Characteristics of Epstein-Barr virus activation of human B lymphocytes

Human B cell immortalization for monoclonal antibody production

Infection of primary B lymphocytes with Epstein-Barr virus gives rise to growth-transformed and immortalized lymphoblastoid cell lines (LCL) in vitro. Among their many applications is the use of LCL to present antigens in a variety of immunologic assays and to generate human monoclonal antibodies. This chapter describes a method to generate LCL from donor peripheral blood with rapid immortalization and cryopreservation times.

Assessment of the effect of TLR7/8, TLR9 agonists and CD40 ligand on the transformation efficiency of Epstein-Barr virus in human B lymphocytes by limiting dilution assay

Infection of human B cells with Epstein-Barr virus (EBV) induces polyclonal activation in almost all infected cells, but a small proportion of infected cells are transformed to immortalized lymphoblastoid cell lines. Since B cells are activated also by CD40 ligand (CD40L) and Toll-like receptor (TLR) agonists via a similar signaling pathway, it is likely that costimulation through these molecules could result in synergistic enhancement of the transformation efficiency of EBV. In this study, the stimulatory effect of TLR7/8 (R848), TLR9 (CpG) agonists and/or CD40L on transformation efficiency of EBV in normal human B cells was assessed using the limiting dilution assay. Costimulation of peripheral blood mononuclear cells (PBMCs) with CpG and R848, but not CD40L, increased significantly the frequency of EBV transformed B cells (p < 0.001). Neither synergistic nor additive effects were observed between TLR agonists and CD40L and also TLR7/8 and TLR9 agonists. Costimulation with R848, CpG and CD40L enhanced the proliferative response of B cells infected with EBV. This effect was more evident when enriched B cells were employed, compared to PBMCs. The promoting effect of TLR agonists stimulation, implies that EBV may take advantage of the genes induced by the TLR stimulation pathway for viral latency and oncogenesis.

Establishment of Epstein-Barr virus growth-transformed lymphoblastoid cell lines

Infection of B cells with Epstein-Barr virus (EBV) leads to proliferation and subsequent immortalization, resulting in establishment of lymphoblastoid cell lines (LCL) in vitro. Since LCL are latently infected with EBV, they provide a model system to investigate EBV latency and virus-driven B cell proliferation and tumorigenesis(1). LCL have been used to present antigens in a variety of immunologic assays(2, 3). In addition, LCL can be used to generate human monoclonal antibodies(4, 5) and provide a potentially unlimited source when access to primary biologic materials is limited(6, 7). A variety of methods have been described to generate LCL. Earlier methods have included the use of mitogens such as phytohemagglutinin, lipopolysaccharide(8), and pokeweed mitogen(9) to increase the efficiency of EBV-mediated immortalization. More recently, others have used immunosuppressive agents such as cyclosporin A to inhibit T cell-mediated killing of infected B cells(7, 10-12). The considerable length of time from EBV infection to establishment of cell lines drives the requirement for quicker and more reliable methods for EBV-driven B cell growth transformation. Using a combination of high titer EBV and an immunosuppressive agent, we are able to consistently infect, transform, and generate LCL from B cells in peripheral blood. This method uses a small amount of peripheral blood mononuclear cells that are infected in vitroclusters of cells can be demonstrated. The presence of CD23 with EBV in the presence of FK506, a T cell immunosuppressant. Traditionally, outgrowth of proliferating B cells is monitored by visualization of microscopic clusters of cells about a week after infection with EBV. Clumps of LCL can be seen by the naked eye after several weeks. We describe an assay to determine early if EBV-mediated growth transformation is successful even before microscopic clusters of cells can be demonstrated. The presence of CD23(hi)CD58(+) cells observed as early as three days post-infection indicates a successful outcome.

An efficient method for the rapid establishment of Epstein-Barr virus immortalization of human B lymphocytes

Several methods have been developed for the immortalization of B lymphocytes by Epstein-Barr virus (EBV). We developed an efficient method which reduces the time from culture initiation to immortalization and cryopreservation. Two infections of EBV to lymphocytes, and the use of phorbol ester-induced EBV stock significantly improved immortalization efficiency and reduced the time between initiation and immortalization and cryopreservation. The resulting cell bank was used to produce DNA for genetic studies focusing on the genes involved in immune and autistic disorders.

Low response to HBsAg vaccine in chronic renal failure patients is not due to intrinsic defect of B cells

OBJECTIVE

The aim of this study was to investigate whether the inability of chronic renal failure patients to mount an adequate antibody response following hepatitis B vaccination was due to an inherent defect in the antibody producing capacity of their B cells.

MATERIAL AND METHODS

Peripheral blood mononuclear cells of end stage renal disease (ESRD) patients, who were not on maintenance hemodialysis (CRF) and those undergoing long-term hemodialysis (HD) were stimulated in vitro with pokeweed mitogen, a B cell mitogen or hepatitis B surface antigen. The total immunoglobulin (IgG, IgM and IgA) levels and anti-HBs specific IgM and IgG were quantitiated by sandwich ELISA and levels between patients who had a good antibody response in vivo and those who failed to mount an antibody response were compared.

RESULTS

Spontaneous IgG production was significantly higher than normals in CRF and HD group; PWM induced IgM, IgG and IgA production was comparable to normals in both groups of patients. The spontaneous IgG and PWM stimulated IgM and IgG production was significantly higher in HD patients as compared to CRF. The in vitro Ig levels in the vaccine responders and non-responders was comparable except for the spontaneous IgG which was highest in the responders. The in vitro anti-HBs production was comparable in HB vaccine responders and non-responders; the in vivo and in vitro anti-HBs titers showed a significant correlation coefficient thereby indicating that the in vitro assay reflects the in vivo functional status of B cells.

CONCLUSION

Our results demonstrate that the B cells in ESRD patients are functionally normal and cannot be the cause of the compromised vaccine response in these patients.

Different individual immune responses elicited by in vitro immunization

We have previously demonstrated that the addition of muramyl dipeptide (MDP), interleukin-2 (IL-2) and IL-4 effectively raises antibody production from L-Leucyl-L-leucine methyl ester (LLME)-treated human peripheral blood lymphocytes (PBLs) against specific soluble antigen when immunized in vitro. However, PBLs from individual donors were separate optimal conditions regarding concentrations for IL-2 and IL-4, which in turn required us to optimize each individual PBLs to effectively produce antigen specific human antibody by in vitro immunization. These individual differences in the requirement for IL-2 and IL-4 reflects the differences in individual immune responses against a specific soluble antigen, which can be elicited by in vitro immunization. In the present study, we investigated these individual differences in the requirement for IL-2 and IL-4 to induce antibody productionin vitro in the PBLs of 12 volunteers (9 healthy donors and 3 allergenic patients). IL-2 requirements for antibody production varied dependent upon each donor, while higher amounts of IL-4 inhibited IgM and IgG production in all of the healthy donors. However, some of the characteristic features for PBLs donated from allergenic included lowered IgM production compared to PBLs derived from healthy donors, and very high IgE production in the absence of cytokines and allergen. These results demonstrate that the sensitivity of PBLs against antigen sensitization differs between healthy donors and atopic patients, which suggests that the frequency of antigen sensitization might be reflected in differing activation states and/or differing subpopulations of lymphocytes in vivo.

