Appearance of Epstein-Barr virus-associated antigens in infected Raji cells

Unravelling the first key steps in equine herpesvirus type 5 (EHV5) pathogenesis using ex vivo and in vitro equine models

Equine herpesvirus type 5 (EHV5) is a ubiquitous, yet obscure pathogen in the horse population and is commonly associated with fatal equine multinodular pulmonary fibrosis (EMPF). To date, little is known about the precise pathogenesis of EHV5. Here, we evaluated the dynamics of EHV5 infection in representative ex vivo and in vitro equine models, using immunofluorescence staining and virus titration. EHV5 was unable to infect epithelial cells lining the mucosa of nasal and tracheal explants. Similarly, primary equine respiratory epithelial cells (EREC) were not susceptible to EHV5 following inoculation at the apical or basolateral surfaces. Upon direct delivery of EHV5 particles to lung explants, few EHV5-positive cell clusters were observed at 72 hours post-inoculation (hpi). These EHV5-positive cells were identified as cytokeratin-positive alveolar cells. Next, we examined the potential of EHV5 to infect three distinct equine PBMC populations (CD172a⁺ monocytes, CD3⁺ T lymphocytes and Ig light chain⁺ B lymphocytes). Monocytes did not support EHV5 replication. In contrast, up to 10% of inoculated equine T and B lymphocytes synthetized intracellular viral antigens 24 hpi and 72 hpi, respectively. Still, the production of mature virus particles was hampered, as we did not observe an increase in extracellular virus titer. After reaching a peak, the percentage of infected T and B lymphocytes decayed, which was partly due to the onset of apoptosis, but not necrosis. Based on these findings, we propose a model for EHV5 pathogenesis in the horse. Uncovering EHV5 pathogenesis is the corner step to finally contain or even eradicate the virus.

Membrane antigen expression in Epstein-Barr virus-infected Raji cells in the presence of phosphonoacetic acid

The expression of the Epstein-Barr virus (EBV)-induced membrane antigen (MA) in Raji cells experimentally infected with EBV concentrates was inhibited by phosphonoacetic acid (PAA) as determined by membrane immunofluorescence and inhibition of antibody-dependent lymphocyte cytotoxicity. PAA was only effective if present during the first 24 hr following virus adsorption, indicating that the synthesis of MA was primarily a late viral gene function requiring viral DNA synthesis.

Direct detection of Epstein-Barr viral antigen in nasopharyngeal swabs from patients with infectious mononucleosis

OBJECTIVE

To determine whether direct immunologic detection of Epstein-Barr virus (EBV) early antigen diffuse component (EA-D) from nasopharyngeal swabs is a feasible approach to the development of a rapid diagnostic test for infectious mononucleosis (IM).

METHODS

Nasopharyngeal swabs from 20 patients presenting with a presumptive diagnosis of IM (having the classic triad of symptoms-acute pharyngitis, fever, and lymphadenopathy) and 5 controls were assayed for EA-D. EBV serologic testing and a heterophil antibody titer (HAT) test also were performed. EA-D was assayed by polyacrylamide gel electrophoresis and subsequent transfer to a nylon membrane, followed by immunoblotting with a monoclonal antibody.

RESULTS

EA-D was detected in 17 of 20 patients (85%) with presumptive diagnoses of IM and in 1 of 5 normal subjects and was highly significant in predicting IM (p < 0.01). There was no significant difference in numbers of positive and negative results using either EA-D assay or HAT test in patients with IM (p < 0.35). Pharyngeal exudate in the 17 pharyngitis patients with this variable documented was significantly correlated with positive EA-D (p < 0.01), but not with the HAT test (p < 1.00).

CONCLUSIONS

Immunologic detection of EBV-derived antigens from nasopharyngeal swabs is a potential early diagnostic tool for clinically suspected IM. Sensitivity and specificity in pediatric and adult populations, patients with other viral etiologies, and patients with streptoccocal pharyngitis should be determined in subsequent investigations.

Interaction of human adenovirus serotype 2 with human lymphoid cells

Human adenoviruses (e.g., Ad2, Ad5) establish chronic infections in human lymphoid-derived cell lines, including Raji and Jijoye (R.E. Wallace, 1969, Proc. Soc. Exp. Biol. Med. 130, 702-710; N. Faucon, G. Ogier, and Y. Chardonnet, 1982, J. Natl. Cancer Inst. 69, 1215-1220); however, the mechanisms by which chronic infections are established and maintained are not understood. When Raji or MOLT-3 cell cultures were infected with Ad2 at high multiplicity, these cell lines continued to grow exponentially and produced only small amounts of infectious virus. Virus-specific antigens, including the DNA-binding protein and hexon, were expressed in only 5% of the Ad2-inoculated cultures. All Raji and MOLT-3 cells were found to have adenovirus receptors, but the Ad2 virions that adsorbed to most Raji cells were sequestered in caps, suggesting that most cells fail to internalize adsorbed Ad2. Cell synchronization experiments showed a correlation between the proportion of cells that became productively infected and the proportion of cells in mitosis at the time of infection. In contrast, primary blood lymphocytes had few, if any, Ad2 receptors and were not productively infected by Ad2.

