transfectants expressing the virus-coded latent membrane protein LMP

Cytotoxic T cells from Epstein-Barr virus (EBV)-immune individuals specifically kill EBV-transformed B cells from HLA class I antigen-matched donors even though the latently infected cells express only a restricted set of virus genes. The virus-induced target antigens recognized by these immune T cells have not been identified. In our experiments, EBV DNA sequences encoding the virus latent gene products Epstein-Barr nuclear antigen (EBNA)1, EBNA 2, and EBNA-LP and the latent membrane protein (LMP) were individually expressed in a virus-negative human B-lymphoma cell line, Louckes. Transfected clones expressing LMP were killed by EBV-specific cytotoxic T-cell preparations from each of three virus-immune donors HLA matched with Louckes through HLA-A2, B44 antigens; control transfectants or clones expressing one of the EBNA proteins were not recognized. Expression of LMP in a second virus-negative B-cell line, BL41, sensitized these cells to EBV-specific cytolysis restricted through the HLA-A11 antigen. To distinguish between the viral protein and an induced human B-cell activation antigen as the target for T-cell recognition, LMP was then expressed in a murine mastocytoma cell line, P815-A11-restricted human T cells. The LMP-expressing P815-A11 transfectants were susceptible to lysis by EBV-specific cytotoxic T cells from three HLA-A11-positive individuals. Both Louckes and P815-A11 cells were also transfected with constructs capable of encoding a truncated form of LMP (Tr-LMP) which lacks the N-terminal 128 amino acids of the full-length protein. Tr-LMP-expressing transfectants were not recognized by the above T-cell preparations. The results suggest that LMP, and, in particular, epitopes derived from the N-terminal region of the protein, provides one of the target antigens for the EBV-induced human cytotoxic T-cell response.

Interleukin 4 and soluble CD23 as progression factors for human B lymphocytes: analysis of their interactions with agonists of the phosphoinositide "dual pathway" of signalling

Human B lymphocytes pre-activated for 24 h with a combination of phorbol dibutyrate [P(Bu)2] and ionomycin were found to provide excellent targets for assessing the detailed action of B cell progression factors. Both recombinant interleukin 4 (IL 4) and affinity-purified 25-kDa fragment of the CD23 molecule (sol-CD23) were shown to be active in this assay. While the progression activity of IL 4 was enhanced by continued co-culture with P(Bu)2, that of sol-CD23 was found to be more strictly dependent upon such a joint application with the phorbol ester. Similar requirements were observed for triggering cell-cycle progression in the pre-activated B cells when using a stimulating CD23 antibody. Ionomycin, in contrast to P(Bu)2, did not augment either IL 4 or sol-CD23 in these assays but did enhance significantly the progression activity of an anti-CDw40 antibody. When added to B cells concomitantly with, or prior to, a high dose of phorbol ester, IL 4 unexpectedly down-regulated the subsequent mitogenic response to this agent whereas, when added 24 h later, IL 4 up-regulated such stimulations. The latter sequence of additions resulted in a particularly dramatic induction of CD23 at the B cell surface, much more so than seen when B cells were incubated with either IL 4 alone or with IL 4 and P(Bu)2 together. This up-regulation of surface CD23 was, in turn, mirrored by the appearance of large amounts of the soluble form of the molecule in such cultures. The findings are discussed with reference to possible mechanisms through which IL 4 and CD23 interact to exert their multiple actions on B cell regulatory pathways.

Expression of CD23 antigen is not necessary for human 12-kDa B cell growth factor-mediated B cell proliferation

In an attempt to understand the relationship between the CD23 antigen and the human 12-kDa B cell growth factor (BCGF) receptor, we have undertaken studies to define the biological efficacy of 12-kDa-BCGF on CD23+ (Raji) and CD23- (P3HR1) human Burkitt B cell lines. Our results show that recombinant 12-kDa-BCGF can induce efficient [3H]thymidine incorporation and proliferation in cells of either phenotype. These results strongly suggest that a functional receptor for the 12-kDa-BCGF may exist independently of the CD23 molecule.

