Epstein-Barr virus transforms precursor B cells even before immunoglobulin gene rearrangements

Role of Epstein-Barr Virus in Pathogenesis and Racial Distribution of IgA Nephropathy

IgA nephropathy (IgAN) is the dominant type of primary glomerulonephritis worldwide. However, IgAN rarely affects African Blacks and is uncommon in African Americans. Polymeric IgA1 with galactose-deficient hinge-region glycans is recognized as auto-antigen by glycan-specific antibodies, leading to formation of circulating immune complexes with nephritogenic consequences. Because human B cells infected in vitro with Epstein-Barr virus (EBV) secrete galactose-deficient IgA1, we examined peripheral blood B cells from adult IgAN patients, and relevant controls, for the presence of EBV and their phenotypic markers. We found that IgAN patients had more lymphoblasts/plasmablasts that were surface-positive for IgA, infected with EBV, and displayed increased expression of homing receptors for targeting the upper respiratory tract. Upon polyclonal stimulation, these cells produced more galactose-deficient IgA1 than did cells from healthy controls. Unexpectedly, in healthy African Americans, EBV was detected preferentially in surface IgM- and IgD-positive cells. Importantly, most African Blacks and African Americans acquire EBV within 2 years of birth. At that time, the IgA system is naturally deficient, manifested as low serum IgA levels and few IgA-producing cells. Consequently, EBV infects cells secreting immunoglobulins other than IgA. Our novel data implicate Epstein-Barr virus infected IgA⁺ cells as the source of galactose-deficient IgA1 and basis for expression of relevant homing receptors. Moreover, the temporal sequence of racial-specific differences in Epstein-Barr virus infection as related to the naturally delayed maturation of the IgA system explains the racial disparity in the prevalence of IgAN.

Upsetting the Balance: When Viruses Manipulate Cell Polarity Control

The central importance of cell polarity control is emphasized by the frequency with which it is targeted by many diverse viruses. It is clear that in targeting key polarity control proteins, viruses affect not only host cell polarity, but also influence many cellular processes, including transcription, replication, and innate and acquired immunity. Examination of the interactions of different virus proteins with the cell and its polarity controls during the virus life cycles, and in virally-induced cell transformation shows ever more clearly how intimately all cellular processes are linked to the control of cell polarity.

[Epstein-Barr virus (EBV) and Kaposi's sarcoma-associated herpesvirus (KSHV, HHV-8)]

Epstein-Barr virus (EBV) and Kaposi's sarcoma-associated herpesvirus (KSHV or human herpesvirus 8, HHV-8) are members of gamma-herpes virus family. Both viruses infect to B cells and cause malignancies such as lymphoma. Since EBV and HHV-8 are so-called 'oncovirus', their oncogenecities have been focused in the researches on EBV and KSHV for a long time. EBV was discovered in 1964, whereas KSHV was identified in 1994. However, KSHV was analyzed rapidly in these fifteen years. One of the recent progresses in the research on EBV and KSHV is that virus-encoded small RNAs were identified in their genomes and characterized. EBV is the first human virus in whose genome microRNA was identified. The oncogenecity of EBV and KSHV remains unclear. Here, I discuss the pathogenesis by EBV and KSHV with special reference to recent progress in this field.

Construction of Japanese BAC library Yamato-2 (JY2): a set of 330K clone resources of damage-minimized DNA taken from a genetically established Japanese individual

A bacterial artificial chromosome (BAC) library referred to as Yamato-2 (JY2), was constructed from a Japanese individual and contained 330,000 clones. Library construction was based on 2 concepts: Japanese pedigree and non-immortalization. Genomic DNA was extracted from white blood cells from umbilical cord blood of a Japanese male individual. Four traits of the sample, (1) amelogenin DNA, (2) short tandem repeat (STR), (3) mitochondrial DNA (mtDNA), and (4) HLA-allele typing, were investigated to verify attribution of the donor. One of the samples with quite good Japanese characteristics was named JY2 and used as a resource for construction of a BAC library. Amelogenin DNA indicated male. STR indicated Mongoloid. MtDNA suggested haplogroup B, which is different from any other diploid whose sequence has been reported. The HLA gene was classified into east-Asian specific haplotype. These results revealed that JY2 was obtained from a Japanese male. We sequenced both ends of 185,012 BAC clones. By using the BLAST search, BAC end sequences (BESs) were mapped on the human reference sequence provided by NCBI. Inserts of individual BAC clones were mapped with both ends properly placed. As a result, 103,647 BAC clones were successfully mapped. The average insert size of BAC calculated from the mapping information was 130 kb. Coverage and redundancy of the reference sequence by successfully mapped BAC clones were 96.4% and 3.9-fold, respectively. This library will be especially suitable as a Japanese standard genome resource. The availability of an accurate library is indispensable for diagnostics or drug-design based on genome information, and JY2 will provide an accurate sequence of the Japanese genome as an important addition to the human genome.

Restricted expression of Epstein-Barr virus latent genes in murine B cells derived from embryonic stem cells

Background

Several human malignancies are associated with Epstein-Barr virus (EBV) and more than 95% of the adult human population carries this virus lifelong. EBV efficiently infects human B cells and persists in this cellular compartment latently. EBV-infected B cells become activated and growth transformed, express a characteristic set of viral latent genes, and acquire the status of proliferating lymphoblastoid cell lines in vitro. Because EBV infects only primate cells, it has not been possible to establish a model of infection in immunocompetent rodents. Such a model would be most desirable in order to study EBV's pathogenesis and latency in a suitable and amenable host.

Methodology/Principal Findings

We stably introduced recombinant EBV genomes into mouse embryonic stem cells and induced their differentiation to B cells in vitro to develop the desired model. In vitro differentiated murine B cells maintained the EBV genomes but expression of viral genes was restricted to the latent membrane proteins (LMPs). In contrast to human B cells, EBV's nuclear antigens (EBNAs) were not expressed detectably and growth transformed murine B cells did not arise in vitro. Aberrant splicing and premature termination of EBNA mRNAs most likely prevented the expression of EBNA genes required for B-cell transformation.

Conclusions/Significance

Our findings indicate that fundamental differences in gene regulation between mouse and man might block the route towards a tractable murine model for EBV.

