Sensitivity of different target cells to the killing action of peripheral lymphocytes stimulated by autologous lymphoblastoid cell lines

CD4 + T cells are found within endemic Burkitt lymphoma and modulate Burkitt lymphoma precursor cell viability and expression of pathogenically relevant Epstein-Barr virus genes

Endemic Burkitt lymphoma (eBL) is an aggressive B cell cancer characterized by an IgH/c-myc translocation and the harboring of Epstein-Barr virus (EBV). Evidence accumulates that CD4 + T cells might contribute to eBL pathogenesis. Here, we investigate the presence of CD4 + T cells in primary eBL tissue and their potential dichotomous impact on an EBV-infected pre-eBL cell model using ex vivo material and in vitro co-cultures. In addition, we establish a novel method to study the effect of IgH/c-myc translocation in primary B cells by employing a CRISPR/Cas9 knock-in approach to introduce and tag de novo translocation. We unprecedently document that CD4 + T cells are present in primary eBL tumor tissue. Furthermore, we demonstrate that CD4 + T cells on the one hand suppress eBL development by killing pre-eBL cells lacking IgH/c-myc translocation in vitro and on the other hand indirectly promote eBL development by inducing crucial EBV Latency III to Latency I switching in pre-eBL cells. Finally, we show that while the mere presence of an IgH/c-myc translocation does not suffice to escape CD4 + T-cell-mediated killing in vitro, the CD4 + T-cell-mediated suppression of EBV's Latency III program in vivo may allow cells harboring an IgH/c-myc translocation and additional mutations to evade immune control and proliferate by means of deregulated c-myc activity, resulting in neoplasia. Thus, our study highlights the dichotomous effects of CD4 + T cells and the mechanisms involved in eBL pathogenesis, suggests mechanisms of their impact on eBL progression, and provides a novel in vitro model for further investigation of IgH/c-myc translocation.

Lymphoblastoid cell lines and Burkitt-lymphoma-derived cell lines differ in the expression of a second Epstein-Barr virus encoded nuclear antigen

Twenty-seven Epstein-Barr virus (EBV)-transformed lymphoblastoid cell lines and 27 EBV-carrying Burkitt-lymphoma-derived lines were analyzed for expression of the second EBV-encoded nuclear antigen (EBNA-2) by immunoblotting and anticomplement immunofluorescence with EBNA-2-specific sera. While all lymphoblastoid cell lines expressed EBNA-2, only 10 of the 27 BL lines were EBNA-2-positive. Comparison of the EBNA-2 coding BamHI W-, Y- and H-fragments of EBV-DNA in the different cell lines by restriction enzyme analysis suggests that EBNA-2 negativity is due either to sequence diversity or to a deletion in the BamHI WYH region.

Regulation of the growth of Epstein-Barr virus-infected B cells: temporal profile of the in vitro development of three distinct cytotoxic cells

The time course of the appearance of cytotoxic cells was examined in cocultures of E-rosetting (E+) cells and EBV-infected non-T cells (4:1 ratio) from the blood of VCA-positive healthy adults. Classical HNK-1+ NK cells were present at the initiation of the cultures and they produced 76 +/- 2% specific 51Cr-release from K-562 cells, but they did not effectively lyse the NK-resistant Daudi cells, nor did they kill autologous EBV-induced lymphoblasts (LCLEBV). The NK activity decreased during the first week in culture to 40 +/- 7% cytotoxicity. At the same time, nonspecific cytotoxic cells capable of killing Daudi as well as K562 developed and persisted into the third week in culture when it declined. This later nonspecific cytotoxicity was mediated by 4F2+, T8-, HNK-1- activated E+ cells. After 10 days in culture, killing of autologous LCLEBV increased continuously, from 4 +/- 3% at Day 10 to 38 +/- 4% by Day 22. The cytotoxicity to LCLEBV was mediated by classical T8+ CTL, and it was antigen specific and at least partially HLA Class I restricted. The regression of BEBV growth that occurs in E+/BEBV cocultures coincides with the development of this CTL-mediated cytotoxicity.