Expression of Epstein-Barr virus-encoded proteins in nasopharyngeal carcinoma

Expression of the Epstein-Barr virus (EBV) encoded nuclear antigens (EBNA 1 to 6) and membrane-associated protein (LMP) was investigated by immunoblotting in 83 nasopharyngeal carcinoma (NPC) biopsies and 25 other tumor and normal tissue specimens from the head and neck region. Fifty-eight of the 83 NPC biopsies were large enough to yield parallel data on virus DNA and viral expression. All 16 cases of clinically diagnosed and histologically confirmed NPCs from North Africa contained EBV DNA and expressed EBNA-1. Of 31 clinically diagnosed NPCs from China, 29 contained EBV DNA and 25 of these expressed EBNA-1. One control tissue biopsy from the oropharynx of NPC patients contained EBV DNA, but none expressed EBNA-1. The latent membrane protein (LMP) was detected in 22/31 of the Chinese and in 10/16 of the North African NPC biopsies. None of the NPC biopsies or control tissues expressed detectable amounts of EBNA 2 or any of the other 4 nuclear antigens which are invariably expressed in EBV-transformed B cells. A smaller number of tumors from Malaysia and East Africa exhibited a similar pattern of expression. EBV was rescued from a nude-mouse-passaged North African NPC tumor by co-cultivation of the tumor cells with umbilical cord blood lymphocytes. The tumor expressed EBNA 1 and LMP, but not EBNA 2 or the other 4 EBNAs. The resulting LCLs expressed all 6 nuclear antigens, EBNA 1 to 6 and LMP. Our data suggest that expression of the EBV genome is regulated in a tissue-specific fashion.

The 5' flanking region of the gene for the Epstein-Barr virus-encoded nuclear antigen 2 contains a cell type specific cis-acting regulatory element that activates transcription in transfected B-cells

We have recently identified the promoter that positions the initiation (cap) site for RNA encoding the Epstein-Barr virus (EBV) determined nuclear antigen 2 (EBNA2) in transfected COS-1 cells. The cells were transfected with recombinant vectors that contained the BamHI WYH region of the EBV genome. In order to delineate regulatory DNA sequences required for the expression of EBNA2 the 5' flanking region of the gene was linked to reporter genes in expression vectors and transfected into EBV genome-negative lymphoid DG75 cells. We demonstrate that several cis-acting elements contribute to a transcriptional enhancer activity found in the region between nucleotides-553 and -86 relative to the cap site. The enhancer was active in lymphoid DG75 cells but not in HeLa cells and stimulated transcription also from the heterologous thymidine kinase (TK) and beta-globin promoters. Nuclear extracts of lymphoid cells contained protein factors that bound to the enhancer. The in vitro introduction of a mutation in the enhancer sequence that substantially reduced the transcription stimulatory activity concurrently blocked the binding of one of the factors.

Maintenance of growth transformation with Epstein-Barr virus is mediated by secretion of autocrine growth factors in two serum-free B-cell lines

The characteristics of two tamarin (Saguinus oedipus) B-cell lines (sfBIT and sfBT) growth-transformed by Epstein-Barr virus (EBV) that proliferate continuously in serum-free medium are described. sfBIT was established by selecting cells for growth in RPMI 1640 supplemented with insulin, transferrin, and selenium (J. E. Shaw, R. G. Petit, and K. Leung, J. Virol. 61:4033-4037, 1987). sfBT, a subline of sfBIT cells reported here for the first time, required transferrin as the only protein supplement for continuous growth in RPMI 1640. Growth of sfBT cells was linear with human transferrin at 10(-2) to 10 micrograms/ml. Transferrin at 5 micrograms/ml yielded a culture density of 5 X 10(5) to 1 X 10(6) cells per ml, a cell doubling time of 2 to 3 days, and a culture viability greater than 95%. sfBIT and sfBT cells released transforming virus during continuous growth in serum-free culture medium without EBV-inducing agents. The spent medium of both serum-free lines supported cell growth at low culture density (1 x 10(4) to 5 X 10(4) cells per ml), but growth was arrested at low culture density with fresh serum-free medium. A procedure to measure growth-promoting activity (GPA) was established, and it revealed that the GPA of spent medium was greater than that of fresh medium for both serum-free cell lines. When fresh and spent media were dialyzed (molecular weight cutoff, 3,500) and subsequently concentrated by lyophilization, only the GPA of spent medium increased. We conclude that maintenance of growth transformation of tamarin cells latently infected with EBV is mediated by growth factors that are entirely autocrine in origin.

