PubMed Health⌕ Search

Biomedical subjects

G Tosato

Publications and source records attributed to G Tosato.

At least 109 records · Page 6Linked to original sources
PubMed1985

Cellular distribution of a human I-A-like (DS/DC) antigen on normal and neoplastic lymphoid cells.

Previous biochemical studies have shown that B cell specific, monoclonal antibody, McAb 33.1, reacts with a class II antigen that represents a human analogue of murine I-A (DS/DC) antigens (J. Exp. Med. 158:1924, 1983). McAb 33.1 recognizes a polymorphic human B lymphocyte specific antigen present on mu+, B1+ peripheral B cells, B lymphoid cell lines, activated B cells, and neoplastic B lymphoid cells. Of 100 HLA-D/DR typed EBV-transformed lymphoblastoid cell lines tested, only those from DR3,3 and DR7,7 individuals failed to react with McAb 33.1. The 33.1 antigen is present at lower concentrations on B cells from blood, tonsil, spleen, and lymph node when compared to B cell lines. By contrast, the antigen is not detectable on blood T lymphocytes, T cell lines, or mitogen activated T cells and it is absent on monocytes of some individuals or is present only on a minor subpopulation (approximately 20%). McAb 33.1 should facilitate the functional, structure, and molecular dissection of the human Ia system.

Animals↗
PubMed1985

Persisting illness and fatigue in adults with evidence of Epstein-Barr virus infection.

Clinical, serologic, virologic, and immunologic evaluations for 31 adults with chronic illness and fatigue suggested that 23 had persisting Epstein-Barr virus infection. Among these 23 patients, cellular immune mechanisms were generally normal, but 4 had mild immunoglobulin deficiencies. However, 20 patients had abnormal serologic profiles specific for Epstein-Barr virus shown by significantly elevated titers of antibodies to the viral capsid antigen or early antigen, or by a deficiency of late-appearing antibodies. In 11 of 15 patients tested, circulating immune complexes were found. Circulating interferon was not found in 18 patients tested, but the activity of 2-5 oligoadenylate synthetase, an interferon-induced enzyme, was increased in 5 patients studied. Of 19 patients, 18 had persisting suppressor T-cell activity typically found in patients recovering from acute infectious mononucleosis. We believe that the Epstein-Barr virus may be associated with chronic illness in adults.

Adolescent↗
PubMed1985

Immunostimulation by cytomegalovirus (CMV): helper T cell-dependent activation of immunoglobulin production in vitro by lymphocytes from CMV-immune donors.

Cytomegalovirus (CMV) is the cause of a number of different diseases ranging from self-limited benign infections in healthy adults to life threatening illnesses among immunocompromised hosts and newborns. Suppression of cell-mediated immunity is often found in cases of acute CMV infection, and in addition, the virus may also be a potent stimulant of lymphoid cells in vivo. We studied cellular proliferation and immunoglobulin (Ig) production induced by CMV to determine its effect on human lymphocytes in vitro. The CMV that was added to cultures of lymphocytes from CMV-seronegative donors failed to induce either significant cellular proliferation or Ig production. By contrast, CMV-stimulated cultures from CMV-seropositive donors induced both prominent cellular proliferation and Ig production. B cell differentiation into Ig-secreting cells required the presence of T cells, and this T cell help was sensitive to irradiation with 2000 rad and to treatment with cyclosporin A. When T cells were depleted of OKT4+ cells with monoclonal antibody and complement, the co-cultured B cells failed to produce Ig, whereas the depletion of OKT8+ cells had no effect on the Ig-secreting cell response. Inactivation of CMV before culture did not result in a reduction of either cellular proliferation or Ig production. Thus, infection of target cells is not required for in vitro lymphocyte activation by CMV. These results demonstrate that CMV is a potent activator of B cells inducing Ig production in vitro, and that this process requires the presence of virus-specific memory T cells.

Adult↗
PubMed1985

Characteristic T cell dysfunction in patients with chronic active Epstein-Barr virus infection (chronic infectious mononucleosis).