Induction of antigen-specific isotype switching by in vitro immunization of human naive B lymphocytes

The use of in vitro immunization technology for the generation of human antigen-specific antibodies has essentially resulted in low affinity IgM antibodies, resembling an in vivo primary immune response. We now describe a detailed reproducible protocol for a two-step in vitro immunization, which yields isotype switched, antigen-specific human antibodies. The immunizing antigen was a 30aa synthetic peptide, containing both a B (15aa V3 peptide of the HIV-1) and a T helper cell epitope (15aa peptide from tetanus toxin). The immunization protocol includes: (i) a selection procedure of donors with a memory T cell response against tetanus toxoid; (ii) immunization of mature naive peripheral B lymphocytes in two distinct phases, involving a primary and a secondary step. None of the donors which were examined after primary immunization showed at any time an IgG anti-V3 specific antibody response, while all the donors showed an IgM response. After the secondary immunization step, anti-V3 antibodies of both IgM and IgG isotypes were detected. The switch frequency event was high among the tested donors (5/8).

An efficient method for routine Epstein-Barr virus immortalization of human B lymphocytes

A variety of methods exist for the immortalization of B lymphocytes by Epstein-Barr virus due to the simplicity of such techniques to establish cell lines with stable genomic DNA. Two different methods for immortalizing lymphoblastoid cell lines were compared for differences in techniques and materials, time between initiation and immortalization, and success rate of immortalization. An incubation period in Epstein-Barr virus and the use of conditioned media improved immortalization efficiency from 86 to 98% and decreased the time (usually weeks) from culture initiation to cryopreservation. The resulting cell bank was used to produce DNA for genetic studies focusing on the genes involved in non-insulin-dependent diabetes mellitus.

An Epstein-Barr virus with a 58-kilobase-pair deletion that includes BARF0 transforms B lymphocytes in vitro

A family of Epstein-Barr virus (EBV)-encoded RNAs found in nasopharyngeal carcinoma cells is also present at low levels in some latently infected and growth-transformed B lymphocytes (P. R. Smith, Y. Gao, L. Karran, M. D. Jones, D. Snudden, and B. E. Griffin, J. Virol. 67:3217-3225, 1993). A molecular genetic approach using EBV recombinants was undertaken to evaluate the role of these transcripts in primary B-lymphocyte growth transformation and latent infection. Since the se transcripts arise from a 22-kbp segment of the EBV genome and construction of large deletion mutants is an improbable result after transfection of infected cells with an EBV DNA fragment with a large deletion mutation, a new approach was taken to make a recombinant with the DNA encoding all of the BARF0 RNAs deleted. The approach derives from a recently described strategy for making recombinants from five overlapping EBV cosmid-cloned DNAs (B. Tomkinson, E. Robertson, R. Yalamanchili, R. Longnecker, and E. Kieff, J. Virol. 67:7298-7306, 1993). A large segment of EBV DNA was deleted from the transfected cosmid DNAs by omitting a cosmid which included all of the DNA encoding the BARF0 RNA and by ligating the distal halves of the two flanking cosmids so as to create one cosmid which had ends that overlapped with the other two unaltered cosmids. EBV recombinants with 58 kbp including BARF0 deleted resulted from transfecting the three overlapping EBV DNA fragments into P3HR-1 cells and simultaneously inducing lytic replication of the endogenous, transformation-defective, P3HR-1 EBV. The endogenous P3HR-1 EBV provided lytic infection and packaging functions. EBV recombinants with intact transforming functions were then selected by infecting primary B lymphocytes and growing the resultant transformed cells in lymphoblastoid cell lines. The efficiency of incorporation of the deletion into transforming EBV recombinants was close to that of a known indifferent marker, the type 1 EBNA 3A gene, indicating the absence of significant selection against the deletion. Cells infected with the deleted recombinant grew similarly to those infected with wild-type recombinants and had a similar level of permissiveness for lytic EBV infection. Thus, the BARF0 transcript is not critical to primary B-lymphocyte growth transformation or to latent infection. This methodology is useful for constructing EBV recombinants which are specifically mutated at other sites in the three cosmids and is a step toward deriving a minimal transforming EBV genome.

Epstein-Barr virus recombinants from overlapping cosmid fragments

Five overlapping type 1 Epstein-Barr virus (EBV) DNA fragments constituting a complete replication- and transformation-competent genome were cloned into cosmids and transfected together into P3HR-1 cells, along with a plasmid encoding the Z immediate-early activator of EBV replication. P3HR-1 cells harbor a type 2 EBV which is unable to transform primary B lymphocytes because of a deletion of DNA encoding EBNA LP and EBNA 2, but the P3HR-1 EBV can provide replication functions in trans and can recombine with the transfected cosmids. EBV recombinants which have the type 1 EBNA LP and 2 genes from the transfected EcoRI-A cosmid DNA were selectively and clonally recovered by exploiting the unique ability of the recombinants to transform primary B lymphocytes into lymphoblastoid cell lines. PCR and immunoblot analyses for seven distinguishing markers of the type 1 transfected DNAs identified cell lines infected with EBV recombinants which had incorporated EBV DNA fragments beyond the transformation marker-rescuing EcoRI-A fragment. Approximately 10% of the transforming virus recombinants had markers mapping at 7, 46 to 52, 93 to 100, 108 to 110, 122, and 152 kbp from the 172-kbp transfected genome. These recombinants probably result from recombination among the transfected cosmid-cloned EBV DNA fragments. The one recombinant virus examined in detail by Southern blot analysis has all the polymorphisms characteristic of the transfected type 1 cosmid DNA and none characteristic of the type 2 P3HR-1 EBV DNA. This recombinant was wild type in primary B-lymphocyte infection, growth transformation, and lytic replication. Overall, the type 1 EBNA 3A gene was incorporated into 26% of the transformation marker-rescued recombinants, a frequency which was considerably higher than that observed in previous experiments with two-cosmid EBV DNA cotransfections into P3HR-1 cells (B. Tomkinson and E. Kieff, J. Virol. 66:780-789, 1992). Of the recombinants which had incorporated the marker-rescuing cosmid DNA fragment and the fragment encoding the type 1 EBNA 3A gene, most had incorporated markers from at least two other transfected cosmid DNA fragments, indicating a propensity for multiple homologous recombinations. The frequency of incorporation of the nonselected transfected type 1 EBNA 3C gene, which is near the end of two of the transfected cosmids, was 26% overall, versus 3% in previous experiments using transfections with two EBV DNA cosmids. In contrast, the frequency of incorporation of a 12-kb EBV DNA deletion which was near the end of two of the transfected cosmids was only 13%.(ABSTRACT TRUNCATED AT 400 WORDS)

Epstein-Barr virus nuclear proteins EBNA-3A and EBNA-3C are essential for B-lymphocyte growth transformation