Effect of activation of the Epstein-Barr virus genome on expression of B cell differentiation antigens of Burkitt's lymphoma lines

Using anti-human B cell monoclonal antibodies prepared against B1 (CD20), B2 (CD21), B4 (CD19), and BB-1 (B lymphoblast antigen-1), we compared the expression of B cell differentiation antigens on a Jijoye-P3HR-1 cell line family of Burkitt's lymphomas. The expression of BB-1 and B2 antigens was faint on P3HR-1 K cell line which is an Epstein-Barr virus (EBV) high producer. On the other hand, B1 and B4 antigens were strongly expressed on it. It was also found that BB-1 expression decreased on P3HR-1 cells after activation of intracellular EBV genes by treating chemically with tumor-promoting agent (TPA) and n-butyrate, or on Raji cells on superinfection with EBV. This decrease of BB-1 was blocked by the additional treatment with retinoic acid, an inhibitor of virus replication. Dual immunofluorescence staining analysis showed that the individual cell expressing EBV-associated antigens expressed BB-1 antigen only marginally. The relationship between the change in phenotypes of host B cells and the activation of the EBV genome is discussed.

Isolation of a normal B cell subset with a Burkitt-like phenotype and transformation in vitro with Epstein-Barr virus

Epstein-Barr virus (EBV) is causally linked with endemic Burkitt's lymphoma (BL), a tumor whose homogeneous cell surface phenotype suggests derivation from a particular subset of activated germinal centre B cells in vivo. Endemic BL also shows an unusual form of EBV infection with down-regulation of certain of the virus latent proteins which are constitutively expressed when EBV infects and transforms normal resting B cells in vitro. Here we question whether this virus:cell interaction is unique to malignant BL cells or whether it might be reproduced by in vitro infection of those particular germinal centre cells displaying the BL-like phenotype. Firstly, we show by biochemical means that a subset of normal tonsillar B cells does indeed express the globotriaosylceramide glycolipid BLA and the common acute lymphoblastic leukaemia antigen CALLA, 2 important markers of the BL phenotype. Secondly, using 2-colour immunofluorescence labelling with anti-BLA and anti-CALLA monoclonal antibodies (MAbs), 4 subsets of low buoyant density tonsillar B cells (BLA+ CALLA+, BLA+ CALLA-, BLA- CALLA+, BLA- CALLA-) have been separated by means of a FACS and tested for their susceptibility to EBV-induced growth transformation in a limiting dilution assay. The BLA+ CALLA+ (i.e., BL-like) subset contained the highest proportion of cells already actively in cycle in vivo and gave the lowest yield of transformants, perhaps reflecting the greater efficiency with which EBV transforms resting target cells. Of the cell lines established from the BLA+ CALLA+ population, a significant number retained BLA expression but CALLA was always lost. In 2 further respects, these lines resembled conventional in vitro transformants rather than lines of BL type; thus the cells expressed cellular "activation" antigens (CD23, CD39, CD30, Ki-24) characteristic of the lymphoblastoid phenotype and contained the full spectrum of EBV latent proteins.

