Characterization of thymus-derived lymphocyte subsets in acute Epstein-Barr virus-induced infectious mononucleosis.

Changes in thymus-derived (T) lymphocyte subpopulation numbers were studied in patients with acute and convalescent Epstein-Barr virus (EBV)-induced infectious mononucleosis (LM). T cell subsets were characterized by the presence of Fc receptors for IgG (TG), for IgM (TM) or by the absence of either receptor (Tnon-M, non-G). We found that in acute IM, total numbers of T and B lymphocytes were elevated (p less than 0.01). Of the T lymphocyte subsets, the total number of Tnon-M, non-G lymphocytes was increased six fold compared to normal subjects (p less than 0.001) and included the majority of the atypical T lymphocytes. The number of total TG and TM lymphocytes was moderately increased (p less than 0.05). In convalescent IM patients, the number of total T cells remained slightly elevated (p less than 0.02) whereas proportions and absolute numbers of B lymphocytes and T cell subsets returned to near normal levels. Thus, acute Epstein-Barr virus-induced IM is associated with a T lymphocytosis which is composed predominantly of atypical T cells which lack detectable Fc receptors for IgG or IgM.     

Enhanced destruction of lymphoid cell lines by peripheral blood leukocytes taken from patients with acute infectious mononucleosis.

The cytotoxicity of peripheral blood leukocytes from normal human donors and from patients with EBV-associated infectious nomonucleosis (IM) has been determined for human lymphoid cell lines (LCL) containing Epstein-Barr virus (EBV) DNA. In a 51Cr release assay, mononuclear leukocytes from all donors are spontaneously cytotoxic. Leukocytes taken from patients within the first 2 weeks of overt IM are significantly more cytotoxic. This increased cytotoxicity declines to the spontaneous level as the disease progesses. The increase shows no correlation with the degree of lymphocytosis but a positive correlation with numbers of circulating atypical cells. The reaction is apparently not directed against histocompatability antigens, known EBV membrane antigens, or other characteristics of fresh human lymphoid cells. Susceptibility to damage is shared by bone marrow-derived (B) cell lines but not thymus derived (T) cell lines. EBV-gene products cannot be soley responsible for expression of the unknown characteristic. Transformation of B cells with EBV in vivo or in vitro, however, may trigger its expression     

Epstein-Barr virus (EBV) receptors, complement receptors, and EBV infectibility of different lymphocyte fractions of human peripheral blood. II. Epstein-Barr virus studies.

In B-cell fractions isolated from human peripheral blood, the frequency of surface immunoglobulin-positive and of complement receptor-positive cells showed a good correlation with the frequency of EBV-binding cells, as detected by membrane fluorescence or by a quantitative bioassay for infectious virus in the absorbed supernatant fluid. There was a close relationship between all three parameters mentioned, the frequency of EBNA-positive cells 2 or 3 days after the infection, and the stimulation of cellular DNA synthesis. So-called O-cell fractions remaining after the removal of nylon adherent and E-rosetting cells contained a certain frequency of complement receptor-positive cells and absorbed EBV to a limited extent, but did not respond to EBV infection with EBNA induction or stimulation of DNA synthesis. None of the T-cell fractions absorbed EBV to a detectable extent. This includes the T_ea+ fraction that contained a certain proportion of complement receptor-positive cells. It is concluded that the previously demonstrated relationship between EBV receptors and complement receptors on B-lymphoblastoid lines also holds for peripheral B lymphocytes. In these cells, virus absorption is followed by an intracellular infectious process, signaled by the appearance of EBNA and cellular DNA synthesis. O cells carry complement receptors and absorb EBV to a certain extent, but do not respond with EBNA synthesis or DNA stimulation, presumably due to intracellular restrictions. T cells do not bind EBV, and the complement receptors present on some cells of the T_ea+ fraction do not function as EBV receptors.     