Epstein-Barr virus exploits BSAP/Pax5 to achieve the B-cell specificity of its growth-transforming program

Epstein-Barr virus (EBV) can infect various cell types but limits its classical growth-transforming function to B lymphocytes, the cells in which it persists in vivo. Transformation initiates with the activation of Wp, a promoter present as tandemly repeated copies in the viral genome. Assays with short Wp reporter constructs have identified two promoter-activating regions, one of which (UAS2) appears to be lineage independent, while the other (UAS1) was B-cell specific and contained two putative binding sites for the B-cell-specific activator protein BSAP/Pax5. To address the physiologic relevance of these findings, we first used chromosome immunoprecipitation assays and found that BSAP is indeed bound to Wp sequences on the EBV genome in transformed cells. Thereafter, we constructed recombinant EBVs carrying two Wp copies, both wild type, with UAS1 or UAS2 deleted, or mutated in the BSAP binding sites. All the viruses delivered their genomes to the B-cell nucleus equally well. However, the BSAP binding mutant (and the virus with UAS1 deleted) showed no detectable activity in B cells, whether measured by early Wp transcription, expression of EBV latent proteins, or outgrowth of transformed cells. This was a B-cell-specific defect since, on entry into epithelial cells, an environment where Wp is not the latent promoter of choice, all the Wp mutant viruses initiated infection as efficiently as wild-type virus. We infer that EBV ensures the B-cell specificity of its growth-transforming function by exploiting BSAP/Pax5 as a lineage-specific activator of the transforming program.

Rescue of "crippled" germinal center B cells from apoptosis by Epstein-Barr virus

Epstein-Barr virus (EBV) is associated with B-cell lymphomas such as Hodgkin lymphoma, Burkitt lymphoma, and post-transplantation lymphoma, which originate from clonal germinal center (GC) B cells. During the process of somatic hypermutation, GC B cells can acquire deleterious or nonsense mutations in the heavy and light immunoglobulin genes. Such mutations abrogate the cell surface expression of the B-cell receptor (BCR), which results in the elimination of these nonfunctional B cells by immediate apoptosis. EBV encodes several latent genes, among them latent membrane protein 1 (LMP1) and LMP2A, which are regularly expressed in EBV-positive Hodgkin lymphoma and posttransplantation lymphomas. Since LMP1 and LMP2A mimic the function of 2 key receptors on B cells, CD40 and BCR, respectively, we wanted to learn whether EBV infection can rescue proapoptotic GC B cells with crippling mutations in the heavy chain immunoglobulin locus from apoptosis. We show here that BCR-negative GC B cells readily enter the cell cycle upon infection with EBV in vitro and yield clonal lymphoblastoid cell lines that are incapable of expressing a functional BCR because the rearranged and formerly functional heavy chain immunoglobulin alleles carry deleterious mutations. Our findings imply an important role for EBV in the process of lymphomagenesis in certain cases of Hodgkin lymphoma and posttransplantation lymphomas.

Latent membrane protein 2A, a viral B cell receptor homologue, induces CD5+ B-1 cell development

The latent membrane protein 2A (LMP2A) of EBV plays a key role in regulating viral latency and EBV pathogenesis by functionally mimicking a constitutively active B cell Ag receptor. When expressed as a B cell-specific transgene in mice, LMP2A drives B cell development, resulting in the bypass of normal developmental checkpoints. In this study, we have demonstrated that expression of LMP2A in transgenic mice results in B cell development that exclusively favors B-1 cells. This switch to B-1 cell development occurs at the pre-B-cell stage of normal B cell development in the bone marrow, a B cell stage much earlier than appreciated for B-1 commitment. This finding indicates that all pre-B cells have the capacity to assume a B-1 cell phenotype if they encounter the appropriate signal during normal development. Furthermore, these studies offer insight into EBV latency and pathogenesis in the human host.

Molecular markers of clonality and identity in epstein-barr virus-associated B-cell lymphoproliferative disease

Epstein-Barr virus (EBV)-associated B-cell lymphoproliferative disease may be polyclonal, oligoclonal, or monoclonal. The degree of tumor clonality reflects the disease pathogenesis and may have implications for disease diagnosis, prognosis, and treatment. In this study, specimens of EBV-associated B-cell lymphoproliferative disease obtained from immunocompromised hosts were analyzed for molecular markers of cellular and virologic clonality and virologic identity. Each tumor specimen was assessed for immunoglobulin gene JH region rearrangement, the structure of the EBV genome termini, and the EBV genotype(s) present using a new EBV genotyping assay based upon LMP-1 gene sequence variation. The results of the JH rearrangement and EBV termini assays were generally concordant in their assessment of tumor specimen clonality, and both assays contributed to establishing clonal identity between different tumor specimens. The EBV genotyping assay did not significantly contribute to the assessment of tumor clonality but did established clear virologic identity between different tumor specimens obtained from the same individual. In one individual, these three assays together characterized a multi-focal, monoclonal tumor that may have arisen through clonal selection after sequential infections with two different EBV genotypes. In summary, the JH rearrangement and EBV termini assays each provided different but complementary information on tumor clonality, while the EBV genotyping assay proved most useful for establishing virologic identity among tumors. Utilization of these three assays together may provide new insight into the pathogenesis of EBV-associated B-cell lymphoproliferative disease.

Nitric oxide induces apoptosis in NALM-6, a leukaemia cell line with low cyclin E protein levels

Intracellular nitric oxide levels may differ in resting and stimulated cells and contribute to the regulation of cell survival and proliferation through a variety of mechanisms and effects. We exposed two B-cell lines to a range of S-nitroso-N-acetyl-D,L-penicillamine (SNAP) concentrations in order to examine their susceptibility to exogenous nitric oxide and the participation of nitric oxide as modulator of cell proliferation. Although both FLEB and NALM-6 decreased their levels of thymidine incorporation, only NALM-6 cells were induced to undergo G1 arrest, phosphatidyl serine exposure and DNA fragmentation when cultured in the presence of 250 microm SNAP. This higher sensitivity of NALM-6 coincided with initially low cyclin E protein levels which were increased 7.8-fold after culture for 24 h with 250 microm SNAP. In contrast, there was no difference in cyclins A and D3, Bcl-2 and actin levels, neither at the beginning nor at the end of the 24 h culture. Our study reveals that FLEB and NALM-6 exhibit different response to the same concentration of nitric oxide, that nitric oxide can simultaneously induce cell cycle alterations and apoptosis, and further suggests an association between these two processes, with the involvement of cell cycle regulatory molecules.

Molecular pathogenesis of Epstein-Barr virus associated posttransplant lymphomas: new insights through latent membrane protein 1 fingerprinting

BACKGROUND

Fingerprint amino acid patterns within the carboxy terminus of the latent membrane protein (LMP1) oncoprotein of Epstein-Barr virus (EBV) allow individual strain identification at the molecular level. LMP1 is expressed in the tumor cells of EBV-associated posttransplant lymphomas (PTLs) and the LMP1 genome is also identified in lymphocytes of most donors of allogeneic bone marrow. Therefore, LMP1 genotyping in donor lymphocytes and PTL tumor cells, together with sex chromatin determination of tumor cells, allows to determine the origin of PTL tumor cells and the origin of individual EBV strains harboured by them.