Expression of the c-fgr related transcripts in Epstein-Barr virus-associated malignancies

The proto-oncogene c-fgr is expressed at high levels in cell lines derived from lymphomas which are infected with Epstein-Barr virus (EBV) (Cheah et al., 1986). mRNA extracted directly from biopsies of EBV-infected tissues was analyzed on Northern blots to determine if c-fgr is expressed during lympho-proliferations induced in vivo by EBV and in nasopharyngeal carcinoma (NPC), the epithelial malignancy associated with the virus. Elevated levels of c-fgr expression were detected in all EBV-positive lympho-proliferations in vivo but not in cell lines established by EBV infection in vitro. This indicates that the induction of the c-fgr proto-oncogene is not an essential component of EBV-induced transformation. Although no c-fgr expression was detected in EBV-positive or -negative epithelial cell lines, the 3.0-kb c-fgr mRNA was detected at low levels in mRNA obtained from NPC biopsy specimens. However, NPC tissue, after passage in nude mice (which eliminates infiltrating lymphoid and myeloid cells) did not contain the 3.0-kb c-fgr mRNA. The absence of expression of c-fgr in the malignant epithelial cells infected with EBV contrasts with the elevated level of the proto-oncogene in EBV-infected lymphoma tissue and cell lines established from lymphomas. This suggests differences in the expression of cellular functions in EBV-induced malignancies of these 2 distinct cell types.

A new Epstein-Barr virus transactivator, R, induces expression of a cytoplasmic early antigen

Several Epstein-Barr virus (EBV) early promoters respond to a new EBV transactivator encoded by BRLF1, designated R. Transactivation was measured in chloramphenicol acetyltransferase assays on Raji, BHK, and Vero cells that were cotransfected with the transactivator and target promoters linked to the cat gene. The divergent promoter of BamHI-H was particularly responsive to R transactivation. This large promoter region consists of a leftward TATA box for the NotI repeat gene (BHLF1) and a probable rightward TATA box for the EA-R gene (BHRF1) separated by 940 base pairs of unusual sequence complexity. Sequences within this divergent promoter region appear to confer inducibility by EBV transactivators R and Z (BZLF1). The Z transactivator stimulated expression in both the leftward and rightward directions, and R stimulated expression primarily in the rightward direction, but the MS transactivator (BMLF1) had no activity in either direction. The adenovirus E3 promoter also responded to the R transactivator, but several other herpesvirus and human promoters were nonresponsive. When the divergent promoter was linked to the EA-R gene as it is in the EBV genome, the R and Z transactivators also induced the expression of EA-R in cotransfected cells. This cytoplasmic early antigen is encoded by BHRF1 and may be anchored in intracellular membranes by a carboxy-terminal transmembrane region.

A sixth Epstein-Barr virus nuclear protein (EBNA3B) is expressed in latently infected growth-transformed lymphocytes

In the Epstein-Barr virus BamHI E genomic fragment, there are three distantly homologous long open reading frames, BERF1, BERF2b, and BERF4, each of which is preceded by a short open reading frame. The most leftward and most rightward short and long open reading frame pairs encode 145- and 155-kilodalton proteins in latently infected cells (EBNA3A and EBNA3C, respectively). In this report, we demonstrate that the middle long open reading frame, BERF2b, encodes part of a 165-kilodalton nuclear protein in every latently infected cell. Therefore, this protein is designated EBNA3B.

Prediction and demonstration of a novel Epstein-Barr virus nuclear antigen

The protein sequence predicted by the Epstein Barr virus (EBV) BERF4 open reading frame includes a tetrapeptide, Lys-Arg-Pro-Arg (KRPR), shown for other proteins to be a component of a signal for rapid nuclear localization. A subgenomic fragment of EBV DNA containing BERF4 has been incorporated into an expression vector, transfected onto primate cells and the nuclear distribution of the resulting protein established by immunofluorescence using EBV positive human sera. These sera contained high titres of antibodies to a fusion protein, produced in E. coli, consisting of beta-galactosidase and the C-terminal 167 amino acids of BERF4. Immunoaffinity purified antibodies reactive with the EBV component of the fusion show the molecular weight of this antigen in EBV immortalized B-cell lines to be about 160 kD. The demonstration that BERF4 contains an exon encoding a nuclear protein identifies a new EBNA gene (EBNA-6) and suggests that KRPR is a signal sequence common to a number of viral and cellular nuclear polypeptides which bind to nucleic acids and may therefore be of predictive value in identifying karyophilic proteins.

