Epstein-Barr herpesvirus infection: inhibition by immunologically induced mediators with interferon-like properties

Reactive T cells in the immune repertoire: self-restricted and allo-restricted helper T-cell clones to Epstein-Barr virus

Helper T-cell clones were generated by stimulation with autologous or allogeneic lymphoblastoid B cells (B-LCL) transformed by the Epstein-Barr virus (EBV). Some of these T-cell clones were allo-reactive and others were specific to EBV-transformed B-LCL. Helper T-cell clones specific to EBV-transformed B-LCL were restricted either by class-I or by class-II HLA molecules of self. T-cell clones restricted by class-I HLA molecules were stained by OKT3 and OKT8 monoclonal antibodies (MAbs), whereas class-II-restricted clones stained with OKT3 and OKT4. Not all helper T-cell clones specific to EBV-transformed B-LCL were restricted to self: one clone restricted by allo-HLA antigen was established. This finding suggests that in humans, as in mice, some T cells in the T-cell repertoire can be allo-restricted. This allo restriction may represent cross-reactivity of T cells, whereby "self + X" equals "allo + Y." Activation of these cross-reacting T cells restricted by allogeneic HLA molecules during infectious mononucleosis will give a T-cell response which may appear unrestricted by self HLA molecules. This mechanism helps to explain, at least in part, the HLA unrestricted cytotoxicity to B-LCL observed in infectious mononucleosis.

Inhibition of Epstein-Barr virus infection in vitro by recombinant human interferons alpha and gamma

The inhibitory effects of pure recombinant human interferons alpha A and gamma (reIFN-alpha A and -gamma) on Epstein-Barr virus (EBV) infection of a human EBV-negative B cell line, BJAB, and of normal adult B lymphocytes were studied. With pretreatment for 24 h, both types of reIFNs were effective in suppressing the production of EBV specific nuclear antigen (EBNA-1) in BJAB cells 24 h after EBV-infection, as determined by the immunoblotting technique. ReIFN-alpha A was, however, a much more potent inhibitor than reIFN-gamma. With treatment starting 1 h after EBV infection, both types of reIFNs were less effective in the suppression of EBNA production. Neither of the reIFNs showed any inhibitory effect on EBNA production in the latently EBV-infected cell lines, Raji and Daudi. These results suggest that reIFNs act in the early phase of EBV infection. Both types of reIFNs were also effective in inhibiting EBV infection of normal adult B lymphocytes as demonstrated by a reduction both in [3H]thymidine incorporation 6 days after EBV infection and in the total number of proliferating cells 21 days after EBV infection. Again, reIFN-alpha A showed a greater inhibitory effect than reIFN-gamma. We also showed that in BJAB cells, reIFN-alpha A strongly induced (2'-5')oligoadenylate synthetase activity, whereas reIFN-gamma increased the surface expression of HLA class I antigens.

Immune function in chronic active Epstein-Barr virus infection

The spectrum of illness attributed to Epstein-Barr virus (EBV) includes patients with symptoms persisting for more than 1 year without any other obvious underlying disease. High titers of antibodies to EBV, either IgG antiviral capsid antigen or anti-early antigen, can be demonstrated. In this study, 13 patients diagnosed as having chronic active EBV infection were examined to determine aspects of their immunologic status. Morphological examination and fluorescent antibody analysis revealed no abnormalities in the phenotypes of peripheral blood white cells present in these patients. Compared to those from healthy control individuals, mononuclear cells from the patients showed a markedly depressed ability to produce both interleukin-2 and interferon after stimulation with mitogen and a phorbol ester. Studies of natural killer (NK) cell activity revealed that unfractionated mononuclear cells from patients with chronic active EBV infection were significantly lower in killing activity compared to the control group. Fractionation procedures to enrich for large granular lymphocytes resulted in an increase in NK activity for all individuals, but killing activity still remained slightly lower in the patients than in the control group. The dysfunctions which were found in patients with chronic active EBV infection may reflect a primary defect in natural immune functions of the patients predisposing them to a chronic or intermittent clinical disease rather than a self-limiting illness. Alternatively, the abnormalities detected in these experiments may be a result of the viral infection itself.