METHODS

We traced the origin of aggressive PTLs occurring in six patients after allogeneic T cell-depleted stem cell transplantation (allo-SCT). DNA was extracted from donor lymphocytes and PTLs of recipients and amplified with LMP1-specific primers in each case. A comparative sequence analysis of the fingerprint LMP1 region identified in donor lymphocytes and lymphoma was performed.

RESULTS

One lymphoma of donor origin occurred after highly selected CD34+ PBSCT and contained the same LMP1 genotype as the donor lymphocytes. Three lymphomas of recipient origin had deletions within the carboxy terminus of LMP1, not identified in the donor strains. All lymphomas occurred in the setting of allo-SCT and had a rapid clinical course.

CONCLUSIONS

These results show that highly selected CD34+ PBSCT does not protect against transfer of EBV positive founder cells of donor type PTL and that, after allo-SCT, recipient type PTLs are not uncommon. Outgrowth of recipient type lymphoma may be favoured by LMP1 deletion variant strains present in recipient lymphocytes.

Epstein-Barr virus LMP2A drives B cell development and survival in the absence of normal B cell receptor signals

Epstein-Barr virus (EBV) establishes a persistent latent infection in peripheral B lymphocytes in humans and is associated with a variety of malignancies and proliferative disorders. Latent membrane protein 2A (LMP2A) is one of only two viral proteins expressed in latently infected B lymphocytes in vivo. LMP2A blocks B cell receptor (BCR) signal transduction in vitro by binding the Syk and Lyn protein tyrosine kinases. To analyze the significance of LMP2A expression in vivo, transgenic mice with B cell lineage expression of LMP2A were generated. LMP2A expression results in the bypass of normal B lymphocyte developmental checkpoints allowing immunoglobulin-negative cells to colonize peripheral lymphoid organs, indicating that LMP2A possesses a constitutive signaling activity in nontransformed cells.

Reappraisal of the relationship between immunoglobulin heavy chain gene rearrangement and Epstein-Barr virus infection in Reed-Sternberg cells of Hodgkin's disease

We investigated 44 cases of Hodgkin's disease for Epstein-Barr virus genome with EBER-1 in situ hybridization. Twenty of 44 (45.5%) were positive for EBV. Simultaneously, immunoglobulin gene rearrangements were assessed in 32 of these 44 cases with PCR on DNA extracted from Reed-Sternberg cell (RS-cell) -rich areas microdissected from paraffin sections. Clonally rearranged immunoglobulin (IgH) gene was observed in 15 cases (46.9%). EBV-negative cases showed more frequent IgH rearrangement than EBV-positive cases (10 and 5 cases, respectively). In 9 cases, the RS cells were CD20-positive immunohistochemically and these were all EBV negative and the IgH gene was rearranged in all except one. These findings may suggest that EBV infection has occurred before the immunoglobulin gene rearrangement or that EBV infection has influenced the rearrangement of the immunoglobulin gene. The results may also hint towards the obscure B-cell nature of the RS cells.

Thioredoxin expression and localization in human cell lines: detection of full-length and truncated species

Thioredoxin (Trx) is an intracellular multifunctional 12-kDa protein with a reduction/oxidation (redox) active disulfide constitutively expressed by most cells of the human body. Trx can also be released by cells such as lymphocytes upon activation or oxidative stress exposure and exert a cocytokine and cytoprotective activity. In addition, a truncated 10-kDa form of Trx has been reported. In order to better understand the function of full-length and truncated Trx, we have produced, for the first time, specific monoclonal antibodies, which can discriminate between the two forms. Using these novel antibodies, designated alpha Trx1 to alpha Trx4, a panel of cell lines derived from human B and T lymphocytes, monocytes, granulocytes, and melanomas was analyzed by immunochemical techniques. The cellular distribution differed between the two forms. All lines contained full-length Trx, also located to a minor extent on the cell surface. One exception was the melanoma cell line FM28.4, which did not show any Trx expression. Truncated Trx was present in most cells in minimal amounts only, whereas the monocytic cell lines THP-1 and U-937 expressed high amounts on the cell surface, as shown by flow cytometric analysis of living cells and confocal laser-scanning microscopy. The biological importance and function of the short versus long forms of Trx as detected by the antibodies are discussed.

DNA demethylation and pericentromeric rearrangements of chromosome 1

Rearrangements in the vicinity of the centromere of chromosome 1 are over-represented in many types of human cancer and are a characteristic feature of a rare genetic disease called ICF (immunodeficiency, centromeric heterochromatin instability, and facial anomalies). Evidence is presented that implicates DNA hypomethylation in the formation of these pericentromeric chromosomal anomalies. The DNA methylation inhibitors 5-azadeoxycytidine and 5-azacytidine, but not other tested genotoxins, induced the preferential formation of pericentromeric rearrangements of chromosome 1 at a very high frequency in a pro-B-cell line (FLEB14) and at a lower frequency in a mature B-cell line (AHH-1). These abnormal chromosomes appear identical to the diagnostic chromosomal aberrations in the ICF syndrome. A major component of the pericentromeric DNA in chromosome 1, satellite 2, was shown to be hypomethylated in an ICF B-cell line, although DNA from this cell line did not display detectable overall hypomethylation. It is hypothesized that demethylation in certain DNA regions, including in pericentromeric satellite DNA, helps lead to pericentromeric chromosomal rearrangements in lymphocytes from ICF patients and in normal lymphoblastoid cells incubated in vitro with DNA demethylating agents.

Human BAC library: construction and rapid screening

We have constructed a human genomic bacterial artificial chromosome (BAC) library using high molecular weight DNA from a pre-pro-B cell line, FLEB14-14, with a normal male diploid karyotype. This BAC library consists of 96,000 clones with an average DNA insert size of 110 kb, covering the human genome approximately 3 times. The library can be screened by three different methods. (1) Probe hybridization to 31 high-density replica (HDR) filters: each filter contains 3072 BAC clones which were gridded in a 6 x 6 pattern. (2) Probe hybridization to two Southern blot filters to which 31 HindIII digests of the pooled 3072 BAC clones were loaded. This identifies a particular HDR filter for which further probe hybridization is performed to identify a particular clone(s). (3) Two-step polymerase chain reaction (PCR). First, PCR is applied to DNA samples prepared from ten superpools of 9600 BAC clones each to identify a particular superpool and the second PCR is applied to 40 unique DNA samples prepared from the four-dimensionally assigned BAC clones of the particular superpool. We present typical examples of the library screening using these three methods. The two-step PCR screening is particularly powerful since it allows us to isolate a desired BAC clone(s) within a day or so. The theoretical consideration of the advantage of this method is presented. Furthermore, we have adapted Vectorette method to our BAC library for the isolation of terminal sequences of the BAC DNA insert to facilitate contig formation by BAC walking.

