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In vitro infection of human B lymphocytes by Epstein-Barr virus (EBV) results in their growth transformation and establishment of immortalized lymphoblastoid cell lines. The virus was found to encode a homologue of the pleiotropic cytokine interleukin-10 (IL-10), which has wide-ranging effects on the immune system. We investigated the effect of human IL-10 (hIL-10) and viral IL-10 (vIL-10) on EBV-specific immunological memory, as assessed by the inhibition of EBV-induced B-cell transformation by the autologous T cells. We found that IL-10 abrogates the inhibitory capacity of T cells. This IL-10 effect is mediated through suppression of T-cell activation-induced IL-2 and interferon-gamma production and through a direct enhancement of EBV-infected B-cell growth.

Several lines of evidence indicate that an impairment of EBV-specific immune responses may contribute to the pathogenesis of Hodgkin's disease (HD). At present, however, it is not clear whether a defective immunity to EBV is a characteristic restricted to EBV-associated HD cases or a more generalized phenomenon, part of the inherent immune deficiency of HD patients. In this study, we have addressed this issue by analyzing EBV-specific responses in infiltrating T lymphocytes (TILs) from one HD biopsy, where the virus was confined to a small proportion of apparently normal lymphocytes. TIL cultures were established using low amounts of recombinant interleukin 2 and in the absence of specific stimulation, conditions that preferentially induce the proliferation of in vivo activated T cells. An EBV-specific cytotoxic component was revealed by the capacity of these TILs to lyse autologous EBV-positive lymphoblastoid cell lines (LCLs) obtained by spontaneous transformation from the lesion but not HLA-mismatched LCLs and autologous phytohemagglutinin blasts. This cytotoxic activity closely resembled that of EBV-specific memory T cells, which may be reactivated from the blood lymphocytes of healthy donors by in vitro stimulation with autologous LCLs. The use of a panel of appropriately HLA-matched B95.8-transformed LCLs as targets in standard 51Cr release assays revealed EBV-specific cytotoxic responses to be restricted mainly through the A11 and B44 HLA alleles with a minor HLA-A26-restricted component. Using autologous fibroblasts infected with recombinant vaccinia viruses expressing the EBV latent antigens, the TIL culture was shown to recognize latent membrane protein 2 and, to a lesser extent, EBV-encoded nuclear antigen 6. In addition, a strong proliferative response was induced by coculture of TILs with autologous but not with allogeneic LCLs or autologous phytohemagglutinin blasts. Six CD4-positive, EBV-specific T-cell clones were isolated by limiting dilution. The study of cytokine mRNA expression, carried out by reverse transcriptase-assisted PCR, revealed that three of these T-cell clones expressed a Th0 phenotype, whereas 1 had a Th2 phenotype. These findings are consistent with the presence in this HD lesion of an ongoing immune response against EBV-carrying cells and suggest that the complex immune deficiency that characterizes HD patients probably does not include a generalized, constitutional defect of EBV-specific T-cell responses.

Epstein-Barr virus has developed multiple strategies to ensure its long-term persistence in the infected B cells of immunocompetent hosts. These include the establishment of cell-phenotype-specific programs of viral gene expression and the transduction of cellular genes that modulate immune responses. Cytotoxic T cells may specifically influence the evolution of this genetically stable virus.

Burkitt's-lymphoma (BL) lines which have maintained in vitro the tumor-cell phenotype (group-I BLs) are poor antigen-presenting cells (APC), in spite of a relatively high surface expression of MHC class II. In order to investigate the mechanism of this deficiency, we have compared group-I BL lines, their sub-lines which have progressed in vitro towards an LCL-like phenotype (group-III BLs), and EBV-transformed lymphoblastoid cell lines (LCLs), for their ability to bind and process tetanus toxoid (TT). The uptake and internalization of 125I-labelled TT was equivalent in the 3 cell types. Only LCLs and group-III BL lines were able to process the TT, as shown by the identification of discrete proteolytic products after separation of whole-cell extracts in tricine-SDS-polyacrylamide gels, and by the recovery of TCA-soluble radioactivity in the culture supernatant. Processing of TT was induced by expression of the EBV-encoded membrane protein LMP 1 in transfected group-1 BLs. The present findings suggest that the inability of group-1 BLs to act as APC is due to their failure to process exogenous antigens. This function appears to be related to phenotypic properties that can be modulated by the expression of LMP1.