Prevention of Epstein-Barr virus-induced B-cell outgrowth by interferon alpha

An in vitro system for determining the efficacy of interferon alpha (IFN-alpha) in preventing B-cell outgrowth due to Epstein-Barr virus (EBV) was developed. Unfractionated cord blood mononuclear cells, T-cell-depleted cord blood mononuclear cells, or adult T-cell-depleted mononuclear cells were exposed to IFN-alpha for 18 to 20 h followed by incubation with the B95-8 strain of EBV for 2 h. B-cell outgrowth was monitored by microscopic examination, [3H]thymidine incorporation, and Epstein-Barr nuclear antigen detection. Cell density and viral inoculum both affected the sensitivity of outgrowth to IFN-alpha. IFN-alpha was most effective when added at each feeding after infection as well as before infection with EBV. The mean of the lowest IFN-alpha concentration tested at which transformation failed to occur after infection with the B95-8 strain of EBV at a 50% transforming dose of 10(2.0) to 10(3.0)/ml was similar for unfractionated cord blood mononuclear cells, T-cell-depleted cord blood mononuclear cells, and adult T-cell-depleted mononuclear cells. The B95-8 strain and clinical EBV isolates required similar IFN-alpha concentrations to prevent outgrowth. In this system, IFN-alpha at pharmacologically achievable concentrations prevented EBV-induced B-cell outgrowth. These data indicate that IFN-alpha deserves further study as a potential therapeutic agent for EBV-induced syndromes.

Interferons on the transformation of non-T blood mononuclear leukocytes by Epstein--Barr virus

The effect of partially purified leukocyte (alpha) and fibroblast (beta)-derived interferons (IFNs) and crude immune (gamma) IFN on the transformation of non-T mononuclear leukocytes by the Epstein--Barr (EBV) virus was studied. The IFN preparations reduced the frequency of cells positive for EBV-specific nuclear antigen but did not significantly prolong the EBV-transformation interval.

Epstein-Barr virus-infected B lymphoblastoid cell lines: dynamics of interferon and 2'5'-oligoadenylate synthetase activity

Levels of 2'-5'-oligoadenylate synthetase (2'-5'OAS) activity measured in cell-free extracts of 23 Epstein-Barr virus transformed beta lymphoblastoid cell lines (LCL) were measured. Enzyme activity was low during stationary or log phase growth, and rapidly rose to peak values during log phase. Peak levels of 2'-5'OAS activity were characteristic for each LCL, and were significantly higher (P less than 0.05) in lines derived from patients with infectious mononucleosis (IM) than in lines from healthy individuals. Peak 2'-5'OAS activity correlated with maximal titers of endogenous human interferon-alpha (HuIFN-alpha); (r = 0.80). Enzyme activity levels could be increased by treating LCLs with exogenous HuIFN-alpha, or decreased by neutralization of endogenous interferon with antibody to HuIFN-alpha. 2'-5'OAS activity always peaked during log-phase growth, even in cultures depleted of interferon by antibody and in cultures which did not produce interferon. Thus, although peak levels of 2'-5'OAS activity in a given LCL correlated with maximal interferon titers, the growth phase associated variations in enzyme activity were independent of interferon. We conclude that regulation of constitutive levels of 2'-5'OAS in LCLs is partially independent of interferon.

Analysis of the defects responsible for the impaired regulation of Epstein-Barr virus-induced B cell proliferation by rheumatoid arthritis lymphocytes. I. Diminished gamma interferon production in response to autologous stimulation

T cells of patients with rheumatoid arthritis (RA) do not control the rate of B lymphoblast transformation induced by Epstein-Barr virus (EBV) as efficiently as T cells from healthy individuals; thus, lymphoblast cell lines are established more readily in RA lymphocytes in vitro after EBV infection. In the present experiments, we have asked whether this T cell regulation can be reproduced by lymphocytes. We found that normal T cells, activated in allogeneic or autologous mixed leukocyte reactions (MLR), produce lymphokines that inhibit in vitro EBV-induced B cell proliferation. Allogeneic MLR supernatants inhibited EBV-induced DNA synthesis 62 +/- 4% (mean +/- SE) at 10 d post-infection, whereas autologous MLR supernatants suppressed it 50 +/- 3%. RA T cell supernatants produced in an allogeneic MLR suppressed as well as normal T cell supernatants (64 +/- 5% inhibition). In contrast, supernatants from RA autologous MLR had little inhibitory activity. EBV-induced DNA synthesis at 10 d was reduced only 8 +/- 3%, compared with the 50 +/- 3% suppressive activity of normal autologous MLR supernatants. The magnitude of the proliferative responses in the autologous MLR regenerating the lymphokines was similar in the normal and RA populations. After depletion of adherent cells from the RA auto-MLR stimulators, supernatant inhibitory activities increased to normal levels (from 11 +/- 6 [SE] to 52 +/- 6% [SE]). The inhibitory factor involved in the regulation of in vitro EBV infection is a protein with a molecular weight of approximately 50,000. Its activity is eliminated by hearing at 56 degrees C and by exposure to acid at pH 2. The inhibitory activity is blocked by mixing the MLR supernatants with a polyvalent antisera or monoclonal antibodies specific for human gamma interferon. Gamma interferon produced by activating T cells in allo- or auto-MLR can reproduce T cell-mediated regulation of EBV-induced B cell proliferation, and the failure of RA auto-MLR to generate that lymphokine parallels the defective T cell regulation of EBV-induced B cell proliferation characteristic of RA lymphoid 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.