Pyothorax-associated lymphoma. An unusual case with biphenotypic character of T and B cells

Pyothorax-associated lymphoma is known to develop in patients who received an artificial pneumothorax for pulmonary tuberculosis some 30 to 40 years previously. Such patients exhibit large, immunoblastic lymphoma cells and often have a B-cell phenotype. We present a patient with an artificial pneumothorax and such a late developing lymphoma but with the unique finding of aberrant T- and B-cell phenotypes. Southern blot hybridization using immunoglobulin gene JH and T-cell receptor beta chain receptors revealed germline configurations. Lymphomas developing in immunocompromised patients, such as those with acquired immunodeficiency syndrome, may show such unusual phenotypes. The unusual phenotypes found in this patient provide evidence that his pyothorax-associated lymphoma was related to an immunocompromised state.

Hodgkin's Disease and Anaplastic Large Cell Lymphoma Revisited. ii. from cytokines to cell lineage

The true identity of Hodgkin's mononuclear cells and Reed-Sternberg (H-RS) cells has been a subject of controversy for decades. Those who believe that Hodgkin's disease (HD) is a heterogeneous disease may consider it to constitute lymphomas of various origins. However, this theory seems incompatible with the finding of similar phenotypic, biologic, and immunologic properties among most HD. We believe that, in the majority of cases, HD, except for LP and some LD-type HD, is a homogeneous disease despite differences in the degree of fibrosis and/or cellular reaction. The heterogeneity in cellular reactions is a result of secretion of various cytokines by H-RS cells, which may or may not be influenced by the presence of EBV. H-RS cells, and anaplastic large cell lymphoma (ALCL) cells as well, can express a combination of cytokines and cytokine receptors that is not seen in other types of lymphomas. The unique cytokine/receptor profile (e.g. the expression of c-kit-R/CD117), along with various properties associated with H-RS/ALCL cells, leads to a hypothesis that H-RS/ALCL cells are related to similar lymphohematopoietic progenitor cells with different etiologies and somewhat limited differentiation capacity. A number of H-RS cells may differentiate with limited capacity along the B-cell pathway and may be infected by EBV, which further complicates the biologic and immunologic properties of these cells. The majority of H-RS cells may also, however, differentiate along the antigen-presenting dendritic cell pathway, as indicated by the abundant expression of restin, CD15, CD40, CD54, CD58, CD80, and CD86. The majority of ALCL cells clearly differentiate to T cells, but some may acquire B-cell or histiocyte phenotypes. The progenitor cell hypothesis may explain (1) the variable expression of CD117, CD43, and CD34 as well as the absence of CD27, CD45 and CD45RA in H-RS cells; (2) the inconsistent and irregular patterns of phenotype and genotype and the various, often very limited, degrees of differentiation among these two types of lymphoma cells; (3) the existence of secondary HD or ALCL associated with rare types of lymphomas or leukemias, or vice versa; (4) the absence of recombinase and of the B-specific transcription factors BSAP; and (5) the frequent expression of IL-7 and IL-9 in H-RS cells. Copyright 1996 S. Karger AG, Basel

The organization of the human immunoglobulin lambda gene locus

To elucidate the complex structure of the human immunoglobulin lambda gene locus, a 1020-kb contig was constructed using 184 cosmid clones and one bacterial artificial chromosome (BAC) clone. A high-resolution physical map of this contig revealed that the entire lambda gene locus is 911 kb in length. It contains seven constant region (C lambda) gene segments and 69 unique EcoRI-HindIII segments that hybridize to variable region gene (V lambda) probes. The VpreB gene, BCRL4, and gamma-glutamyl transpeptidase gene (GGT)-like sequences are also located within the lambda gene locus. Hybridization analysis suggested that the lambda gene locus has undergone extensive amplification events in evolution.

Molecular genetic analysis demonstrates that multiple posttransplantation lymphoproliferative disorders occurring in one anatomic site in a single patient represent distinct primary lymphoid neoplasms

BACKGROUND

Posttransplantation lymphoproliferative disorders (PT-LPDs) are a clinicopathologically heterogeneous group of lymphoid proliferations of varied clonal composition, the majority of which are associated with Epstein-Barr virus (EBV) infection. The clonal content and clonal relatedness of 24 separate PT-LPD lesions occurring synchronously in one organ in a single patient were investigated.

METHODS

Twenty-four separate PT-LPD lesions from the colon and mesentery of a 15-year-old male, developing 4 months after cardiac transplantation, were studied for clonality based on immunoglobulin heavy chain (IgH) gene rearrangements for the presence, clonality, and type of EBV infection and for the presence of c-myc, ras, and p53 gene alterations. Southern blot hybridization, polymerase chain reaction, and single strand conformation polymorphism assays were employed.

RESULTS

All 24 lesions were histologically similar (polymorphic B-cell lymphomas) but exhibited varied clonality and were clonally distinct with respect to both IgH gene rearrangements and EBV infection. All lesions were infected with EBV type A. Structural alterations of oncogenes or tumor suppressor genes were not identified.

CONCLUSIONS

Separate PT-LPD lesions occurring synchronously in a single organ or patient may be clonally distinct, suggesting that they represent multiple distinct primary lymphoid proliferations rather than metastatic disease as in conventional malignant lymphomas. This may explain partially the rapid development in some patients of a large PT-LPD tumor burden that may regress rapidly after reduction of immunosuppression.

Evidence for lytic infection by Epstein-Barr virus in mucosal lymphocytes instead of nasopharyngeal epithelial cells in normal individuals

Normal nasopharyngeal tissues from 23 individuals who died of causes unrelated to the upper respiratory system and had no evidence of Epstein-Barr virus (EBV)-related diseases were studied using in situ hybridisation (ISH) and immunohistochemistry for the detection of EBV RNA and expression of EBV proteins, respectively. ISH using 35S-labelled riboprobe for EBV EBER RNA showed occasional to a few EBER+ lymphocytes in the stroma of nasopharyngeal mucosa in 14/16 cases with available paraffin-embedded tissues. In addition, very rare intraepithelial EBER+ lymphocytes were also detected in 3/16 cases. However, in none of these cases was EBER detected in the epithelial cells. Similar results were obtained using a nonradioactive ISH method for EBER (Dako). In 3/23 cases, immunostaining using monoclonal antibodies for EBV proteins on cryostat sections showed occasional cells in the stroma expressing EBV nuclear antigen 2 (EBNA2), latent membrane protein-1 (LMP), and switch protein encoded by BZLF1 gene (ZEBRA) in two cases and only very rare LMP+ and ZEBRA+ cells in one other case. Double immunostaining combining alkaline phosphatase anti-alkaline phosphatase (APAAP) for CD markers and indirect immunofluorescence for LMP showed that the LMP+ cells were either CD19+ or less frequently CD3+, but none were CD68+. These results show that both B and T lymphocytes harbouring EBV can be found in the normal nasopharyngeal tissues. Interestingly, EBV proteins associated with lytic viral replication--diffuse early antigen (EA-D), viral capsid antigen (VCA), or membrane antigen (MA)--were also detected in rare cells in the stroma in one case, and in another case only one MA+ cell was detected.(ABSTRACT TRUNCATED AT 250 WORDS)