Activated lymphocytes during acute Epstein-Barr virus infection

Activated lymphocytes, as identified by HLA-DR expression, associated with acute Epstein-Barr virus (EBV)-induced infectious mononucleosis (IM) were shown to be a heterogeneous population containing significantly elevated cytotoxic/suppressor (CD8) T cells, natural killer (CD16) cells and helper (CD4) T cells. CD8 T cells were the primary activated population representing 24.5% of the total lymphocyte population. The activated CD4 T cells and natural killer cells accounted for 6.7% and 3.5% of the total lymphocyte population, respectively. Analysis of serum soluble interleukin 2 receptors (IL-2R) demonstrated significantly (p less than 0.001) elevated levels in the serum of acute IM patients compared with normal controls. Elevated levels of serum IL-2R were correlated (r = 0.67) with increased percentages of Leu 2a+/HLA-DR+T cells (i.e., activated CD8 T cells). Patients with X-linked lymphoproliferative syndrome and virus-associated hemophagocytic syndrome, two syndromes associated with severe acute EBV infections, demonstrated the most dramatic increase in serum IL-2R levels. These data demonstrate that EBV is associated with intense immune stimulation and that during acute IM activated lymphocytes, other than the CD8 T cells, may contribute to the immune response to EBV.     

外周血T细胞CD38和HLA-DR的表达水平在儿童传染性单核细胞增多症中的临床意义

摘要 目的：探讨传染性单核细胞增多症（IM）患儿外周血T细胞活化分子CD38和人类白细胞抗原DR（HLA-DR）表达水平的临床意义。方法：采用流式细胞术分别检测45例IM患儿急性期和恢复期的活化分子CD38和HLA-DR在T细胞的表达水平,并与30例健康体检儿童进行对比。分析IM患儿急性期CD38和HLA-DR在T细胞的表达水平与EB病毒载量、肝功能指标、外周血异型淋巴细胞比例、淋巴细胞计数的相关性,并采用ROC曲线分析CD8⁺CD38⁺T和CD8⁺HLA-DR+T细胞百分比的诊断效能。结果：与对照组比较,IM急性期患儿的CD38和HLA-DR在T细胞的表达水平显著升高（P＜0.05）。CD8⁺CD38⁺T、CD8⁺HLA-DR+T细胞百分比分别与EBV-DNA、ALT、AST、LDH、异型淋巴细胞百分比、淋巴细胞计数呈正相关（P＜0.05）,与白蛋白（ALB）呈负相关（P＜0.05）;CD4⁺CD38⁺T、CD4⁺HLA-DR+T细胞百分比与上述指标无显著相关性（P均＞0.05）。IM恢复期CD38和HLA-DR在T细胞的表达水平较急性期明显降低（P＜0.05）。ROC曲线分析CD8⁺CD38⁺T、CD8⁺HLA-DR+T细胞百分比显示诊断儿童IM的AUC值分别为0.931和0.993,特异度均为100%,灵敏度分别为88.89 %和93.33 %。结论：流式法检测CD38和HLA-DR在T细胞的变化有助于判断病情变化。外周血CD8⁺CD38⁺T、CD8⁺HLA-DR+T细胞百分比不仅能反映出IM急性期肝功能损伤严重程度,还可作为儿童IM的流式诊断指标。     

Cellular immunity in infectious mononucleosis. II. Specific reactivity to Epstein-Barr Virus antigens and correlation with clinical and hematologic parameters.

Infectious mononucleosis (IM) patients, Epstein-Barr virus (EBV)-seropositive and seronegative healthy donors, and patients with other viral infections were tested for lymphocyte blastogenesis (LB) with phytohemagglutinin and six EBV (virus concentrate, culture supernatant, and soluble [S] antigen) or control antigens. Fluorescent antibodies to EBV viral capsid antigen of IgG, IgM, IgA specificities, to nuclear antigen (EBNA), and heterophile antibodies were also assayed. These were correlated with clinical parameters (fever, pharyngitis, adenopathy, hepatitis, splenomegaly, atypical lymphocytes, and total mononuclear cell counts). EBV viral and S antigen-induced LB was significantly greater in seropositive donors. IM patients had antigenspecific LB below that of seropositive donors initially and low responses for the acute phase of illness when clinical symptoms were present and antibody titers were maximal. Specific LB rose to a peak at 3.5 to 9 weeks when the patients had recovered, most laboratory findings had returned to normal, and antibodies had declined. At peak, specific LB in IM patients exceeded that of seropositive donors, but later declined. These results demonstrate specific cell-mediated immunity (CMI) to EBV, and indicate that this develops slowly in IM and contrasts with the evolution of the clinical events and humoral immunity. This correlation supports the hypothesis that CMI is the mechanism of terminating lymphoproliferation in IM.     

