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Biomedical subjects

C G Fathman

Publications and source records attributed to C G Fathman.

At least 109 records · Page 6Linked to original sources
PubMed1989

Presentation of exogenous protein antigens by dendritic cells to T cell clones. Intact protein is presented best by immature, epidermal Langerhans cells.

The capacity of dendritic cells to present protein antigens has been studied with two MHC class II-restricted, myoglobin-specific, T cell clones. Spleen dendritic cells and cultured epidermal Langerhans cells (LC) presented native myoglobin weakly and often not at all. These same populations were powerful stimulators of allogeneic T cells in the primary MLR. Freshly isolated LC were in contrast very active in presenting proteins to T cell clones but were weak stimulators of the MLR. Both fresh and cultured LC could present specific peptide fragments of myoglobin to the clones. These results suggest that dendritic cells in nonlymphoid tissues like skin can act as sentinels for presenting antigens in situ, their accessory function developing in two phases. First antigens are captured and appropriately presented. Further handling of antigen then is downregulated while the cells acquire strong sensitizing activity for the growth and function of resting T lymphocytes. The potent MLR stimulating activity of cultured epidermal LC and lymphoid dendritic cells probably reflects prior handling of antigens leading to the formation of allogeneic MHC-peptide complexes.

Animals↗
PubMed1989

Enhanced cell-mediated protection against fatal Escherichia coli septicemia induced by treatment with recombinant IL-2.

Administration of rIL-2 to BALB/c mice induces a rapid, cell-mediated response that is sufficient to protect mice from a lethal i.p. dose of Escherichia coli. Mice were protected from septic death if IL-2 was administered i.p. within 1 h after the bacterial challenge. Optimal protection was provided by treating the lethally challenged mice with rIL-2 at 1 and 5 h or 1, 5, and 10 h after the bacterial challenge and was dose-dependent (greater than or equal to 5.0 x 10(5) U/kg). Furthermore, treatment of mice with anti-IL-2R antibody abolished the protective effect induced by rIL-2 administration. These data suggest that the rIL-2-induced protection against septic death in mice is mediated by a cell type expressing a functional IL-2R. One potentially important therapeutic application of rIL-2 may be to modulate the course of sepsis once the host has been exposed to potentially lethal microbial pathogens.

Animals↗
PubMed1989

Cardiac allograft prolongation in mice treated with combined posttransplantation total-lymphoid irradiation and anti-L3T4 antibody therapy.

Neonatal cardiac allograft survival was examined in mice treated with anti-L3T4 antibody, posttransplantation total lymphoid irradiation (TLI) or a combination of both therapies. Independently, both posttransplantation TLI and short-course antibody treatment allowed minimal prolongation. However, synergistic prolongation in graft survival was observed with the combination (synergistic) therapy. Fluorescence-activated cell sorter analysis of peripheral blood lymphocytes from animals treated with combined anti-L3T4 and posttransplantation TLI additionally revealed "synergy" with respect to the degree of peripheral lymphocyte depletion.

Animals↗
PubMed1989

Immunosuppression by anti-CD4 treatment in vivo. Persistence of secondary antiviral immune responses.

Elimination of CD4+ helper T cells by treatment with monoclonal antibodies (mcAb) in vivo has been used as a new mode of immunosuppression in organ transplantation and autoimmune diseases. To explore the potential risks of this therapeutic approach we have studied antiviral responses in mice depleted of CD4+ T cells. Depletion of CD4+ T cells in vivo completely suppressed the generation of a primary virus-specific cytotoxic response. Injection of high doses of recombinant interleukin-2 (rIL-2) given after virus immunization restored the responsiveness of helper cell-depleted mice to virus-expressing target cells, suggesting a crucial role of IL-2 in antiviral defense mechanisms. In contrast to primary responses, memory cytolytic responses to viral antigens persisted despite depletion of greater than 90% of CD4+ helper T cells. The generation of such memory cytotoxic responses was dependent upon help provided by CD4+ lymphocytes surviving the antibody therapy. After antibody treatment, frequencies of virus-specific helper cells were minimal in primed mice, excluding insufficient helper cell elimination as the reason for the persistence of memory responses. Data presented here suggest that there exist distinct helper pathways in primary and secondary cytolytic antiviral responses that might represent several subsets of helper T cells as well as differences in helper signals required by distinct effector cells.

Animals↗
PubMed1989

Immunosuppression by anti-CD4 treatment in vivo. Cellular and humoral responses to alloantigens.