Epstein-Barr virus, a lymphotropic herpesvirus of humans, has potent B cell growth transforming activity yet persists in the lymphoid tissues of most individuals as a lifelong asymptomatic infection. Virus induced B cell growth transformation in vitro is associated with the expression of a limited set of viral genes encoding six nuclear antigens (EBNA 1, 2, 3A, 3B, 3C and LP) and two latent membrane proteins (LMP 1, 2). Healthy virus carriers possess strong EBV specific CTL memory that can be reactivated in vitro. Here, we summarize experiments in which the antigenic specificities of these HLA class I restricted memory CTL responses have been mapped in a range of individuals with different HLA backgrounds. Of the known EBV latent proteins, EBNA 3A, 3B and 3C are frequently the dominant targets for such responses, but examples of responses directed against epitopes of EBNA 2, EBNA-LP or the LMP have been identified; by contrast, CTL responses against epitopes of EBNA 1 have not been observed. Epstein-Barr virus is associated with at least three malignancies of lymphoid origin--immunoblastic lymphomas of the immunosuppressed, endemic Burkitt's lymphoma and a subset of Hodgkin's disease. The immunoblastic lymphomas express the complete spectrum of EBV coded latent proteins and a cellular phenotype similar to that of in vitro transformed B lymphoblastoid cell lines; accordingly, they remain sensitive to EBV specific CTL recognition. Endemic BL cells are not recognized by such CTL, and at least three consistent features of this tumour could contribute to immune escape: (a) allele specific downregulation of HLA class I antigen expression, (b) absence/low expression of cellular adhesion molecules and (c) restriction of EBV latent protein expression to EBNA 1 only. The relative importance of these three features of the BL cell phenotype with regard to sensitivity to CTL recognition is re-interpreted in the light of recent results. Finally, the pattern of virus latent protein expression in EBV positive Hodgkin's disease is described, and the possibility of EBV specific CTL control against this tumour is discussed.

Lymphocytes from two patients with multiple myeloma stage I and one patient with monoclonal gammopathy of undetermined significance were found to proliferate specifically in response to low concentrations of F(ab')2 fragments of the autologous M component. T cell clones isolated from repeatedly stimulated cultures bound specifically the autologous idiotype and proliferated after addition of soluble idiotype and exogenous interleukin-2. The majority of clones were CD8+ and showed negligible staining for CD4. Idiotype-binding clones could not be isolated from cultures of lymphocytes from a healthy control stimulated under the same conditions. The study provides support for the existence of idiotype-reactive T cells in monoclonal gammopathies. Such cells might have a regulatory role on the tumor cell clone and may be important for a future therapeutic approach.

The ability of B cells, B blasts, and macrophages to present Epstein-Barr virion antigens to autologous T cells and trigger their capacity to inhibit Epstein-Barr virus-induced B-cell transformation was tested. Macrophages were as efficient as B cells and B blasts in presenting the virus to T lymphocytes. This function required antigen processing, because it was inhibited by chloroquine treatment and by fixation of the antigen-presenting cells immediately after viral exposure but not 18 h later. T cells exposed to the purified Epstein-Barr virus envelope antigen gp350 coupled to immunostimulating complexes also showed inhibitory function. These results suggest that recognition of processed virion antigens elicits the generation of T-cell-mediated inhibition of Epstein-Barr virus-induced B-cell transformation.

T cell growth factor (TCGF) has become a valuable means of maintaining T lymphocytes in long-term culture and of studying T cell function. Numerous problems have been met in the production of TCGF of consistently good quality and in the maintenance of human T cell lines over long periods. We have investigated optimal conditions for TCGF production, and simplified assay systems for TCGF activity. The best TCGF production was obtained by short-term treatment with high concentrations of phytohemagglutinin (PHA). The TCGF producing lymphocytes could be re-used for TCGF production up to 1 month after the first treatment course. Human cultured T cell lines, fresh lymphocytes, short-term PHA stimulated lymphocytes and cultured marmoset T lymphocyte lines were all used for assay of TCGF. We recommend PHA stimulation of human lymphocytes for this assay on a routine basis, comparing results with a standard TCGF batch and calculating a growth index. Adherent cells impair TCGF production. Optimal TCGF production was seen when lymphocyte preparations without adherent cells from different donors were used.

