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Biomedical subjects

R E Callard

Publications and source records attributed to R E Callard.

At least 73 records · Page 4Linked to original sources
PubMed1984

Antigen-specific suppression of human antibody responses by allogeneic T cells. I. Frequency and antigen specificity of allogeneic suppressor T cells and their role in major histocompatibility complex-controlled genetic restriction.

Specific antibody responses to influenza virus were obtained in vitro from human blood mononuclear cells (PBM). The addition of allogeneic T cells to responding PBM profoundly suppressed antigen-induced antibody responses, but had no effect on pokeweed mitogen (PWM)-induced polyclonal Ig formation. This raised the possibility that suppression by allogeneic T cells may result from the activation of antigen-specific T suppressor (Ts) cells rather than nonspecific allogeneic effects. The frequency of allogeneic Ts in PBM from a number of different donors, estimated in a series of limiting dilution analyses, was found to range from 0.8 X 10(-5) to 4.5 X 10(-5), which is more typical of antigen-specific than alloreactive T cells. By adding limiting numbers of allogeneic T cells to antibody-forming cultures stimulated simultaneously with two non-cross-reacting antigens (influenza A and B strain viruses A/X31 and B/HK), it was possible to demonstrate suppression of the response to one antigen, but not the other, in the same culture well. Moreover, the frequency of wells in which the response to both antigens was suppressed was not significantly different from that predicted from the calculated frequency of specific allogeneic Ts. These results show that allogeneic suppression was antigen specific, and was not due to non-specific allogeneic effects. By separating T cell preparations into Leu-3a+ (helper) and Leu-2a+ (suppressor/cytotoxic) T cell subsets, suppression was shown to be mediated by a radiosensitive Leu-2a+ T cell. The removal of Leu-2a+ cells from T cell preparations abrogated the suppressor effect and permitted T cell collaboration with B cells, across an HLA-A, -B, and -DR barrier. This result shows that in at least some combinations, suppression rather than major histocompatibility complex restriction is the reason for the failure of allogeneic T and B cells to collaborate in T cell-dependent antibody responses.

Antibody-Producing Cells↗
PubMed1984

Relative sensitivity of human T cell subsets to deoxyadenosine toxicity.

In the presence of adenosine deaminase (ADA) inhibitors, human T cells are highly sensitive to the cytotoxic action of deoxyadenosine (dAdo). On this basis, patients with T cell malignancies have been treated with the ADA inhibitor, deoxycoformycin. It is not known, however, whether T suppressor/cytotoxic (Leu 2a+) and T helper/inducer (Leu 3a+) subsets have different sensitivities to dAdo toxicity. In the present study, peripheral blood T (E+) cells from normal volunteers were incubated with dAdo in the presence of the ADA inhibitor, EHNA, and the proportion of viable Leu 2a+ and Leu 3a+ cells compared after 1, 2 and 3 days. Leu 2a+ T cells were found to be significantly more sensitive than Leu 3a+ cells as evidenced by an increase in the Leu 3a+/Leu 2a+ ratio from 1.9 to 3.0 over 3 days. This finding was confirmed by comparing the cytotoxic action of dAdo on separated Leu 2a+ and Leu 3a+ T cells. The action of dAdo on T helper and T suppressor cell function in antibody responses by human blood lymphocytes was also tested. As Leu 2a+ T cells were more sensitive to the cytotoxic action of dAdo than Leu 3a+ T cells, it was thought that a dose of dAdo plus EHNA could be chosen which would abrogate suppression but leave T helper cell function intact. We were, however, unable to obtain this result indicating that the biochemical mechanism by which T helper and suppressor cells are functionally inhibited is different to that resulting in cell death, and is unable to discriminate between them.

Antibodies, Viral↗
PubMed1983

Acquired immune deficiency syndrome. A prodromal form.

Only one case of the acquired immune deficiency syndrome (AIDS) has been conclusively documented in Australia despite a large at-risk population and the endemic nature of the syndrome in the United States. In this article, the cases of two homosexual men who had the clinical and laboratory features of a prodromal form of AIDS are presented. Such cases should serve to alert the medical profession and public health authorities to the possible existence of the syndrome in Australia.

Acquired Immunodeficiency Syndrome↗
PubMed1983

Standardization of antigen E in ragweed pollen extracts using a monoclonal antibody-based enzyme immunoassay.

A hybridoma-derived monoclonal IgG antibody specific for ragweed AgE was used to develop a competitive binding enzyme immunoassay suitable for quantitation of antigen E levels in ragweed pollen extracts. The assay was capable of detecting as little as 30 ng/ml AgE in crude pollen extracts. The monoclonal antibody was shown to react with AgE present in commercial pooled pollen extracts from a number of ragweed species as well as a laboratory extract from a single species. In contrast to previous conventional xenoantisera, it could distinguish true ragweed (Ambrosia sp) from false ragweed (Franseria sp). The use of monoclonal antibodies in assay systems such as this offers a reproducible and widely applicable method for allergen standardization.

