Biomedical subjects

Andrew J Caton

Publications and source records attributed to Andrew J Caton.

At least 19 recordsLinked to original sources

PubMed2007

Activation of CD4+ CD25+ regulatory T cell suppressor function by analogs of the selecting peptide.

CD4+ CD25+ Foxp3+ regulatory T (Treg) cells can undergo both thymic selection and peripheral expansion in response to self peptides that are agonists for their T cell receptors (TCR). However, the specificity by which these TCR must recognize peptide:MHC complexes to activate Treg cell function is not known. We show that CD4+ CD25+ Foxp3+ Treg cells can mediate suppression in response to peptides that are only weakly cross-reactive with the self peptide that induced their formation in vivo. Moreover, suppression could be efficiently activated by peptide analogs that were inefficient at inducing CD69 up-regulation, and that also induced little or no proliferation of naïve CD4+ CD25- Foxp3- T cells expressing the same TCR. These findings provide evidence that self peptide-specific CD4+ CD25+ Foxp3+ Treg cells can exert regulatory function in response to self- and/or pathogen-derived peptides with which they are only weakly cross-reactive.

Animals↗

PubMed2006

B cell-mediated antigen presentation is required for the pathogenesis of acute cardiac allograft rejection.

Acute allograft rejection requires the activation of alloreactive CD4 T cells. Despite the capacity of B cells to act as potent APCs capable of activating CD4 T cells in vivo, their role in the progression of acute allograft rejection was unclear. To determine the contribution of B cell APC function in alloimmunity, we engineered mice with a targeted deficiency of MHC class II-mediated Ag presentation confined to the B cell compartment. Cardiac allograft survival was markedly prolonged in these mice as compared to control counterparts (median survival time, >70 vs 9.5 days). Mechanistically, deficient B cell-mediated Ag presentation disrupted both alloantibody production and the progression of CD4 T cell activation following heart transplantation. These findings demonstrate that indirect alloantigen presentation by recipients' B cells plays an important role in the efficient progression of acute vascularized allograft rejection.

Animals↗

PubMed2006

Impact of effector cell differentiation on CD4+ T cells that evade negative selection by a self-peptide.

We have used a transgenic mouse system to examine how differing reactivities of TCRs expressed by naive versus effector cells can shape the functional potential of autoreactive CD4+ T cells. Transgenic mice expressing TCRs that exhibit either high (TS1) or low [TS1(SW)] reactivity toward the I-Ed-restricted determinant S1 from the influenza virus PR8 hemagglutinin (HA) were mated with transgenic mice expressing HA under the control of different promoters. HACII mice express HA driven by an MHC class II promoter, and both the TS1 and TS1(SW) TCRs underwent substantial deletion in this background. HA104 mice express HA driven by an SV40 promoter, and the highly reactive TS1 TCR was substantially deleted. By contrast, the less reactive TS1(SW) TCR underwent little or no deletion in TS1(SW) x HA104 mice, although CD5 up-regulation indicated that they had interacted with the S1 self-peptide. In adoptive transfer studies, naive CD4+ T cells expressing the TS1(SW) TCR failed to proliferate in response to the S1 peptide in HA104 mice, and were inefficient at providing help for HA-specific antibody responses. However, effector CD4+ T cells generated from TS1(SW) x HA104 mice acquired the ability to proliferate in response to the S1 peptide in HA104 mice, and were as efficient as CD4+ T cells expressing the high reactivity TS1 TCR in helping HA-specific antibody responses. Collectively, these studies demonstrate a basis by which CD4+ T cells expressing TCRs with low reactivity toward self-peptides can evade negative selection and acquire enhanced autoreactivity following activation by a cross-reactive antigen.

Animals↗

PubMed2006

T-reg mediated suppression of the allograft response in the draining lymph node.

We previously demonstrated that T-regs inhibit proliferation of graft-reactive T cells in the draining lymph node (DLN), suggesting that this site may be important for regulation. TCR transgenic mice (TS1) specific for viral hemagglutinin (HA) provided antigen-specific T cells for adoptive transfer into syngeneic Balb/c hosts bearing HA+ skin grafts. T-regs were obtained from (TS1xHA28)F1 mice known to have an expanded population of HA-specific T-regs. To determine whether the lymph node is an independent site of suppression, we developed a model in which donor antigen that migrates from the allograft to the DLN drives T-cell activation after graft removal. T-regs that did not encounter the allograft itself remained able to inhibit graft antigen-specific T-cell proliferation in the DLN. Alloantigen-induced regulation can occur in the absence of the graft. This finding identifies the DLN as a potentially critical site of regulation in the early posttransplant period.