Purification of a polypeptide complex (p52) belonging to the D-subspecificites of Epstein-Barr virus-induced early antigens

A two-dimensional immunoblot analysis of chemically induced EBV DNA carrying Burkitt's lymphoma cell lines shows besides a large number of minor components at least two major groups of polypeptides: the most prominent group of polypeptides is observed in the range of 48 to 58 kDa (pI 4.5 to 8.5) and another group at 38/36 kDa (pI 4.4). A polypeptide complex (p52) belonging to the Epstein-Barr virus (EBV)-induced early antigen complex (EA) has been isolated from IdU-induced Raji and B95-8 cells as well as from n-butyrate-induced P3HR-1 cells. The p52 polypeptides have been purified by chromatography on Blue-, DEAE-, CM-, and Phenyl-Sepharose. The purification of these components of the EA complex was monitored by ELISA and by two-dimensional immunoblots using a well-characterized high anti-EBV positive human serum. The isolated polypeptides have an apparent mol wt of about 52,000 Da as determined under nondenaturing conditions by gel filtration chromatography on Sephacryl S-300. One- and two-dimensional immunoblots show a major group of polypeptides of 52 kDa (pI 8.5 to 5.5) with EA activity and some minor components with smaller size up to 40 kDa. The latter seem to be generated by limited proteolysis of p52 polypeptides. The EA activity of the isolated polypeptides could be confirmed by their reaction with IgG anti-EA positive as well as IgA anti-EA positive sera by ELISA. The purified polypeptide complex did not react with anti-EA-D negative, anti-EA-R positive sera obtained from patients with African Burkitt's lymphoma, suggesting that these polypeptides belong to the EA-D complex. The monoclonal antibody R3 reacted with the isolated 52 kDa components of EA suggesting a common epitope present on these polypeptides, the same result was obtained with three rabbit sera produced against the isolated polypeptide complex.

Protection of cottontop tamarins against Epstein-Barr virus-induced malignant lymphoma by a prototype subunit vaccine

Epstein-Barr (EB) virus is one of the five herpesviruses of man. Strong links between this agent and the chain of events causing two human cancers, endemic Burkitt's lymphoma and undifferentiated nasopharyngeal carcinoma, have long been evident (reviewed in ref. 1). Because of this, and because of the very high incidence of nasopharyngeal carcinoma in certain large populations, it was suggested in 1976 that a vaccine should be developed against EB virus to prevent infection and thereby reduce tumour incidence amongst those at risk. The virus-determined membrane antigen (MA) was proposed as immunogen because it was known to elicit naturally occurring virus-neutralizing antibodies in man and because analogous antigens had been shown to act as effective experimental vaccines for preventing the herpesvirus-induced lymphomas of Marek's disease in chickens. Progress has been achieved in defining, quantifying and preparing MA molecules, and in enhancing their immunogenicity; a sensitive assay for antibodies to MA has been elaborated. Here we report that isolated cell membranes expressing MA, or purified MA glycoprotein of relative molecular mass (Mr) 340,000 (gp340), have been used to vaccinate cottontop tamarins (Saguinus oedipus oedipus), and that animals receiving either preparation were protected against the effects of a 100% tumour-inducing challenge dose of EB virus.

Inhibition of Epstein-Barr virus (EBV) release from the P3HR-1 Burkitt's lymphoma cell line by a monoclonal antibody against a 200,000 dalton EBV membrane antigen

In raising murine hybridoma antibodies against Epstein-Barr virus (EBV)-induced membrane antigens (MA), we found one antibody that blocked the release of infectious EBV from cultured P3HR-1 cells. This monoclonal antibody (mAb) recognized a 200 kD, phosphonoacetic acid-sensitive (late) MA, and did not directly neutralize virus without complement. When this mAb was added to 33 degrees C-cultured, spontaneously EBV-producing P3HR-1 cells, the intracellular expression of viral capsid antigen and infectious virus was not inhibited, but the appearance of infectious virus in the culture medium was significantly reduced. The duration of this suppression was dependent upon the concentration of the mAb, an effect being observed to a 1:4 X 10(5) titer of the ascites mAb preparation. A more acute effect of suppression of EBV release was observed in a second model of 12-o-tetradecanoyl phorbol-13-acetate and n-butyrate induction of EBV in 37 degrees C-cultured P3HR-1 cells. Again, intracellular infectious virus production was not inhibited, but the level of infectious virus in the culture medium was significantly reduced as early as 1 and 2 d of culture with antibody. This effect was reversed within 31 h after replacement of mAb-containing medium with fresh medium. This description of antibody-mediated inhibition of EBV release might lead to the characterization of another form of immune defense for the control of EBV infections.

Large-scale purification of Epstein-Barr virus membrane antigen gp340 with a monoclonal antibody immunoabsorbent

A purification method has been elaborated to isolate Epstein-Barr (EB) virus membrane antigen, gp340, in milligram amounts. The gp340 was prepared from detergent extracts of B95-8 cells by affinity chromatography with a monoclonal antibody immunoabsorbent. Bound material was eluted and the eluate, consisting of 50% gp340, was then fractionated by gel filtration. The final gp340 product was antigenically active and 95% pure. The purification method was found to be rapid and reproducible with no loss of the ability of the immunoabsorbent to retain gp340 after repeated elution. The procedure provides suitable material to permit the detailed structural analysis of gp340 necessary for both vaccine design and for the investigation of the role of gp340 in immunity to EB virus infection.