Distinct clonotypic Epstein-Barr virus-induced fatal lymphoproliferative disorder in a patient with Wiskott-Aldrich syndrome

BACKGROUND

Recently, reports of Epstein-Barr virus (EBV)-induced lymphoproliferative disorders (LPD) have increased in number among immunosuppressed recipients of organ transplants. The importance of analyzing both the immunoglobulin gene and EBV termini is advocated for the investigation of pathogenetic mechanisms for clonal proliferation in EBV-induced LPD; however, the oncogenic mechanisms of EBV-induced LPD remain unclear. Furthermore, there are very few clonotypic studies of EBV-induced LPD in patients with primary immunodeficiency diseases. The authors studied the clonality of an EBV-induced fatal LPD in a 20-year-old patient with Wiskott-Aldrich syndrome (WAS), an X-linked recessive primary immunodeficiency disease.

METHODS AND RESULTS

An autopsy showed non-Hodgkin lymphoma of B-cell origin with diffuse large cells in both systemic lymph nodes and extranodal organs. Immunohistochemical and Southern blot analyses showed polyclonal rearrangement of immunoglobulin genes in most of the lesions except for the pulmonary hilar lymph node. Furthermore, the analysis of restriction fragment length polymorphism with several fragments from EBV genome indicated that EBV genomes in all lesions were identical; however, a single but different-sized EBV termini was detected in every EBV-positive lesion when probed with the EcoRI-Dhet spanning terminal repeat region of EBV.

CONCLUSIONS

The EBV-induced fatal LPD in a patient with WAS showed the characteristic clonotype, polyclonal immunoglobulin gene rearrangement, and monoclonal EBV terminal configuration. Furthermore, EBV termini in each lesion varied in size. This particular clonotype implicates several unique pathogenetic mechanisms for clonal proliferation of EBV-induced LPD.

Signal sequence trap: a cloning strategy for secreted proteins and type I membrane proteins

A method was developed to clone, without the use of specific functional assays, complementary DNAs (cDNAs) that carry specific amino-terminal signal sequences, such as those encoding intercellular signal-transducing molecules and receptors. The vector used in this system directed the cell surface expression of interleukin-2 receptor fusion proteins when inserts with signal sequences were cloned in-frame with the correct orientation. An expression cDNA library was constructed from a bone marrow stromal cell line, which contained 5' portion-enriched cDNAs (the average size was 400 base pairs). Two cDNAs that encoded putative cytokine molecules, stromal cell-derived factor-1 alpha (SDF-1 alpha) and SDF-1 beta, which belong to the intercrine-macrophage inflammatory protein superfamily, were cloned.

The gene loci for immunoglobulin heavy chains in precursor B cell lines from a patient with severe combined immunodeficiency appear able to participate in DNA rearrangement but have a germ-line configuration

In a previous study (Immunogenetics 1988. 27:330) with Epstein-Barr virus, we established lines of precursor B cells from bone marrow cells of a patient with severe combined immunodeficiency in whom the numbers of B cells and T cells were markedly reduced. Although based on their surface markers these cell lines appeared to be at an early stage of B cell differentiation, the gene loci for immunoglobulin heavy chains (IgH) retained the germ-line configuration on both chromosomes in almost all the transformants. In this study, we found that the enhancer sequence, located between the JH and mu genes, was hypomethylated and an abundance of the germ-line Cmu transcript was detected in these cell lines by Northern hybridization. These results suggest that the chromatin structure of the IgH gene locus in these cell lines is accessible to VDJ recombinase and is able to participate fully in DNA rearrangement. By contrast, we did not detect transcripts of the RAG-1 and RAG-2 genes, which are required for V(D)J recombination at gene loci for immunoglobulin and T cell receptors. Thus, it seems likely that these cell lines fail to initiate the V(D)J recombination process because of some deficiency in the formation of VDJ recombinase, which includes the inability to express RAG genes.

Three cases of human herpesvirus-6 latent infection: integration of viral genome in peripheral blood mononuclear cell DNA

Saliva and peripheral blood mononuclear cells from three patients, two with lymphoproliferative disorders and one suffering from multiple sclerosis, were examined for the presence of human herpesvirus-6 (HHV-6) genome by using the polymerase chain reaction and Southern blot analysis. The search for anti-HHV-6 antibodies, carried out in the sera of the same cases by an immunofluorescence assay, was negative in two cases at the lowest dilution used (1:40). These three patients had a high number of HHV-6 specific sequences in uncultured peripheral blood mononuclear cells, which are thought to be a normal site of viral latency although, in healthy individuals, the infected cells are extremely rare. In order to gain some insight into the state of the viral genome in this latent HHV-6 infection, we used pulsed field gel electrophoresis to separate HHV-6 DNA directly from HHV-6 (strain GS) infected HSB-2 cells and from the peripheral blood mononuclear cells of these three patients. Our study showed the presence of intact viral genome, of the expected length of 170 kb, persisting as free extrachromosomal element in the HSB-2 cells but not in patients' peripheral blood mononuclear cells. On the other hand, in strong contrast with the results obtained in infected HSB-2 DNA, the restriction analysis of the three patients' peripheral blood mononuclear cell DNA showed fragments of molecular weight constantly higher than the 170 kb segment, indicating that the viral sequences are linked to high molecular weight cellular DNA.(ABSTRACT TRUNCATED AT 250 WORDS)

Significance of the detection of Epstein-Barr virus DNA in lymph nodes in patients with Hodgkin's disease

Epstein-Barr virus (EBV) DNA is frequently identified in benign and malignant lymphoproliferative conditions. As shown by in situ hybridization studies viral DNA is localized within malignant cells as well as benign lymphocytes. Clonal and nonclonal EBV genomes are present in Hodgkin's disease (HD), lymphomas of the immunocompromised host and reactive lymph node hyperplasia. Lytic infection with formation of linear genomes is observed in the same conditions but appears to be infrequent in HD as shown by quantitation of mRNA coding for viral capsid antigen. Expression of the oncogene LMP (latent membrane protein) is seen in Sternberg-Reed (SR) cells and immunoblasts of AIDS-related lymphoma and infectious mononucleosis (IM). In HD, the region of the BNLF1 oncogene coding for the amino terminal and transmembrane domains (associated with oncogenic function) of LMP appears to be homogeneous whereas the region coding for the intracytoplasmic (carboxy terminal) domain of LMP is heterogeneous. Cytological similarities between SR cells and immunoblasts of IM and AIDS-related lymphomas are consistent with the hypothesis that the BNLF1 oncogene is one possible inducer of morphological features of SR cells. Whether chromosomal integration of EBV DNA is an important factor in activation of such a transforming activity remains to be elucidated. EBV DNA positive and negative HD cases with numerous SR cells lack significant mRNA expression of the two recombinase activating genes (RAG-1 and RAG-2). Therefore the SR cells appear to be derived from lymphocytes beyond the pre-B-cell or common thymocyte stage which may or may not subsequently become infected by EBV.