Antibody-mediated elimination of CD4+ lymphocytes in vivo has been successfully used to suppress the humoral response to foreign antigens and to induce long-term tolerance. However, secondary humoral responses, as well as secondary cytolytic responses specific for viral antigens, could not be prevented, providing evidence for functional heterogeneity within the helper cell compartment. Data presented here support the notion that helper cell requirements for cellular responses to alloantigens are unique and do not involve CD4+ T lymphocytes. While the administration of anti-CD4 mcAb failed to suppress allospecific CTL responses, the formation of alloantibodies was initially inhibited in parallel to the deficiency in CD4+ helper cells. After regeneration of CD4+ T cells, the animals regained the ability to produce specific IgG alloantibodies. The dichotomy of helper pathways in humoral and cellular alloreactive responses challenges the concept of a single CD4+ helper cell population. Insights into the functional heterogeneity of helper cells for primary, secondary, and allospecific responses might open new avenues for selective manipulation of helper subpopulations.

Animals↗
PubMed1988

A new look at the shared epitope hypothesis.

The striking correlation observed between T cell recognition and the sharing of the DR-beta-1 gene sequences (position 67-74) among patients with rheumatoid arthritis studied suggests that the third hypervariable region might be an important contribution to one restriction site for the putative causative agent(s) in rheumatoid arthritis. The fact that this sequence was found in DR1, DR4,Dw14, and DR4,Dw15 beta-1 genes lends support to the hypothesis that, in some cases, human leukocyte antigen and disease association may involve the association of discrete disease-related epitopes rather than entire human leukocyte antigen genes and that these epitopes are immunologically relevant in terms of T cell recognition. The association of these polymorphisms with susceptibility to rheumatoid arthritis would then support the hypothesis that binding and presentation of "arthritogenic peptides" by major histocompatibility complex class II molecules is one of the pathogenic events in developing rheumatoid arthritis.

Animals↗
PubMed1988

Immunotherapy of the nonobese diabetic mouse: treatment with an antibody to T-helper lymphocytes.

Spontaneous diabetes mellitus was blocked in nonobese diabetic mice by treatment with a monoclonal antibody against the L3T4 determinant present on the surface of T-helper lymphocytes. Sustained treatment with the monoclonal antibody led to cessation of the lymphocytic infiltration associated with the destruction of the insulin-producing beta cells. Moreover, the mice remained normoglycemic after the antibody therapy was stopped. These studies indicate that immunotherapy with monoclonal antibodies to the lymphocyte subset may not only halt the progression of diabetes, but may lead to long-term reversal of the disease after therapy has ended.

Animals↗
PubMed1988

Use of anti-L3T4 and anti-Ia treatments for prolongation of xenogeneic islet transplants.

The effects of T helper lymphocyte and Ia+ cell depletion were examined for their ability to independently and synergistically achieve prolongation of xenogeneic (rat-to-mouse) islet transplants. Recipient mice were depleted of T helper lymphocytes by short-term treatment with the anti-L3T4 monoclonal antibody GK1.5. Donor rat islets were treated prior to transplantation with a concentration of anti-Ia immunotoxin (13.4 x RT) that selectively depleted Ia+ cells within the islets while leaving functional insulin-secreting beta-cells unaffected. Anti-L3T4 treatment alone allowed transplants to be prolonged compared with untreated controls; however, all such treated mice rejected their xenogeneic transplant within 22 days. Although 13.4 x RT treatment of donor islets alone did not prolong engraftment, when donor rat islets were pretreated with the anti-Ia immunotoxin and grafted into L3T4-depleted mice, normoglycemia was maintained for greater than 50 days in 56% of transplants. These results suggest that neither L3T4 depletion nor anti-Ia immunotoxin treatment alone is enough to achieve indefinite survival of xenogeneic islets. However, decreasing the immunogenicity of the transplanted islets by anti-Ia immunotoxin treatment prior to transplantation into anti-L3T4 treated mice can allow greatly prolonged xenogeneic graft survival.

Animals↗
PubMed1987

Correlation of T cell receptor V beta gene family with MHC restriction.

We have studied a panel of DBA/2 T cell clones specific for sperm whale myoglobin (SpW Mb) for TCR (T cell receptor) beta chain gene expression by FACS analysis using the monoclonal antibodies F23.1 and KJ16 specific for the V beta 8 family of the TCR beta chain genes. Within any given specificity group, all the clones tested came from different mice. 10 of 11 I-Ed-restricted SpW Mb-specific T cell clones were F23.1+; 8 of these were also KJ16+. Only one of the three I-Ad-restricted clones tested was F23.1+; this clone was KJ16 negative. This study has demonstrated that I-Ed-restricted T cell clones from DBA/2 mice express members of the TCR V beta 8 family irrespective of the epitopes of SpW Mb recognized. These data suggest an apparent correlation between TCR V beta expression and MHC restriction.