Binding of monoclonal antibody to the Epstein Barr virus (EBV)/CR2 receptor induces activation and differentiation of human B lymphocytes

A panel of B cell-specific monoclonal antibodies that identify the CR2/EBV receptor were examined for their ability to mimic the T-independent mitogenic agent, EBV, and thus activate human peripheral blood B lymphocytes. Two of four different anti-CR2/EBV monoclonal antibodies, OKB7 and AB-1, produced a 50-fold to 200-fold dose-dependent stimulation of DNA synthesis of peripheral blood mononuclear cells. One of the other monoclonal antibodies, anti-B2, had slight activity, and the other, HB-5, was completely inactive. One of the mitogenic antibodies, OKB7, which directly inhibits binding and infection of B cells by EBV in the absence of a second anti-immunoglobulin antibody, was examined in further detail. Both the intact antibody in soluble form and its pepsin-derived F(ab')2 fragment stimulated DNA synthesis of unseparated B and T lymphocytes. Peak stimulation of DNA synthesis in peripheral blood mononuclear cells occurred between 4 to 6 days. B cells were responsible for incorporation of [3H]thymidine. However, T cells were required for activation of peripheral blood mononuclear cells by OKB7. OKB7, as well as the other mitogenic monoclonal anti-EBV/CR2 receptor antibody, also induced B cells to differentiate after 6 to 10 days of culture as indicated by polyclonal Ig secretion. IgM was the predominate immunoglobulin secreted. These studies thus indicate that certain epitopes on the EBV/CR2 receptor trigger B cells to divide and differentiate. This pathway of B cell activation, in contrast to that produced by EBV, is T cell dependent.     

Serum leucine aminopeptidase for monitoring viral infections with plasmacytoid reaction

Analysis of data on 9 cases with active cytomegalovirus infection in patients with kidney grafts showed a positive association of serum leucine aminopeptidase activity concentration with the appearance of plasmacytoid lymphocytes in blood. Additional studies indicate that like the liver, the lymphocytes contain leucine aminopeptidase in relatively large quantities and that this enzyme is increased about 3-fold in plasmacytoid lymphocytes when compared with the activity in normal lymphocytes. In contrast, the 'hepatic' enzyme alanine aminotransferase is practically absent in both lymphocytes and plasmacytoid cells. Therefore, the difference in serum between the relative increases of leucine aminopeptidase and alanine aminotransferase may be attributed to proliferating plasmacytoid lymphocytes. Earlier observations on a large number of cases of acute viral hepatitis A or B lend credence to this assumption. However, in this disease, the serum enzyme changes reflect the much greater involvement of the liver and the relatively slight, but significant, proliferation of plasmacytoid lymphocytes. Our hypothesis is confirmed by the recent observation of 3 cases of acute EBV infection (infectious mononucleosis) in otherwise healthy individuals showing greatly elevated leucine aminopeptidase in contrast to normal or slightly raised alanine aminotransferase in serum.     

Pathophysiologic analysis of peripheral blood lymphocytes from patients with primary immunodeficiency. I. Ig synthesis by peripheral blood lymphocytes stimulated with either pokeweed mitogen or Epstein-Barr virus in vitro

In the present study 5 patients with common variable hypogammaglobulinemia (CVH) and 4 patients with selective IgA deficiency (IgA-D) were analyzed for the cellular defects responsible for impaired Ig synthesis with use of peripheral blood lymphocytes stimulated with either PWM or EBV in vitro. By the use of co-culture with PWM, all the patients examined had intrinsic B cell defects restricted to the synthesis of Ig class corresponding to the low or absent Ig class(es) in the sera. Two types of excessive suppressor T activity were found, which were abrogated by irradiation. One was isotype-nonspecific and the other was IgA-specific. Moreover, failure of IgA-specific helper T activity was demonstrated. The use of EBV as an agent that polyclonally activates B cells independently of T cells and monocytes should allow a clearer delineation of the level of the B cell defects. When co-cultured with EBV, B cells from 3 patients with CVH produced normal to subnormal quantities of IgM although they could produce no IgM upon co-culturing with normal T cells and PWM. B cells from 2 patients with CVH could produce IgM normally by stimulation with either PWM or EBV; however, there was no restoration to produce IgG or IgA in these patients. In addition, B cells from 2 patients with IgA-D produced not only IgG and IgM but also IgA almost normally at 4 days after in vitro stimulation with EBV.     