Human recombinant interleukin 4 induces Fc epsilon R2/CD23 on normal human monocytes

rIL-4 (B cell stimulatory factor 1) induces the expression of Fc epsilon R2/CD23 on normal human monocytes (Mo). Fc epsilon R2/CD23 induction was detectable both by flow cytometry using anti-CD23 mAbs as well as soluble IgE, and by the immunoprecipitation with CD23-specific mAb or IgE of a 45-kD band from 125I-lactoperoxidase-labeled Mo. Fc epsilon R2/CD23 was fully expressed after a 24-h incubation with rIL-4, and was still detectable after 72 h from the addition of IL-4. This effect was specific, because none of the other rILs tested (IL-1, IL-2, IL-3, IL-5, B cell stimulatory factor 2, granulocyte-macrophage colony stimulating factor, and IFN-gamma) could induce FC epsilon R2/CD23, either alone or in various combinations. No synergism was observed between IL-4 and other ILs. IFN-gamma was not able to inhibit the IL-4-induced expression of Fc epsilon R2/CD23 on Mo, neither when added to the culture together with IL-4, nor when added 36 h earlier.

Characterization of a T-lymphocyte Epstein-Barr virus/C3d receptor (CD21)

The Epstein-Barr virus/C3d receptor (EBVR-CR2) was detected on three T-lymphoblastoid cell lines. The apparent Mrs of purified EBVR-CR2 of T-cell and B-cell origin were identical. The N-terminal amino acid sequence from the T-cell EBVR-CR2 confirmed the placement of this receptor in a multigene family of complement regulatory proteins. All EBVR-CR2-positive T-cell lines were T6 and T4-T8 antigen positive.

A fifth Epstein-Barr virus nuclear protein (EBNA3C) is expressed in latently infected growth-transformed lymphocytes

Three distantly homologous neighboring long open reading frames in the Epstein-Barr virus (EBV) genome are preceded by short open reading frames. The leftmost short and long open reading frames encode EBNA3, a nuclear protein which is slightly smaller (145 kilodaltons [kDa]) than two other nuclear proteins (150 to 155 kDa) detected in Western blots (immunoblots) of latently infected cell protein (K. Hennessy, F. Wang, E. Woodland-Bushman, and E. Kieff, Proc. Natl. Acad. Sci. USA 83:5693-5697, 1986; I. Joab, D. T. Rowe, M. Bodescot, J.-C. Nicolas, P. J. Farrell, and M. Perricaudet, J. Virol. 61:3340-3344, 1987). We have demonstrated that the most rightward short (BERF3) and long (BERF4) open reading frames are spliced in frame at the 3' end of a 5-kilobase latently infected cell RNA and that this RNA begins within or upstream of the EBV long internal repeat. EBV-immune human antibodies specific for the long open reading frame translation product identified a 155-kDa protein on Western blots of latently infected cell protein and specifically reacted with large nonnucleolar nuclear granules in every latently infected cell. Expression of the cDNA in BALB/c 3T3 cells resulted in translation of full-size EBNA3C but had no effect on cell morphology, contact inhibition, or serum independence.

Different patterns of Epstein-Barr virus gene expression and of cytotoxic T-cell recognition in B-cell lines infected with transforming (B95.8) or nontransforming (P3HR1) virus strains