Animals↗

PubMed2006

Role of TCR specificity in CD4+ CD25+ regulatory T-cell selection.

CD4+ CD25+ regulatory T cells play a crucial role in preventing autoimmune disease and can also modulate immune responses in settings such as transplantation and infection. We have developed a transgenic mouse system in which the role that T-cell receptor (TCR) specificity for self-peptides plays in the formation of CD4+ CD25+ regulatory T cells can be examined. We have shown that interactions with a single self-peptide can induce thymocytes bearing an autoreactive TCR to undergo selection to become CD4+ CD25+ regulatory T cells and that thymocytes bearing TCRs with low affinity for the selecting peptide do not appear to undergo selection into this pathway. In addition, thymocytes with identical specificity for the selecting self-peptide can undergo overt deletion versus abundant selection to become CD4+ CD25+ regulatory T cells in response to variations in expression of the selecting peptide in different lineages of transgenic mice. Finally, we have shown that CD4+ CD25+ T cells proliferate in response to their selecting self-peptide in the periphery, but these cells do not proliferate in response to lymphopenia in the absence of the selecting self-peptide. These studies are determining how the specificity of the TCR for self-peptides directs the thymic selection and peripheral expansion of CD4+ CD25+ regulatory T cells.

Animals↗

PubMed2005

CD4+ CD25+ regulatory T cells inhibit the maturation but not the initiation of an autoantibody response.

To investigate the mechanism by which T regulatory (Treg) cells may control the early onset of autoimmunity, we have used an adoptive transfer model to track Treg, Th, and anti-chromatin B cell interactions in vivo. We show that anti-chromatin B cells secrete Abs by day 8 in vivo upon provision of undeviated, Th1- or Th2-type CD4+ T cell help, but this secretion is blocked by the coinjection of CD4+ CD25+ Treg cells. Although Treg cells do not interfere with the initial follicular entry or activation of Th or B cells at day 3, ICOS levels on Th cells are decreased. Furthermore, Treg cells must be administered during the initial phases of the Ab response to exert full suppression of autoantibody production. These studies indicate that CD25+ Treg cells act to inhibit the maturation, rather than the initiation, of autoantibody responses.

Animals↗

PubMed2005

The influence of effector T cells and Fas ligand on lupus-associated B cells.

Circulating autoantibodies against dsDNA and chromatin are a characteristic of systemic lupus erythematosus in humans and many mouse models of this disease. B cells expressing these autoantibodies are normally regulated in nonautoimmune-prone mice but are induced to secrete Abs following T cell help. Likewise, anti-chromatin autoantibody production is T cell-dependent in Fas/Fas ligand (FasL)-deficient (lpr/lpr or gld/gld) mice. In this study, we demonstrate that Th2 cells promote anti-chromatin B cell survival and autoantibody production in vivo. FasL influences the ability of Th2 cells to help B cells, as Th2-gld/gld cells support higher titers of anti-chromatin Abs than their FasL-sufficient counterparts and promote anti-chromatin B cell participation in germinal centers. Th1 cells induce anti-chromatin B cell germinal centers regardless of FasL status; however, their ability to stimulate anti-chromatin Ab production positively correlates with their level of IFN-gamma production. This distinction is lost if FasL-deficient T cells are used: Th1-gld/gld cells promote significant titers of anti-chromatin Abs regardless of IFN-gamma production levels. Thus, FasL from effector T cells plays an important role in determining the fate of anti-chromatin B cells.

Adoptive Transfer↗

PubMed2005

Positive and negative regulation of the IL-27 receptor during lymphoid cell activation.

Previous reports have focused on the ability of IL-27 to promote naive T cell responses but the present study reveals that surface expression of WSX-1, the ligand-specific component of the IL-27R, is low on these cells and that highest levels are found on effector and memory CD4(+) and CD8(+) T cells. Accordingly, during infection with Toxoplasma gondii, in vivo T cell activation is associated with enhanced expression of WSX-1, and, in vitro, TCR ligation can induce expression of WSX-1 regardless of the polarizing (Th1/Th2) environment present at the time of priming. However, while these data establish that mitogenic stimulation promotes expression of WSX-1 by T cells, activation of NK cells and NKT cells prompts a reduction in WSX-1 levels during acute toxoplasmosis. Together, with the finding that IL-2 can suppress expression of WSX-1 by activated CD4(+) T cells, these studies indicate that surface levels of the IL-27R can be regulated by positive and negative signals associated with lymphoid cell activation. Additionally, since high levels of WSX-1 are evident on resting NK cells, resting NKT cells, effector T cells, regulatory T cells, and memory T cells, the current work demonstrates that IL-27 can influence multiple effector cells of innate and adaptive immunity.