Recombinant Epstein-Barr viruses (EBV) with a translation termination codon mutation inserted into the nuclear protein 3A (EBNA-3A) or 3C (EBNA-3C) open reading frame were generated by second-site homologous recombination. These mutant viruses were used to infect primary B lymphocytes to assess the requirement of EBNA-3A or -3C for growth transformation. The frequency of obtaining transformants infected with a wild-type EBNA-3A recombinant EBV was 10 to 15%. In contrast, the frequency of obtaining transformants infected with a mutant EBNA-3A recombinant EBV was only 1.4% (9 mutants in 627 transformants analyzed). Transformants infected with mutant EBNA-3A recombinant virus could be obtained only by coinfection with another transformation-defective EBV which provided wild-type EBNA-3A in trans. Cells infected with mutant EBNA-3A recombinant virus lost the EBNA-3A mutation with expansion of the culture. The decreased frequency of recovery of the EBNA-3A mutation, the requirement for transformation-defective EBV coinfection, and the inability to maintain the EBNA-3A mutation indicate that EBNA-3A is essential or critical for lymphocyte growth transformation and that the EBNA-3A mutation has a partial dominant negative effect. Five transformants infected with mutant EBNA-3C recombinant virus EBV were also identified and expanded. All five also required wild-type EBNA-3C in trans. Serial passage of the mutant recombinant virus into primary B lymphocytes resulted in transformants only when wild-type EBNA-3C was provided in trans by coinfection with a transformation-defective EBV carrying a wild-type EBNA-3C gene. A secondary recombinant virus in which the mutated EBNA-3C gene was replaced by wild-type EBNA-3C was able to transform B lymphocytes. Thus, EBNA-3C is also essential or critical for primary B-lymphocyte growth transformation.

CD5 and immunoglobulin VH gene expression in B-cell lines from patients with autoimmune diseases

We studied the CD5 mRNA expression and VH gene family usage in Epstein-Barr virus (EBV)-immortalized B-cell lines derived from the blood of patients with type 1 diabetes (IDDM) of recent onset and of patients with polyneuritis cranialis multiplex (cranial neuritis; CN). After immortalization with EBV, at least 10 cell lines from each subject were tested for surface CD5 and CD20. mRNA expression was studied using cDNA probes for the six VH families as well as for CD5. The EBV lines from the IDDM patients used the VHIV family more frequently and VHI and VHII families less frequently than lines from controls. EBV lines from CN patients expressed the VHI and VHII families more often than those of the controls. When the IDDM and CN lines were compared, the lines derived from IDDM patients were found to use VH families I and II less frequently and VH families IV and V more frequently than lines from CN patients. There were no significant differences in the mean numbers of CD5+ B cells in the cell lines tested. More than half of the lines from each patient expressed CD5 at the mRNA level. No correlation was seen between the expression of surface CD5 and the level of CD5 mRNA expression. There was, however, a positive correlation between the usage of VH families III, V and VI, and the CD5 mRNA expression. In conclusion, the usage of VH families I to VI seemed to differ in patients with IDDM and CN. No differences were seen in the surface CD5 expression, but the lines expressing CD5 mRNA preferentially used the VH families III, V and VI.

Use of second-site homologous recombination to demonstrate that Epstein-Barr virus nuclear protein 3B is not important for lymphocyte infection or growth transformation in vitro

Recombinant Epstein-Barr viruses with a stop codon inserted into the nuclear protein 3B (EBNA 3B) open reading frame were generated by second-site homologous recombination. These mutant viruses infected and growth transformed primary B lymphocytes, resulting in the establishment of lymphoblastoid cell lines (LCLs). Polymerase chain reaction analysis and Southern hybridizations with infected cell DNA demonstrated the presence of the mutant EBNA 3B and the absence of wild-type EBNA 3B. Immunoblot analysis of the LCLs with affinity-purified EBNA 3B antibodies confirmed the absence of EBNA 3B cross-reactive protein. Virus was reactivated from two of these infected LCLs and serially passaged through primary B lymphocytes. The newly infected cells contained only the mutant recombinant virus. No difference was noted between mutant and wild-type recombinants, derived in parallel, in latent (other than EBNA 3B) or lytic cycle-infected cell virus protein expression or in the growth of the latently infected transformed cell lines. These data indicate that the EBNA 3B protein is not critical for primary B-lymphocyte infection, growth transformation, or lytic virus infection in vitro.

Stable expression and function of EBV/C3d receptor following genomic transfection into murine fibroblast L cells

The Epstein-Barr virus (EBV) and the C3d component of complement bind to the same cell surface receptor (EBVR/CR2) which is part of the B lymphocyte differentiation antigen recognized by the monoclonal antibodies (mAb) of the cluster of differentiation 21 (CD21). To analyze EBV and C3d binding to this receptor, mouse fibroblasts were transfected with human genomic DNA and rare CD21-positive cells were selected and cloned by cell sorting. The presence of the human gene in host cell DNA as well as its transcription product were assayed with a cloned EBVR/CR2 cDNA by Southern and Northern blotting analysis, respectively. A glycoprotein of apparent molecular mass of 140 kDa, similar to that found in human B lymphocytes, was immunoprecipitated with anti-CD21 mAb and proved to be functional since both C3d and EBV bound efficiently and specifically to mouse cells expressing EBVR/CR2. However, no expression of EBV nuclear antigens, early antigens and viral capsid antigens was detected in cells exposed to EBV. This indicates that the presence of EBVR/CR2 is not sufficient to allow full infection of mouse fibroblasts.

IgM autoantibodies against two cellular antigens always appear in acute Epstein-Barr virus infection

In the course of infectious mononucleosis, IgM antibodies are formed against 2 proteins present in nucleated and non-nucleated vertebrate cells. Antibodies were found in sera of all patients suffering from acute Epstein-Barr virus infection. In 40% of the cases these antibodies are monoclonal. Persons with former Epstein-Barr virus infection were negative. The antibodies against the 2 proteins were first detected in Raji cells with an IgM-specific immunofluorescence test. The proteins were demonstrated in extracts of different cells and tissues by immunoblot technique. The molecular weight of the proteins measured in SDS polyacrylamide gel electrophoresis was 26 kd and 29 kd, respectively. Their presence in the cells does not depend on the presence of the Epstein-Barr virus genome. The relevance of the new findings concerning diagnostics as well as pathogenetic aspects remains to be established.

Epstein-Barr virus and rheumatoid arthritis: cellular and molecular aspects

Several lines of research have indicated a possible association of the Epstein-Barr virus and rheumatoid arthritis (RA). The earliest evidence suggested that RA patients develop a stronger humoral immune response to EBV nuclear antigens (EBNA) which may in part account for the increased titers of antibody to the RA nuclear antigen (RANA). It was then pointed out that mononuclear cells from RA patients may be impaired in their capacity to control EBV infection. This may be related to a decrease in the production of IFN gamma and a consequence of monocyte-derived inhibitory activities. These cellular defects, however, are not specific for RA and may rather be the result of chronic inflammatory responses. These findings and the lack of increased virus presence in RA tissues did not provide a strong basis for a possible association of EBV and RA. A new concept for this association is now being tested on the basis of the sequence homology between the genetic RA susceptibility determinant HLA DR4 and the EBV glycoprotein 110.

