Membrane antigen on Epstein--Barr virus-infected human B cells recognized by a monoclonal antibody

Biochemical identification of the antigen recognized by the monoclonal pan-B cell antibody Y29/55

To examine the biochemical structure of the antigen recognized by the monoclonal pan-B cell antibody, Y29/55, the Daudi- and Jurkat-cell lines were labeled by two different methods and immunoprecipitation experiments were carried out. After surface labeling with iodine, two bands with molecular weights of about 38 and 42 kD were observed. The same two proteins were precipitated after biosynthetic labeling with (35S)-methionine from B cells and, to a lesser extent, from T cells. Therefore, it seems that the same proteins, or proteins with similar molecular weight, exist intracellularly in T cells as exist on the surface of, and possibly intracellularly, in B cells. It was confirmed that 80-90% of normal blood-derived B cells were stained with Y29/55 by indirect immunofluorescence. Double-labeling experiments with the pan-B cell antibodies Leu 16 (CD 20) and Leu 12 (CD 19) showed a B-cell population which could be stained with both antibodies (Y29/55 and Leu 16 or Y29/55 and Leu 12). A minor cell population was stained with the antibody Y29/55 alone. Our findings indicate that the antibody Y29/55 recognizes a B-cell antigen, which has not been described previously.

Expression and functional role of CD23 on T cells

We have found that approximately 10%-15% of tonsil, but not peripheral blood, T cells express the CD23 antigen following activation with 12-O-tetradecanoylphorbol 13-acetate (TPA), phytohemagglutinin (PHA) or recombinant interleukin 4. The proliferative response of tonsil T cells is significantly increased when CD23 monoclonal antibodies (mAb) are present in the cultures. In contrast, no such proliferative augmentation is seen when peripheral blood T cells are cultured in this way. Supernatant (SN) of Epstein-Barr Virus-transformed B lymphoblastoid cell lines (EBVLCL), is found to have a similar co-stimulatory effect on the proliferation of tonsil T cells to that seen with CD23 mAb. This effect is greatly diminished by preclearing SN with CD23 mAb. Similarly, SN from a CD23+ L cell transfectant augments the proliferative response of tonsil T cells to both TPA and PHA. The CD23 molecule expressed by TPA-driven T cell blasts appears identical in size to the 45-kDa glycoprotein present on EBVLCL and activated B cells. In contrast, a 42-kDa molecule is observed when CD23 is precipitated from T cells activated with PHA. The results presented here demonstrate that CD23 is expressed on activated tonsil, but not peripheral blood T cells and plays a role, via the binding of CD23 mAb and CD23+ material, present in EBVLCL and CD23+ transfectant SN, in the regulation of T cell proliferation in response to mitogens such as PHA and TPA.

AIDS-related Kaposi's sarcoma displays differential expression of endothelial surface antigens

The authors studied 11 cases of Kaposi's sarcoma (KS) in patients with the acquired immunodeficiency syndrome (AIDS) for their reactivity with two monoclonal antibodies (B721 and E431) that recognize endothelial cell surface antigens. Reactivity of these antibodies with KS was compared with the reactivity of other known endothelial markers (F8rAg, Ia, HCL-1). Staining was done with avidin-biotin-alkaline phosphatase immunohistochemistry on acetone-fixed frozen sections. In all samples of tumor both the spindle cell component and the vascular lining cells stained with both B721 and E431. In general, the spindle cells stained less intensely than did the vascular lining cells. There was both intratumor and intertumor variability. B721 and E431 are proposed as two additional markers for KS, and it is suggested that their reactivity with the tumor supports the hypothesis that KS is derived from vascular endothelium. The possibility is also raised that the variability of staining for vascular markers could have diagnostic possibilities, and further studies for investigation of this hypothesis are suggested.