We evaluated immune functions in 16 patients with chronic active Epstein-Barr virus (EBV) infection (chronic infectious mononucleosis). Chronic infectious mononucleosis is an illness characterized primarily by chronic and occasionally disabling fatigue and other constitutional complaints, only sometimes beginning with an episode of acute infectious mononucleosis, and associated with an abnormal pattern of serum antibodies to EBV. In these patients, the frequency of circulating EBV-infected B cells that manifested spontaneous outgrowth in vitro was comparable to that found in EBV-seropositive normals, and the levels of EBV-specific suppressor activity were also normal. Upon stimulation with polyclonal activators, unseparated cells from these patients produced a relatively normal number of immunoglobulin-secreting cells. However, when purified T cells from these patients were mixed with normal mononuclear cells in co-culture, immunoglobulin production was strikingly suppressed. The degree of this T cell suppression correlated directly with the abnormally elevated titer of antibody to the early antigens of EBV. Interestingly, during normal convalescence from acute EBV-induced infectious mononucleosis a period is also seen during which T cells suppress the response of allogeneic but not autologous cells. Thus, from an immunologic viewpoint, patients with chronic active EBV infection appear "frozen" in a state typically found only briefly during the convalescence from acute EBV infection.

Adolescent↗
PubMed1985

Relationship between immunoglobulin production and immortalization by Epstein Barr virus.

After infection with Epstein Barr virus (EBV), human B lymphocytes actively secrete immunoglobulin (Ig) and are immortalized to become long-term cell lines. In these studies, we investigated the relationship between these virally induced processes utilizing limiting dilution culture techniques, and asked whether all B cells stimulated by EBV to secrete Ig are also immortalized. The activation of B cells by EBV resulting in Ig production and immortalization involved a single precursor cell, required live viral particles, and was independent of immunity to EBV by the lymphocyte donor. However, the precursor frequency of B cells activated to secrete Ig (mean 4.7%) was higher than the precursor frequency of B cells activated to long-term in vitro growth (mean 2.1%). When examined at a single cell level, it appeared that although the vast majority of the immortalized B cells also secrete Ig, only approximately 50% of the B cell precursors induced by EBV to secrete Ig go on to form long-term cell lines. In addition, although immortalized B cell clones producing all major classes of Ig were detected, IgM-committed precursors were more likely to become immortal than were precursors committed to IgG or IgA production. In contrast to these findings in B cells freshly infected with EBV, Ig production was almost always associated with evidence of long-term growth when B cells from previously established EBV-induced B cell lines were tested in identical limiting dilution cultures. Thus, after infection with EBV, human B cells can either become transiently activated to proliferate and to secrete Ig, or become transformed into long-term cell lines most of which produce Ig.

Adult↗
PubMed1985

Defective allosuppression in patients with ataxia-telangiectasia.

We describe a novel in vitro assay system that detects the generation of suppressor T cells after exposure of human lymphocytes to class I alloantigens. We have used this system to study immune functions in a group of seven patients with ataxia-telangiectasia (AT). Normal T lymphocytes exposed to cells differing at the A and B locus histocompatibility locus antigens (HLA) become activated for suppression of Epstein-Barr virus (EBV)-induced immunoglobulin (Ig) production. In contrast to the normal, T cells from patients with AT demonstrate no inhibitory effect after allostimulation. These data indicate that patients with AT have a profound defect involving responses to class I antigens of the major histocompatibility complex (MHC).

Adolescent↗
PubMed1984

Abnormally elevated frequency of Epstein-Barr virus-infected B cells in the blood of patients with rheumatoid arthritis.

Patients with rheumatoid arthritis (RA) are known to have in vitro regulatory T cell abnormalities relating to Epstein-Barr virus (EBV). In this report, we asked whether patients with RA have more circulating EBV-infected B cells than normals. To address this question, we determined the frequency of spontaneously transforming B cells in the peripheral blood of 18 normals, 15 patients with RA, and 8 patients with systemic lupus erythematosus (SLE). The mean frequency of spontaneously transforming B cells in RA patients was 10.1/10(6) B cells, which was significantly greater than that of the normal controls, 2.8/10(6) B cells (P less than 0.005). The group of patients with SLE did not differ from the normals (P greater than 0.4). In further studies undertaken to investigate as to whether RA B cells are more easily transformed by EBV than normal B cells, we determined that the frequencies of transforming B cells in the presence of exogenous EBV were similar in RA patients and normals. Lymphocytes obtained from patients with RA demonstrate a profound T cell defect in their EBV-specific suppression, as measured in vitro; there was no direct correlation, however, between this in vitro T cell abnormality and the number of circulating EBV-infected B cells. Thus, patients with RA, as a group, have abnormally elevated numbers of circulating EBV-infected B cells, and this abnormality most likely derives from a complex dysregulation of the defense mechanisms for infection with EBV.