Differential activation of cytotoxic responses by Burkitt's lymphoma (BL)-cell lines: relationship to the BL-cell surface phenotype

Epstein-Barr (EB) virus-positive Burkitt's lymphoma (BL) cell lines, recently established from tumour biopsies and displaying chromosomal translocations indicative of their malignant origin, can be classified into two broad sets: (i) lines growing predominantly as single cells/small clumps whose cell surface markers remain close to those of the original tumour cells, and (ii) lines whose growth pattern and cell surface markers have progressed closer to the more "lymphoblastoid" phenotype displayed by all in vitro transformed B-cell lines (LCLs) of normal origin. When compared to LCLs derived from normal B cells of the same patient, BL-cell lines in set (i) generally showed a lower expression of HLA class I and class II antigens and a reduced ability to activate both allospecific and nonspecific (natural killer-like) cytotoxic responses when cocultured with peripheral blood lymphocytes. By contrast, the HLA antigen expression and in vitro stimulatory capacity of most BL-cell lines in set (ii) were much closer to the values displayed by their corresponding LCLs. Since set (i) rather than set (ii) BL cell lines are phenotypically representative of the malignant cells as they exist in vivo, this work suggests that successful outgrowth of the virus-carrying tumour cells in the affected host may be facilitated by the inability of these cells to stimulate strong cytotoxic responses.

Selective reactivation of Epstein-Barr virus-specific cytotoxic T cells by stimulation in vitro with allogeneic virus-transformed HLA-homozygous typing cells

Epstein-Barr (EB) virus-specific cytotoxic T-cell preparations, produced by stimulation in vitro of peripheral blood lymphocytes with the autologous virus-transformed cell line, are HLA-A and B antigen-restricted and, with some donors, show preferential restriction through one or two of the four relevant antigens of the donor's HLA type. It has now been demonstrated that such EB virus-specific cytotoxic T cells may also be reactivated by stimulation with allogeneic virus-transformed cells provided that there is no mismatch of the HLA-A and B antigens between the responder and stimulator cell donors. In particular, virus-transformed cell lines from HLA-homozygous donors HLA-A and B antigen-matched to one of the haplotypes of an HLA-heterozygous responder were shown to reactivate selectively only those EB virus-specific cytotoxic T cells restricted through the HLA-A and B antigens present on the allogeneic stimulating cells. In addition to confirming the polyclonal nature of the HLA-restricted EB virus-specific cytotoxic T-cell response, this new experimental procedure has allowed the production, and subsequent expansion as cell lines dependent upon T-cell growth factor, of those effector cells restricted through the "nonpreferred" HLA antigens that are poorly represented in the response induced by stimulation with autologous virus-transformed cells.

Expression of Helix pomatia (HP) haemagglutinin receptors on cytolytic lymphocytes activated in mixed cultures

The expression of receptors for Helix pomatia (HP) haemagglutinin, a T cell marker, was assayed on human lymphocytes cultivated with K562 or allogeneic lymphocytes. The receptor was detected on the cells after neuraminidase treatment by reactivity with FITC conjugated HP. By affinity chromatography the lymphocyte populations were separated into 3 subsets: (1) a subset which did not attach to the lectin column; (2) and (3) two subsets attaching with different avidities, and therefore eluting with different concentrations of the lectin-binding sugar hapten. The subsets were characterized for T cell markers, HP and E receptors, the B cell marker SIg and also for Fc receptors, and were tested for lytic potential against K562 and allogeneic blasts. A high proportion of HP receptor positive T blasts did not attach to the lectin column, and thus had low avidity HP receptors, confirming that activation of T lymphocytes is accompanied by decreased expression of T markers. The passed fraction which was enriched in blasts had the strongest cytotoxic function, while the fraction rich in cells with high avidity HP receptors and containing mainly small cells, had weak activity. This was true for both the anti-K562 and allospecific activities. Thus the phenotypic characteristics of the cells exerting the two types of lytic function were similar. The distribution of the lytic potential in the three subsets correlated with the presence of E and EA receptor positive blasts.

Cytotoxic T cell recognition of Epstein-Barr virus-infected B cells. I. Specificity and HLA restriction of effector cells reactivated in vitro

The experiments show that the phenomenon of regression, seen exclusively in Epstein-Barr (EB) virus-infected cultures of mononuclear cells from EB virus antibody-positive donors, is mediated by cytotoxic T cells reactivated in vitro and specifically recognizing an EB virus-induced lymphocyte-detected membrane antigen LYDMA. Thus, effector T cells from regressing cultures kill autologous EB virus-transformed cells but not autologous pokeweed mitogen-stimulates lymphoblasts nor any of a range of EB virus genome-negative human hemopoietic cell lines (K562, HSB2, BJAB, EB4) particularly sensitive to nonspecific natural killer-like activities. Moreover, these reactivated effector cells exhibit classical HLA restriction of target cell recognition; in a survey of 14 effector cell donors, preferential lysis of the autologous virus-transformed line was a consistent feature, while the relative degree of lysis of allogeneic lines was in general directly related to the number of HLA-A and B antigens shared between effector and target cells. The pattern of reactivity shown by effector T cell preparations from any one donor was strikingly reproducible, and the results from a number of donors revealed differences between particular HLA-A and B antigens with respect to the level of EB virus-specific killing which was associated with sharing through these determinants.