Inhibition of polyamine synthesis in human B lymphocytes during primary infection with Epstein-Barr virus (EBV) blocks cellular DNA synthesis but not the expression of EBV-encoded nuclear antigens (EBNA)

Inhibition of polyamine synthesis by 2-difluoromethylornithine (DFMO) treatment had no apparent effect on the initial manifestation of Epstein-Barr virus (EBV) infection in human B lymphocytes, because the expression of EBV-encoded nuclear antigens (EBNA) occurred normally. However, many subsequent steps in the transformation process were inhibited by DFMO treatment. These include cellular DNA synthesis and immunoglobulin (IgM, IgG and IgA) synthesis and secretion. Consequently, DFMO treatment blocked the progression of the transformation process of EBV-infected B lymphocytes. EBV-carrying marmoset B lymphocytes (B95-8 cells) were also blocked in their DNA synthesis when treated with DFMO. At variance with other DNA synthesis inhibitors, which induce virus production very effectively in B95-8 cells, DFMO caused no increase in the number of cells expressing the early antigens associated with the lytic cycle.

Epstein-Barr virus: the hematologic and oncologic consequences of virus-host interaction

Varicella-zoster virus (VZV) and Epstein-Barr virus (EBV) are two of the human herpesviruses. The others include herpes simplex virus (HSV) type 1, HSV type 2, and cytomegalovirus (CMV). In a series of two articles, we review the clinical diseases caused by VZV and EBV infections; we pay particular attention to the manifestations of these two viral infections in immunosuppressed and immunocompromised patients. In addition to the clinical reviews, each of the two articles begins with a brief discussion of the molecular aspects of VZV and EBV, respectively; this introduction describes features of the genome and immunogenic viral proteins which have clinical relevance. A model for pathogenesis is included. The first review concerns VZV infections. Recent data about the DNA sequence of the entire VZV genome are included, as well as a review of the VZV glycoproteins. Primary VZV infection (chickenpox) and VZV reactivation (zoster) are described in detail in both healthy individuals and people with cancer. The decade-long VZV vaccine trials in children with leukemia receive special emphasis because they have engendered considerable interest and debate. The second review (published here) covers EBV infections. This virus has been implicated in the causation of a wide variety of human hematological and oncological disorders, besides classical infectious mononucleosis. In particular, Burkitt's lymphoma, nasopharyngeal carcinoma, and lymphoproliferative disorders are strongly associated with EBV infection of the transformed cells. In addition, immunologically mediated cytopenias occasionally follow EBV infection. Finally, treatment regimens with antiviral chemotherapy and other agents are discussed for both VZV and EBV infections.

Selective decrease in Leu8-negative T cell subpopulations following treatment with recombinant interferon-alpha 2a (rIFN-alpha 2a)

The effects of in vivo treatment with recombinant human IFN-alpha 2a (rIFN-alpha 2a) on the distribution of T cell subpopulations were examined in 21 patients with renal cell adenocarcinoma, using two-color flow cytometry with anti-Leu8 in combination with anti-Leu2 and anti-Leu3. Other parameters indicative of immune status, such as the number and percentage of total (CD3) T cells, in vitro proliferation to mitogen, and spontaneous immunoglobulin secretion, were also measured, prior to the initiation of treatment with rIFN-alpha 2a, and during treatment. Total T cell number decreased after treatment with rIFN-alpha 2a, to a low of 54% of mean pretreatment values after 4 weeks. The CD4/CD8 ratio did not change appreciably following treatment with rIFN-alpha 2a. However, the number of Leu8-negative T cells, within both the CD4 and the CD8 T cell populations, decreased more than the number of Leu8-positive T cells. An increase in spontaneous immunoglobulin-secreting cells followed treatment with rIFN-alpha 2a.

Demonstration of impaired T cell regulation of Epstein-Barr virus stimulated B lymphocytes in rheumatoid arthritis with HLA identical, disease discordant sibling pairs

Lymphocytes from patients with rheumatoid arthritis (RA) show an abnormal response after stimulation with Epstein-Barr virus (EBV), a potent B cell mitogen. In vitro IgM production from EBV stimulated lymphocytes was measured over a 21 day period. In keeping with previous studies, RA lymphocytes showed increasing IgM production between 14 and 21 days, whereas IgM production decreased during this period in normal lymphocytes (p less than 0.001). Experiments on 12 HLA identical, RA discordant sibling pairs were also undertaken. B enriched and T enriched lymphocyte populations were obtained and recombined in both an autologous and homologous manner. The abnormality in IgM production in patients with RA was shown to reside in the RA T cell population (p less than 0.005), and RA B cells combined with normal T cells behaved similarly to autologous cultures of normal B and T cells. The study shows that impaired immunoregulation of EBV stimulated B cells in RA is secondary to a functional defect in RA T cells, but no difference in the concentration of T suppressor/cytotoxic cells could be found between the disease discordant siblings. The abnormality in immunoregulation appears to be secondary to RA, rather than a product of genes encoded within the major histocompatibility complex (MHC) region, as defined by HLA-DR, A, B, and C typing.

Immunoglobulin secretion of mononuclear cells induced by various mitogens

Immunosufficiency can be evaluated by Ig secretion subsequent to mitogenic stimulation of human mononuclear cells (MNC). It seems that there are significant differences in immunoglobulin class secreted by these cells when stimulated with various polyclonal activators. The aim of the current study was to analyse these differences. MNC cells was randomly obtained from nine healthy blood donors and were activated by Epstein-Barr virus (EBV), group-A streptococcus (A-ScM), Staphylococcus aureus (SAC), Klebsiella pneumonia (Kleb-M) and pokeweed mitogen (PWM). Significantly increased levels of IgM were recorded after a 7 day incubation followed by stimulation with Kleb-M (6.2 +/- 2.9) and EBV (5.9 +/- 4.5) compared to inactivated MNC (1.6 +/- 1.4), and following 10 days incubation then stimulation by EBV (13.4 +/- 5.5) and Kleb-M (9.9 +/- 4.2) compared to unstimulated cells (2.9 +/- 1.8). Significantly greater IgG levels were achieved following incubation with EBV (3.0 +/- 4.0) and PWM (2.4 +/- 1.3) after 7 days (vs 0.6 +/- 0.4 in unstimulated cells) and by PWM (11.7 +/- 5.3) and Kleb-M (8.8 +/- 3.9, vs 2.3 +/- 2.2) after 10 days. The present data emphasize the significance of merging both mitogen selection and culture duration for acquiring information and high fidelity results of immunoglobulin secretion by polyclonal activators.

Effects of interferons on human B-cell differentiation in vitro

The effects of interferons (IFN) on in vitro differentiation of B-lymphocytes were studied. Peripheral lymphocytes from normal subjects were cultivated under polyclonal activator pokeweed mitogen (PWN) or Epstein-Barr virus (EBV) stimulation. The secreted Ig in the culture supernatants were measured for IgM by ELISA method.

To determine the cellular level of IFN action T-cell enriched fraction (Te) or B-cell enriched fraction (Be) were preincubated with IFN prior to recombination culture.