The Leeuwenhoek lecture, 1983. A prototype vaccine to prevent Epstein-Barr virus-associated tumours

EB virus is a herpesvirus that infects all human communities. The infection is life-long and usually asymptomatic. Excessive reaction to primary infection leads to infectious mononucleosis while immunological failures give fatal lymphoproliferative diseases. The virus is associated with endemic Burkitt's lymphoma and undifferentiated nasopharyngeal carcinoma. In world cancer terms Burkitt's lymphoma is insignificant, but nasopharyngeal carcinoma has a high incidence in certain important populations. By analogy with herpesvirus-induced animal cancers, prevention of infection should greatly reduce subsequent development of tumours. A prototype vaccine has therefore been produced based on the virus-determined antigen (MA gp340) that elicits virus-neutralizing antibodies. A sensitive assay has permitted the elaboration of an efficient antigen preparation method and the product has been rendered highly immunogenic, as tested in mice and rabbits, by incorporation in liposomes. The only animal suitable for experimental EB virus infection is the little-known cottontop tamarin; a breeding colony has been successfully established and protection against virus challenge assessed in immunized tamarins. The overall structure of the antigen has been determined in preparation for future production by synthesis or rDNA technology.

Comparative immunogenicity studies on Epstein-Barr virus membrane antigen (MA) gp340 with novel adjuvants in mice, rabbits, and cotton-top tamarins

The effectiveness of immunisation of mice, rabbits, and cotton-top tamarins with small amounts of EB virus MA glycoprotein gp340 , incorporated into artificial liposomes, has been compared using various routes of injection with or without additional adjuvants. Liposomes containing gp340 gave specific high titre antibodies after i.p. or i.v. administration, and the addition of lipid A to the liposomes resulted in a significant enhancement of the response. Antibodies generated by the above procedure were virus neutralising and bound gp340 specifically. These findings indicate an advantageous approach for use with a prototype vaccine for the prevention of EB virus infection.

Binding of adult T-cell leukemia virus to various hematopoietic cells

A newly found human retrovirus, adult T-cell leukemia virus (ATLV) was shown by means of membrane immunofluorescence to bind to various hematopoietic cells including T-, B- and non-T, non-B-cell lines. Partially purified viral gp46 from culture fluids of ATL virus producer lines also bound efficiently to an ATLV-negative T-cell line, CCRF-CEM cells. When the viruses were pre-incubated with anti-ATLV-positive human sera, ATLV binding to the cells was clearly inhibited but not by pre-incubation with anti-ATLV-negative sera. These data suggest that: (1) ATLV binds not only to T-cells but also to multiple types of cells of hematopoietic origin; (2) anti-ATLV antibody-positive human sera have the blocking antibody for the binding of ATLV to lymphoid cells.

Identification of polypeptide components of the Epstein-Barr virus early antigen complex with monoclonal antibodies

Three monoclonal antibodies were produced against the Epstein-Barr virus-induced early antigen complex. These antibodies were shown to be specific for the early antigen complex by the fact that they only reacted with cells supporting a permissive or abortive Epstein-Barr virus infection and their synthesis was not affected by inhibitors of viral DNA synthesis. One monoclonal antibody, designated R3, was directed against a diffuse component of the early antigen complex since it reacted by immunofluorescence with cells fixed in acetone or methanol. The other two monoclonal antibodies, designated K8 and K9, reacted with a methanol-sensitive restricted component of this complex. The appearance of the R3 antigen in P3HR-1 superinfected Raji cells occurred approximately 4 h earlier than the antigen detected by K8. By both sodium dodecyl sulfate-polyacrylamide gel electrophoresis and radioimmunoelectrophoresis, it was determined that the R3 monoclonal antibody recognized two major polypeptides with molecular weights of approximately 50,000 to 52,000, whereas K8 and K9 precipitated a protein of approximately 85,000. The R3 monoclonal antibody also immunoprecipitated an in vitro primary translation product. It was, therefore, possible to map this product to the Epstein-Barr virus DNA BamH1 M fragment. These in vitro products were slightly smaller than the in vivo proteins, suggesting that these proteins probably undergo posttranslational modification during the virus replication cycle.

Effects of DNA synthesis inhibitors on early antigen expression following primary infection or superinfection by Epstein-Barr virus