Animals↗

PubMed2005

The role of self-peptides in the development of CD4+ CD25+ regulatory T cells.

The thymus produces a unique lineage of cells known as CD4+ CD25+ regulatory T cells, and the exact processes leading to their development continue to be defined. Highly specific interactions between developing thymocytes and cognate self-antigens expressed by radioresistant elements in the thymus have been shown to drive CD4+ CD25+ regulatory-T-cell development. The self-peptide(s) that mediate thymic selection of CD4+ CD25+ regulatory T cells can also promote their expansion in the periphery, and self-peptides might also play a role in the conversion of CD4+ CD25- T cells into CD25+ regulatory T cells.

Animals↗

PubMed2005

The regulation and activation of lupus-associated B cells.

Anti-double-stranded DNA (anti-dsDNA) B cells are regulated in non-autoimmune mice. While some are deleted or undergo receptor editing, a population of anti-dsDNA (VH3H9/V lambda 1) B cells that emigrate into the periphery has also been identified. These cells have an altered phenotype relative to normal B cells in that they have a reduced lifespan, appear developmentally arrested, and localize primarily to the T/B-cell interface in the spleen. This phenotype may be the consequence of immature B cells encountering antigen in the absence of T-cell help. When provided with T-cell help, the anti-dsDNA B cells differentiate into antibody-forming cells. In the context of the autoimmune-prone lpr/lpr or gld/gld mutations, the VH3H9/V lambda 1 anti-dsDNA B cells populate the B-cell follicle and by 12 weeks of age produce serum autoantibodies. The early event of anti-dsDNA B-cell follicular entry, in the absence of autoantibody production, is dependent upon CD4(+) T cells. We hypothesize that control of autoantibody production in young autoimmune-prone mice may be regulated by the counterbalancing effect of T-regulatory (T(reg)) cells. Consistent with this model, we have demonstrated that T(reg) cells are able to prevent autoantibody production induced by T-cell help. Additional studies are aimed at investigating the mechanisms of this suppression as well as probing the impact of distinct forms of T-cell-dependent and -independent activation on anti-dsDNA B cells.

Animals↗

PubMed2004

Specificity-based negative selection of autoreactive B cells during memory formation.

Autoreactive B cells are not completely purged from the primary B cell repertoire, and whether they can be prevented from maturation into memory B cells has been uncertain. We show here that a population of B cells that dominates primary immune responses of BALB/c mice to influenza virus A/PR/8/34 hemagglutinin (HA) are negatively selected in transgenic mice expressing PR8 HA as an abundant membrane-bound Ag (HACII mice). However, a separate population of B cells that contains precursors of memory B cells is activated by PR8 virus immunization and is subsequently negatively selected during the formation of the memory response. Negative selection of PR8 HA-specific B cells altered the specificity of the memory B cell response to a mutant virus containing a single amino acid substitution in a B cell epitope. Strikingly, this skewed reactivity resulted from an increase in the formation of memory B cells directed to non-self-epitopes on the mutant virus, which increased 8-fold in HACII mice relative to nontransgenic mice and precisely compensated for the absence of autoreactive PR8 HA-specific memory B cells. Negative selection of PR8 HA-specific B cells was a dominant process, since B cells from HACII mice could induce negative selection of PR8 HA-specific B cells from BALB/c mice. Lastly, HA-specific memory responses were unaffected by self-tolerance in another lineage of HA-transgenic mice (HA104 mice), indicating that the amount and/or cell type in which self-Ags are expressed can determine their ability to prevent autoreactive memory B cell formation.

Animals↗

PubMed2004

CD4+ CD25+ regulatory T cell repertoire formation in response to varying expression of a neo-self-antigen.

