Thymocyte emigration is mediated by active movement away from stroma-derived factors
Mark C. Poznansky, Ivona T. Olszak, Richard H. Evans, Zhengyu Wang, Russell B. Foxall, Douglas P. Olson, Kathryn Weibrecht, Andrew D. Luster, David T. Scadden
Mark C. Poznansky, Ivona T. Olszak, Richard H. Evans, Zhengyu Wang, Russell B. Foxall, Douglas P. Olson, Kathryn Weibrecht, Andrew D. Luster, David T. Scadden
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Article Immunology

Thymocyte emigration is mediated by active movement away from stroma-derived factors

Abstract

T cells leave the thymus at a specific time during differentiation and do not return despite elaboration of known T cell chemoattractants by thymic stroma. We observed differentiation stage–restricted egress of thymocytes from an artificial thymus in which vascular structures or hemodynamics could not have been playing a role. Hypothesizing that active movement of cells away from a thymic product may be responsible, we demonstrated selective reduction in emigration from primary thymus by inhibitors of active movement down a concentration gradient (chemofugetaxis). Immature intrathymic precursors were insensitive to an emigration signal, whereas mature thymocytes and peripheral blood T cells were sensitive. Thymic stroma was noted to elaborate at least two proteins capable of inducing emigration, one of which was stromal cell–derived factor-1. Thymic emigration is mediated, at least in part, by specific fugetaxis-inducing factors to which only mature cells respond.

Authors

Mark C. Poznansky, Ivona T. Olszak, Richard H. Evans, Zhengyu Wang, Russell B. Foxall, Douglas P. Olson, Kathryn Weibrecht, Andrew D. Luster, David T. Scadden

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(a) CXCR4 and SDF-1 and the emigration of SP thymocytes from thymic orga...
(a) CXCR4 and SDF-1 and the emigration of SP thymocytes from thymic organoid. Purified human thymocyte subpopulations, and peripheral blood (PB) T cells were plated directly onto a three-dimensional grid coated with thymic stroma in the upper chamber of a transwell. Emigration from the grid and upper chamber into the lower chamber was quantitated (black bars). Cells in the upper chamber were pretreated with anti-CXCR4 (white bars) or SDF-1 (1 μg/ml) was added to the lower chamber of the transwell (gray bars) prior to the addition of purified thymocyte populations. The percentage of cells emigrating under each of the conditions was assessed in three independent experiments, and the mean migration with SE bars is shown. (b) Inhibitor profile for emigration of SP thymocytes from murine thymic tissue fragment. The 2-mm3 murine thymic tissue fragments were cultured on a 3-μm-pore transwell membrane. The number of SP thymocytes emigrating from each tissue fragment was quantitated. Inhibitors were added to the well for the second period of 3 hours. The number and phenotype of thymocytes emigrating from each thymic tissue fragment were quantitated and compared directly with the emigrants from the first 3-hour time period. The data are expressed as the percentage of inhibition of SP thymocyte emigration from the thymic fragment in the presence of putative inhibitors of this process. Thymic fragments were treated with PTX, isotype IgG, anti-CXCR4 Ab, wortmannin, genistein, 8-Br-cGMP, or 8-Br-cAMP. The data represent the mean ± SEM for three experiments.