IFN had modulatory activities on Ig production; at low to moderately high doses (10–1000 U/ml of IFN-alpha or 12–120 U/ml of IFN-gamma) stimulating when IFN was added until 48 hr after the start of the culture, while after 72 hr from culture start IFN suppressed Ig production.

Preincubation of Be-cells with moderately high doses of IFN (120 U/ml of IFN-gamma or 1000 U/ml of IFN-alpha) prior to PWM-stimulation suppressed Ig production. Likewise, in EBV-stimulated culture, high dose IFN suppressed Ig production. But low dose of IFN enhanced ig production in EBV-stimulated culture.

Preincubation of Te-cells with IFN prior to PWM-stimulation with Be-cells enhanced the Ig production. The T-cell subset analysis at the end of these culture showed enhanced ratio of T-helper cell relative to T-suppressor cells, suggesting increased T-helper cell proliferation after incubation with IFN.

Thus, it is concluded that IFNs have modulatory activities on B-cell differentiation. The mechanism seems to be direct effects on B-cells (in PWM and EBV system) as well as through T-helper cell mediation (PWM system). The IFN-gamma showed more potent (2-to 6-fold) stimulatory activities than IFN-alpha.

Increased spontaneous immunoglobulin secretion associated with cyclophosphamide-induced immune suppression

Spontaneous immunoglobulin (Ig) secretion by cells from multiple sclerosis (MS) patients (in the progressive phase) treated with monthly pulse doses of cyclophosphamide (CY) (1000-1600 mg/M2) was measured using the protein A plaque assay, to evaluate the effect of CY treatment on B-cell function. Surprisingly, an increase, rather than a decrease, in Ig-secreting cells was seen following CY treatment. CY-treated MS patients averaged 1380 +/- 535 spontaneous total (IgM + G + A) Ig plaque-forming cells (PFC) per 1 X 10(6) peripheral blood mononuclear cells (MNC), measured at 15-22 days after monthly CY administration, while healthy adults had 280 +/- 47 Ig PFC/10(6) MNC, and MS patients not treated with CY had 300 +/- 43 Ig PFC/10(6) MNC. The observed increase was due to an increase in IgG and IgA PFC. PFC levels remained elevated for 4 weeks following CY treatment, decreasing to control levels by 7-8 weeks post-CY. A small increase in serum IgG level was noted after greater than 12 months of pulse CY therapy; no increase was seen in CSF IgG levels. A preferential decrease in the number of CD4+ T cells was also seen in the CY-treated MS patients. We propose that the observed increase in the number of spontaneous Ig PFC was due to the CY-induced disruption of the CD4+ T cell-mediated control of in vivo activated B cells.

CD5 positive B cells in patients with rheumatoid arthritis: phorbol ester mediated enhancement of detection

CD5 molecules present on human T cells are detectable but weakly expressed on some human B cells. We have increased the sensitivity of their detection by treating the B enriched cells with phorbol myristic acetate (PMA), a tumour promoting agent. The numbers of CD5+ B cells in the blood of patients with rheumatoid arthritis (RA) were higher than in control blood, and after PMA treatment this was statistically significant. CD5+ B cells were also increased in tonsils, lymph nodes, and spleens after PMA activation. There were no significant differences between the percentages of B cells carrying chi or lambda light chains in their expression of CD5 molecules in patients with RA.

Jacalin, an IgA-binding lectin, inhibits differentiation of human B cells by both a direct effect and by activating T-suppressor cells

Jacalin, a lectin extracted from the seeds of Artocarpus intergifolia (jackfruit), has been reported to bind specifically to IgA while inducing B-cell polyclonal immunoglobulin secretion. We confirmed that jacalin only binds to IgA and not to IgG or IgM and extended these findings by showing that it does not bind to IgE. Addition of jacalin to either unfractioned peripheral blood lymphocytes or purified B cells failed to induce immunoglobulin synthesis; indeed immunoglobulin production was diminished in the presence of jacalin. We found that jacalin directly inhibited the induction of immunoglobulin synthesis from B cells in the presence of T-cell replacing factor. Cell lines making IgG, IgM, and IgA were inhibited by jacalin. Furthermore, T cells incubated with jacalin also inhibited immunoglobulin production by stimulated B cells. Under these conditions jacalin was found to be a potent mitogen for T cells but to induce little or no activation of B cells. Jacalin appears to be a potent T-cell mitogen which can induce suppressor T cells for Ig production. It also has a direct inhibitory effect on B-cell Ig production.

Humoral immune deficiency in multiple myeloma patients due to compromised B-cell function

Patients with multiple myeloma are generally immunodeficient, with pronounced depression in primary antibody responses. We have attempted to delineate the reasons for the humoral immunodeficiency by analyzing the specificity repertoire of the surface immunoglobulin (Ig)-positive B cells in patients with multiple myeloma or monoclonal gammopathy of undetermined significance (MGUS), in comparison with normal donors. B lymphocytes from 26 patients with multiple myeloma, 12 patients with MGUS, and 8 normal donors were transformed with Epstein-Barr virus (EBV) and cultured at limiting dilution for clonal analysis. The Ig secreted by each clone was analyzed for class and anti-tetanus toxoid (TT) specificity to determine the frequencies of IgM, IgG, anti-TT IgM, and anti-TT IgG antibody-secreting clones. Our objective was to establish whether the inability to mount humoral responses to common environmental pathogens was due to a lack of specific B cells or to inhibition of B-cell function. Our results indicate that the quantitative B-cell deficiency in patients was due to a nonrandom loss of selected sets of B cells. Although most patients had a reduced aggregate number of B cells, the number of TT-specific B cells was normal. There was, on average, a threefold increase in the proportion of the B-cell specificity repertoire devoted to recognition of TT. Forty-four percent of the patients with MGUS were also affected. In addition, the TT-specific B cells in multiple myeloma patients were severely compromised in their ability to secrete antibody or to differentiate to antibody-secreting cells in vivo. This arrest in differentiation appears to be extrinsic to the B cells, as they were fully able to secrete anti-TT antibody after transformation and culture in vitro. We postulate the existence of an autoimmune inhibitory network mediating the arrest in B-cell differentiation and the humoral immune deficiency.

A routine method for the establishment of permanent growing lymphoblastoid cell lines

Permanent lymphoblastoid cell lines are of great practical value in human clinical and experimental genetics. A detailed protocol for routine use is given for the establishment of lymphoblastoid lines from peripheral blood using Epstein-Barr virus and the immunosuppressivum Cyclosporin A. In addition, the biologic basis of this transformation system is briefly summarized.