We have examined the development of self-peptide-specific CD4+ CD25+ regulatory T cells in lineages of transgenic mice that express the influenza virus PR8 hemagglutinin (HA) under the control of several different promoters (HA transgenic mice). By mating these lineages with TS1-transgenic mice expressing a TCR that recognizes the major I-E(d)-restricted determinant from HA (site 1 (S1)), we show that S1-specific T cells undergo selection to become CD4+ CD25+ regulatory T cells in each of the lineages, although in varying numbers. In some lineages, S1-specific CD4+ CD25+ regulatory T cells are highly abundant; indeed, TS1xHA-transgenic mice can contain as many S1-specific CD4+ T cells as are present in TS1 mice, which do not express the neo-self HA. In another lineage, however, S1-specific thymocytes are subjected to more extensive deletion and far fewer S1-specific CD4+ CD25+ regulatory T cells accumulate in the periphery. We show that radioresistant stromal cells can direct both deletion and CD4+ CD25+ regulatory T cell selection of S1-specific thymocytes. Interestingly, even though their numbers can vary, the S1-specific CD4+ CD25+ regulatory T cells in all cases coexist with clonally related CD4+ CD25- T cells that lack regulatory function. These findings show that the formation of the CD4+ CD25+ regulatory T cell repertoire is sensitive to variations in the expression of self-peptides.

Animals↗

PubMed2004

Promotion of allograft survival by CD4+CD25+ regulatory T cells: evidence for in vivo inhibition of effector cell proliferation.

Regulatory T cells preserve tolerance to peripheral self-Ags and may control the response to allogeneic tissues to promote transplantation tolerance. Although prior studies have demonstrated prolonged allograft survival in the presence of regulatory T cells (T-reg), data documenting the capacity of these cells to promote tolerance in immunocompetent transplant models are lacking, and the mechanism of suppression in vivo remains unclear. We used a TCR transgenic model of allograft rejection to characterize the in vivo activity of CD4(+)CD25(+) T-reg. We demonstrate that graft Ag-specific T-reg effectively intercede in the rejection response of naive T cells to established skin allografts. Furthermore, CFSE labeling demonstrates impaired proliferation of naive graft Ag-specific T cells in the draining lymph node in the presence of T-reg. These results confirm the efficacy of T-reg in promoting graft survival and suggest that their suppressive action is accomplished in part through inhibition of proliferation.

Animals↗

PubMed2004

CD4(+) CD25(+) regulatory T cell selection.

Accumulating evidence indicates that regulatory T cells play a crucial role in preventing autoimmunity. To examine the processes by which regulatory CD4(+) T cells are produced during immune repertoire formation, we have developed transgenic mice that express the influenza virus hemagglutinin (HA) and coexpress major histocompatibility complex class II-restricted T cell receptors (TCRs) with varying affinities for the HA-derived CD4(+) T cell determinant S1. We show that interactions with a single self-peptide can induce thymocytes bearing an autoreactive TCR to undergo selection to become CD4(+) CD25(+) regulatory T cells, and that thymocytes bearing TCRs with low affinity for S1 do not undergo selection into this pathway. We show that CD4(+) thymocytes with identical specificity for the S1 self-peptide can undergo overt deletion versus abundant selection to become CD4(+) CD25(+) regulatory T cells in response to variations in expression of the S1 self-peptide in different lineages of HA transgenic mice. We also show that CD4(+) CD25(+) T cells proliferate in response to their selecting self-peptide in the periphery. Moreover, they do not proliferate in response to lymphopenia in the absence of the selecting self-peptide, reflecting a low level of expression of the high-affinity receptor for IL-7 (CD127) relative to conventional CD4(+) T cells. These studies are determining how specificity for self-peptides directs the thymic selection and peripheral expansion of CD4(+) CD25(+) regulatory T cells. Moreover, the differing responsiveness of CD4(+) CD25(+) regulatory T cells to cytokine- versus self-peptide-mediated signals may direct their accumulation to sites where the self-peptide is expressed.

Animals↗

PubMed2003

Alloreactive CD4 T cell activation in vivo: an autonomous function of the indirect pathway of alloantigen presentation.

Activation of alloreactive CD4 T cells occurs via the direct and indirect pathways of alloantigen presentation. A novel TCR/alloantigen transgenic system was designed that permitted in vivo visualization of CD4 T cell priming through these pathways. When both pathways of alloantigen presentation were intact, CD4 T cell activation in response to cardiac allografts was rapid and systemic by day 4 after transplantation, in contrast to that seen in response to skin allografts, which was delayed until 10-12 days after transplantation. Despite this systemic CD4 T cell activation in response to cardiac allografts, there was a paucity of activated graft-infiltrating CD4 T cells at 4 days posttransplantation. This finding suggests that the initial priming of alloimmune CD4 T cell responses occurs within draining lymphoid organs. Furthermore, alloantigens derived from cardiac allografts failed to promote thymic negative selection of developing thymocytes expressing the alloreactive TCR clonotype. In the absence of a functional direct pathway, the kinetics of activation, anatomic localization, and effector function of alloreactive CD4 T cells remained unchanged. Overall, the present study defines the anatomic and temporal characteristics of CD4 T cell alloimmune responses and demonstrates that CD4 T cell priming via the indirect pathway proceeds optimally in the absence of the direct pathway of alloantigen presentation.