Allergens↗
PubMed1983

Production of human monoclonal antibody to X31 influenza virus nucleoprotein.

In vitro stimulation of human peripheral blood mononuclear cells with X31 influenza virus antigen has been used to enrich for specific anti-X31 antibody-producing cells. Following Epstein-Barr virus transformation of these stimulated cells, a cell line which produces human antibody to X31 virus was derived and subsequently cloned. The cloned cells secrete and IgGl kappa antibody which is directed against the nucleoprotein of A type influenza virus. Culture supernatants contain 10 to 20 micrograms/ml of specific antibody which is now used as a standard for the ELISA assay used in our laboratory to detect antibodies to influenza virus.

Antibodies, Monoclonal↗
PubMed1983

Fine specificity of the in vitro antibody response to influenza virus by human blood lymphocytes.

The fine specificity of anti-influenza antibody produced in vitro by human PBM stimulated with different strains of influenza virus was examined by competition binding in solid phase enzyme immunoassay. Most of the antibody produced in vitro is directed to strain-specific or cross-reactive determinants on the hemagglutinin molecule. The extent of cross-reactivity is dependent on the strain of virus used to stimulate PBM as well as the individual tested and presumably on his previous exposure to influenza viruses. PBM from some individuals produced antibody that bound to the stimulating strain of influenza virus but not to other strains of the same subtype. In other individuals, antibody was produced in vitro that cross-reacted with all viruses in the same subtype (e.g., H3N2; A/X31, A/X47, and A/Texas) but did not bind to other (H2N1 or H1N1) subtypes, and in a few individuals, extensive cross-reaction between subtypes was seen. The presence of antibody to hemagglutinin in these culture supernatants was confirmed by competition binding to highly purified hemagglutinin. This in vitro culture system allows the immunologic memory of individuals to a wide range of stimulating virus strains to be examined simultaneously in terms of specificity of the antibody response by human PBM to influenza virus after natural infection or immunization.

Adult↗
PubMed1983

Accessory cell and HLA compatibility requirements for the generation of specific in-vitro antibody responses to influenza virus by human blood lymphocytes.

The role of antigen presenting cells in specific in-vitro antibody responses to influenza virus by human lymphocytes was investigated. Demonstration of a requirement for accessory cells necessitated vigorous depletion procedures. Accessory cells were removed by passage of mononuclear cells through a Sephadex G10 column followed by separation of cells bearing antigens defined by the monoclonal antibodies OKM1 and UCHM1 by fluorescence-activated cell sorting or panning. Peripheral blood mononuclear cells treated in this way were unable to respond to influenza virus by antibody production in either round-bottom or flat-bottom culture wells. The response could be reconstituted by either irradiated plastic-adherent cells or G10 non-adherent OKM1/UCHM1 positive cells in both autologous or allogeneic (HLA-DR different) combinations. The absence of HLA restriction was not due to non-specific allogeneic effects and was confirmed using irradiated, antigen-pulsed accessory cells which were extensively washed, incubated overnight and washed again to remove free antigen. These data suggest that the normal T-cell repertoire contains T helper cells specific for antigen plus self and antigen plus allo MHC.

Antibodies, Monoclonal↗
PubMed1982

Phenotype of human T helper and suppressor cells in an in vitro specific antibody response.

Monoclonal anti-human T cell antibodies have been used to identify cells which provide help for an in vitro specific antibody response to influenza virus and also those which suppress the response of allogeneic peripheral blood mononuclear cells. The helper cells carry antigens defined by the Leu 3a and OKT4-antisera, whereas the suppressor cells are predominantly Leu 2a- and OKT8-positive. Help and suppression in this secondary in vitro antibody response are therefore provided by antigenically distinct T cell subsets.

Antibodies, Monoclonal↗
PubMed1982

Cytopenia and T cell proliferation.

A group of patients with neutropenia or erythroid aplasia associated with T cell proliferation were evaluated to assess the phenotype(s) and functions of T cells observed in these conditions. These patients have near normal numbers of helper/inducer cells but an excess of cells belonging to the suppressor/cytotoxic subset. The characteristic phenotype of these cells is E+, OKT3+, OKT1+1-, OKT8+, Fc gamma R+, and they frequently bear HLA-DR antigen. These cells respond poorly to T cell mitogens and will suppress the response of normal peripheral blood mononuclear cells to mitogens. They fail to suppress PWM-induced immunoglobulin synthesis. Although the natural killer activity in these patients is sometimes low, this subset of T cells possesses cytotoxic capability demonstrable in assays for antibody-dependent cell-mediated cytotoxicity. The evidence for a direct effect of the T cells on BFUE and CFUGM is poor.