Establishment of peripheral lymphoid cell cultures from patients with Hodgkin's disease depending on Epstein-Barr-Virus-reactivity and cellular immunity.

Peripheral blood lymphocytes from 43 patients with Hodgkin's disease were studied for spontaneous growth in longterm cultures in vitro. The rate of culture establishment in Hodgkin's patients was dependant on a positive Epstein-Barr-Virus (EBV)-seroreactivity and intact delayed hypersensitivity reaction to tuberculin. Localized and inactive disease, as well as the absence of atypical mononuclear cells in the peripheral blood had a favourable influence on the longterm in vitro growth. The overall establishment rate in Hodgkin patients was 18 out of 60 attempts (30%), 16 out of 34 (47%) in patients without treatment, only 2 out of 26 (7.7%) attempts during treatment. These results were compared with culture attempts of peripheral blood cells from healthy individuals and umbilical cord blood lymphocytes. Only 12 out of 60 attempts in healthy donors (18.2%) and 0 out of 49 attempts with umbilical cord blood lymphocytes were successful.     

Infectious Mononucleosis and Mononucleosis Syndromes: Clinical,Virological and Immunological Features

Infectious mononucleosis (IM) and cytomegalovirus (CMV) mononucleosis are caused by a primary infection with related viruses, Epstein-Barr virus (EBV) and CMV. Despite the similarity of clinical manifestations, basic differences exist: (1) The heterophil antibody (HA) response is absent in CMV mononucleosis, whereas it is present in IM. (2) In IM atypical lymphocytosis reflects proliferation of B cells early and of T cells later in the disease course; in CMV mononucleosis the situation appears complex. (3) In blood, EBV is restricted to B lymphocytes, whereas CMV is found in polymorphonuclear and mononuclear leukocytes. (4) Complications of CMV mononucleosis such as hepatitis and pneumonitis may be due to virus cytopathic effect in target organs. Prominent tonsillopharyngitis with adenopathy, and visceral complications of IM are related to lymphoproliferation which is self-limited except in males with a rare familial defect in defense against EBV. Immune complex-mediated pathology may occur in both diseases. (5) CMV is frequently transmitted to a fetus in utero or to an infant during or after birth, and this occasionally leads to severe cytomegalic inclusion disease; vertical transmission of EBV appears to be exceptional. (6) Secondary EBV infections are associated with certain malignancies whereas such an association has not been recognized in the case of CMV.Toxoplasma gondii is another cause of HA-negative mononucleosis. Its complications in the heart, in skeletal muscle and in the central nervous system are related to direct invasion by the parasite. Cellular immunity plays an important role in defense against all three agents.     

Impaired Epstein-Barr Virus-Specific Neutralizing Antibody Response during Acute Infectious Mononucleosis Is Coincident with Global B-Cell Dysfunction

Here we present evidence for previously unappreciated B-cell immune dysregulation during acute Epstein-Barr virus (EBV)-associated infectious mononucleosis (IM). Longitudinal analyses revealed that patients with acute IM have undetectable EBV-specific neutralizing antibodies and gp350-specific B-cell responses, which were associated with a significant reduction in memory B cells and no evidence of circulating antibody-secreting cells. These observations correlate with dysregulation of tumor necrosis factor family members BAFF and APRIL and increased expression of FAS on circulating B cells.     

EBV与HCMV传染性单核细胞增多症患儿的实验室指标比较

目的观察EB病毒（EBV）与人类巨细胞病毒（HCMV）感染所致的传染性单核细胞增多症（IM）患儿超敏C-反应蛋白（hs-CRP）、白细胞（WBC）计数、嗜中性粒细胞比值（N）、异常淋巴细胞（异淋）、嗜异性抗体和血清酶的变化。方法选择70例确诊有EBV病毒感染且具备传染性单核细胞增多症临床特点的患儿（A组）进行实验室检测指标分析及总结;并与37例HCMV相关传染性单核细胞增多症患儿（B组）进行比较。结果与EB组（A组）比较,HCMV组（B组）感染患儿hs-CRP水平、肌酸激酶同功酶（CK-MB）、丙氨酸氨基转移酶（ALT）、外周血WBC计数、异型淋巴细胞增高程度较低（P〈0.05）,嗜异性抗体常为阴性,两组N值差异无统计学意义（P〉0.05）。结论 EBV与HCMV感染所致的传染性单核细胞增多症患儿的实验室指标变化不同,应重视IM患儿的实验室检查以辅助诊断。     

Cytotoxic lymphocytes in infectious mononucleosis.