After Epstein-Barr virus (EBV) infection in vivo, B-cells with latent virus infection persist indefinitely through life. These cells grow in vitro on explanation and can be established as immortal B-cell lines. To reconcile the unlimited growth potential in vitro with the maintenance of a low proportion of B-cells infected by EBV in vivo, a strict in vivo control mechanism has to be postulated. Certain aspects of this control are apparent when the primary infection is followed by infectious mononucleosis. This is characterized by lymphocytosis and the presence of activated T-cells. The T-cell proliferation is probably the manifestation of the immune response against EBV antigens. However, the reaction of T-cells upon encounter of B-blasts is also likely to contribute to the events. At present, it is difficult to detect an EBV-specific component in the action of the T-cells in the acute phase of mononucleosis exerted on B-cells. However, for the clinical course of the disease the activation of T-cells is important. The activated T-cells may control and also eliminate the B-cells infected by EBV. In addition to the immunity which develops during the disease, th immunoregulatory mechanism is likely to have a role in the inhibition of B-cell proliferation.

Three males with the X-linked lymphoproliferative syndrome (XLP) with hypo- or agammaglobulinemia following Epstein-Barr virus (EBV) infection and two males with the chronic mononucleosis syndrome were investigated for immune responses to EBV-determined antigens. Males with XLP showed profound cellular immune defects. Markedly diminished responses of natural killer cell and interferon-activated killer cell activities and impaired leukocyte migration inhibition responses to phytohemagglutinin were determined in patients with XLP. The two patients with chronic mononucleosis showed less severe defects. All patients showed partial or complete impairment of their EBV-specific immune responses as measured by leukocyte migration inhibition. EBV-specific antibodies were markedly diminished against EBV-associated nuclear antigen, early antigen, and viral capsid antigen in males with XLP. In contrast, patients with chronic mononucleosis had elevated antibodies to most EBV-specific antigens. Individuals with life-threatening EBV-induced lymphoproliferative disorders may exhibit multiple defective immune mechanisms against the virus.

We have analyzed the effect of cyclosporin-A (CsA) on the proliferative and cytotoxic responses induced by mixed-lymphocyte cultures (MLC-s) on low and high density T lymphocytes. Allogeneic stimulation had a different impact on the two subsets. Proliferative and cytotoxic responses were inversely correlated; i.e., high density cells proliferated but exerted low levels of cytotoxicity while the lytic activity of the low density subset was stronger and the proliferation was weak. CsA impaired the proliferative and cytotoxic responses of the high density T lymphocytes but influenced less markedly the response of the low density cells. In both subsets CsA inhibited the MLC-induced interleukin 2 (IL-2) production. The generation of specific cytotoxicity was markedly suppressed by CsA, whereas the generation of anomalous activity was less affected. Addition of exogenous IL-2 to the CsA-containing cultures fully restored the proliferation and the generation of nonspecific cytotoxicity. In contrast, addition of interferon gamma (IFN-gamma) restored neither of these responses. However, for complete restoration of the stimulation-specific cytotoxicity, addition of both lymphokines was required. Taken together these results suggest that the CsA-induced suppression of the lymphokine production has different consequences in the low and high density subsets; the expression of anomalous and specific cytotoxicities require different signals; CsA interferes with several steps in the T-cell activation.

In order to analyze the components of EBV-specific immunological memory that contribute to the T-cell-mediated inhibition of EBV-induced B-cell transformation, we have investigated the growth inhibitory potential of T cells cultured for 3 days with B cells exposed to transforming and non-transforming EBV preparations. T cells cultured for 3 days with EBV-infected autologous B cells inhibited the transformation of newly infected B lymphocytes. T cells cultured with the virus, with autologous uninfected B cells, or in the presence of 10 micrograms/ml Con-A had a significantly weaker inhibitory capacity. The inhibitory capacity was induced by co-cultivation with B cells infected with the transforming B95-8 virus strain, with the non-transforming P3HRI virus strain, and also with UV-inactivated B95-8 virus. B-cells infected with transforming B95-8 virus induced the strongest growth inhibitory activity. Activation of the T cells was shown by their IL-2 production, proliferation, and generation of non-specific cytotoxicity. These results suggest that the initial event of the T-cell response in EBV-infected cultures is induced by antigens associated with the viral particles presented by B lymphocytes.

