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Irina Apostolou

Publications and source records attributed to Irina Apostolou.

10 recordsLinked to original sources
PubMed2006

A multistep adhesion cascade for lymphoid progenitor cell homing to the thymus.

Homing of bone marrow (BM)-derived progenitors to the thymus is essential for T cell development. We have previously reported that two subpopulations of common lymphoid progenitors, CLP-1 and CLP-2, coexist in the BM and give rise to lymphocytes. We demonstrate that CLP-2 migrate to the thymus more efficiently than any other BM-derived progenitors. Short-term adoptive transfer experiments revealed that CLP-2 homing involves P-selectin/P-selectin glycoprotein ligand 1 interactions, pertussis toxin-sensitive chemoattractant signaling by CC chemokine ligand 25 through CC chemokine receptor 9, and binding of the integrins alpha4beta1 and alphaLbeta2 to their respective ligands, vascular cell adhesion molecule 1 and intercellular adhesion molecule 1. Preferential thymus-tropism of CLP-2 correlated with higher chemokine receptor 9 expression than on other BM progenitors. Thus, CLP access to the thymus is controlled by a tissue-specific and subset-selective multistep adhesion cascade.

Adoptive Transfer↗
PubMed2006

Instruction of Treg commitment in peripheral T cells is suited to reverse autoimmunity.

In order to exploit regulatory T cells in a clinical setting it is desirable to be able to generate such cells by a variety of antigens that elicit unwanted immune responses. This goal has been achieved by targeting antigen to dendritic cells under subimmunogenic conditions which results in the conversion of naïve Foxp3 negative T cells into Foxp3-expressing regulatory T cells that are indistinguishable from what has been referred to as natural Treg. Such cells have the ability to interfere with immunity at early as well as late stages of the immune response during which effector cells have already been formed. This suggests that Treg cannot only be exploited to prevent immune responses but also to interfere with already established immunity.

Animals↗
PubMed2006

Making regulatory T cells with defined antigen specificity: role in autoimmunity and cancer.

There is increasing evidence that agonist ligand presentation either intrathymically or extrathymically plays a crucial if not essential role in the generation of regulatory T cells (Tregs). Thus, it is possible to induce Tregs of any desired specificity in vivo. The same goal can be achieved in vitro by expanding antigen-specific CD4+ T cells and retrovirally transducing them. In contrast, in vitro expansion of Tregs is limited to antigens that have resulted in Treg generation in vivo. Antigen-specific Tregs can be used in cellular therapy with the goal to prevent autoimmune disease or even to interfere with established autoimmunity. The latter requires that the Tregs can suppress effector cells that have already caused harm, which is possible because of the antigen-dependent homing properties of Tregs, i.e. these cells can accumulate in antigen-draining lymph nodes and exit into inflamed tissue. Generally, the in vivo interference is dependent on cytokines such as transforming growth factor-beta and interleukin-10 that were dispensable in in vivo analysis of immunosuppression. The precise mechanisms of suppression remain enigmatic, however, but may be further elucidated by the molecular analysis of suppressed versus non-suppressed T cells.

Animals↗
PubMed2006

Adoptively transferred allergen-specific T cells cause maternal transmission of asthma risk.

In addition to genetics and environment, maternal asthma is an identified risk factor for developing the disease during childhood. The mechanisms of this maternal effect remain poorly understood. We tested the role of allergen-specific T cells in the maternal transmission of asthma risk by modifying a model where offspring of asthmatic mothers are more prone to develop asthma after an intentionally suboptimal asthma induction. Normal BALB/c females were injected with allergen-specific T cells from ovalbumin-specific T cell receptor (TCR) transgenic DO11.10 donors before mating. Using the protocol of suboptimal asthma induction, offspring of normal and recipient mothers were tested for their susceptibility to develop asthma. Only pups of recipient mothers showed increased airway responsiveness (Penh), allergic airway inflammation with eosinophilia, and local Th2-skewed cytokine production. Although recipient mothers did not develop asthma, serum levels of interferon-gamma, interleukin (IL)-4, IL-10, and IL-13 were significantly increased during pregnancy. Consistent with this finding, a subset of DO11.10 T cells persisted in the spleen and placenta of expectant recipient mothers. We conclude that allergen-specific T cells are sufficient to orchestrate the maternal transmission of asthma risk. Because overt maternal asthma was not required, our results suggest that similar maternal-fetal interactions may occur in other allergic disorders.

Adoptive Transfer↗
PubMed2005

Inducing and expanding regulatory T cell populations by foreign antigen.