IgG anti-tetanus toxoid antibody production induced by Epstein-Barr virus from B cells of human marrow transplant recipients

This investigation shows that Epstein-Barr virus (EBV)-activated human B cells from marrow transplant recipients can produce in vitro IgG anti-tetanus toxoid antibody (anti-TT) without booster immunizations with tetanus toxoid (TT). Purified B cells (E-rosette negative) from 8 normal subjects, 6 healthy long-term marrow graft recipients, and 15 long-term marrow graft recipients with chronic graft-vs-host disease (GVHD), were stimulated for 12 days with EBV to induce anti-TT production in culture supernatants. The amount of anti-TT in culture supernatants was quantitated using a enzyme-linked immunosorbent assay. B cells from all 8 normal controls produced in vitro IgG anti-TT after EBV stimulation. Five of 6 healthy recipients had B cells that produced anti-TT after EBV stimulation. Four of 15 recipients with chronic GVHD had B cells capable of producing anti-TT after EBV stimulation. The number of cultures making anti-TT responses was less in those with chronic GVHD than in those without chronic GVHD or normal individuals (P less than 0.001). B cells from patients with chronic GVHD had fewer responses exceeding the overall median of 0.7 ng/ml when compared with the other two groups (P less than 0.03). These data show that B cells of donor origin can produce in vitro IgG anti-TT antibody to tetanus toxoid antigen in a T-independent fashion.

The Epstein-Barr virus-induced production of IgE by human B cells

B cells, isolated from the blood of healthy individuals and patients allergic to pollen, produced IgE when exposed to the human B-cell polyclonal activator, Epstein-Barr virus (EBV) in vitro and placed in culture. Secreted IgM and IgE were measured using immunoenzymatic assays. No difference was seen between healthy donors and allergic patients in the amount of IgE (or IgM) secreted. Cells were placed in limiting dilution cultures in order to determine the frequency of cells producing IgE or IgM (total and pollen specific) on exposure to EBV. Again, no significant differences in EBV-driven, B-cell precursor frequencies (PF) were seen between normal and allergic individuals. EBV-driven B-cell PF for total IgM and IgE, and pollen-specific IgM and IgE secretion, were 1/450, 1/6500, 1/83,000, and less than 1 per 2,500,000, respectively, for cells from healthy donors, and 1/140, 1/4000, 1/56,000 and less than or equal to 1 per 2,000,000, respectively, for cells from allergic patients. We propose that the increased IgE levels seen in atopic individuals result solely from regulatory defects, rather than an increase in the frequency of B cells committed to the secretion of IgE.

Protoporphyrinogen oxidase and porphobilinogen deaminase in variegate porphyria

Two enzymes of the haem biosynthetic pathway were investigated in patients with variegate porphyria. Protoporphyrinogen oxidase in cultures of Epstein-Barr virus transformed lymphoblasts from twenty-seven patients showed a mean maximal velocity (Vmax) of 0.39 +/- 0.08+ nmol of protoporphyrin mg protein-1 h-1, a 52% reduction (P less than 0.001) from a non-porphyric control group (0.82 +/- 0.10). Km values (1.00 +/- 0.27 microM) did not differ significantly (P greater than 0.05) from control values in any of the patients. The mean Vmax of porphobilinogen deaminase in the cultures was 1.50 +/- 0.18 nmol of uroporphyrin mg protein-1 min-1, a 24% reduction (P less than 0.001) from controls (1.94 +/- 0.14). Mean porphobilinogen deaminase activity in the erythrocytes of twenty-one patients with variegate porphyria was 8.37 +/- 1.99 nmol of uroporphyrin 1 erythrocytes-1 s-1, a 28% reduction (P less than 0.001) from normal (11.98 +/- 2.11). The reduced activities of these two enzymes comply with the expression of variegate porphyria during its quiescent and acute phases.

Epstein-Barr virus-transformed lymphocytes from patients with bullous diseases produce autoantibodies to cytokeratins

Human cell lines obtained after Epstein-Barr virus transformation of lymphocytes from seven patients with bullous diseases (Bullous pemphigoid, Pemphigus) and five controls were screened for the production of autoantibodies against skin antigens. In five out of seven patients, the culture supernatants tested by indirect immunofluorescence on frozen sections of normal human skin and rabbit lip showed the production of autoantibodies with different specificities: basal epidermal cells, whole epidermis, Merkel cells, fibroblasts endothelial cells, etc. All autoantibodies were of IgM class and reacted with intracellular structures. Some of them were further tested by immunoblotting against epidermal keratins and were found to react with the main human epidermal keratins (56 to 67 kDa). In contrast, even when patients had circulating autoantibodies, no supernatant showed any reactivity against the antigens usually involved in these diseases, i.e., the dermoepidermal junction or the intercellular spaces of epidermis. Supernatants from controls did not show any reactivity by immunofluorescence. The results demonstrated that human lymphoid cell lines obtained from patients with bullous diseases elicited the production of anti-intermediate filament autoantibodies known to occur spontaneously in normal patients. It is suggested that this phenomenon may be linked to the blistering conditions that provoke tissue destruction.

Modulation of Epstein-Barr virus-induced B-cell activation by concanavalin A

Direct addition of the T-cell mitogen, concanavalin A (Con A), to cultures of Epstein-Barr virus (EBV)-stimulated peripheral blood mononuclear cells (PBMC) resulted in a dose-dependent inhibition of immunoglobulin M (IgM) secreted in the supernatant, as measured by an enzyme-linked immunosorbent assay. Furthermore, Con A inhibited IgM secretion of isolated T-depleted cells stimulated with EBV, and both the proliferation and IgM secretion of EBV-driven lymphoblastoid cell lines. T-Enriched cells, precultured for 48 hr with Con A, were also able to suppress the IgM response of fresh autologous PBMC stimulated with EBV. This suppression was radiation sensitive (2000 rad), a procedure which resulted in enhancement of the IgM secretion of the responder cells in two out of three experiments. Studies on the long-term effects of Con A showed that the early suppression of IgM secretion was transient and that the mitogen prevented the development of the cytotoxic T-cell response normally seen with lymphocytes from EBV-seropositive donors after 5 weeks of culture. Thus, Con A appears to modulate human lymphocyte responses to EBV by multiple mechanisms.

Cell replication in an immunologically(?) Stimulated cell population in human bone marrow

In AIDS, although there is a lack of humoral responsiveness in vitro and in vivo, many patients persistently have an increased number of B cells which continue to produce increased amounts of immunoglobulin. An objective, reproducible morphologic classification scheme for B cells was devised. Comparison of cell kinetic parameters in various disease states will require such a classification. Although not immunologically responsive to new stimuli, the marrow B cells in the AIDS patients were shown to be replicating and turning over. The latter may be due to either death in situ or to migration. Plasmacytic lymphocytes and lymphocytic plasma cells, morphologic transitions between lymphocytes and mature plasma cells, had the largest fractions in DNA synthesis. Because of their relative cell numbers, the lymphocytic plasma cells contained most of the cells in DNA synthesis. The position of plasmablasts in the sequential compartments is unclear. Only small numbers are dividing. Within a given morphologic category, large cells were more likely to be in DNA synthesis than smaller cells. These studies can serve as a basis for comparison with marrow B-cell proliferation in other disease states.