Human T cell activation. III. Rapid induction of a phosphorylated 28 kD/32 kD disulfide-linked early activation antigen (EA 1) by 12-o-tetradecanoyl phorbol-13-acetate, mitogens, and antigens

With human T cells activated by 12-o-tetradecanoyl phorbol-13-acetate (TPA) as immunogen, an IgG2a mAb, early activation antigen 1 (EA 1), was generated against a 60-kD protein with disulfide-linked 28-kD and 32-kD subunits. Both subunits were phosphorylated. The antigen, EA 1, was readily detected on approximately 60% of isolated and cryopreserved thymocytes, as determined by indirect immunofluorescence. A low level of EA 1 expression was detectable on 6-7% of blood lymphocytes. TPA-activated T cells expressed EA 1 as early as 30 min after activation. By 1 h, 85-90% of the T cells stained with mAb EA 1. By 3-4 h, the expression of EA 1 was detected in greater than 95% of the T cells. Although the percentages of EA 1+ T cells did not change, the intensity of staining increased slightly. After 18-24 h, both the percentage of EA 1+ cells and the intensity of staining decreased gradually. TPA-induced EA 1 expression was independent of monocytes. EA 1 expression was slightly delayed in T cells that were isolated without the rosette selection and treated with TPA. Nevertheless, greater than 85% of these T cells expressed EA 1 within 1 h, and the maximal number of EA 1+ T cells was also detected at 3-4 h. In T cell populations with 1-2% monocytes, about 50-90% of the PHA- or Con A-activated T cells expressed EA 1 with a slower kinetics. EA 1 expression preceded that of IL-2-R in these activation processes. Similarly, T cells activated by soluble antigens (tetanus toxoid and PPD) and alloantigens in MLR also expressed EA 1 after a longer incubation. Approximately 20% of the T cells stained for EA 1 at day 6. EA 1 expression was not limited to activated T cells. B cells activated by TPA or anti-IgM antibody plus B cell growth factor expressed EA 1. The kinetics of EA 1 expression was markedly slower and the staining was less intense. Repeated attempts to detect EA 1 on resting and TPA-activated monocytes and granulocytes have not been successful. However, the detection of EA 1 in nonlymphoid cell lines would indicate that EA 1 may have a broader cell distribution. EA 1 expression was due to de novo synthesis, as the induction of EA 1 was blocked by cycloheximide and actinomycin D.(ABSTRACT TRUNCATED AT 400 WORDS)

Evidence for an association between CD23 and the receptor for a low molecular weight B cell growth factor

Low molecular weight B cell growth factor (BCGF) and a monoclonal antibody (MHM6) to the 45-kDa, B lineage-restricted, CD23 activation antigen (BLAST-2; EBVCS) were found to be indistinguishable in their biological effects. Individually, both augmented DNA synthesis in activated, but not resting, B lymphocytes while no additional enhancement resulted from using the two agonists in combination. Furthermore, by increasing the expression of Tac, both MHM6 and BCGF promoted activated B cells to respond more vigorously to the late addition of recombinant interleukin 2. The presence of BCGF during B cell activations was found to down-regulate the expression of the CD23 antigen while the coating of activated cells with MHM6 antibody diminished their capacity to absorb BCGF activity. The findings demonstrate that CD23 and a low molecular weight BCGF deliver a comparable growth-promoting signal to activated B cells. A possible relationship between CD23 and the receptor for the low molecular weight BCGF is discussed.

Autocrine growth of human B lymphocytes: maintained response to autostimulatory factors is the special feature of immortalization by Epstein-Barr virus--a hypothesis

The autocrine growth profile of human B lymphocytes transformed with Epstein-Barr virus (EBV) was found to comprise three distinct components: a B-cell growth factor (BCGF); an interleukin-1 (IL-1)-like activity; an activity requiring cell-to-cell contact for its action. Observations on the inhibition of the EBV-carrying Daudi lymphoma line by alpha-interferon indicated that loss of response to these autostimulatory factors was underlying growth cessation. Furthermore, a putative receptor for BCGF was found to be down-regulated on B cells stimulated with non-transforming mitogens but constitutively expressed following EBV-transformation. Taken together with recent evidence that normal B cells produce autostimulatory factors, these findings suggest that the special feature of autocrine growth by EBV-immortalized cells is a maintenance of what should normally be a transient phenotype, possibly through deregulation of receptor expression. This hypothesis is discussed.