Epstein-Barr virus (EBV)-negative Burkitt's lymphoma (BL) cell lines have been converted to EBV genome positivity by in vitro infection with the transforming EBV strain B95.8 and with the nontransforming mutant strain P3HR1, which has a deletion in the gene encoding the nuclear antigen EBNA2. These B95.8- and P3HR1-converted lines have been compared for their patterns of expression of EBV latent genes (i.e., those viral genes constitutively expressed in all EBV-transformed lines of normal B-cell origin) and for their recognition by EBV-specific cytotoxic T lymphocytes (CTLs), in an effort to identify which latent gene products provide target antigens for the T-cell response. B95.8-converted lines on several different EBV-negative BL-cell backgrounds all showed detectable expression of the nuclear antigens EBNA1, EBNA2, and EBNA3 and of the latent membrane protein (LMP); such converts were also clearly recognized by EBV-specific CTL preparations with restriction through selected human leukocyte antigen (HLA) class I antigens on the target cell surface. The corresponding P3HR1-converted lines (lacking an EBNA2 gene) expressed EBNA1 and EBNA3 but, surprisingly, showed no detectable LMP; furthermore, these converts were not recognized by EBV-specific CTLs. Such differences in T-cell recognition were not due to any differences in expression of the relevant HLA-restricting determinants between the two types of convert, as shown by binding of specific monoclonal antibodies and by the susceptibility of both B95.8 and P3HR1 converts to allospecific CTLs directed against these same HLA molecules. The results suggest that in the normal infectious cycle, EBNA2 may be required for subsequent expression of LMP and that both EBNA2 and LMP (but not EBNA1 or EBNA3) may provide target antigens for the EBV-specific T-cell response.

Soluble CD23 is released by B lymphocytes cycling in response to interleukin 4 and anti-Bp50 (CDw40)

An enzyme-linked immunoassay was developed to quantitate the production of soluble CD23 from cycling B lymphocytes. This molecule has identity both with B cell-derived B cell growth factor and with an IgE-binding factor. B lymphocytes, which had been stimulated for 3 days with phorbol dibutyrate and calcium ionophore, washed and recultured, failed to produce detectable levels of CD23 over the following 3 days. Soluble CD23 was found, however, in the supernatant of cultures where recombinant interleukin 4 had been included. The level of CD23 rose dramatically when anti-Bp50 had also been added. By contrast, anti-Bp50, alone or together with low molecular weight T cell-derived B cell growth factor, failed to promote the release of CD23 in detectable amounts. There was a strong correlation between the appearance of soluble CD23 in culture supernatants and the expression of CD23 on the surface of restimulated cells. The level of CD23 release appeared to relate more to the continued cycling of cells than to their differentiation to immunoglobulin secretion. These findings are discussed with particular emphasis on the role of CD23 as an important multi-functional lymphokine in B lymphocyte physiology.

Receptors for B cell stimulatory factor 2. Quantitation, specificity, distribution, and regulation of their expression

B cell stimulatory factor 2 receptors (BSF-2-R) were studied using radioiodinated recombinant BSF-2 with a specific activity of 6.16 X 10(13) cpm/g. Kinetic studies showed that binding of 125I-BSF-2 to CESS cells reached maximum level within 150 min at 0 degrees C. There was a single class of receptors with high affinity (Kd 3.4 X 10(-10) M) on CESS, and the number of receptors was 2,700 per cell. Binding of 125I-BSF-2 to CESS was competitively inhibited by unlabeled BSF-2 but not by IL-1, IL-2, IFN-beta, IFN-gamma, and G-CSF, indicating the presence of the receptors specific for BSF-2. EBV-transformed B lymphoblastoid cell lines (CESS, SKW6-CL4, LCL13, and LCL14) expressed BSF-2-R, whereas Burkitt's lines did not. EBV or EBNA2 did not induce the expression of the receptors on Burkitt's cells. The plasma cell lines (ARH-77 and U266) expressed BSF-2-R, fitting the function of BSF-2 as plasma cell growth factor. Several other cell lines, the histiocytic line U937, the promyelocytic line HL60, the astrocytoma line U373 and the glioblastoma line SK-MG-4, in which BSF-2 was inducible with IL-1 or TPA, displayed BSF-2-R with Kd in the range of 1.3-6.4 X 10(-10) M, suggesting the autocrine mechanism in BSF-2 function. The four T cell lines (CEM, HSB, Jurkat, and OM 1) did not express a detectable number of receptors, but normal resting T cells expressed 100-1,000 receptors per cell. BSF-2-R were not present on normal resting B cells but expressed on activated B cells with a Kd of 3.6-5.0 X 10(-10) M, fitting the function of BSF-2, which acts on B cells at the final maturation stage to induce immunoglobulin production.