Recent results on the biology of Hodgkin and Reed-Sternberg cells. I. Biopsy material

The most recent sophisticated investigations have provided new and revealing, but also contradictory and controversial information on the biological nature and the cellular origin of Hodgkin and Reed-Sternberg cells (H-RS). Immunophenotypic analyses have shown variable phenotypic antigen expression; but, on balance the data suggest a lymphoid cell expressing T- and/or B-cell-associated markers and certain activation antigens while lacking immunological features of monocytes-macrophages or other lineages. Molecular genetic studies have demonstrated heterogenous findings with respect to rearrangements of T-cell receptor and immunoglobulin genes. Only a small percentage of the cases has rearrangements; this might be due to the threshold of sensitivity of the method combined with the scarcity of the malignant cells. Epstein-Barr virus (EBV) genomes are clonally integrated in the H-RS cells of about half the cases. The significance of these findings--whether EBV is a causative agent or an epiphenomenon--remains to be elucidated. H-RS cells express mRNA and proteins of various cytokines and cytokine receptors implying a predominant role for cytokines in the pathophysiology of HD. The mononuclear and polynuclear H-RS cells are capable of DNA synthesis and nuclear division; the lack of cellular division leads to multinuclearity through the process of endomitosis. Mutations and expression of only a limited number of oncogenes have been tested thus far. Whether the bcl-2 oncogene is involved in HD remains a matter of debate. Aneuploidy and non-random chromosomal abnormalities are the results of cytogenetic analyses of H-RS cells. However, no chromosomal marker specific for HD has yet been found. Thus, while studies of EBV involvement, growth factor production, oncogene expression and chromosomal abnormalities contributed a fair amount of new data on the nature of H-RS cells, only immunophenotyping and genotyping provided some indication of the cellular derivation: an activated lymphoid cell that possibly expresses oncogenes, that probably is infected with EBV, that most likely produces cytokines, that certainly has multiple karyotypic abnormalities.

Shotgun polymerase chain reaction: construction of clone libraries specific to a NotI fragment of flow-sorted human chromosome 22

We have developed the "shotgun polymerase chain reaction," a method for obtaining a large number of DNA markers specific to a giant DNA fragment, which facilitates analysis of a particular chromosomal region. We applied this method to a giant NotI fragment which carries the immunoglobulin lambda constant region on chromosome 22. NotI digests of chromosome 22 flow-sorted from human B-lymphoblastoid cell line GM130B were size fractionated by pulsed-field gel electrophoresis. Preliminary Southern hybridization analysis revealed that the immunoglobulin lambda constant region was conveyed on 1.4- and 1.3-Mb NotI fragments in this cell line. The agarose gel corresponding to 1.2 to 1.5 Mb in size was excised into slices and subjected to polymerase chain reaction to identify gel slices containing NotI fragments carrying Ke-Oz+, a subtype of the immunoglobulin lambda constant region. From the NotI fragment thus identified, a large number of small DNA segments were amplified through the ligation-mediated random polymerase chain reaction method. The amplified products were cloned and analyzed for chromosomal origin and localization to particular NotI fragments. Seven of eighteen clones originated from the 1.4-Mb NotI fragment of chromosome 22 in GM130B cells, which appears to be exactly the same as detected by a probe for the immunoglobulin lambda constant region.

Differential c-myc protein expression in Burkitt's lymphomas and EBV-transformed lymphoblastoid lines

The levels of c-myc protein expression in three types of Epstein-Barr virus (EBV) transformed human B-cell derived lines were examined with an ELISA assay. Six independently maintained sublines of the same EBV-transformed pro-B-cell line (FLEB-14), six B-cell lines (LCL) and six Burkitt's lymphoma lines (BL) were compared. The average amount of c-myc protein, calculated from at least three independent tests on each line, differed between the three groups. Expressed in relative units, the ratio of the means was 1:2:5 for the LCL:FLEB:BL lines. The differences were statistically significant at P less than 0.01.

Isotype commitment of human B cells that are transformed by Epstein-Barr virus

Epstein-Barr virus (EBV) can transform a subpopulation of preactivated B cells thus promoting their growth and differentiation into plasma cells. In EBV-transformed clones of IgM-producing cells, the heavy chain constant region (CH) genes on the productive allele are fixed in germ-line configuration, whereas in isotype-switched clones the CH genes proximal to the expressed CH gene are deleted. In order to define more precisely the EBV-susceptible B cells, we sorted subpopulations of B cells on the basis of their cell surface Ig (sIg) isotypes, infected them with EBV, and determined which isotypes they could produce following transformation. Most precursors of IgM-producing plasma cells expressed both IgM and IgD on their surface, while a minority expressed IgM alone. Some B cell precursors of IgG- and IgA-producing cells also expressed sIgM, but surprisingly none expressed IgD. Those precursors of IgG and IgA producers, which bore sIgM, expressed it in relatively low levels, whereas B cells expressing high levels of sIgM were incapable of generating IgG and IgA producers. All of the precursors of IgG and IgA plasma cells expressed these isotypes on their cell surface. Interestingly, precursor B cells capable of producing the IgG3 and IgA2 subclasses could be respectively enriched on the basis of the presence or absence of cell sIgM. These results demonstrate the isotype precommitment of EBV-transformable B cells. They further suggest that residual IgM is transiently expressed on the surface of the IgG- and IgA-committed B cell precursors, whereas sIgD expression is extinguished earlier in the process of isotype switching via CH gene deletion.