Autocrine models of B-lymphocyte growth. I. Role of cell contact and soluble factors in T-independent B-cell responses

The requirements for triggering human B cells to DNA synthesis by T-independent polyclonal activators were examined. Optimal S phase entry of purified resting B cells infected with Epstein-Barr virus (EBV) or confronted with killed particles of Staphylococcus aureus Cowan Strain I (SAC) required a high density of cells in culture. Experiments varying culture vessel geometry and culture volumes revealed that the initial limiting quantity was a soluble activity generated in the B-cell cultures. A parallel observation was noted in the requirements for the sustained growth of EBV-transformed lymphoblasts. Autostimulatory soluble factors harvested from such cultures were able to augment DNA synthesis in low density cultures of resting cells triggered by EBV or SAC. Below a critical cell number, however, soluble factors by themselves, were not sufficient either for supporting primary B-cell responses or for maintaining the proliferation of transformed lymphoblasts. By employing conditions which encouraged cell contact it was found that a second, non-harvestable factor requiring cell proximity for its action was also necessary to promote B-cell growth. The implications of these findings for autocrine and paracrine models of B-cell activation are discussed.

Different defects of T cell regulation of Epstein-Barr virus-induced B cell activation in rheumatoid arthritis

Several reports have shown a defective Epstein-Barr virus (EBV)-specific suppressor T cell function in rheumatoid arthritis (RA), suggesting that EBV may have a role in the pathogenesis of RA. EBV-specific T cell regulation was studied in 47 EBV-immune RA patients and in 14 EBV-immune control subjects by comparing the secretion of IgM into supernatants of 28-day cultures of B cells alone and cocultures of B and autologous T cells. In control subjects, autologous T cells mediated a significant decrease in the secretion of IgM by B cells at 12 and 16 days of culture. Analysis of individual responses demonstrated the existence of 3 subgroups of RA patients: group I (18 patients) had a suppressor T cell function similar to that of controls; group II (21 patients) had a defective T cell function; group III (8 patients) was characterized by a "late help phenomenon." Moreover, in RA group III, IgM secretion in cultures of B cells alone was lower than that seen in controls, RA group I, or RA group II. Differences in the duration or severity of the disease, or in the use of slow-acting therapeutic agents, corticosteroids, and nonsteroidal antiinflammatory drugs could not account for these subdivisions. Thus, our study demonstrates that several immunoregulatory defects exist in subgroups of RA patients.

Abnormal responses of rheumatoid arthritis lymphocytes to Epstein-Barr virus infection in vitro: evidence for multiple defects

Blood lymphocytes from 53 patients with rheumatoid arthritis (RA) and 44 controls were cultured with the polyclonal B cell activator Epstein-Barr virus (EBV). Culture supernatants were removed at weekly intervals and the amount of IgM secreted by the lymphocytes measured by an enzyme-linked immunosorbent assay (ELISA). Three major differences in the pattern of EBV-induced IgM synthesis by RA versus control lymphocytes were observed. Lymphocytes from RA patients, in general, produced less IgM after one week in culture than controls. In contrast, they increased their IgM secretion significantly by the end of the second week, whereas control lymphocyte cultures showed little change in IgM secretion at this time. Control lymphocytes from EBV seropositive individuals produced undetectable amounts of IgM after five weeks in culture. However, lymphocytes from 40% of the RA patients, even though they were EBV seropositive, secreted greater than 2000 ng/ml (microgram/l) IgM after five weeks. The data are discussed in terms of defective B and T cell responses to EBV in lymphocytes from patients with RA.

Specificity repertoire of lymphocytes from multiple myeloma patients. I. High frequency of B cells specific for idiotypic and F(ab')2-region determinants on immunoglobulin

The specificity repertoire of B lymphocytes from 14 multiple myeloma patients has been studied using the technique of Epstein-Barr virus (EBV) transformation of peripheral blood lymphocytes (PBL) coupled with clonal analysis by limiting dilution. We find that up to 100% of the B cells from myeloma patients undergoing EBV transformation secrete IgM specific for determinants on the F(ab')2 region of autologous and/or heterologous monoclonal immunoglobulin. In normal individuals 0.02-0.73% of the transformed B cells secrete IgM specific for F(ab')2 determinants. Two patients with monoclonal gammopathy of undetermined significance had only a weak reactivity to F(ab')2 fragments. The number of anti-F(ab')2 B cells was up to 145-fold greater in patients than in normal donors. The majority of antibodies from patient clones recognized determinants shared among 3-12 different F(ab')2 fragments, whereas those originating from normal donor B cells saw determinants expressed on only one or two of the panel of test F(ab')2 fragments. There was a preference for autologous M components and a high proportion of antiidiotypic reactivity in five of eight patients so analyzed. We speculate that these findings indicate the existence of an anti-F(ab')2 immunoregulatory network mediating patient immunodeficiency network mediating patient immunodeficiency, thereby creating an abnormality that may enable the progression of multiple myeloma.

Effects of pure interferons on Epstein-Barr virus infection in vitro

Pure human gamma-interferon as well as alpha-interferon inhibited induction of immunoglobulin synthesis by Epstein-Barr virus but not by pokeweed mitogen in B lymphocytes from adult but not from newborn humans. The interferons inhibited the infected B lymphocytes directly, irrespective of the Epstein-Barr virus immune status of the donor, and their inhibitory effect was synergistic.

Rescue of IgM, IgG, and IgA production in common varied immunodeficiency by T cell-independent stimulation with Epstein-Barr virus

We previously defined three categories of B-cell defects in common varied immunodeficiency (CVI): failure to produce IgG and IgA in response to T cell-dependent (TD) stimulation by Staphylococcus bacteria (Sac) plus pokeweed mitogen or B-cell inducing factor (BIF), failure to produce any immunoglobulin, and failure of Sac-induced proliferation and differentiation. The present study includes the responses of 22 CVI patients to T cell-independent (TI) stimulation by Epstein-Barr virus (EBV). In the majority of patients, EBV-stimulated B cells showed normal proliferation and IgM production. In addition, IgG and IgA production was in the range of that for EBV-stimulated normal cells in many patients. Among 11 patients with no TD production of immunoglobulin of any isotype, two showed normal IgM secretion in response to EBV and five others had significant but subnormal responses. Four patients never had humoral responses despite repeated testing and removal of potentially suppressing T cells and monocytes. Concanavalin A stimulation of the T cells from all the patients tested resulted in the production of B-cell inducing factor at higher levels than for normal donor T cells, as assayed on normal Sac-stimulated B cells. These results show that many cases of B-cell defects in CVI patients involving TD production of IgM, switching to TD production of IgG and IgA, and mitogen responses to Sac are not absolute defects. The B cells will respond normally to some stimuli.

Immunoglobulin M and immunoglobulin G secretion by human B cells exposed to RU 41.740, a glycoprotein extract from Klebsiella pneumoniae

RU 41.740, a glycoprotein extract from Klebsiella pneumoniae, was seen to activate human B cells to immunoglobulin secretion in vitro. The effects of RU 41.740 on human B cells were compared to those induced by pokeweed mitogen, a T-cell-dependent polyclonal B-cell activator, and Epstein-Barr virus, a T-cell-independent polyclonal B-cell activator. Exposure of human B cells to all of these agents resulted in increased immunoglobulin M (IgM) and immunoglobulin G (IgG) secretion. IgM and IgG secretion induced by RU 41.740 appeared to be T cell dependent when B cells were isolated from human peripheral blood. However, this activity may have been T cell independent when B cells were isolated from human spleen. RU 41.740-induced IgM secretion by peripheral blood B cells was seen to peak after 6 days in culture; IgG secretion peaked after 7 days in culture. The optimal concentration of RU 41.740 for the induction of IgM and IgG secretion by human B cells in vitro was seen to be 200 micrograms/ml.