Adoptive Transfer↗

PubMed2003

Cutting edge: self-peptides drive the peripheral expansion of CD4+CD25+ regulatory T cells.

CD4(+)CD25(+) regulatory T cell selection is initiated by high-specificity interactions with self-peptides in the thymus, although how these cells respond to cytokine-derived signals and to re-exposure to self-peptide:MHC complexes in the periphery is not well understood. We have used a transgenic mouse system, in which the peptide that induces thymic selection of a clonal population of CD4(+)CD25(+) regulatory T cells is known, to show that CD4(+)CD25(+) T cells proliferate in response to their selecting self-peptide in vivo. Moreover, they do not proliferate in response to lymphopenia in the absence of the selecting self-peptide, reflecting a low level of expression of the high affinity receptor for IL-7 (CD127) relative to conventional CD4(+) T cells. That their selecting self-peptide is both required for and promotes the peripheral expansion of CD4(+)CD25(+) regulatory T cells may direct their accumulation in sites where the self-peptide is expressed.

Adoptive Transfer↗

PubMed2003

Vulnerability of allografts to rejection by MHC class II-restricted T-cell receptor transgenic mice.

BACKGROUND: Examination of the in vivo activation and function of CD4+ T cells in response to allografts may advance our understanding of the rejection process. We analyzed the capacity of transgenic class II-restricted CD4 T cells to reject skin, cardiac, and islet transplants. METHODS: TS1 mice possess a high frequency of CD4+ T cells specific for the immunodominant epitope of the viral hemagglutinin (HA) protein. We analyzed the kinetics of rejection of skin, heart, and islet grafts by naïve and sensitized TS1 mice and by adoptively transferred TS1 lymphocytes. RESULTS: Rejection of heart transplants was more rapid than skin grafts (mean survival time, 12.9 vs. 26.6 days), and islet grafts survived indefinitely in TS1 mice. These findings may be partly attributable to the supranormal frequency of HA-reactive cells in TS1 mice. In support of this, we found that adoptive transfer of 5 x 10(5) TS1 lymphocytes to Balb/c hosts effected consistent rejection of HA-bearing skin transplants, whereas a significantly greater number (3 x 10(6)) was required for heart transplant rejection. The in vivo proliferative response of HA-specific T cells to heart and skin was found to be robust and predominantly localized to the draining lymph nodes. CONCLUSION: We developed a model of allograft rejection in which the responding T cells and relevant graft antigen are specifically defined. Adoptive transfer of carboxy-fluorescein succinimidyl ester-labeled transgenic T cells allowed us to visualize a robust proliferative response in vivo to heart and skin allografts, which in both cases was localized to regional lymph nodes.

Adoptive Transfer↗

PubMed2003

CD25+ immunoregulatory CD4 T cells mediate acquired central transplantation tolerance.

Transplantation tolerance is induced reliably in experimental animals following intrathymic inoculation with the relevant donor strain Ags; however, the immunological mechanisms responsible for the induction and maintenance of the tolerant state remain unknown. We investigated these mechanisms using TCR transgenic mice (TS1) that carry T cells specific for an immunodominant, MHC class II-restricted peptide (S1) of the influenza PR8 hemagglutinin (HA) molecule. We demonstrated that TS1 mice reject skin grafts that have transgene-encoded HA molecules (HA104) as their sole antigenic disparity and that intrathymic but not i.v. inoculation of TS1 mice with S1 peptide induces tolerance to HA-expressing skin grafts. Intrathymic peptide inoculation was associated with a dose-dependent reduction in T cells bearing high levels of TCR specific for HA. However, this reduction was both incomplete and transient, with a full recovery of S1-specific thymocytes by 4 wk. Peptide inoculation into the thymus also resulted in the generation of immunoregulatory T cells (CD4+CD25+) that migrated to the peripheral lymphoid organs. Adoptive transfer experiments using FACS sorted CD4+CD25- and CD4+CD25+ T cells from tolerant mice revealed that the former but not the latter maintain the capacity to induce rejection of HA bearing skin allografts in syngeneic hosts. Our results suggest that both clonal frequency reduction in the thymus and immunoregulatory T cells exported from the thymus are critical to transplantation tolerance induced by intrathymic Ag inoculation.

Adoptive Transfer↗