Seven lymphoid cell lines previously characterized with respect to their resident Epstein-Barr virus (EBV) genome content were infected or superinfected with concentrated EBV from supernatant of the P3HR-1 cell line. Immunofluorescence assays were conducted on smears 48 hours after infection, using human sera containing antibodies to EBV early antigen (EA). Two EBV nuclear antigen (EBNA) negative cell lines containing no detectable resident EBV DNA and five EBNA positive cell lines containing EBV genomes were tested. The cell lines did not spontaneously express EBV EA (i.e., they were non-producers). All cell lines responded to infection or superinfection with EBV by expressing EA. Treatment of the cell lines with arabinosylcytosine (Ara-C) 10 micrograms/ml, at the time of infection resulted in significant decreases in the number of cells expressing detectable EA after drug treatment in all cell lines (72 +/- 5 percent inhibition of EA expression). Experiments were also conducted with hydroxyurea (HU) and phosphonoacetic acid (PAA). It was found that treatment with HU (100 micrograms/ml) inhibited EA production in cell lines containing EBV genome copies by 81 percent as compared to the superinfected cultures receiving no drug. In primary infection of EBNA negative cell lines, HU had minimal effects. PAA (100 micrograms/ml), on the other hand, had very little effect on EA expression following superinfection of cell lines harboring the EBV genome, but reduced the EA expression after primary infection of EBNA negative cell lines by 70 to 80 percent. All drugs were used at concentrations having little effect on RNA and protein synthesis. However, HU and Ara-C significantly reduced DNA synthesis and cell division in the treated cultures.

p105, an Epstein-Barr virus-induced, phosphonoacetic acid-insensitive glycoprotein target of the anti-Epstein-Barr virus immune response

To describe structures and biological functions of targets for antibody-mediated immune responses to Epstein-Barr virus (EBV)-infected lymphoid cells, we have characterized a membrane-associated protein of 105,000 daltons, p105, which was prominently recognized in immunoprecipitates with some EBV antigen-reactive patients' sera. A rabbit antiserum to immunopurified p105 was developed. [35S]methionine-labeled p105 was specific to EBV-superinfected Raji cells, and its synthesis was not blocked with phosphonoacetic acid, indicating that it is an "early" viral antigen. Phosphonoacetic acid treatment of EBV-superinfected Raji cells was associated with the accumulation, mainly in the cytosol, of an 88,000-dalton protein, p88, which was also recognized with anti-p105 serum, but was not detected in superinfected cells which had not been treated with phosphonoacetic acid. Although anti-p105 serum immunoprecipitated a membrane fraction protein, it did not neutralize P3HR-1 virus and was not considered to be an exposed virion component. We conclude that p105 is an early, EBV-induced, membrane fraction antigen to which EBV-infected patients generate a substantial antibody response.

Mapping of polypeptides encoded by the Epstein-Barr virus genome in productive infection

Over 30 viral-specified polypeptides are translated in vitro from RNA of cells productively infected with Epstein-Barr virus (EBV). The polypeptides map to sites in EBV DNA by hybrid selection. Almost all of the polypeptides are reactive with EBV immune human serum. Several of the polypeptides are part of the early antigen complex. Two others are likely to be major structural components of the virus. Genes encoding persistent early and late polypeptides are intermixed through most of the EBV genome.

Monoclonal antibodies to Epstein-Barr virus-induced, transformation-associated cell surface antigens: binding patterns and effect upon virus-specific T-cell cytotoxicity

Spleen cells from mice immunized with Epstein-Barr virus-transformed lymphoblastoid cells (EB-LCL) were used to generate monoclonal antibodies to cell surface antigens associated with the EB virus-transformed state. Radioimmune and immunofluorescence binding assays identified two antibodies, MHM6 and AC2, which reacted consistently with all EB-LCL tested, with a subpopulation of cells in some but not all EB virus genome-positive Burkitt lymphoma lines, but with none of a range of EB virus genome-negative cell lines of lymphoma or leukaemia origin. While MHM6 appeared to bind an EB virus-related antigen, AC2 bound some other cell surface antigen which was also found on a small subpopulation of cells in lymphocyte cultures stimulated with phytohaemagglutinin or with pokeweed mitogen. MHM6 and AC2 recognized single polypeptides with apparent molecular weights of 45 kd and 80 kd respectively as shown by sodium dodecylsulphate polyacrylamide gel electrophoresis (SDS-PAGE) analysis of 125I-labeled cell surface polypeptides immunoprecipitated with these antibodies. These polypeptides were induced on experimentally-infected B cells within 24 h of the expression of the EB virus nuclear antigen, EBNA, at a time known to coincide with the appearance of the lymphocyte-detected membrane antigen, LYDMA. However, saturating concentration of MHM6 and AC2 were unable to protect EB-LCL target cells from lysis by LYDMA-specific cytotoxic T cells in a chromium-release assay.

Characterization of the Epstein-Barr virion-associated DNA polymerase as isolated from superinfected and drug-stimulated cells

We reported previously that Epstein-Barr (EB) virions and detergent-treated nucleocapsids co-purified with significant amounts of DNA polymerase activity that did not resemble other known host or viral polymerases. We report here that this species of DNA polymerase activity is present at early times after infection in lymphocytes abortively lytically infected (superinfected) with EB virus. However, studies with [35S]methionine labeling suggest de novo synthesis of enzyme has not occurred. Conversely, drug-stimulated lymphocytes that synthesize EB viral late proteins and virions contain this species of polymerase to the virtual exclusion of all others. This EB viral polymerase shows a marked preference for nicked and gapped double-stranded rather than primed single-stranded DNA templates. Its processiveness as measured on primed theta X174 phage DNA template is lower than that of lymphocyte beta polymerase. The data reported here are consistent with the hypothesis that the EB virion-associated DNA polymerase is synthesized at late times in the viral life cycle as are other structural proteins but it plays an important role early after viral infection. It is known that mature herpes virion DNA (including that of EB virus) is nicked and gapped and we propose that virion polymerase repairs the viral DNA at an early stage in infection before viral DNA replication begins.