Human monoclonal antibodies produced by Epstein-Barr virus transformed cell lines bind protein A

Epstein-Barr virus (EBV) is a polyclonal T-independent activator of viral receptor positive human B lymphocytes. Lymphocytes infected in vitro with the virus are transformed into immortalized cell lines [Nilsson, K, and Klein, G. (1982) Adv. Cancer Res. 37, 319]. In this way human cell lines that secrete specific IgM, IgG and IgA monoclonal antibodies are established. Protein A is also a polyclonal T-independent B cell activator [Langone, J. J. (1982) Adv. Immunol. 32, 157], the targets of which are surface immunoglobulin and C3d receptor positive cells, as are the targets of EBV. We found that almost all (16 out of 17) of the specific monoclonal antibodies (IgM, IgG and IgA) produced in vitro by EBV cell lines bind protein A. Unlike these in vitro produced antibodies, a substantial fraction of the immunoglobulins in human serum does not bind protein A. Thus, those plasma cells which in vivo secrete protein A nonbinding immunoglobulins originate from precursors of B cell that were EBV noninfective. Alternatively, during in vivo B differentiation some immunoglobulins undergo a change from protein A binding to protein A nonbinding molecules.

Differentiation of chronic lymphocytic leukemia cells after in vitro treatment with Epstein-Barr virus or phorbol ester. I. Immunologic and morphologic studies

Leukemic cells from ten patients with "nonsecretory," B-type chronic lymphocytic leukemia (CLL) were cultured alone or in the presence of Epstein-Barr virus (EBV) or a phorbol ester (12-0-tetradecanoylphorbol-13-acetate; TPA) for 7 days. At periodic intervals the cell morphology, cytoplasmic immunoglobulin content (direct immunofluorescence) and capacity for immunoglobulin secretion (hemolytic plaque assay) were assessed. A variable but significant number of the TPA-treated CLL cells from all patients expressed cytoplasmic immunoglobulin of a single light-chain type at some stage, usually within the first 3 days. EBV induced similar changes in seven of eight cases tested. Untreated cell cultures were negative or contained a few cytoplasmic immunoglobulin-positive cells. Cells from five of nine cases secreted immunoglobulin of a single light-chain type. In every instance this was identical to the surface and cytoplasmic immunoglobulin. Cytologic changes were observed in the leukemic cells after treatment with one or both agents in nine of ten cases. The major feature was an increase in cell size associated with immunoblastic or plasma-cytoid features. Mitotic figures and binucleate cells were also present. These studies indicate that EBV and TPA are effective at inducing immunoglobulin synthesis and secretion in "nonsecretory" B cell neoplasms and are useful tools for studying the maturation potential inherent in these tumors. The study also suggests that the secreted immunoglobulin is a monoclonal product.

Secretion of gamma-interferon at the cellular level. Induction by Epstein-Barr virus

Using a haemolytic plaque assay for gamma-interferon (IFN-gamma) secretion we found that in vitro Epstein-Barr virus (EBV) exposure of peripheral blood mononuclear cells from EBV immune individuals led to IFN-gamma secretion, which was apparent within 6 h after virus contact and peaked 12-24 h after induction. Live, ultraviolet-light-irradiated and heat-inactivated virions all caused IFN-gamma secretion. In contrast, blood mononuclear cells from EBV non-immune adults or neonates could not be activated to IFN-gamma production by EBV.

Epstein-Barr virus-transformed lymphocytes produce monoclonal autoantibodies that react with antigens in multiple organs

Peripheral blood lymphocytes from normal individuals and patients with autoimmune abnormalities such as insulin-dependent diabetes mellitus and thyroiditis were infected with Epstein-Barr virus, and the culture supernatants were tested for autoantibodies that reacted with normal tissues. Between 58 and 86% of Epstein-Barr virus-transformed cultures produced immunoglobulin M antibodies, and between 9 and 24% of the transformed cultures produced immunoglobulin G antibodies that reacted with normal tissues. Ten Epstein-Barr virus-transformed clones secreting human immunoglobulin M monoclonal autoantibodies were isolated. Four of these monoclonal autoantibodies were studied in depth and found to react with antigens in multiple organs, including thyroid, pancreas, stomach, smooth muscle, and nerves. It is concluded that Epstein-Barr virus can trigger the production of autoantibodies without infecting the target cells to which the autoantibodies are directed.

Limiting dilution analysis of Epstein-Barr virus-induced immunoglobulin production

The major goal of this work is to establish a culture system for the growth of human B lymphocytes at the single-cell level so that the immunoglobulin secreted by the clonal progeny of that cell can be analyzed. A method which involves culturing small numbers (1-1000) of lymphocytes, which have been infected with Epstein-Barr virus (EBV) prior to plating, in round-bottom microtiter plates is described. A feeder layer of irradiated (2500 R) umbilical cord blood lymphocytes to which phytohemagglutinin has been added was found to be optimal. Culture supernatants collected from 3 to 6 weeks postinfection are assayed for the production of IgG and IgM by radioimmunoassay in order to determine the overall cloning efficiency of the system. We have shown that up to 33% of surface Ig-positive cells produce detectable clones in this system. Umbilical cord blood cells are superior to T-cell and macrophage cell lines as feeder layers. Furthermore, culture supernatants from phytohemagglutinin-stimulated umbilical cord lymphocytes do not adequately replace these cells. We also observed that while most IgM-secreting clones continued to produce immunoglobulin during the 7-week time period analyzed, the majority of IgG-secreting clones had a relatively short half-life in vitro. This culture system allows us to examine a significant proportion of the human B-cell population and carry out studies on the frequency of specific antibody- and isotype-producing clones.

Frequencies of the separate human B cell subsets activatable to Ig secretion by Epstein-Barr virus and pokeweed mitogen

We have developed a microculture system suitable for limiting dilution analysis of Epstein-Barr virus (EBV)- and pokeweed mitogen (PWM)-induced activation of immunoglobulin secretion by human B cells. It was found that exogenous filler cells were not required to obtain optimal EBV-induced B cell precursor frequency (PF) estimates, although filler T cells were required for optimal PWM activation. In fact, when autologous T cells were used as filler cells, a marked decrease in the EBV-induced IgM PF was noted. Treatment of the T cells with cyclosporin A partially eliminated, and irradiation of the T cells completely eliminated, this decrease. The calculated PF of B cells activated by EBV was from 1/290 to 1/3,700 for IgM, and from 1/920 to 1/3,250 for IgG secretion. PWM activated from 1/140 to 1/3,200 B cells to IgM secretion. The results of experiments in which EBV and PWM were mixed, indicated that these two polyclonal activators operated on different B cell subpopulations. Therefore, both these agents seem to activate small, discrete subpopulations of human peripheral blood B cells to Ig secretion.