Activation of human B cells mediated through two distinct cell surface differentiation antigens, Bp35 and Bp50

Two human B-cell differentiation antigens, Bp35 and Bp50, apparently play distinct roles as signal receptors in B-cell activation. Monoclonal antibodies (mAbs) to either Bp35 or Bp50 deliver positive signals to B cells that stimulate their transition through the cell cycle. mAb to Bp35, like anti-immunoglobulin antibodies, functions principally to activate resting B cells to become competent to enter the G1 phase of the cell cycle. In contrast, mAb to Bp50, a 50-kDa polypeptide expressed on all B cells, functions to stimulate activated B cells to traverse the cell cycle. mAb to Bp35, like anti-immunoglobulin antibodies, activates tonsillar B cells and induces low levels of B-cell proliferation. In contrast, anti-Bp50 mAb alone neither activates B cells nor induces B cells to proliferate but, together with anti-Bp35 or anti-immunoglobulin, augments B-cell proliferation. In this respect the action of anti-Bp50 antibody resembles the activity of B-cell growth factor(s) (BCGF). As little as 0.05 microgram of anti-Bp50 per ml is needed to augment proliferation and, like BCGF, anti-Bp50 is effective even when added 12-24 hr after B cells are activated with anti-immunoglobulin or anti-Bp35. Without additional exogenous signals, anti-Bp35 and anti-Bp50 together induce strong proliferation of purified resting B cells. These results suggest that the Bp35 and Bp50 surface molecules function in the regulatory control of B-cell activation and progression through the cell cycle.

Presence of an endothelial antigen on the syncytiotrophoblast of human chorionic villi: detection by a monoclonal antibody

We describe a monoclonal antibody, B721. This antibody reacts with an antigen present on vascular endothelium and on the syncytiotrophoblast of term chorionic villi. The antigen is absent from the trophoblast of the chorion, from the amniotic epithelium, and from normal peripheral blood or lymph node lymphocytes. We discuss the possible functional roles of the antigen. We propose that the syncytiotrophoblast, by expressing endothelial antigens, mimics endothelium and may perform endothelial functions.

Two related but differentially expressed potential membrane proteins encoded by the EcoRI Dhet region of Epstein-Barr virus B95-8

Three mRNAs in the EcoRI Dhet region of Epstein-Barr virus B95-8 were mapped. Their 3' ends are coterminal. A latent gene containing three exons is transcribed from the ED-L1 promoter and was predicted to lead to expression of a 42-kilodalton protein. An unspliced late mRNA is produced by transcription from the ED-L1A promoter within the first intron of the above gene and was predicted to lead to expression of a 28-kilodalton protein corresponding to the C-terminal two-thirds of the 42-kilodalton protein. Both proteins would have hydrophobic N-terminal domains and highly acidic C-terminal domains and were predicted to span the cell membrane. An early promoter (ED-L2) is located in the 3' untranslated region of the above genes and was predicted to lead to expression of a 6.5-kilodalton polypeptide containing a C-terminal hydrophobic region.

Selective inhibition of growth factor-dependent human B cell proliferation by monoclonal antibody AB1 to an antigen expressed by activated B cells

A monoclonal antibody, AB1, was established with activated human B cells as immunogen. AB1 stained activated B cells but not activated T cells. Its selective reactivity to activated B cells was further documented by its nonreactivity to activated T cells, resting T and B cells, monocytes, granulocytes, bone marrow cells, leukemic cells, and cells from cell lines of T, B, and myeloid lineages. Upon activation, the antigen appeared on B cells as early as 3-4 h after stimulation and was fully expressed by 38 h. The expression of this antigen was not dependent on the presence of B cell stimulatory factor(s). Anti-IgM antibodies by themselves induced its expression. AB1 inhibited B cell proliferation that was induced by a low dose anti-IgM antibody and conditioned medium containing B cell stimulatory factor. It did not inhibit B cell proliferation induced by either high doses of anti-IgM antibodies or by formalinized Staphylococcus aureus. It also failed to inhibit T cell mitogenesis. The possibility exists that this antigen is related to the receptor for B cell stimulatory factor.