Adult↗
PubMed1984

Pure red blood cell aplasia associated with chronic Epstein-Barr virus infection: evidence for T cell-mediated suppression of erythroid colony forming units.

A prominent T cell suppressor response is known to develop and inhibit the polyclonal B cell activation induced by Epstein-Barr virus infection. Exuberant T suppressor cell activity suppressing erythropoiesis has been demonstrated in certain cases of pure red blood cell aplasia. We studied a 19-year-old man who developed pure red cell aplasia after Epstein-Barr virus infection. Over a 70-week period, lymphocyte function and serologic evidence for chronic Epstein-Barr virus infection was demonstrated. On two separate occasions, no evidence for serum inhibition of bone marrow erythroid colony formation in methylcellulose was observed. Growth of granulocyte-macrophage progenitors from the patient's bone marrow was normal. The patient's bone marrow cultures yielded 81.6 +/- 11.2 erythroid colony-forming units per 10(5) bone marrow mononuclear cells, which was approximately 50% of levels in normal control bone marrow. Culture of peripheral blood mononuclear cells for erythroid burst-forming units revealed minimal growth (less than 1% of control values). Depletion of bone marrow T cells by E-rosetting resulted in a threefold increase in erythroid colony-forming units in the patient's bone marrow but no significant increase from control bone marrow. In the patient, addition of bone marrow T cells but not peripheral blood T cells significantly suppressed autologous erythroid colony-forming unit proliferation from T cell-depleted bone marrow. These results suggest that the pure red cell aplasia associated with chronic Epstein-Barr virus infection in this case was caused by bone marrow T cell-mediated suppression of erythroid colony-forming unit proliferation.

Adult↗
PubMed1983

Reversal of infectious mononucleosis-associated suppressor T cell activity by D-mannose.

Epstein-Barr virus-induced infectious mononucleosis (IM) is associated with the activation of suppressor T lymphocytes that profoundly inhibit immunoglobulin (Ig) production in vitro. We have examined the nature of signals operating in the interaction between IM suppressor T cells and their targets, and explored the possibility that a lectin-like receptor molecule and its specific sugar might provide specificity to this interaction. When D-mannose or some of its derivatives, including alpha-methyl-D-mannoside, mannose-6-phosphate, and mannan, were added to suppressed cultures containing IM T lymphocytes and pokeweed mitogen (PWM)-stimulated normal mononuclear cells, a significant enhancement of Ig production was observed. These sugars had little or no effect on Ig production by the PWM-stimulated responder cells alone and thus the enhanced Ig production could be attributed to the reversal of suppression in the co-cultures by these sugars. This was further confirmed by the observation that the sugars were effective only if present during the first 24 h of culture, a time when IM suppressor T cells exert their principal effect. The effect of sugars on Ig production by suppressed cultures was similar to that achieved by decreasing by about fourfold the number of IM T cells in culture. The effect of the sugars is unlikely to represent a form of nonspecific toxicity, since inhibited cultures become responders in the presence of the sugar. Furthermore, toxicity restricted to the suppressor T cells is unlikely, since preincubation of the T cells with the sugars did not reduce their subsequent ability to suppress in secondary indicator cultures. In addition, there was no correlation between the effect of the sugars on T cell proliferation and their effect on T cell-mediated suppression. The reversal of suppression by sugars was dose dependent and demonstrated stereo-specificity in that L-mannose was without effect while D-mannose reversed suppression. These data indicate that D-mannose and some of its derivatives consistently reverse suppression of Ig production by IM T cells and strongly suggest a role for saccharides as critical components in the cellular receptors involved in certain physiologic immune cell interactions.

Acute Disease↗
PubMed1983

Limiting dilution analysis of Epstein-Barr virus-induced immunoglobulin production by human B cells.