Epstein-Barr virus membrane antigens: characterization, distribution, and strain differences

The Epstein-Barr virus (EBV)-associated membrane antigen polypeptides (350,000, 220,000, 140,000, and 85,000 daltons) are recognized by a rabbit anti-EBV serum and are present on the plasma membranes of producer cell lines, as we demonstrated previously. In this report, we show that these polypeptides are present on intact virus particles. Subcellular fractionation revealed that these antigens are distributed throughout the cell, except for the 85,000-dalton protein, which was poorly represented in the nuclear fraction. In addition, an EBV-associated protein of 160,000 daltons, which comigrates with a major component of the viral capsid, was detected in the cytoplasmic and nuclear fractions. The immunoprecipitation patterns of 13 different EBV isolates were similar, with two exceptions. First, the 350,000- and 220,000-dalton polypeptides from marmoset cell lines had slightly larger molecular sizes than the corresponding polypeptides from human cell lines. Second, B95-8 virus and B95-8-derived human and marmoset cell lines contained little of the 220,000-dalton protein; however, 883L, the human parent line of B95-8, has a normal amount of the 220,000-dalton protein. Thus, the B95-8 strain of EBV appears to be a structurally defective variant. We have not observed any variation in protein patterns associated with different EBV disease states. The 350,000-, 220,000-, and 85,000-dalton polypeptides were shown to be glycoproteins by incorporation of [3H]mannose and [3H]glucosamine and to contain N-asparagine-linked glycosyl groups by their sensitivity to tunicamycin. To simplify future work, the following nomenclature for these EBV-associated polypeptides is suggested: 350,000 (gp350), 220,000 (gp220), 160,000 (p160), 140,000 (p140), and 85,000 (gp85).

Observations on the EB virus envelope and virus-determined membrane antigen (MA) polypeptides

Experiments have been carried out to identify the polypeptide components of the Epstein-Barr (EB) virus-determined membrane antigen (MA) complex. Cells were radioiodinated using lactoperoxidase and the 125I-labelled surface antigens, released by Triton X100, were analysed by sodium dodecyl sulphate polyacrylamide gel electrophoresis (SDS-PAGE) after complexing either with human sera having anti-MA activity or with a rabbit antiserum to EB virus. Using cells carrying EB virus isolated from four different conditions, including for the first time nasopharyngeal carcinoma (NPC), we have demonstrated four major polypeptides. One, with a molecular weight of 85,000, was remarkedly constant irrespective of the cell line from which it came; two, with molecular weights varying from 240,000 to 270,000 and from 320,000 to 340,000, showed minor differences in mobility apparently depending on the species of origin of the cells (human or marmoset), rather than disparity between strains of virus. A fourth component, of 160,000 daltons, was found on only two of the cell lines studied. In addition, it has been shown for the first time that the same polypeptides composing the MA complex are present on the viral envelope itself. The fact that the rabbit antiserum to EV virus recognized only the two highest molecular weight MA components, yet showed virus-neutralizing activity, indicates the importance of these two polypeptides for use in a vaccine designed to induce virus-neutralizing antibodies.

Differential inhibition of Epstein-Barr virus induction by the amino acid analogue, L-canavanine

The effect of an amino acid analogue, L-canavanine, on the synthesis of Epstein-Barr virus (EBV) antigens was investigated in lymphoblastoid cells. The analysis revealed that after infection of BJAB and NC-37 cells with P3HR-I EBV synthesis of early antigen (EA) was not affected by canavanine in concentrations up to 8.4 mM. The synthesis of EBV-determined nuclear antigen (EBNA) and of viral capsid antigen (VCA) was significantly inhibited at concentrations higher than 2.8 mM. Spontaneous induction of EA in P3HR-I cells was not affected by canavanine. On the other hand, EA induction by the tumor promoter TPA resulted in some viral antigen induction depending on the time period of TPA exposure. Pretreatment of the cells overnight with canavanine followed by washing and addition of the tumor promoter did not suppress EA induction by TPA. These data support the concept that EA induction by superinfection follows a different pathway from antigen induction by chemical inducers.

IgM antibodies to Epstein-Barr virus-associated membrane antigen in sera of infectious mononucleosis patients

By the indirect immunofluorescence technique, IgM antibodies to the cell surface of an Epstein-Barr virus (EBV) producer cell line, P3HR-1, were detected in sera from infectious mononucleosis (IM) patients but not in sera from patients with Burkitt lymphoma or nasopharyngeal carcinoma nor in sera from healthy adult donors having antibodies to EBV-specific viral capsid antigen (VCA). Titers of the IgM antibodies were higher in the earlier stages of IM, a pattern similar to that for IgM antibodies to VCA. The IgM antibodies to the cell surface were identified as being those against the EBV-specific membrane antigen (MA) by the following criteria: (1) The antibodies were reactive to MA-positive cell preparations but to MA-negative cell preparations. (2) Titers of the IgM antibodies were not significantly affected after absorption of sera with sheep red blood cells which could completely eliminate heterophil antibodies in the same sera. Detection of the IgM antibodies to MA may have a particular diagnostic value for providing evidence of a recent EBV infection.