Effect of transforming growth factor-beta 1 and -beta 2 on the proliferation of Burkitt lymphoma and lymphoblastoid cell lines

We tested the effect of transforming growth factor (TGF)-beta 1 and TGF-beta 2 on the proliferation of human B cell lines. The panel was selected to give information whether (1) their origin, (2) their phenotype, (3) their Epstein-Barr virus (EBV) carrier state, influence their responsiveness. The growth of lymphoblastoid cell lines (LCL) was not inhibited by TGF-beta 1. The EBV-carrying Burkitt lymphoma (BL) lines, Daudi, Jijoye, Rael but not Raji were inhibited. Three EBV-negative BL lines and the majority of their converted sublines were sensitive. The cell lines tested expressed TGF-beta receptors and TGF-beta 1 transcripts. The proliferation of EBV-infected B cells was inhibited by TGF-beta, their sensitivity decreased, however, after 3 days. The results suggest that the activation state of the B cells is decisive for TGF-beta sensitivity and EBV influences it indirectly by changing the cell phenotype.

Immortalizing genes of Epstein-Barr virus

EBV immortalizes human B lymphocytes efficiently. Ten of its approximately 100 genes are expressed in these proliferating lymphoblasts and are candidates for mediating the changes central to the immortalization of the cell. Enough has been learned now about three of these viral genes to indicate that they are likely to be required for immortalization. As more is learned, additional genes of EBV will probably be found to support the process of immortalization of the host cell. EBNA-2 has been shown genetically to be required for EBV to immortalize an infected B lymphocyte. The biochemical activities of EBNA-2 that constitute this requirement have not been identified. Many experiments indicate that EBNA-2 affects the accumulation of specific viral and cellular RNAs. These effects, however, can be detected only in certain EBV-negative B-lymphoblastoid cells. It is, therefore, not clear that the known effects of EBNA-2 adequately explain its ubiquitous requirement in the immortalization of primary human B lymphocytes. LMP is likely to be required for immortalization because it can affect the growth properties of established human lymphoid and epithelial cells and can transform at least two established rodent cells to proliferate in an anchorage-independent manner. The structure of this viral protein, its position in the plasma membrane, many of its biochemical properties, as well as studies of its mutant derivatives are consistent with its acting as a growth factor receptor or affecting the activity of such a receptor. However, no biochemical activity has been assigned directly to LMP, and both its mechanism of action and its possible contribution to immortalization by EBV remain enigmatic. EBNA-1 presumably is required for EBV to immortalize a B lymphocyte because it is essential for the initiation of plasmid DNA replication by EBV. Circumstantial observations indicate also that EBNA-1 is probably necessary for sustaining viral DNA replication in the proliferating cell population. EBNA-1 may well affect the regulation of transcription of viral genes that themselves are required for immortalization. These roles of EBNA-1 are performed in part by its site-specific binding to the elements of oriP required in cis for the replication of EBV plasmid DNAs. It is probable that EBNA-1 also binds both to a set of cellular proteins that function in transcription and to a nonidentical set of cellular proteins that function in replication. EBV effects a fascinating phenotypic change in B lymphocytes it infects. It does so by using several viral genes that alter the physiology of the cell by different means.(ABSTRACT TRUNCATED AT 400 WORDS)

Presence of Epstein-Barr virus DNA in nasal lymphomas of B and 'T' cell type

We studied 12 tumours from 11 Chinese patients with primary nasal lymphoma for presence of Epstein-Barr Virus (EBV) DNA, using Southern-blot analysis. These results were correlated with immunophenotype and T-cell receptor (TcR) or immunoglobulin gene rearrangement patterns. EBV DNA was detected in all nine tumours with a 'T' phenotype, in both primary and secondary sites. When the structure of the viral genomic termini was studied using the EcoRI-Dhet probe, a single clonal episomal band was demonstrated in five tumour samples, with one other case showing a biclonal pattern. However, none of these cases showed clonal rearrangement of TcR beta chain gene, and TcR gamma rearrangement was found only in one. The lineage of these phenotypic 'T' lymphomas therefore require further studies for confirmation. Two out of three B-lymphomas were also EBV DNA+; clonal EBV DNA was found in one. Their B-lineage was confirmed by detection of clonal immunoglobulin gene rearrangements. The association of EBV with an increasing number of lymphomas of different types highlights the need for continued study into its role in oncogenesis.

A novel B-cell lineage-specific transcription factor present at early but not late stages of differentiation

A novel B-cell-specific transcription factor, BSAP, was identified as a mammalian homolog of the sea urchin protein TSAP, which interacts with the promoters of four tissue-specific late histone H2A-2 and H2B-2 genes. As shown by mobility-shift, methylation interference, and mutational analyses, the mammalian protein BSAP recognizes all four sea urchin binding sites in a manner indistinguishable from TSAP; however, the two proteins differ in molecular weight. BSAP is exclusively restricted to the B-cell lineage of lymphoid differentiation. Its expression appears to be activated during pro-B-cell development, is abundant at the pre-B- and mature B-cell stages, but is absent in terminally differentiated plasma cells. Moreover, BSAP is clearly a B-cell-specific transcription factor, as a wild-type but not a mutant TSAP-binding site of the sea urchin functions only in transfected B cells as an upstream promoter element. Competition experiments did not reveal any high-affinity binding site for BSAP in known regulatory regions of immunoglobulin and class II major histocompatibility (MHC) genes, suggesting that BSAP is a regulator of a different set of B-lymphoid-specific genes.

Molecular analysis of a chromosomal translocation, t(9;14)(p13;q32), in a diffuse large-cell lymphoma cell line expressing the Ki-1 antigen

We have studied a translocation, t(9;14)(p13;q32), in a diffuse large-cell lymphoma cell line, KIS-1, that expresses the Ki-1 (CD30) antigen. Molecular cloning of the immunoglobulin heavy-chain locus (IGH) of this cell line revealed an unknown segment linked 5' to IGH. The breakpoint on chromosome 14 was 265 base pairs downstream from the 3' border of the JH6 joining gene segment. Class switch recombination deleted most of the constant genes of IGH (CH) and juxtaposed the C alpha 2 gene downstream of the translocation junction. Analysis of somatic cell hybrids and in situ chromosomal hybridization demonstrated that the translocated segment was normally located at band p13 of chromosome 9. The chromosome 9 sequences were transcriptionally active, giving rise to transcripts of approximately 11 kilobases. The KIS-1 cells seemed to have a small quantity of chimeric transcripts containing both chromosome 9 and C alpha 2 sequences.

