The Fate of Thymocytes Labeledin Vivowith CFSE

107

Our current view of T cell differentiation and population dynamics is assembled from pieces of data obtained from separate experimental systems and is thus patchy. We reassessed homeostasis and dynamics of T cells 1) by generating a mathematical model describing the spatiotemporal features of T cell differentiation, and 2) by fitting this model to experimental data generated by disturbing T cell differentiation through transient depletion of dividing T cells in mice. This specific depletion was obtained by administration of ganciclovir to mice expressing the conditional thymidine kinase suicide gene in T cells. With this experimental approach, we could derive quantitative parameters describing the cell fluxes, residence times, and rates of import, export, proliferation, and death across cell compartments for thymocytes and recent thymic emigrants (RTEs). Among other parameters, we show that 93% of thymocytes produced before single-positive stages are eliminated through the selection process. Then, a postselection peripheral expansion of naive T cells contributes three times more to naive T cell production than the thymus, with half of the naive T cells consisting of dividing RTEs. Altogether, this work provides a quantitative population dynamical framework of thymocyte development, RTEs, and naive T cells.

Section: Selection In the Thymus And Export Rate To Peripherymentioning

confidence: 66%

mentioning

confidence: 99%

Comprehensive Assessment and Mathematical Modeling of T Cell Population Dynamics and Homeostasis

Thomas‐Vaslin

Altes

Boer

et al. 2008

107

“…To accomplish this analysis, we labeled thymocytes in vivo with CFSE, as described by Graziano et al (33). With this technique, CFSE-positive T cells could be identified subsequently in peripheral lymphoid organs with ϳ2% of peripheral T cells CFSE ϩ at 4 and 7 days.…”

Section: Detection Of Recent Thymic Emigrants In the Periphery Followmentioning

confidence: 99%

CD25+ Immunoregulatory CD4 T Cells Mediate Acquired Central Transplantation Tolerance

Trani

Moore

Jarrett

et al. 2003

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.

“…In one set of experiments a single-cell suspension of peripheral lymph node (inguinal, axillary, and brachial) cells prepared as previously described (15) from C57BL/6-CD45.1 mice were labeled with CFSE (Molecular Probes, Eugene, OR) to monitor proliferation (17,18). Cells were resuspended in PBS at 20 ϫ 10 6 cells/ml.…”

Section: Fluorescent Dye Labeling Of Cells and Injection Into Recipiementioning

confidence: 99%

IL-7 Administration Alters the CD4:CD8 Ratio, Increases T Cell Numbers, and Increases T Cell Function in the Absence of Activation

Geiselhart¹,

Humphries²,

Gregorio

et al. 2001

130

IL-7 is vital for the development of the immune system and profoundly enhances the function of mature T cells. Chronic administration of IL-7 to mice markedly increases T cell numbers, especially CD8+ T cells, and enhances T cell functional potential. However, the mechanism by which these effects occur remains unclear. This report demonstrates that only 2 days of IL-7 treatment is needed for maximal enhancement of T cell function, as measured by proliferation, with a 6- to 12-fold increase in the proportion of CD4+ and CD8+ T cells in cell cycle by 18 h of ex vivo stimulation. Moreover, a 2-day administration of IL-7 in vivo increases basal proliferation by 4- and 14-fold in CD4+ and CD8+ T cells, respectively. These effects occur in the absence of cytokine production, increases in most activation markers, and changes in memory markers. This enhanced basal proliferation is the basis for the increase in T cell numbers in that IL-7 induces an additional 60% and 85% of resting CD4+ and CD8+ T cells, respectively, to enter cell cycle in mice given IL-7 for 7 days. These results demonstrate that in vivo administration of IL-7 increases T cell numbers and functional potential via a homeostatic, nonactivating process. These findings may suggest a unique clinical niche for IL-7 in that IL-7 therapy may increase T cell numbers and enhance responses to specific antigenic targets while avoiding a general, nonspecific activation of the T cell population.