Immunohistologic characterization of synovial membrane lymphocytes in rheumatoid arthritis

Synovial membrane biopsy specimens from 15 rheumatoid arthritis patients were examined using routine histologic stains and monoclonal antibodies directed against cell surface antigens. Three patterns of lymphoid cell infiltrates were recognized: 1) diffuse infiltration of T cells that surrounded clusters of germinal center B cells (3 patients); 2) diffuse T cell infiltration, lacking germinal centers (8 patients); and 3) proliferation of subsynovial fibroblasts, with relatively few lymphoid cells (4 patients). The synovial, subsynovial, and perivascular tissues in each of the patterns exhibited a high frequency of HLA-DR antigen, HLA-DS antigen, transferrin receptor, and/or epidermal growth factor receptor. In contrast, normal or osteoarthritic synovial tissues did not display a marked increase of these antigens or receptors. Cells bearing natural killer antigen were infrequent in each of these patterns. Active synovitis, synovial effusions, anemia, and elevated sedimentation rate were present in rheumatoid arthritis patients with each of the three histologic patterns. Immunohistologic characterization of synovial membrane infiltrates by these monoclonal antibodies provides additional information about pathogenesis of rheumatoid arthritis and may help in predicting responses to different therapeutic modalities.

The application of monoclonal antibodies in the study of viruses

This chapter discusses the applications of monoclonal antibodies in virology. A single monoclonal antibody can provide information on protein “relatedness,” structure, function, synthesis, processing, and cellular or tissue distribution and on the association among molecules. The use of monoclonal antibodies provides valuable insight into the working of the protein both as an enzyme and as a target for the host immune response, evolving in reaction to that response. Monoclonal antibodies find application in two main areas: (1) in the field of rapid diagnosis of virus disease in man, animals, and plants and (2) in the extension of virus taxonomy. Monoclonal antibodies may be used to analyze the role of a protein. This ability to distinguish related proteins can be used to provide a genetic marker in recombination experiments. Monoclonal antibodies can detect low amounts of individual virus proteins within the infected cell. They can, thus, provide information concerning the temporal and spatial separation of protein formation and accumulation, and data on protein modification and processing in the infected cell.

Characterization of an antigen whose cell surface expression is induced by infection with Epstein-Barr virus

Metabolically labeled monoclonal antibodies were used to measure the number of determinants per cell for an Epstein-Barr virus (EBV) cell surface antigen (EBVCS) (C. Kintner and B. Sugden, Nature [London] 294:458-460, 1981) which is expressed on the surface of EBV-transformed cells. The antigenic determinants were present approximately 5 X 10(5) times per in vitro-transformed cell. Immunoprecipitation followed by electrophoresis in polyacrylamide gels containing sodium dodecyl sulfate indicated that four independent monoclonal antibodies to EBVCS recognized a protein of 47,000 daltons. The identification of EBVCS isolated from EBV-transformed cells grown in tunicamycin demonstrated that the antigen when isolated from cells grown without this drug was glycosylated. Finally, preclearing experiments with monoclonal antibodies to EBVCS or to HLA (class I products of the human major histocompatibility locus) and to beta 2-microglobulin indicated that EBVCS is not a major histocompatibility type 1 antigen.

Monoclonal antibody specific for capsid antigen of Epstein-Barr virus

A hybrid cell line (Cl-51) producing an anti-capsid antibody was obtained by fusion of mouse myeloma cells with spleen cells from mice immunized with purified P3HR-1 Epstein-Barr virus (EBV). Immunofluorescence showed that the Cl-51 antibody reacted with the cytoplasm and the nucleus of P3HR-1 and B95-8 cells, but not with Raji, BJAB, Molt-4, and superinfected Raji cells in the presence of cytosine arabinoside (Ara-C). The viable P3HR-1 and B95-8 cells were not stained nor was the viral infectivity neutralized. The Cl-51 antibody immunoprecipitated 123,000 and 120,000 dalton polypeptides of P3HR-1 and B95-8 cells, respectively, and both were sensitive to phosphonoacetic acid. Specific reactions were not evident with extracts of Raji cells and superinfected Raji cells in the presence of Ara-C. An analysis of the purified virus particles showed that this antibody recognized a capsid component of EBV.