Interferon-induced NK augmentation in humans. An analysis of target recognition, effector cell recruitment and effector cell recycling

By combining a single-cell cytotoxicity assay in agarose with estimations of the maximal natural killer (NK) cell potential (Vmax) by 51Cr release, the mechanism behind interferon augmentation of human NK cells were analysed. The number of target-binding cells (TBCs) the fraction of active TBCs and NK cell recycling were studied after short-term interferon treatment. The results demonstrate a dual effect of interferon on human NK cells: effector cell recruitment and increased effector cell recycling. Both of these variables were increased when NK cells were tested against the standard target K-562 and against Daudi and BJAB cells, derived from B-type lymphomas. However, when T cell lines derived from acute lymphocytic leukaemia (Molt-4 and 1310) were used as targets, a larger fraction of active NK cells were found among untreated TBCs, whereas interferon treatment only resulted in increased effector cell recycling and not in effector cell recruitment. No increase in TBCs after interferon treatment could be detected with any cell line tested. The difference seen between T and non-T cell lines with regard to interferon-induced effector cell recruitment is discussed in relation to known characteristics of the human NK system.

Reactivation of Epstein-Barr virus-specific cytotoxic T cells by in vitro stimulation with the autologous lymphoblastoid cell line

Unfractionated mononuclear (UM) cells and T cells freshly prepared from the blood of adult donors were co-cultivated in microtest plate wells with progressively lower numbers of cells from the autologous EB-virus-transformed B-cell line. The fresh cells present in co-cultures from EB virus antibody-negative (seronegative) donors regularly facilitated autologous cell line outgrowth, monitored after 4 weeks, whereas outgrowth was markedly inhibited in the corresponding co-cultures from seropositive donors. Larger-scale co-cultures, set up at a ratio of 80-100 fresh UM cells to one autologous virus-transformed B cell, were harvested after 8 to 12 days and the T-cell subpopulation was examined for cytotoxicity both by growth inhibition and by chromium release assays. Cytotoxic T cells were generated exclusively in seropositive donor co-cultures and were strongly active against the autologous virus-transformed cell line without affecting either autologous uninfected B cells or any of a range of EB virus genome-negative target cell lines chosen as sensitive indicators of non-specific cytotoxicity. Recognition of allogeneic EB-virus-transformed cells was restricted to those whose HLA-A and/or B and/or B and/or C antigen expression matched that of the effector cells themselves;; moreover target cell lysis was specifically inhibited in the presence of monoclonal antibodies binding to these HLA antigens. The results indicate that EB-virus-specific HLA-restricted memory T cells, present in the blood of previously-infected individuals, can be reactivated in vitro using the established autologous virus-transformed cell line as a stimulus. THe reactivated cytotoxic cells appear to recognize a virus-induced lymphocyte-detected membrane antigen, LYD-MA, analogous to that first invoked to explain the cytotoxic response to primary EB virus infection observed during infectious monoucleosis.

Induction of natural killer cell activity and allocytotoxicity in human peripheral blood lymphocytes after mixed lymphocyte culture

The K-562 tumour cell is a highly susceptible target for natural killer (NK) cell lysis by lymphocytes of human peripheral blood. We have studied the antigenic relationship between the recognition sites for lysis of lymphoid and various tumour target cells by cytolytic T lymphocytes (CTL) and NK cells induced in mixed lymphocyte cultures (MLC). The characteristics of these two effector cell types have also been investigated. It was demonstrated that fresh NK cells lose their NK lytic activity when cultured alone. Cell lines not susceptible to lysis by fresh NK cells are lysed by MLC-induced NK cells. There is no antigenic relationship between the recognition sites for the alloreactive T lymphocytes and MLC-generated NK cells expressed on the lymphoid target cells and the tumour target cells, respectively. The MLC-generated alloreactive T cells and NK cells are not identical. The MLC-generated NK cells are different from the fresh NK cells present in the peripheral blood.