Seven patients with a clinical diagnosis of infectious mononucleosis (IM) and detectable heterophil antibodies were found to have peripheral blood lymphocytes that were cytotoxic for lymphoid cells containing Epstein-Barr virus from a patient with Burkitt''s lymphoma. The cytotoxic lymphocytes persisted in the peripheral circulation for up to 45 days. Patients who had had IM 1 to 5 years previously lacked such cytotoxic lymphocytes. Patients who had signs and symptoms of IM but no detectable heterophil antibodies lacked cytotoxic lymphocytes. The lymphocytes of one patient with IM showed progressive diminution of cytotoxic ability after prednisone treatment.     

In vitro regulation of IgA subclass production. III. Selective transformation of IgA1 producing cells by Epstein-Barr virus

In past experiments, using limited dilution analysis, we have demonstrated that a high percentage of immunoglobulin-secreting clones derived from Epstein-Barr virus- (EBV) stimulated lymphocytes secrete IgA. To further characterize the IgA produced by these clones, the IgA subclass of supernatants from clones stimulated 4 to 6 wk previously with EBV was determined by radioimmunoassay. All of 17 IgA-producing clones secreted IgA1; none secreted IgA2. Because we have shown that surface IgM+ (sIgM+) B cells are an enriched source of IgA2 plasma cell precursors, panning techniques were used to purify sIgM+ B cells from tonsils. Of 103 clones derived from these sIgM+ B cells, 102 secreted IgA1 and only one secreted IgA2. The relative absence of IgA2-producing clones could not be attributed to an absence of EBV receptors on IgA2 cells. A mean of 84 +/- 4% of freshly isolated IgA2 B cells and 78 +/- 6% of IgA1 B cells could be stained with a monoclonal antibody binding the EBV receptor; and there was no failure of EBV to infect IgA2 plasma cells precursors. Of IgA2 plasma cells derived from peripheral blood lymphocytes stimulated 7 days previously with EBV, 54 +/- 7% were positive for the EBV nuclear antigen, compared with 54 +/- 18% of IgA1 plasma cells from the same cultures. Seven days after EBV stimulation, a mean of 25% of the total IgA plasma cells were positive for cytoplasmic IgA2, whereas by 21 days after stimulation only 7% were positive for IgA2. This shift in the proportions of IgA1 and IgA2 plasma cells could be attributed to a failure of the IgA2 plasma cell number to increase after 10 days in culture. There was no evidence for selective suppression of IgA2 production by T cells or selective lysis of IgA2 plasma cells by infectious EBV particles. These results demonstrate that although precursors for both IgA1- and IgA2-producing cells can be stimulated to differentiate in response to EBV, there is preferential transformation of IgA1-producing cells.     

EB病毒抗体和DNA联合检测可提高儿童传染性单核细胞增多症的诊断灵敏度

目的评估EB病毒抗体VCA-IgM、VCA-IgG、EA-IgG、EBNA-1-IgG及EBV-DNA载量检测在儿童传染性单核细胞增多症(传单)中的诊断意义。方法用ELISA方法检测70例传单患儿和25例健康儿童血清中EBV四种抗体及PCR荧光定量法检测外周血单个核细胞EBV-DNA载量。结果传单患儿组EBV-DNA的阳性率为87.14%(61/70),对照组阳性率为8.00%(2/25),传单组与对照组EBV-DNA的阳性率比较差异有统计学意义(P<0.01)。EBV抗体检测中,传单组的VCA-IgM阳性率最高,达91.43%(64/70),对照组VCA-IgM全部阴性。传单组EB病毒VCA-IgM和EBV-DNA联合检测的阳性率97.1%。结论 EBV抗体和EBV-DNA载量检测对儿童传单的诊断有极高的价值,尤其是VCA-IgM抗体和EBV-DNA联合检测,可提高儿童传单的临床诊断的敏感性。     

