The medulla controls effector primed γδT-Cell developmenti in the adult mouse thymus.

γδT-cells are produced in the thymus throughout life, and provide immunity at epithelial-rich sites. Unlike conventional αβT-cells, γδT-cell development involves intrathymic acquisition of effector function, with priming for either IL17 or IFNγ production occurring during embryonic or adult life, respectively. How the thymus controls effector primed γδT-cell generation in adulthood is poorly understood. Here, we distinguished de novo γδT-cells from those undergoing thymus recirculation and/or retention using Rag2GFP mice alongside markers of maturation/effector priming including CD24, CD25, CD73 and IFNγ, the latter by crossing with IFNγ YFP GREAT mice. We categorise newly developing γδT-cells into an ordered sequence where CD25 + CD73 - IFNγ YFP- precursors are followed sequentially by CD25 - CD73 + IFNγ YFP- intermediates and CD25 - CD73 + IFNγ YFP+ effectors. To determine intrathymic requirements controlling this sequence, we examined γδT-cell development in Relb -/- thymus grafts that lack medullary microenvironments. Interestingly, medulla deficiency did not alter CD25 + γδT-cell precursor generation, but significantly impaired development of effector primed stages. This impact on γδT-cell priming was mirrored in plt/plt mice lacking the medullary chemoattractants CCL19 and CCL21, and also Ccl21a -/- but not Ccl19 -/- mice. Collectively, we identify the medulla as an important site for effector priming during adult γδT-cell development, and demonstrate a specific role for the medullary epithelial product CCL21 in this process. This article is protected by copyright. All rights reserved.