Tumor biopsy cells participating in systems in which cytotoxicity of lymphocytes is generated. Autologous and allogeneic studies

Freshly separated tumor cells from sarcomas and carcinomas were used in various roles in lymphocyte-target cell interaction assays. They were poorer allogeneic stimulators than lymphocytes. They were however good allotargets for the cytotoxicity generated in mixed lymphocyte cultures. They were also killed as third party targets by lymphocytes activated in MLC. In a proportion of experiments, lymphocytes activated in MLC killed autologous tumor cells. Autotumor killer effect was generated in the majority of mixed cultures containing lymphocytes and tumor biopsy cells from the same individual. Generation of cytotoxicity against K562 was a good measure of lymphocyte activation and could be used as a sensitive indicator for the occurrence of the recognition step in the mixed cultures. We propose that for the search of lymphocytes with specific receptors, activation is a more reliable parameter than specific cytotoxicity since the latter function is also influenced by the sensitivity of the target. The results confirmed that patients with carcinomas and sarcomas possess autotumor-reactive lymphocytes. These can be activated for cytotoxicity by in vitro confrontation with the tumor cells and occasionally through stimulation which is unrelated to the tumor cells.

Interferon production and activation of non-specific effector cells by stimulation with lymphoblastoid cell lines in vitro

A population of non-specific effector lymphocytes is generated in response to stimulation with lymphoblastoid cell lines (LCL). These cytotoxic cells have an activity analogous to that exhibited by natural killer (NK) cells. When lymphoid cells lines established by transformation with Epstein-Barr virus (EBV) are used to stimulate autochthonous T-cell-enriched lymphocytes, the activity against the NK-sensitive target, K562, is increased up to 14-fold. The stimulated T lymphocytes produce interferon, and this factor augments the cytotoxic activity of unstimulated cells. The size distribution of cytotoxic lymphocytes after stimulation with the autochthonous EBV line is unlike that of either T-cells or interferon-augmented T-cells. Autochthonous stimulated lymphocytes which kill K562 are of several size classes, and are included in populations containing large blast cells. In contrast, the K562 activity of both unstimulated T-cells and interferon-augmented T-cells is contained in a more discrete population of cells, just slightly larger than the majority of lymphocytes. Thus, the generation of non-specific effector cells during stimulation with lymphoblastoid cell lines appears to involve the activation of a population of blast-size cells in addition to those initially responsive to interferon augmentation.

Long-term maintenance of "cloned" human PLT cells in TCGF with LCL cells as a feeder layer

The long-term maintenance of T cells "cloned" by limiting dilution in TCGF was enhanced by the use of irradiated autologous lymphoblastoid cell line (LCL) cells as well as irradiated LCL cells of the individual to which the T cells were originally primed. It was possible to obtain more than 1 X 10(12) cells from a "clone" seeded at one cell per well. Some of the clones tested express primed LD-typing activity.

Long-term T-cell-mediated immunity to Epstein-Barr virus in man. III. Activation of cytotoxic T cells in virus-infected leukocyte cultures

Experiments have been conducted to determine the role played by immune T cells in the regression of EB-virus-induced transformation which is exclusively seen in leukocyte cultures from sero-positive donors. Kinetic studies suggest that, in virus-infected cultures from such donors, a population of T cells proliferates within the first 2 weeks apparently in response to the appearance of virus-infected B cells. This proliferation continues to some extent during the period of regression. Nonspecific induction of T-cell proliferation by PHA did not induce regression in virus-infected cultures from seronegative donors and acutally prevented the regression in seropositive donor cultures. T cells harvested from seropositive donor cultures 11-14 days post infection were generally much more inhibitory to the growth of the autologous EB-virus-transformed cell line than were T cells either freshly prepared from whole blood or harvested from corresponding uninfected cultures; this inhibitory activity was either absent or much diminished when assayed against allogeneic target cell lines. The results suggest that virus-specific memory T cells capable of mounting a cytotoxic response when properly challenged in vitro.

Lymphoblastoid cell lines are polyclonal activators of human T lymphocytes

Following stimulation with autologous or allogeneic lymphoblastoid cell lines (LCL) human T lymphocytes acquire two properties which suggest that LCL act as polyclonal activators. Cytotoxic activity, which has an antigen-specific component, is produced towards normal lymphocytes and LCL, and the cells become capable of mounting proliferative responses to antigens on human B lymphocytes which have accelerated secondary-type kinetics. Only weak responses to autologous cells occur. In addition, repeated restimulation with the original LCL leads to a progressive increase in the number of cells in the culture for a period of about 4 weeks. This approach may prove a useful way to grow large numbers of human T lymphocytes for further study.

