Lymphocyte responses to EBV-associated antigens in infectious mononucleosis, and Hodgkin's and non-Hodgkin's lymphoma patients, with the leukocyte adherence inhibition assay

EBV-Specific Immune Response: Early Research and Personal Reminiscences

Early research on Epstein-Barr virus (EBV) developed from serological observations that were made soon after the discovery of the virus. Indeed, the definition of the humoral response to a variety of EBV proteins dominated the early literature and was instrumental in providing the key evidence for the association of the virus with infectious mononucleosis (IM), Burkitt's lymphoma (BL), and nasopharyngeal carcinoma (NPC). Each of these disease associations involved a distinct pattern of serological reactivity to the EBV membrane antigens (MA), early antigens (EA), and the EBV nuclear antigen (EBNA). When it became generally accepted that the marked lymphocytosis , which is a hallmark of acute IM, was dominated by T cells, considerable effort was directed toward untangling the specificities that might be associated with restricting the proliferation of newly infected B cells. Early evidence was divided between support for both EBV non-specific and/or HLA non-restricted components. However, all results needed to be reassessed in light of the observation that T cells died by apoptosis within hours of separation from fresh blood from acute IM patients. The observation that EBV-infected cultures from immune (but not non-immune) individuals began to die (termed regression) about 10 days post-seeding, provided the first evidence of a specific memory response which was apparently capable of controlling the small pool of latently infected B cells which all immune individuals possess. In this early era, CD8(+) T cells were thought to be the effector population responsible for this phenomenon, but later studies suggested a role for CD4(+) cells. This historical review includes reference to key early observations in regard to both the specific humoral and cellular responses to EBV infection from the time of the discovery of the virus until 1990. As well, we have included personal recollections in regard to the events surrounding the discovery of the memory T cell response since we believe they add a human dimension to a chapter focussed on early history.

Elevated antibody titers to Epstein-Barr virus prior to the diagnosis of Epstein-Barr-virus-associated gastric adenocarcinoma

Epstein-Barr virus (EBV) has recently been identified in the tumor cells of patients with gastric carcinoma. We tested pre-morbid serum samples from a carefully monitored cohort of Japanese men in order to investigate the possibility that patients with EBV-associated gastric cancer represent a sub-set of individuals with long-standing difficulties in appropriately managing EBV infection. From a serum bank, we obtained 108 samples derived from 54 patients destined to develop gastric adenocarcinoma and 54 controls. Samples were tested under code for antibodies to EBV-capsid antigen, early antigen and nuclear antigen. Individuals who were positive for IgA antibodies against EBV viral-capsid antigen (VCA) and IgG antibodies against the R component of EBV early antigen were at a 3.9-fold and 1.9-fold excess risk of disease, respectively. Antibody titers to EBV VCA were significantly higher in those destined to get EBV-associated gastric cancer than those subsequently developing non-EBV-associated gastric cancer or age-and-gender-matched controls. These findings suggest that the inability to control EBV infection on a long-term basis exists many years prior to the development of EBV-associated gastric cancer, and that EBV may play an etiologic role in this sub-set of malignancies.

Antibodies to human herpes virus-6 and clinical course in patients with Hodgkin's disease

Serial serum samples from 37 patients with Hodgkin's disease (HD) and 39 healthy controls were studied for antibodies to human herpes virus-6 (HHV-6) using ELISA and indirect immunofluorescent antibody (IFA) tests and to the Epstein-Barr virus (EBV) using a radio-complement fixation assay. Antibodies to HHV-6 in the pre-treatment sera from the HD patients were not significantly different from those of controls, but significant changes in titers related to clinical course were noted among the HD patients. HHV-6 IFA titers increased significantly in the course of follow-up in patients who relapsed and decreased significantly over time in patients who did not. These serologic studies support tissue-based investigations indicating that EBV plays a greater etiologic role in HD than HHV-6, although HHV-6 serology may be of prognostic value or may assist in identifying individuals with immunologic abnormalities. The identification of diverse HHV-6 antibody patterns using different assays may reflect the presence of a number of antibodies with varying implications, similar to those identified for EBV.