Evidence suggests that regulatory T cells expressing the transcription factor Foxp3 develop extrathymically and intrathymically. Mechanisms of extrathymic induction require further scrutiny, especially as proliferation and/or phenotypic changes of preexisting suppressor cells must be distinguished from true de novo generation. Here we report the conversion of truly naive CD4(+) T cells into suppressor cells expressing Foxp3 by targeting of peptide-agonist ligands to dendritic cells and by analysis of Foxp3 expression at the level of single cells. We show that conversion was achieved by minute antigen doses with suboptimal dendritic cell activation. The addition of transforming growth factor-beta or the absence of interleukin 2 production, which reduces proliferation, enhanced the conversion rate. In addition, regulatory T cell populations induced in subimmunogenic conditions could subsequently be expanded by delivery of antigen in immunogenic conditions. The extrathymic generation and proliferation of regulatory T cells may contribute to self-tolerance as well as the poor immunogenicity of tumors and may be exploited clinically to prevent or reverse unwanted immunity.

Animals↗
PubMed2004

In vivo instruction of suppressor commitment in naive T cells.

The induction of antigen-specific tolerance in the mature immune system of the intact organism has met with limited success. Therefore, nonspecific immunosuppression has been the treatment of choice to prevent unwanted immunity. Here, it is shown that prolonged subcutaneous infusion of low doses of peptide by means of osmotic pumps transforms mature T cells into CD4+25+ suppressor cells that can persist for long periods of time in the absence of antigen and confer specific immunologic tolerance upon challenge with antigen. The described procedure resembles approaches of tolerance induction used decades ago, induces tolerance in the absence of immunity, and holds the promise to become an effective means of inducing antigen-specific tolerance prospectively, whereas its power to suppress already ongoing immune responses remains to be determined.

Animals↗
PubMed2003

Effective destruction of Fas-deficient insulin-producing beta cells in type 1 diabetes.

In type 1 diabetes, autoimmune T cells cause destruction of pancreatic beta cells by largely unknown mechanism. Previous analyses have shown that beta cell destruction is delayed but can occur in perforin-deficient nonobese diabetic (NOD) mice and that Fas-deficient NOD mice do not develop diabetes. However, because of possible pleiotropic functions of Fas, it was not clear whether the Fas receptor was an essential mediator of beta cell death in type 1 diabetes. To directly test this hypothesis, we have generated a beta cell-specific knockout of the Fas gene in a transgenic model of type 1 autoimmune diabetes in which CD4+ T cells with a transgenic TCR specific for influenza hemagglutinin (HA) are causing diabetes in mice that express HA under control of the rat insulin promoter. Here we show that the Fas-deficient mice develop autoimmune diabetes with slightly accelerated kinetics indicating that Fas-dependent apoptosis of beta cells is a dispensable mode of cell death in this disease.

Animals↗
PubMed2003

Thymic selection revisited: how essential is it?

Intrathymic T cell development represents one of the best studied paradigms of mammalian development. Lymphoid committed precursors enter the thymus and the Notch1 receptor plays an essential role in committing them to the T cell lineages. The pre-T cell receptor (TCR), as an autonomous cell signaling receptor, commits cells to the alphabeta lineage while its rival, the gammadeltaTCR, is involved in generating the gammadelta lineage of T cells. Positive and negative selection of immature alphabetaTCR-expressing cells are essential mechanisms for generating mature T cells, committing them to the CD4 and CD8 lineages and avoiding autoimmunity. Additional lineages of alphabetaT cells, such as the natural killer T cell lineage and the CD25+ regulatory T cell lineage, are formed when the alphabetaTCR encounters specific ligands in suitable microenvironments. Thus, positive selection and receptor-instructed lineage commitment represent a hallmark of the thymus. Ectopically expressed organ-specific antigens contribute to thymic self-nonself discrimination, which represents an essential feature for the evolutionary fitness of mammalian species.

Animals↗
PubMed2002

Origin of regulatory T cells with known specificity for antigen.

T cell receptor agonists can induce the differentiation of regulatory T (T(R)) cells. We report here that the immunoglobulin kappa-controlled expression of an agonist in different cell types correlated with the phenotype of the generated T(R) cells. We found that aberrant expression on thymic stroma yielded predominantly CD4(+)CD25(+) T(R) cells, which--under physiological conditions--may be induced by ectopically expressed organ-specific antigens and thus prevent organ-specific autoimmunity. Expression of the agonist antigen by nonactivated hematopoietic cells produced mostly CD4(+)CD25(-) T(R) cells. This subset can be derived from mature monospecific T cells without "tutoring" by other T cells and can be generated in the absence of a functioning thymus. Suppression of CD4(+) T cell proliferative responses by both CD25(+) and CD25(-) subsets was interleukin 10 (IL-10) independent and was overcome by IL-2. These data suggest that distinct pathways can be exploited to interfere with unwanted immune responses.

Animals↗