Alloantigen-induced enhancement and suppression of human cytotoxic lymphocyte responses to autologous lymphoblastoid cell lines

In vitro sensitization of human lymphocytes to autologous lymphoblastoid cell lines (LCL) has been shown to give rise to cytotoxic lymphocytes capable of lysing autologous as well as allogeneic LCL cells. However, allogeneic LCL cells were found to be markedly less effective than autologous LCL cells in terms of generating lymphocytes capable of lysing autologous LCL cells. The addition of allogeneic LCL cells or allogeneic normal lymphocytes to a mixture of responding lymphocytes and X-irradiated autologous LCL cells suppressed the generation of cytotoxic lymphocytes against autologous LCL cells. Furthermore, suppressor T cells generated in allogeneic mixed leucocyte culture (MLC) and supernatants from MLC likewise decreased the generation of cytotoxic lymphocytes to X-irradiated autologous LCL cells. In contrast to the findings that alloantigens suppress the generation of cytotoxicity of X-irradiated autologous LCL cells, which ordinarily induce strong cytotoxic responses, were the findings that allogeneic stimulating cells and supernatants from MLC enhanced cytotoxic responses to autologous ultraviolet light or extensively heat-treated LCL cells that induce weaker cytotoxic responses. The possible mechanisms whereby alloantigens enhance or suppress cytotoxic responses to autologous abnormal cells and the implications of these findings are discussed.

Response of remission lymphocytes to autochthonous leukaemic myeloblasts

Thymidine incorporation in vitro by remission lymphocytes from a total of 6 patients with acute myeloid leukaemia (AML) was measured following stimulation by autochthonous and allogeneic AML blasts and cell lines. The early peak response to autochthonous blasts in 2 of these patients (48-72 h) is consistent with the concept of a population of lymphocytes pre-immunized to antigens carried by the blasts. Although stimulation in one patient was increased in the presence of more stimulating (S) blasts than responding (R) lymphocytes, positive responses in other tests were obtained at an S : R ratio of 1 : 1-5. When different methods of treatment of the stimulating autochthonous blasts were compared with untreated cells, mitomycin C gave the highest stimulation indices 2 out of 3 tests. Tissue culture medium in which autochthonous blasts had been incubated for 3-5 days failed to stimulate either remission lymphocytes alone, or combined cultures of lymphocytes with autochthonous or allogeneic blasts, suggesting that mitogenic factors released from autochthonous blasts are not responsible for lymphocyte stimulation. Treatment of autochthonous or allogeneic AML blasts with glycine-HC1(pH 3-0) to remove putative "blocking" factors failed to increase the stimulatory capacity of the leukaemic blasts.

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.

Long-term maintenance in vitro of human T cells by repeated exposure to the same stimulator cells. Differences when using repeated stimulation in allogeneic mixed leukocyte culture and when using stimulation with autologous lymphoblastoid cells

Cells from one-way human mixed leukocyte cultures (MLC) which had reverted to small lymphocytes after 2 weeks' incubation responded with accelerated kinetics and higher thymidine incorporation on restimulation with lymphocytes or lymphoblastoid cell line (LCL) cells having relevant antigens. In contrast to fresh lymphocytes, they did not respond to autologous LCL cells. Cultures could be restimulated every second week with relevant allogeneic lymphocytes and could thus be maintained for periods of up to 4 months. Almost all these cultured cells had T-cell characteristics, during stimulation as well as in their reverted phase. The response to phytohemagglutinin (PHA) successively disappeared with repeated allogeneic restimulation, whereas the response to the relevant lymphocytes and cells of related donors was maintained. When lymphocytes had been stimulated with autologous LCL cells, the restimulation response was accelerated, although lower than after the primary stimulation. Restimulated cultures could not be maintained by further restimulation. Allogeneic and autologous LCL were equally efficient restumulators. A low level of stimulation was also achieved with allogeneic lymphocytes. The PHA response was usually reduced.