Infection and persistence of varicella-zoster virus in lymphoblastoid Raji cell line

Infection of Raji cells by varicella-zoster virus (VZV) resulted in permissive infection with establishment of a persistently infected lymphoblastoid cell line. VZV antigens of the membrane and nuclear type, as detected by the indirect immunofluorescence membrane antigen (IFAMA) and anticomplement immunofluorescence (ACIF) tests, were observed. Minute amounts of infectious virus were detected by co-cultivation of VZV-infected Raji cells (Raji-VZV), with permissive human embryo fibroblasts (HEF). The virus isolated was found to be similar to the parent strain. Transient induction of Epstein-Barr viral capsid antigen (EB-VCA) was also observed. The persistently infected Raji-VZV cell line, when free of EB-VCA, was found suitable for measuring antibodies to varicella-zoster virus. The possible interaction in the infected Raji cells between EBV, which is implicated in human malignancy, and VZV which belongs also to the herpes group of viruses, is discussed.

Abortive expression of the Epstein-Barr virus (EBV) cycle in a variety of EBV DNA-containing cell lines, as reflected by nucleic acid hybridization in situ

A variety of Epstein-Barr virus (EBV) DNA-containing cell lines have been tested for the expression of the EBV-associated antigens EBNA (nuclear antigen), EA (early antigen), and VCA (viral capsid antigen), and for the presence of cells containing disproportionate amounts of EBV DNA. The antigen tests utilized immunofluorescence and 125I-labelled antibodies combined with autoradiography. EBV-DNA was detected by in situ hybridization with 3H-labelled EBV RNA complementary to P3HR-1 EBV DNA (P-EBVcRNA). The P-EBVcRNA has been shown to represent the majority of the P3HR-1 EBV DNA sequences. It was concluded that EBV DNA-containing cell lines can be divided into those that express only EBNA, those that express EBNA and EA and those that express EBNA, EA and VCA and also contain cells that undergo disproportionate EBV DNA synthesis. Consequently, in some cell lines there is an abortive expression of the EBV cycle in that some cells spontaneously express EA but fail to continue further to viral DNA synthesis. A similar pattern can be found after experimental induction of the EBV cycle, suggesting that related mechanisms govern the spontaneous expression of the EBV cycle and the extent of its inducibility.

Epstein-Barr virus-induced membrane antigens: immunochemical characterization of Triton X-100 solubilized viral membrane antigens from EBV-superinfected Raji cells

In an attempt to qualitatively identify the membrane antigen (MA) complex induced by Epstein-Barr virus (EBV) infection of lymphoblastoid cells, superinfected Raji cells were surface labelled with 125I by the lactoperoxidase method and solubilized with Triton X-100, then the 125I-labelled membrane proteins were precipitated by sera containing high antibody titers to MA. Analysis of these immune precipitates on sodium dodecyl sulfate polyacrylamide gel eletrophoresis identified four major EBV-specific membrane proteins with molecular weights (mol. wt) of 280,000, 250,000, 170,000 and 90,000. Sera from patients with Burkitt's lymphoma (BL), nasopharyngeal carcinoma (NPC) and infectious mononucleosis (IM) and from EBV-infected disease-free individuals showed differential patterns of reactivity to these antigens with some sera only recognizing three or less of the antigens. The results from invesigations with these sera also indicated that these major proteins were not related to EBV-induced viral capsid antigens (VCA) or the virus-associated early antigen (EA) complexes as defined by immunofluorescence. Metabolic labelling of EBV-infected Raji cells with [14C]glucosamine, followed by Triton X-100 solubilization and radioimmune precipitation, identified the 280,000, 250,000 and 90,000 components as glycoproteins. The lactoperoxidase-labelled 170,000 molecular weight component was not significantly glycosylated and, therefore, could not be categorized as a glycoprotein on the basis of this study. In addition, a glycoprotein with a mol. wt of 130,000 was identified by this approach which also appeared to be specified by EBV. The results from these investigations, therefore, indicated that the EBV-induced MA complex was composed of four major glycoproteins and one nonglycosylated high mol. wt protein.

Interaction of the B95-8 and P3HR-1 substrains of Epstein-Barr virus (EBV) with peripheral human lymphocytes

Two substrains of the Epstein-Barr virus derived from the B95-8 and P3HR-1 cell lines were studied for their interaction with human peripheral lymphocytes. It has been previously shown that B95-8 virus has and P3HR-1 virus lacks lymphocyte-transforming ("immortalizing") properties. DNA stimulation induced by B95-8 virus showed a good correlation with the number of surface Ig-positive cells. P3HR-1 virus added before B95-8 virus completely abolished the stimulation of DNA synthesis. It also prevented EBNA induction by B95-8 virus. P3HR-1 virus added after B95-8 virus diminished DNA stimulation by the latter in a time-dependent fashion. P3HR-1 virus did not inhibit DNA stimulation by phytohaemagglutinin but was inhibitory if added before a B cell mitogen (Staphylococcus Aureus). The origin of P3HR-1 virus and its relationship to the transformation process are discussed.