儿童传染性单核细胞增多症淋巴细胞亚群的变化及意义

目的 通过对儿童传染性单核细胞增多症(infectious mononucleosis,IM)外周血淋巴细胞亚群的检测,探讨其细胞免疫功能变化与疾病的关系.方法 采用流式细胞仪对35例IM患儿外周血T、B和NK淋巴细胞亚群进行检测,30例健康儿童作为对照组;对患儿中的7例进行治疗2周后细胞亚群的测定以观察动态变化;对患儿进行外周血异型淋巴细胞计数.结果 IM患儿CD3、CD8 T淋巴细胞水平明显升高,CD19、NK、CD4和CD4/CD8值水平明显降低,分别与正常对照组比较差异均有统计学意义.7例IM患儿治疗2周后T细胞亚群的测定值与入院时比较差异有统计学意义,治疗前CD4、CD4/CD8值低于治疗后,治疗前CD8高于治疗后.IM患儿急性期CD8、CD4/CD8水平与患儿外周血异型淋巴细胞百分率(≤10％和＞10％)的差异有统计学意义.结论 检测淋巴细胞亚群对评估IM患儿的细胞免疫状况,辅助诊断和指导治疗具有重要的临床价值.     

Monitoring of CD95 (APO-1/Fas) ligand expression in human T cells by quantitative RT-PCR

CD95 (APO-1/Fas) receptor/ligand interaction is a key regulatory pathway for apoptosis in lymphoid cells. We developed a quantitative RT-PCR for the human CD95-L to determine expression levels in lymphoid cell lines and in lymphocytes derived from blood of healthy individuals. In untreated peripheral blood T lymphocytes and T cell lines constitutive expression of the CD95-L mRNA was found at low levels. Stimulation of T cells by treatment with PMA and ionomycine (P/I) lead up to a 100-fold maximal increase in CD95-L mRNA after 4 h. CD95-L mRNA is produced by activated CD8 and CD4T cells. In vivo increased CD95-L mRNA expression was found in freshly isolated T cells during the acute phase of EBV infection. In contrast to T cells, CD95-L mRNA could be induced in some B lineage cell lines only after five days of stimulation. Since defective or accelerated CD95/CD95-L interaction is considered to be involved in the pathogenesis of lymphoproliferation, autoimmunity and AIDS, the quantitative RT-PCR assay described in this paper may provide a powerful tool for monitoring CD95-L expression in these diseases.     

Detection of Epstein-Barr virus-associated antigen in fine needle aspiration smears from cervical lymph nodes in the diagnosis of nasopharyngeal carcinoma

Epstein-Barr virus (EBV) has consistently been shown to be associated with undifferentiated nasopharyngeal carcinoma, and an EBV-associated nuclear antigen (EBNA) has been detected in the cells of nasopharyngeal carcinoma. A study on the applicability of EBNA detection in fine needle aspiration (FNA) smears from cervical lymph nodes in the diagnosis of metastatic nasopharyngeal carcinoma was performed. All 11 cases (100%) with metastatic nasopharyngeal carcinoma showed EBNA-positive tumor cells, characterized by bright, granulated nuclear fluorescence. Three (50%) of six cases with other metastatic head and neck carcinomas also showed EBNA-positive tumor cells. These findings suggest that the presence of EBNA-positive tumor cells in FNA smears from cervical lymph nodes is not specific for metastatic nasopharyngeal carcinoma. On the other hand, a negative result in the presence of tumor cells may help to exclude it. A larger study is required to verify these preliminary findings.     

Acute infection with Epstein-Barr virus targets and overwhelms the peripheral memory B-cell compartment with resting, latently infected cells

In this paper we demonstrate that during acute infection with Epstein-Barr virus (EBV), the peripheral blood fills up with latently infected, resting memory B cells to the point where up to 50% of all the memory cells may carry EBV. Despite this massive invasion of the memory compartment, the virus remains tightly restricted to memory cells, such that, in one donor, fewer than 1 in 10(4) infected cells were found in the naive compartment. We conclude that, even during acute infection, EBV persistence is tightly regulated. This result confirms the prediction that during the early phase of infection, before cellular immunity is effective, there is nothing to prevent amplification of the viral cycle of infection, differentiation, and reactivation, causing the peripheral memory compartment to fill up with latently infected cells. Subsequently, there is a rapid decline in infected cells for the first few weeks that approximates the decay in the cytotoxic-T-cell responses to viral replicative antigens. This phase is followed by a slower decline that, even by 1 year, had not reached a steady state. Therefore, EBV may approach but never reach a stable equilibrium.