T lymphocytes in infectious mononucleosis; effect of IL-2 on the outgrowth of Epstein-Barr virus-infected cells

The addition of interleukin-2 (IL-2) to lymphocyte cultures from acute infectious mononucleosis (IM) donors dramatically increased the incidence of regression in such cultures and resulted in the emergence of an IL-2 dependent, CD3 Epstein-Barr virus nuclear antigen (EBNA)-negative cell population. Corresponding cultures seeded in the absence of IL-2 rarely regressed and were quickly dominated by IL-2 independent, CD3-negative, EBNA-positive cells. Lymphocyte cultures from Epstein-Barr virus (EBV) seropositive donors showed enhanced regression in the presence of IL-2 but failed to regress after the removal of the E-rosetting population. Cultures from EBV-seronegative donors showed no evidence of regression in the presence or absence of IL-2. E-rosetting cells isolated from cultures from acute IM donors that had been cultured in the presence of IL-2 lysed autologous and allogeneic lymphoblastoid cell lines.

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 T-cell-mediated immunity to Epstein-Barr virus in man. IV. Development of T-cell memory in convalescent infectious mononucleosis patients

Under appropriate culture conditions, EB virus infection of lymphocytes from seropositive donors leads to regression of transformation, and this was shown previously to be due to activation in a secondary immune response to T lymphocytes inhibitory for the autologous lymphoblastoid cell line. Regression can be quantified by determining the number of cells required for its expression. To investigate the development of memory T cells with EB-virus specificity in the primary infection, a comparison was made of the capacity for regression of lymphocytes from 16 cases of infectious mononucleosis (IM) and 13 normal donors. With 9 normal seropositive donors a mean lymphocyte concentration of 4.6 X 10(5)/ml was required to achieve 50% regression. In contrast, with 8 cases of IM tested within 1 week of onset, a much higher mean lymphocyte concentration (3.7 X 10(6)/ml) was necessary. Six of these IM cases, and another not tested in the first week, were tested on several occasions between 5 and 23 weeks after onset, and showed a slight reduction in the mean cell concentration required for regression (1.5 X 10(6)/ml). Six additional were tested 23--83 weeks after onset by which time the cell concentration required for 50% regression (mean = 4.5 X 10(5)/ml) had reached the level shown by normal seropositive donors. Regression did not occur with lymphocytes from seronegative donors, even at the highest cell concentration. Recombination cultures of T-cell-depleted and T-cell-enriched lymphocyte populations from 3 IM cases in ratios of 1:7 to 7:1 showed that the failure of regression in acute IM was not due simply to lack of sufficient numbers of T cells. The results indicate that EB-virus-specific memory T-cell activity as detected by the regression test is absent in the acute phase of IM, becomes evident at low levels 5--23 weeks after onset, and reaches a maximum after about 6 months.

Elevated titer of antibodies to Simian sarcoma virus envelope antigen (gp70) and normal response to influenza virus in untreated Danish Hodgkin's patients

Untreated Danish Hodgkin's disease (HD) patients and paired age- and sex-matched controls were tested for serum antibodies to Epstein-Barr virus (EBV), six strains of influenza virus and Simian sarcoma virus/Simian sarcoma-associated virus [SSV(SSAV)] antigens. HD sera showed significantly elevated titers against EBV and both increased incidence and mean titer of antibodies to the envelope glycoprotein of SSV(SSAV), whereas testing against the influenza viruses revealed no differences between HD and controls. A focus reduction assay demonstrated a low incidence in HD and controls of sera with neutralizing effects against SSV(SSAV) and the "baboon" C-type virus component of the human HL-23 virus complex, which seemed coupled to HL-A type W19.

Delayed hypersensitivity reactions of cancer patients to antigens on lymphoid cell lines

Four-hundred and fifty nine cancer patients were skin tested with extracts from five lymphoid cell lines. More than 50% of patients with lymphoma had positive skin tests with the extracts prepared from the cell line derived from Burkitt's lymphoma (BL) and more than 50% of nasopharyngeal carcinoma (NPC) patients reacted to the NPC-derived cell line extracts. Although the significant association between patient diagnosis and orgin of cell lines suggested that tumor-associated antigens were responsible for the pattern of delayed hypersensitivity, problems in standardization of antigen potency and non-specificity need to be resolved before this in vivo assay achieves its full potential.