Relationship between Epstein-Barr virus (EBV)-production and the loss of the EBV receptor/complement receptor complex in a series of sublines derived from the same original Burkitt's lymphoma

Virus production, EBV (P3HR-1 substrain) superinfectability, IdUrd inducibility, EBV receptor and complement (C3) receptor expression were assessed in two independently maintained jijoye lines, the derived P3HR-1 clone that releases a growth inhibitory and cytopathic, non-transforming viral mutant, and in non-producer sublines derived from the P3HR-1 line by the spontaneous cessation of virus production. Both jijoye lines were superinfectable, inducible, and carried EBV and C3 receptors. Virus-producing P3HR-1 cells and recently derived non-producer sublines lacked EBV-receptors and C3 receptors, could not be superinfected, but were IdUrd inducible. Two long-passaged, non-producer sublines of P3HR-1 reexpressed EBV and C3 receptors to an equal degree (different in the two sublines). EBV-superinfectability became partially reestablished in the subline with the higher expression of EBV and C3 receptors. These findings support the hypothesis that the EBV-receptor/C3 receptor negativity of the producer P3HR-1 sublines and their recent non-producer derivatives is due to negative selection by the growth-inhibitory, cytopathic P3HR-1 virus variant. The closely linked disappearance and reappearance of EBV-receptors and complement receptors gives further support to the idea that these two receptors are either identical or closely linked constituents of the cell membrane.

Production of rabbit antibodies against the viral capsid antigen (VCA) of the Epstein-Barr virus (EBV)

Rabbits were immunized with nuclear or cytoplasmic extracts of the Epstein-Barr virus (EBV)-producing marmoset cell line B95-8. Following extensive absorption with human EBV-negative cells (HeP-2, Ramos and BJAB), sera were obtained that no longer reacted with cellular or serum proteins of human origin, but gave a single precipitin band with extracts of the human EBV-producing line, P3HR-1. Immunofluorescence tests performed with appropriate parallel human serum controls showed that the rabbit serum contained no activity against EBNA + EA - VCA - Raji cells, or against P3HR-1 virus superinfected, cytosine arabinoside-treated Raji cells that contained EBNA and EA, but not VCA. The sera gave a brilliant indirect immunofluorescence reaction with the virus-producing (EBNA+ EA+ VCA+) P3HR-1 lines. Two-color fluorescence tests, performed with a direct TRITC-labelled VCA conjugate and indirect FITC-staining with the rabbit serum, showed that the same cells reacted in both red and green fluorescence, confirming that the rabbit serum was directed specifically against some antigen formed in the virus-producer cells. Since the synthesis of the relevant antigen was prevented by cytosine arabinoside it cannot be EA and must be a late antigen. The morphology and localization of the antigen support the conclusion that the antigen is VCA or some part of the VCA complex.

Detection of Epstein-Barr virus antigens and antibodies by peroxidase-labeled specific immunoglobulins

Detection of the Epstein-Barr (EBV) antigens, early antigen (EA), viral capsid antigen (VCA), and nuclear antigen (EBNA) by the indirect immunoperoxidase technique was highly sensitive. Antibody titers to EBNA, EA, and VCA were determined in more than 25 sera of patients with Burkitt lymphoma (BL), nasopharyngeal carcinoma (NPC), or normal persons. A good correlation between the titers of these antigens was obtained by the immunoperoxidase and immunofluorescence methods. The indirect (anti-IgG) immunoperoxidase technique for the detection of EBNA is, in contrast to the indirect immunofluorescence method, highly sensitive. EBNA was associated with the chromosomes in cells arrested in the metaphase with colchicine.

Differential induction of Epstein-Barr virus-related antigens in heterokaryon cultures

Different paterns of induction of Epstein-Barr virus (EBV)-related antigens were observed in heterokaryons produced by Sendai virus-mediated fusion of producer and non-producer human lymphoblastoid cells with various other cell types. EBV-related early antigens (EA) and viral capsid antigen (VCA) could obviously be induced in heterokaryons between producer cells (P3HR-1 and QIMR-WIL), normally expressing these natigens at very low frequency, and human FL or HeLa cells. Positive cells were detected as early as 3 h after fusion and there often followed a rapid increase in positive cells. In contrast, in heterokaryons between non-producer cells (Raji and NC-37) and FL or HeLa cells, only EA but not VCA was induced. EA induction was also evident in fusion of human lymphoblastoid cells with monkey cells (Vero) but with mouse cells (L-M(TK-) C11D and MCB-2) no EBV induction occurred. The EBV induction in heterokaryons was significantly enhanced by 5-iododeoxyuridine treatment.

Cell-killing by Epstein-Barr virus: analysis by colony inhibition procedure

The P3HR-1 and B95-8 strains of Epstein-Barr virus (EBV) were cytocidal for EBV-carrier human cell lines, as revealed by a colony inhibition procedure. The cytocidal activity was proportional to virus dose added. The cell killing was neutralized by anti-EBV antibody-positive but not -negative human sera. When the relative sensitivity to ultraviolet light of EBV activities was examined, the cytocidal actitivy was much more resistant than the viral infectivity as assayed by early antigen-forming activity (P3HR-1 virus) or leukocyte-transforming activity (B95-8 virus), but it closely paralleled the ability to adsorb to cells.