Animals↗
PubMed1987

Islet allograft survival after a single course of treatment of recipient with antibody to L3T4.

Allografts of pancreatic islets of Langerhans were induced to survive for an indefinite period in diabetic mice if, at the time of engraftment, the mice received a single course of treatment with a monoclonal antibody directed against the L3T4 determinant, a nonpolymorphic cell surface glycoprotein present on the cell surface of the murine T helper-inducer lymphocyte subset. This treatment allowed the survival of islets of Langerhans transplanted across a major histocompatibility barrier without additional immunosuppression. The results demonstrate that the lymphocyte subset defined by the expression of the L3T4 molecules is central to the induction of allograft rejection and provides a model for tolerance induction for organ allograft transplantation.

Animals↗
PubMed1987

Heterogeneity of signal requirements in T cell activation within a panel of human proliferative T cell clones.

Activation of T lymphocytes is initiated by receptor ligand interactions at the cell surface leading to the transduction of intracellular signals followed by the de novo synthesis and expression of T cell activation markers (including receptors for interleukin 2 (IL 2) and transferrin), production of lymphokines, and T cell proliferation. This requisite first step for activation of T lymphocytes can be mimicked in certain situations with a variety of stimuli. These include antibodies to certain integral membrane proteins, phorbol esters, and plant lectins that act as mitogens. In this paper, we report that at least two classes of human T cell clones can be distinguished based upon signal requirements necessary to induce proliferation. Although all clones analyzed expressed IL 2 receptors and secreted IL 2 after non-antigenic activation, one subset of clones did not proliferate in response to the same non-antigenic signals. In that subset, complete activation leading to proliferation required interaction of the T cell with specific antigen. The ability to subset these T cell clones into two groups did not correlate with phenotypic differences, source of the clone, nor with magnitude of intracellular calcium mobilization. By studying the stimulation requirements of these two subsets of human T cell clones through the use of specific antigen or antigen-independent stimuli, it was possible to demonstrate that different stimuli varied in their ability to induce steps of T cell activation. Analysis of reactivity of these clones to suboptimal stimulation allowed the definition of intermediate stages of T cell activation. Such intermediate stages might reflect a diversity of intracellular signaling pathways or a complexity of regulatory mechanisms distal to the events that allow intracellular calcium mobilization. Thus for the first time, it has been possible to study ordered events of T cell activation in non-transformed, antigen-dependent human T lymphocytes. The data presented in this paper suggest that T cell activation is not an all or nothing phenomenon, and there is an ordered sequence of events that can be differentiated based upon signal requirements at the T cell membrane.

Antigens, Differentiation, T-Lymphocyte↗
PubMed1987

Modulation of CD4 by antigenic activation.

Cell surface expression of CD4, an invariant membrane glycoprotein, is characteristic of the MHC class II-restricted T cell helper/inducer subset. Although the specificity and restriction patterns of T lymphocytes are determined by the T cell receptor for antigen, CD4 might represent an additional "interaction" molecule that is required to strengthen the interaction between T cells, antigen, and antigen-presenting cells. In this manuscript, we have shown that the cell surface expression of CD4 is correlated with activation of T cells. Data presented in this paper have demonstrated, for the first time, that antigenic stimulation of human T cell clones caused a decrease in the expression of the CD4 marker (as well as to the CD3 marker) to about 50% of the constitutive level. As previously demonstrated, PMA caused modulation of CD4 and CD3, which suggested that phosphorylation by protein kinase C played a crucial role in the regulation of the expression of both markers. The parallel down-regulation of CD3 and CD4 after antigen stimulation suggested that both markers might be members of a multimolecular complex mediating T cell activation.

Antigens, Differentiation, T-Lymphocyte↗
PubMed1987

The structure of T-cell epitopes.

We have reviewed here studies using synthetic peptides to analyze some of the properties of T-cell epitopes. Several general conclusions can be drawn. First, T-cell epitopes can usually be defined by linear sequences of about seven amino acids. However, the observation that increasing peptide length often results in increased antigenic potency has suggested that antigenicity may crucially depend upon the ability of peptides to adopt appropriate secondary structures. Two models for the prediction of T-cell epitopes on the basis of primary sequence data alone were discussed. Biophysical studies on the association of peptides with Ia molecules have shown that antigenic peptides bind directly to Ia; the evidence suggests that a binary association between Ia and peptide occurs in the absence of specific T-cells. Finally, a hypothesis to explain the observation that B-cells and T-cells generally recognize distinct epitopes on multideterminant antigens has been examined.

Amino Acid Sequence↗