Lymphocyte subsets separated on the basis of nylon-wool adherence and E and EA rosetting, and characterized for the presence of esterase-positive phagocytic cells were investigated for production of leukocyte migration inhibitory factor (LIF) in response to polyclonal T- and B-cell activators, PHA, ConA, PWM, and Epstein-Barr virus (EBV). In the nylon-passed population only the high avidity E+EA+ cells responded to ConA, PHA-induced LIF production in all E-rosetting subsets. The nylon-adherent E+ subset, which contains activated T cells, produced LIF spontaneously. B cells produced LIF when exposed to PWM or uv-inactivated EBV. In accordance with the known T-cell dependence of PWM activation, LIF was detected only in supernatants of reconstituted populations containing both B and T cells. In contrast, uv-inactivated EBV, devoid of transforming potential, elicited LIF production in the pure B-cell population. LIF production in response to polyclonal activators seemed to be independent of accessory cells since reconstitution with autologous macrophages or semipurified monokine, high-molecular-weight Interleukin 1 (IL-1), did not alter the results.

We have analyzed the effect of Cyclosporin-A (CsA) on the in vitro suppression of Epstein-Barr virus (EBV)-induced B-cell proliferations separated on the basis of cell density. CsA abolished the growth-inhibitory capacity of high-density T cells but influenced only marginally the activity of low-density lymphocytes; this suggested that different mechanisms mediate suppression in the two subsets. Stimulation with irradiated EBV-transformed cells had a different impact on the activity of low- and high-density lymphocytes. Proliferative and cytotoxic responses were inversely correlated, i.e. high-density cells proliferated but exerted low cytotoxicity, while the lytic activity of the low-density subset was stronger in the absence of significant cell proliferation. Proliferation and generation of cytotoxicity were abrogated by CsA in both subsets. The activities could be restored by addition of exogenous IL-2, suggesting that the drug may interfere with the cascade of lymphokine--cell interactions which leads to activation of immune responses. From the analysis of athe CsA effects on the two subsets it seems that the high-density one contains specific memory T cells which are activated and proliferate upon encounter with EBV-infected cells. On the other hand, low-density lymphocytes are induced to release soluble factors with antiproliferative activity. The secretory function was resistant to the suppressive effect of CsA.

Blood lymphocytes from tumor patients were cocultivated with allogeneic lymphocytes (MLC) or autologous tumor cells (ATS), and their cytotoxicity was characterized. The main objective of the study was the lysis of autologous tumor biopsy cells by such effectors. Lymphocytes of patients activated in MLC lysed allogeneic third-party cells and in some cases also lysed autologous tumor cells. Allogeneic but not autologous PHA blasts were also damaged by these effectors. The cytotoxic potential of MLC-activated lymphocytes from healthy donors was similar; allogeneic tumors and phytohemagglutinin (PHA) blasts but not autologous PHA blasts were lysed. The cytotoxicity of lymphocytes activated in ATS were specific for the stimulator because they acted only on the autologous tumor cells. Allogeneic tumors and autologous and allogeneic PHA blasts were not lysed. The pattern of cytotoxicity with regard to this target panel was maintained when the MLC or ATS cultures were further propagated with TCGF. Results obtained in cold target competition assays suggested (a) activated lymphocyte lyse the third party tumor targets because of alloantigen recognition; (b) in MLC several different sets of alloreactive cytotoxic lymphocytes are present simultaneously; and (c) the alloreactive cells are different than those that act on the autologous tumor cells. Thus, the lysis of allogeneic tumor cells by lymphocytes of the patient is not due to recognition of cross-reacting tumor-related antigens, and the autotumor cytotoxicity of the patients' MLC-activated lymphocytes if performed by specifically reacting cells.