Persistence of Epstein-Barr viral nuclear antigen (EBNA) in cells entering the EB viral cycle

It was shown by double immunofluorescence studies that Epstein-Barr viral nuclear antigen (EBNA) was preserved in EBV-infected cells after they had entered the productive viral cycle, as signalled by the appearance of the early antigen (EA)complex. A nuclear component of the EA comples could be clearly distinguished from EBNA with regard to antigenic specificity.

Analysis of cell-surface markers with staphylococcal protein A: fluorescence studies on mammalian lymphoid determinants

Membrane antigens including different classes of immunoglobulins, transplantation antigens, beta2-microglobulin, T lymphocyte specific antigens, and virally determined surface components were investigated using fluorescein-labeled Staphylococcal protein A in combination with cytofluorometric studies. Lymphocytes of seven species: mouse, rat, guinea pig, pig, cow, monkey, and human, and of ten human lymphoma-derived lines were tested. Analysis of the differential expression of surface markers revealed a reproducible reaction of protein A with cell-surface Fc of IgG actively produced by lymphoid cells from human, monkey, guinea pig, and pig, and with passively attached IgG molecules in the form of antibodies, directed against cell surface antigens of all lymphoid cells tested. No surface Ig was detected on so-called T lymphocytes. The distribution of cell-bound Ig density among surface Ig-positive cells was found to be different depending upon the origin of the cells with regard to lymphoid organ; it was parallel among the lymphoma lines tested and on peripheral blood cells from human, monkey, and pig, although large variations in fluorescence intensity among individual cells and among the different lines were recorded. Beta2-microglobulin determinants were found equally well on enriched human T and B cells. Transplantation, and T lymphocyte-specific antigens were detected on the majority of the lymphoid cells and on a restricted population respectively.

Burkitt's lymphoma - a human tumor model system for immunological studies

Burkitt's lymphoma occurs mainly in parts of tropical Africa and has attracted the attention of experimental workers due to its epidemiological and clinical features, which indicate a viral etiology and a host immune response to the tumor. As a result of virological studies, Epstein-Barr virus (EBV) DNA has been demonstrated in almost all tested biopsies of African BL. This contrasts to the absence of EBV in all, or almost all, of the non-African Burkitt's lymphoma-like tumors, even though the number of tested tumors in this group is small, and to the lack of EBV in all other types of lymphoma or leukemia. Immunological studies have revealed the presence of antibodies to different EBV-associated antigens in all African patients with Burkitt's lymphoma. However the antibodies are not specific for Burkitt's lymphoma but are found in most adults all over the world, although at lower levels. They cannot therefore serve diagnostic purposes, but they can give prognostic information and occasionally give clues to the mechanisms behind late tumor recurrences, and possibly guide so-called immunotherapy. Burkitt's lymphoma patients contrast to appropriate control groups where some of the persons are anti-EBV seronegative, and this, together with the presence of EBV in Burkitt's lymphoma biopsies and the absence of EBV in other lymphomas, even though the cell type involved may be infectable by EBV in vitro and the tumor may arise in an EBV-carrying person, favors an etiological role in EBV in Burkitt's lymphoma and speaks against the "passenger" hypothesis, according to which EBV is picked up by the Burkitt's lymphoma cell which happens to be particularly suitable for EBV persistence. To explain the geographical distribution, a cofactor, such as certain forms of malaria, has been implied.

Antibodies to Epstein-Barr virus in patients with Hodgkin's disease and leukemia

Sera from 67 Hodgkin's disease patients, 71 leukemia patients, and 186 healthy subjects were tested for antibodies to Epstein-Barr (EB) viral antigens by immunofluorescence methods. In both disease categories, in particular Hodgkin's disease patients, levels of antibodies to the viral capsid antigen (EBV-VCA) and MGT were higher than in the healthy controls. Significantly higher titers were found in Jewish patients of Asian-African origin, as compared to Jews of European origin, with Arab patients as intermediates. The effect of ethnic origin was independant of age and histopathologic type. Sex had no effect on titer. Inconsistent differences in titer were found between age groups in the various ethnic-histopathologic type groups. Some of the leukemia patients had no detectable antibodies to EBV, while all Hodgkin's disease patients showed previous contact with EB virus. Antibodies to the early antigen (EBV-EA) were found in 27% of Hodgkin's and 37% of leukemia patients, and in none of the healthy controls tested.

Ultraviolet inactivation of Epstein-Barr virus: effect on synthesis of virus-associated antigens

The relative sensitivity to ultraviolet (UV) light of genome functions of the P3HR-1 strain of Epstein-Barr virus (EBV) was studied. The formation of viral capsid antigen (VCA) appeared to be more sensitive than that of early antigen (EA), while the synthesis of membrane antigen (MA) was most resistant, as seen on examination in the presence of cytosine arabinoside (Ara-C). However, the appearance of both VCA and EA, but not that of MA, was delayed with UV-irradiated virus, in either the presence or absence of Ara-C. The synthesis of EA and VCA induced by UV-irradiated virus was suppressed in the presence of Ara-C, while that of MA was not.