Molecular structure of the gene and the 5'-flanking region of the human lymphocyte immunoglobulin E receptor

Overlapping clones which contain the complete gene encoding the human lymphocyte IgE receptor (MW:45kd; identical with CD23), were isolated from human genomic lambda-libraries. The gene spans approximately 13kb and comprises 11 exons. The 5'-end of the mRNA was mapped by primer extension and S1-mapping, revealing two initiation sites for transcription. Two corresponding TATA boxes were identified by sequencing the 5'-flanking region. A 188bp long inverted repeat was found which flanks the promoter region and could possibly be involved in gene regulation. Exons 9 to 11 code for the IgE-binding domain of the receptor which shows homology to several lectins, particularly to the asialoglycoprotein receptor. A comparison of the exon/intron arrangement of these genes implies that their lectin domains have evolved from a common ancestral cassette.

Differences in B cell growth phenotype reflect novel patterns of Epstein-Barr virus latent gene expression in Burkitt's lymphoma cells

Recently established Epstein-Barr virus (EBV)-positive Burkitt's lymphoma (BL) cell lines, carrying chromosomal translocations indicative of their malignant origin, have been monitored for their degree of in vitro progression towards a more 'lymphoblastoid' cell surface phenotype and growth pattern, and for their expression of three EBV latent gene products which are constitutively present in all virus-transformed normal lymphoblastoid cell lines (LCLs). BL cell lines which stably retained the original tumour biopsy phenotype on serial passage were all positive for the nuclear antigen EBNA 1 but did not express detectable amounts of two other 'transforming' proteins, EBNA 2 and the latent membrane protein (LMP). This novel pattern of EBV gene expression was also observed on direct analysis of BL biopsy tissue. All three viral proteins became detectable, however, in BL cell lines which had progressed towards a more LCL-like phenotype in vitro. This work establishes a link between B cell phenotype and the accompanying pattern of EBV latent gene expression, and identifies a novel type of EBV:cell interaction which may be unique to BL cells.

Epstein-Barr virus-transformed human precursor B cell lines: altered growth phenotype of lines with germ-line or rearranged but nonexpressed heavy chain genes

A series of lymphoblastoid cell lines (LCLs) have been established by in vitro infection of fetal bone marrow and fetal liver cells with Epstein-Barr virus (EBV). While most lines showed the usual mature B cell phenotype, a small proportion were cytoplasmic and surface immunoglobulin (Ig) heavy and light chain negative. Analysis of gene rearrangements indicated that the Ig- lines were either germ-line or nonproductively rearranged when probed for JH and were in germ-line configuration for C chi; no mu or chi mRNA could be detected in such cells. Precursor B cell lines were indistinguishable from their normal Ig+ counterparts in their expression of a wide variety of cell surface markers including "activation" antigens usually associated with the lymphoblastoid state; even the single LCL showing germ-line heavy and light chain genes expressed B lineage-specific cell surface antigens. However, the Ig- lines were distinct from their Ig+ counterparts in three important respects: (a) they grew much more slowly and achieved lower saturation densities, (b) they showed unusually high proportions (8-16%) of cells in EBV-productive cycle, and (c) they contained unusually high proportions (up to 40%) of cells expressing free joining (J) chain. These results suggest that precursor B cells differ in their response to the growth-transforming effects of EBV such that the virus-cell interaction in precursor B cell lines is inherently less stable than in conventional LCL. In particular there may be a greater movement of cells out of cycle and along the B cell maturation pathway. It is possible that such movement leads in individual cells either to virus replication or to a "sterile" plasmacytoid differentiation with J chain expression in the absence of Ig synthesis.