Agranulocytosis↗
PubMed1982

Immunological parameters in the aged and in Alzheimer's disease.

Peripheral blood from patients with Alzheimer's disease, elderly normal subjects and young (normal subjects) was examined with respect to leucocyte phenotypes and proliferative responses to lectins. Whole blood cell analysis showed that the neutrophil count was similar in all three groups. However, the lymphocyte count was depressed in the Alzheimer group. The monocyte count was reduced in the healthy aged and further reduced in the Alzheimer group. Analysis of peripheral blood mononuclear cells showed no change in the proportion of E+ cells, total T determined with the monoclonal antibody UCHT1 (similar to OKT3) and the T cell subsets: active E and T dot (discrete esterase staining). However, the proportion of T cells bearing the antigen detected by UCHT3 monoclonal antibody (similar to Leu 1 and OKT1) was reduced in the healthy aged and further reduced in the Alzheimer group. Proliferative responses to PHA, Con A, PA, and PWM were similarly depressed in both the aged and Alzheimer groups.

Adult↗
PubMed1981

Histocompatibility requirements for T cell help in specific in vitro antibody responses to influenza virus by human blood lymphocytes.

Specific antibody responses to influenza virus were obtained in vitro from human blood mononuclear cells (PBM). The response was T cell-dependent, as shown by separation of PBM into E rosette-positive (E+) and -negative (E-) populations. The histocompatibility requirements for T-B cells interactions in this response were analyzed by recombining E- and E+ fractions from donors with varying degrees of HLA compatibility. No antibody formation was obtained from any allogeneic combination except for the special case of HLA identical siblings. As these experiments included combinations with shared or identical HLA-DR specificities, it was unlikely that genetic restriction alone could account for the failure of T-B cell collaboration. Evidence that suppression was responsible for the lack of antibody formation was obtained from experiments in which allogeneic E+ cells profoundly depressed specific antibody responses of intact PBM. In contrast, no such suppression was seen in pokeweed mitogen-driven polyclonal Ig synthesis for which there are no major histocompatibility complex requirements for T cell help. The suppressor activity of allogeneic E+ cells was found to be radiation-sensitive. By irradiating E+ cells, it was, therefore, possible to test for T cell help across an HLA barrier without unwanted suppressor effects. Under these conditions, (irradiated) E+ cells were able to collaborate with allogeneic E- cells even with no HLA alleles in common. This was true even when autologous monocytes were depleted from the helper E+ population. Supernatants collected from antigen-driven cultures of allogeneic E- and E+ cells were able to replace helper T cells in the specific antibody response to influenza virus. The apparent lack of genetic restriction in these responses might, therefore, be explained by the production of a nonrestricted helper factor.

Antibodies, Viral↗
PubMed1981

Distinctive functional characteristics of human "T" lymphocytes defined by E rosetting or a monoclonal anti-T cell antibody.

The properties of human lymphocyte fractions isolated either by sheep red cell(E) rosetting or by fluorescence-activated cell sorting after staining with UCHT1 monoclonal anti-T cell antibody have been compared. Two populations of E+ cells with very different phenotype and function have been identified. E+/UCHT1+ cells respond well to the T cell mitogens phytohemagglutinin and concanavalin A and provide help for an in vitro specific antibody response. They can also suppress the antibody response of allegeneic peripheral blood mononuclear cells. In contrast, the E+/UCHT1- population, which has no other markers characteristic of T cells, fails to respond to mitogens or to provide help or suppression for an antibody response. These cells, however, are highly active natural killers. They possess Fc gamma receptors and have a characteristic staining pattern of nonspecific esterase enzyme activity. It is concluded that not all cells capable of forming E rosettes are thymus-processed cells and that this heterogeneity can be revealed by staining with the monoclonal anti-T cell reagent UCHT1.

Animals↗
PubMed1981

Abnormalities of T-cell subsets in patients with neutropenia and an excess of lymphocytes in the bone marrow.

Morphological, surface-marker and culture studies were performed in three patients who had in common neutropenia and an excess of lymphocytes in the bone marrow, but who differed from each other in certain regards such as age and peripheral lymphocyte numbers. All three patients had an increased proportion of E-rosetting cells bearing Fc receptors for IgG. These cells were shown to be T lymphocytes by staining with monoclonal anti-T-cell sera and their subset phenotype was established as OKT4- OKT8+; in addition, a variable proportion of the cells was Ia+. The functional significance of this expanded subpopulation of T cells was not clear, but it was shown that they did not inhibit colony formation in vitro.

Adult↗