Isolation of early immunoglobulin lambda-like gene transcripts in human fetal liver

In an attempt to identify early events of human Ig gene expression, we have screened a human fetal liver cDNA library (less than 90 days of gestation) with C mu-, C gamma-, C kappa-, C lambda-specific probes and we report the characterization of two clones, F lambda 1 and F lambda 8, that hybridized with a human C lambda gene. These two clones, which are only 85% homologous to the functional C lambda genes, were shown to be additional nonallelic members of the 14.1/16.1 C lambda-like family. Using pulsed field gel electrophoresis these three C lambda-like genes were shown to be present on a 200-kb DNA fragment, defining a cluster distinct from that of the C lambda one. F lambda 1 and F lambda 8 contained an identical C lambda-like region, and differed from each other by a splicing event which joins a J lambda-like to the C lambda-like exon in the F lambda 1 clone in the absence of any rearrangement. Homologies observed between F lambda 1 and the mouse lambda 5 gene suggest that this human clone may contain the exon 2 and 3 equivalents of lambda 5. Since lambda 5 is selectively expressed in pre-B cells, our proposal is also supported by the early expression of this clone, together with the presence of full-length mu and gamma transcripts and the absence of functional Ig light chain transcripts. The presence of one nucleotide deletion in the C region of F lambda 1 conferring it a pseudogene status, the actual lambda 5 equivalent might be either one of the 14.1 or 16.1 human C lambda-like genes, the function of which is so far unknown.

Growing human B-cell precursors in vitro: the continuing challenge

Methods for propagating murine B-cell precursors in vitro have been instrumental in unraveling the cells and molecules regulating murine B-cell ontogeny. However, similar methods are not available for studying human B-cell ontogeny. Here, Tucker LeBien discusses why efforts to grow human B-cell precursors in vitro have been largely unsuccessful and proposes alternative strategies that may prove useful.

Predilection of a nasopharyngeal carcinoma-derived isolate of Epstein-Barr virus for infection of specific subsets of B lymphocytes

It is important to know whether there are variants of Epstein-Barr virus (EBV) with biological properties that are different from the prototype viruses that have been studied in detail, such as P3HR-1 and B95-8. We have studied an EBV isolate derived from a nasopharyngeal carcinoma (NPC) tumor, designated NPC-EBV. We have examined the target B lymphocytes infected and growth-transformed with NPC-EBV as compared with two common EBV isolates, B95-8 and AG876 EBV, for stage of maturation using antibodies to several immunoglobulin chains. Typing of the NPC-EBV transformed lymphoblastoid cell lines revealed the predilection of the NPC-EBV isolate to infect immature B lymphocytes. This was not the case for the B95-8 and AG876 isolates. The reason for the predilection of NPC-EBV for immature B lymphocytes remains to be explored further. However, these results may be important in understanding the pathophysiology of EBV-associated diseases.

Epstein-Barr virus-transformed pro-B cells are prone to illegitimate recombination between the switch region of the mu chain gene and other chromosomes

Six independently maintained sublines of FLEB 14, a fetal-liver-derived Epstein-Barr virus-transformed pro-B cell line that has not yet rearranged its immunoglobulin genes, were examined after in vitro propagation during 19-36 months. Two lines showed no immunoglobulin heavy chain gene rearrangement, whereas one allele was rearranged with breakpoints inside the switch region of the mu chain gene in the remaining four. These rearrangements had been generated by the translocation of different chromosome fragments to the immunoglobulin heavy chain gene cluster-carrying 14q32 band in each of the four lines. Previously, a similar rearrangement was found in a fifth subline concurrently with a reciprocal 6;14 translocation. The transposed pieces have been derived from chromosomes 16 and 18 in two of the more recently rearranged lines. Their origins could not be determined in the remaining two lines, but they were different from each other and the other three 14q+ markers. The 14q+ marker-carrying variant has replaced its diploid progenitor suggesting that the translocation has conveyed some in vitro growth advantage on its carrier. This was also supported by the duplication of the 14q+ marker and the loss of its normal chromosome 14 homologue in one subline during serial culturing. The vulnerability of the switch region of the mu chain gene to illegitimate recombination at the pro-B stage and the possible relevance of this finding for the origin of the Burkitt lymphoma-associated 8;14 (immunoglobulin heavy chain gene cluster/MYC) translocation is discussed.

Frequency of VH-gene utilization in human EBV-transformed B-cell lines: the most JH-proximal VH segment encodes autoantibodies

We have studied VH-gene utilization in a collection of 187 IgM-secreting EBV-transformed cell lines and have begun to correlate VH-gene family expression with binding properties of the secreted immunoglobulins. The results of these studies demonstrate that (1) frequency of VH-gene utilization in fetal and adult tissue-derived cell lines correlates with the complexity of the family and (2) the single-membered most JH-proximal VH-6 family encodes autoantibodies reminiscent of autoantibodies found in the sera of patients with systemic lupus erythematosus. Nucleotide sequence analysis of VH-6-expressing clones revealed that each clone utilizes a short DH segment, resulting in a CDR3 region of conserved length. Our data suggest that EBV does not selectively transform human B cells on the basis of VH-gene family expression and that the VH-6 family encodes polyspecific autoantibodies that may serve an important regulatory function in the immune system.

Early human IgH gene assembly in Epstein-Barr virus-transformed fetal B cell lines. Preferential utilization of the most JH-proximal D segment (DQ52) and two unusual VH-related rearrangements

We have analyzed the phenotypic characteristics and IgH gene rearrangements in a panel of EBV-transformed B lineage cell lines from human fetal liver and bone marrow. Some lines contained only populations of immature, Ig- Be cells, while others contained mixed populations of mature and immature B cells. The majority of identifiable IgH rearrangements involved joining of the most JH-proximal D segment, DQ52, to various JH segments, implying that DQ52 is a preferred target for initial DJH rearrangements. Three other rearrangements involving VH-related sequences were also characterized. Two involved VHDJH joining using VH3 genes, although one of these had a very unusual DJH structure. The third consisted of inverted 3' signal sequences and flanking regions of a VH4 gene appended to a JH. The mechanisms by which the later rearrangement could have occurred and its potential physiological significance are discussed.

Light-chain gene expression before heavy-chain gene rearrangement in pre-B cells transformed by Epstein-Barr virus

Epstein-Barr virus transformation of B-cell-depleted bone marrow cells from human fetuses allowed us to identify novel cell types characterized by the expression of immunoglobulin kappa or lambda light chain without heavy chains. Four kappa-only clones with normal karyotype were obtained and examined for their immunoglobulin gene configurations and expression. All four clones had kappa-chain gene rearrangements at either one or both alleles, but the heavy-chain gene loci in these clones either were in germ-line context or had undergone only D-JH rearrangements (D and JH represent diversity and joining gene segments). All clones contained kappa mRNA of normal size at levels consistent with the protein level, except for one clone that no longer produced kappa protein. No mu mRNA or immunoglobulin heavy-chain molecules were detected in any of the kappa+ clones. The results suggest that the mu heavy-chain protein is not an obligatory prerequisite for light-chain gene rearrangements.