Deficiency of the Metalloproteinase-Disintegrin ADAM8 Is Associated with Thymic Hyper-Cellularity

Klaus Gossens,Hermann J Ziltener,Silvia Naus,Georg A Holländer

doi:10.1371/journal.pone.0012766

Abstract

BackgroundThymopoiesis requires thymocyte-stroma interactions and proteases that promote cell migration by degrading extracellular matrix and releasing essential cytokines and chemokines. A role for several members of the A Disintegrin and Metalloprotease (ADAM) family in T cell development has been reported in the past.Methodology/Principal FindingsHere, we present data indicating that the family member ADAM8 plays a role in thymic T cell development. We used qrtPCR on FACS sorted thymic subsets together with immunofluorescene to analyze thymic ADAM8 expression. We found that ADAM8 was expressed in murine thymic stromal cells and at lower levels in thymocytes where its expression increased as cell matured, suggesting involvement of ADAM8 in thymopoiesis. Further flow cytometry analysis revealed that ADAM8 deficient mice showed normal development and expansion of immature thymocyte subsets. There was however an intrathymic accumulation of single positive CD4 and CD8 T cells which was most noticeable in the late mature T cell subsets. Accumulation of single positive T cells coincided with changes in the thymic architecture manifest in a decreased cortex/medulla ratio and an increase in medullary epithelial cells as determined by histology and flow cytometry. The increase in single positive T cells was thymus-intrinsic, independent of progenitor homing to the thymus or thymic exit rate of mature T cells. Chemotaxis assays revealed that ADAM8 deficiency was associated with reduced migration of single positive thymocytes towards CCL21.Conclusions/SignificanceOur results show that ADAM8 is involved in T cell maturation in the medulla and suggest a role for this protease in fine-tuning maturation of thymocytes in the medulla. In contrast to ADAM10 and ADAM17 lack of ADAM8 appears to have a relatively minor impact on T cell development, which was unexpected given that maturation of thymocytes is dependent on proper localization and timing of migration.

Highlights

Thymic development of T cells is characterized by a series of complex processes including gene rearrangement, positive and negative selection for T cell receptor specificity, proliferation and differentiation (Reviewed in [1])
We comparatively analyzed wt and ADAM82/2 mice to identify in more detail the thymic cell subsets that express ADAM8 and to identify a potential function for ADAM8 in T cell development
We show that ADAM8 was expressed in thymic stromal cells and thymocytes and that ADAM8 RNA expression was most abundant in medullary TEC (mTEC) and in mature thymocytes

Summary

Introduction

Thymic development of T cells is characterized by a series of complex processes including gene rearrangement, positive and negative selection for T cell receptor specificity, proliferation and differentiation (Reviewed in [1]). T cell precursors enter the thymus from the blood near the cortico-medullary junction, migrate into the cortex and subsequently undergo four successive CD4/CD8 double negative (DN) stages: DN1 (CD44+, CD252), DN2 (CD44+, CD25+), DN3 (CD442, CD25+) and pre-double positive (pre-DP; (CD442, CD252). Upon rearrangement of the a-chain of the TCR thymocytes undergo positive selection that is followed by a down-regulation of one of the TCR co-receptors CD4 or CD8 according to the MHC restriction of the TCR. Single positive (SP) CD4 or CD8 thymocytes migrate to the medulla where they undergo negative selection, a process controlled by medullary thymic epithelial and dendritic cells that removes cells expressing auto-reactive TCR. A role for several members of the A Disintegrin and Metalloprotease (ADAM) family in T cell development has been reported in the past

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