Stimulation of normal lymphocytes with autologous lymphoid cell lines: properties of derived killer cells

Lymphocytes from normal adults, with or without serological signs of previous Epstein-Barr virus (EBV) infection, could be stimulated to proliferate and produce killer cells by incubation with autologous EBV-genome-positive lymphoid cell lines (LCLs). The stimulated cells were most probably of T-cell origin, although at the peak of stimulation many of them lacked the sheep erythrocyte marker. Direct effector-target cell contact was necessary for lysis to occur. The cytotoxicity of autologously stimulated (AS) lymphocytes was not restricted to EBV-genome-positive LCLs, nor to cell lines of hematopoietic origin. It was equally broad if cells carrying complement receptor had been removed before stimulation. Fresh lymphocytes, blasts induced by phytohemagglutinin or concanavalin A, and Burkitt's lymphoma biopsy cells were resistant or considerably less sensitive. Mouse cells--even cell lines--were resistant. The sensitivity of target cells to lysis correlated positively with their capacity to block AS lymphocyte lysis of autologous LCLs in competition experiments. The cytotoxicity of AS lymphocytes was blocked by EBV-genome-positive and -negative cell lines, whereas the EBV-related cytotoxicity of T cells from acute cases of infectious mononucleosis was blocked by EBV-genome-positive LCL only.

Specificity of cell-mediated cytotoxicity against human melanoma lines: evidence for "non-specific" killing by activated T-cells

The specificity of cell-mediated cytotoxicity against melanoma cells in vitro has been analyzed in a large number of studies with cells both from normal and melanoma subjects. As in a number of other, recent, similar human studies, no evidence for tumour specificity was found. Effector cells in peripheral blood responsible for the cytotoxic raction were examined by cell separation methods based on red cell rosette formation and separation through Hypaque-Ficoll mixtures. The evidence suggests that non-specificity results from killing by cells separating largely in the non-sheep red blood cell rosetting fraction and which have cytotoxic specificity directed broadly to cells with abnormal membranes. Further analysis revealed that the cells were non-phagocytic and did not bear receptors for complement. They appear to be activated into cell division and to bear surface receptors for the Fc portion of IgG. Additional evidence is presented suggesting that the cells mainly responsible are activated thymus-dependent cells present in the circulation of both tumour-bearing and normal subjects.

Studies of Epstein-Barr virus (ebv)-associated nuclear antigen. I. assay in human lymphoblastoid cell lines by direct and indirect determination of 125I-IgG binding

A quantitative assay for EBNA in human lymphoblastiod cell lines has been developed. The assay employs EBNA-positive and -negative 125-I-IgG preparations as reagents and can be used in a direct or indirect manner. EBNA specificity has been demonstrated in a number of ways. The antigenic relationship between EBNA present in Raji cells and in a number of other human lymphoblastiod cell lines of diverse origins and between the cell-associated antigen present in FT Raji cells and that present in isolated Raji nuclei has been studied. The possibility of carrying out blocking titrations for anti-EBNA determination has been demonstrated and the effect of glutaraldehyde and formaldehyde upon antigenic activity in FT Raji cells has been studied.

Infectious mononucleosis: model for self-limiting lymphoproliferation

Evidence for the extensive lymphoproliferation which characterises infectious mononucleosis (I.M.) is summarised, and some of the mechanisms which are though to control lymphoproliferative activity in this disease are discussed. The main host responses which appear to limit lymphoproliferation in I.M. include the development of humoral antibodies against the Epstein-Barr (E.B.) virus-associated membrane antigen (present on the E.B. viral envelope and on E.B.-virus-infected cells) and cellular immune responses directed against E.B.-virus-containing lymphocytes. Recent evidence is reviewed which indicates that E.B. virus preferentially infects B lymphocytes and that these E.B.-virus-containing cells, which are altered antigenically, evoke a massive response in the host T cells which do not carry E.B. virus; in the presence of E.B.-virus-infected B cells, T cells are transformed and become cytotoxic for B cells. Some of the general implications of the predominant T-cell response in I.M. are discussed with particular relation to autoantibody formation and antigenic competition. The possible role of the distinctive heterophil antigens and antibodies in determining the self-limiting course of I.M. is briefly considered. The general status of I.M. as a self-limiting, albeit intense, lymphoproliferative disease is appraised and the tenuous relationship between I.M. and irreversible lymphoproliferative states is discussed.

Possible use of established cell lines for MLR locus typing

MLR histocompatibility typing was performed by in vitro stimulation of lymphocytes from various persons with fresh lymphocytes (irradiated) or with lymphoblostoid cell lines (mito-mycin-treated) derived from donors homozygous at the MLR locus. MLC responses to both types of stimulation correlated strongly suggesting that a) established lymphoblastoid line cells can express products of the MLR loc and b) fresh lymphocytes can be replaced by these long term lines in MLR typing. Two lines (LV-B and MS-B) derived from two MLR homozygous donors (lv and MS) were used throughout these experiments. It is possible that as additional lines are established from such MLR homozygous donors, a panel of typing cells could be created which would serve to standardize MLR typing and allow selection of unrelated but histocompatible donors for transplantation.