Interferon suppresses antigen- and mitogen-induced leukocyte migration inhibition

Although first recognized by its effect on virus-cell interactions, interferon (IFN) has a variety of other effects. It can affect cell proliferation, modify the immune response at several levels, enhance the cytotoxic action of lymphocytes, suppress antibody formation and inhibit the development of delayed-type hypersensitivity (DTH) reactions. Therefore we have now tested the effect of interferon on leukocyte migration inhibition (LMI), regarded as the counterpart in vitro of DTH in humans. We have found that IFN suppresses both mitogen-and antigen-induced LMI, acting directly on the granulocytes but also affecting the lymphokine production of the lymphocytes.

Relationship of in vitro immune responses to Epstein-Barr herpesvirus and severity of infectious mononucleosis

Immune responses to Epstein-Barr herpesvirus (EBV) and EBV-related antigens were studied serially in 18 patients with heterophil antibody-positive infectious mononucleosis and in 18 control subjects. Enhanced cellular immune responses to EBV particles and to EBV intracellular soluble antigens were found in the patients at convalescence, suggesting that the development of specific cellular immune responses was associated with apparent control of the virus infection. In addition, a correlation between severity of disease and specific cellular immune response was found. Patients with severe clinical signs were found to have a more active cellular immune response to EBV intracellular soluble antigens early in the infection compared with patients with mild disease. This suggests that an increased immune reactivity to intracellular antigens during the early part of the illness is related to the severity of clinical manifestations in infectious mononucleosis. Serum antibody to viral capsid antigen and early antigen was not related to the severity of clinical disease.

Long-term C-cell-mediated immunity to Epstein-Barr virus in man. II. Components necessary for regression in virus-infected leukocyte cultures

Regression of EB-virus-induced transformation occurs exclusively in cultures of leukocytes from seropositive donors. Studies have shown that the strength of regression could be assayed in terms of the proportion of T cells which must be added to the autologous EB virus-infected T-cell-depleted population in order to establish regression in the culture. The in vitro regression phenomenon was strongly T-cell-dependent but did not require the presence of either monocytes or, as a potential antigenic stimulus, the residual viral envelope material on the surface of virus-infected B cells. The T-cell-depleted population from seropositive donors sometimes transformed (7/60 cultures) without the experimental addition of virus. Regression appeared to be independent of cytotoxic mechanisms involving anti-viral antibodies and not to be mediated by soluble factors released into culture medium.

Long-term T-cell-mediated immunity to Epstein-Barr virus in man. I. Complete regression of virus-induced transformation in cultures of seropositive donor leukocytes

Peripheral blood mononuclear cells from donors of known serological status with respect to EB virus were exposed to the virus in vitro and then cultured at various cell concentrations. All cultures from nine seronegative adult and 12 foetal donors gave rise to cell lines following subculture 4 weeks post infection. In contrast, seropositive donor cultures seeded at the higher cell concentrations developed foci of proliferating EBNA-positive cells within the first 1--2 weeks but thereafter regressed completely and subcultures made after 4 weeks never gave rise to cell lines. Out of 18 seropositive donors tested, 15 showed regression in all cultures seeded at 10(6) cells/ml and above, and with the other three donors a proportion of replicate cultures regressed. T-cell depletion and reconstitution experiments showed that the effect was absolutely dependent upon the presence in the cultures of T cells from these seropositive donors. The results strongly suggest that the regression phenomenon is an in vitro expression of long-term T-cell-mediated immunity to EB virus which the large majority, if not all, infected individuals possess.