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Clonally diverse T cell homeostasis is maintained by a common program of cell-cycle control.

ABSTRACT: Lymphopenia induces T cells to undergo cell divisions as part of a homeostatic response mechanism. The clonal response to lymphopenia is extremely diverse, and it is unknown whether this heterogeneity represents distinct mechanisms of cell-cycle control or whether a common mechanism can account for the diversity. We addressed this question by combining in vivo and mathematical modeling of lymphopenia-induced proliferation (LIP) of two distinct T cell clonotypes. OT-I T cells undergo rapid LIP accompanied by differentiation that superficially resembles Ag-induced proliferation, whereas F5 T cells divide slowly and remain naive. Both F5 and OT-I LIP responses were most accurately described by a single stochastic division model where the rate of cell division was exponentially decreased with increasing cell numbers. The model successfully identified key biological parameters of the response and accurately predicted the homeostatic set point of each clone. Significantly, the model was successful in predicting interclonal competition between OT-I and F5 T cells, consistent with competition for the same resource(s) required for homeostatic proliferation. Our results show that diverse and heterogeneous clonal T cell responses can be accounted for by a single common model of homeostasis.

SUBMITTER: Hogan T

PROVIDER: S-EPMC3619530 | biostudies-other | 2013 Apr

REPOSITORIES: biostudies-other

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Project description:Background: The co-stimulatory CD40-CD40L dyad is an important driver of atherosclerosis. CD40 exerts divergent, cell-specific roles, which differentially impact atherogenesis. Objectives: We here investigate the role of the most prominent CD40-expressing cell-type, the B-cell, in atherosclerosis. Methods: B-cell subset specific CD40-expression of patients with mild and severe coronary artery disease (CAD) was determined by mass-cytometry and correlated to CAD severity. Underlying mechanisms were elucidated using B-cell CD40-deficient CD19Cre-CD40flfl-ApoE-/-(CD40BKO) mice and control littermates (CD40BWT). Results: Patients with severe CAD had similar CD40 expression levels on most B-cell subsets but showed a profound decrease in CD40 on putative B1 cells. This was associated with increased atherosclerotic plaque burden and decreased plaque fibrosis. Likewise, CD40BKO mice exhibited an increased plaque area and more advanced staging of atherosclerosis. Absence of CD40 on B-cells caused a decrease in immunoglobulin (Ig) producing cells, including germinal center-, plasma-, but especially B1 cells, thereby reducing levels of (anti-ox/MDA-LDL) IgG and protective (anti-ox/MDA-LDL) IgM. Transcriptomics analysis revealed that the absence of CD40 on B1b cells caused altered gene expression pathways related to lipid uptake (Cd36, Ldlr), cellular stress and metabolism (Nr4a1, Hif1a), and cell death (Naip5/6, Ccnd2). Indeed, in vitro analysis showed that B1bCD40KO cells took up excessive amounts of ac/oxLDL, exhibited defective BCR signaling, and were prone to apoptosis, especially in hyperlipidemic conditions. Transfer of wild-type B1b cells in CD40BKO mice prevented the increase in atherosclerosis. Conclusions: Patients with severe CAD had similar CD40 expression levels on most B-cell subsets but showed a profound decrease in CD40 on putative B1 cells. This was associated with increased atherosclerotic plaque burden and decreased plaque fibrosis. Likewise, CD40BKO mice exhibited an increased plaque area and more advanced staging of atherosclerosis. Absence of CD40 on B-cells caused a decrease in immunoglobulin (Ig) producing cells, including germinal center-, plasma-, but especially B1 cells, thereby reducing levels of (anti-ox/MDA-LDL) IgG and protective (anti-ox/MDA-LDL) IgM. Transcriptomics analysis revealed that the absence of CD40 on B1b cells caused altered gene expression pathways related to lipid uptake (Cd36, Ldlr), cellular stress and metabolism (Nr4a1, Hif1a), and cell death (Naip5/6, Ccnd2). Indeed, in vitro analysis showed that B1bCD40KO cells took up excessive amounts of ac/oxLDL, exhibited defective BCR signaling, and were prone to apoptosis, especially in hyperlipidemic conditions. Transfer of wild-type B1b cells in CD40BKO mice prevented the increase in atherosclerosis.

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Clonally diverse T cell homeostasis is maintained by a common program of cell-cycle control.

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