Thymocytes in Lyve1-CRE/S1pr1f/f Mice Accumulate in the Thymus due to Cell-Intrinsic Loss of Sphingosine-1-Phosphate Receptor Expression

Akira Takeda; Mohammad Shahadat Hossain; Pia Rantakari; Szandor Simmons; Naoko Sasaki; Marko Salmi; Sirpa Jalkanen; Masayuki Miyasaka

doi:10.3389/fimmu.2016.00489

Thymocytes in Lyve1-CRE/S1pr1^f/f Mice Accumulate in the Thymus due to Cell-Intrinsic Loss of Sphingosine-1-Phosphate Receptor Expression

Front Immunol. 2016 Nov 8:7:489. doi: 10.3389/fimmu.2016.00489. eCollection 2016.

Authors

Akira Takeda¹, Mohammad Shahadat Hossain¹, Pia Rantakari¹, Szandor Simmons², Naoko Sasaki³, Marko Salmi⁴, Sirpa Jalkanen¹, Masayuki Miyasaka⁵

Affiliations

¹ MediCity Research Laboratory, University of Turku , Turku , Finland.
² Department of Immunology and Cell Biology, Graduate School of Medicine and Frontier Biosciences, Osaka University, Suita, Japan; WPI Immunology Frontier Research Center, Osaka University, Suita, Japan.
³ Department of Microbiology and Immunology, Graduate School of Medicine, Osaka University , Suita , Japan.
⁴ MediCity Research Laboratory, University of Turku, Turku, Finland; Department of Medical Microbiology and Immunology, University of Turku, Turku, Finland.
⁵ MediCity Research Laboratory, University of Turku, Turku, Finland; WPI Immunology Frontier Research Center, Osaka University, Suita, Japan; Interdisciplinary Program for Biomedical Sciences, Institute for Academic Initiatives, Osaka University, Suita, Japan.

Abstract

T cell emigration from the thymus is essential for immunological homeostasis. While stromal cell-produced sphingosine-1-phosphate (S1P) has been shown to promote thymocyte egress via the S1P receptor, S1PR1, the significance of S1P/S1PR1 signaling in the thymic stromal cells that surround T cells remains unclear. To address this issue, we developed conditional knockout mice (Lyve1-CRE/S1pr1^f/f mice) in which S1pr1 was selectively targeted in cells expressing the lymphatic endothelial cell marker, Lyve1. In these mice, T cells were significantly reduced in secondary lymphoid tissues, and CD62L⁺ mature CD4 and CD8 single-positive (SP) T cells accumulated in the medulla failed to undergo thymus egress. Using a Lyve1 reporter strain in which Lyve1 lineage cells expressed tdTomato fluorescent protein, we unexpectedly found that a considerable proportion of the thymocytes were fluorescently labeled, indicating that they belonged to the Lyve1 lineage. The CD4 and CD8 SP thymocytes in Lyve1-CRE/S1pr1^f/f mice exhibited an egress-competent phenotype (HSA^low, CD62L^high, and Qa-2^high), but were CD69^high and lacked S1PR1 expression. In addition, CD4 SP thymocytes from these mice were unable to migrate to the periphery after their intrathymic injection into wild-type (WT) mice. In contrast, WT T cells could migrate to the periphery in both WT and Lyve1-CRE/S1pr1^f/f thymuses. These results demonstrated that thymocyte egress is mediated by T cell-expressed, but not stromal cell-expressed, S1PR1 and caution against using the Lyve1-CRE system for selectively gene deletion in lymphatic endothelial cells.

Keywords: Lyve1; S1PR1; egress; sphingosine-1-phosphate; thymus.