The Epstein-Barr virus (EBV) is a herpes virus that has the capacity to infect human B cells and to induce them to secrete immunoglobulin (Ig). In the current experiments, Poisson analysis of limiting dilution cultures has been used to study the activation of human peripheral B cells by the B95-8 strain of EBV. Under the culture conditions used, 0.2-1% of peripheral blood B cells were activated by EBV to secrete IgM or IgG. In addition, when multiple replicate cultures containing limited numbers of B cells were tested for IgM and for IgG production, the precursors for IgM and IgG segregated independently; thus, individual B cell precursors matured into cells secreting IgM or IgG but not both classes of Ig. Additional experiments using limiting dilutions of EBV were undertaken to study the viral requirements for B cell activation. These studies indicated that B cell activation by EBV to produce Ig was consistent with a "one-hit" model and inconsistent with a "two-hit" model. Taken together, these results indicate that infection by one EBV virion is sufficient to induce a precursor peripheral blood B cell to secrete Ig and that only one isotype of Ig is then secreted.

Antibody Formation↗
PubMed1982

Interferon-mediated inhibition of human polyclonal immunoglobulin synthesis.

Human lymphoblastoid IFN suppressed human polyclonal Ig synthesis in a dose-related manner, with 71% mean inhibition of antibody production found when 1000 units of IFN were added to the cultures. This suppression was demonstrated to be mediated by an electrophoretically pure preparation of IFN. Furthermore, IFN inhibition of both the T-dependent and the T-independent polyclonal activators was not the result of direct cellular cytotoxicity. IFN-mediated suppression of human polyclonal Ig production does not result from induction of T suppressor cells, and in a T helper cell-independent system this inhibition appears to result from either a direct action on the B cells or an indirect effect via monocytes.

Antibody Formation↗
PubMed1982

T cell-mediated immunoregulation of Epstein Barr virus- (EBV) induced B lymphocyte activation in EBV-seropositive and EBV-seronegative individuals.

Infection with Epstein Barr virus (EBV) is accompanied by seroconversion and life-long persistence of the virus in B lymphocytes. During acute EBV-induced infectious mononucleosis, suppressor T cells become activated, which may provide an additional mechanism of host defense against the causative agent. When cultures of lymphocytes from normal adults seropositive for EBV were stimulated with the B95-8 strain of EBV, purified B cells produced increasingly higher numbers of immunoglobulin- (Ig) secreting cells, whereas in co-cultures of autologous B and T cells a profound suppressor T cell activity inhibited further B cell activation after 10 to 12 days in culture. No such T cell-mediated inhibitory effect was seen in cultures of lymphocytes obtained from normal adults seronegative for EBV, indicating a correlation between the suppressor effect with evidence of prior immunity to this virus. The T cell-mediated suppression in patients with infectious mononucleosis is characterized by an early-acting inhibitory effect on B cell differentiation that is not specific in that all polyclonal B cell activators are inhibited, whereas in EBV-seropositive normal subjects suppression is delayed in time and affects only EBV-activated cultures. These data indicate that after infection with EBV, immunoregulatory T cells are generated that are capable of inhibiting further EBV-induced activation of autologous B cells and thus may provide an additional unique mechanism of host defense against persisting EBV-infected B cells.

Antibody-Producing Cells↗
PubMed1981

Defective EBV-specific suppressor T-cell function in rheumatoid arthritis.

Several lines of evidence, including high antibody titers to Epstein-Barr virus (EBV)-associated antigens and rapid transformation of B cells into lymphoblastoid cells lines, suggest an association between EBV and rheumatoid arthritis. When lymphocytes from normal immune donors were infected with EBV in culture, they produced an exponentially increasing number of immunoglobulin-secreting cells for eight to 10 days. Thereafter, there was a marked late suppression of their response, mediated by immunoregulatory T cells; by 12 days in culture, this suppression averaged 90 per cent. Lymphocytes from 20 EBV-immune patients with rheumatoid arthritis also responded with increasing production of immunoglobulin-secreting cells, but the late suppression expected in immune donors was absent. Tests of several other T-cell functions in these patients gave normal results, suggesting a more restricted defect in suppressor-T cell function relating specifically to EBV. Since EBV persists in host B cells and thus represents a potential stimulus for immunoglobulin production, this persistence, along with a specific regulatory T-cell defect, may contribute to many of the immune abnormalities underlying rheumatoid arthritis.

Adult↗