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Thymocyte-Dendritic Cell Interactions near Sources of CCR7 Ligands in the Thymic Cortex¹

Ena Ladi^*, Tanja A. Schwickert^*,, Tatyana Chtanova^*, Ying Chen, Paul Herzmark^*, Xinye Yin^*, Holly Aaron^*, Shiao Wei Chan^*, Martin Lipp, Badrinath Roysam and Ellen A. Robey^2,*

^* Division of Immunology, Department of Molecular and Cell Biology, University of California, Berkeley, CA 94720; Laboratory of Molecular Immunology, the Rockefeller University and Howard Hughes Medical Institute, New York, NY 10065; Department of Electrical, Computer, and System Engineering, Rensselaer Polytechnic Institute, Troy, NY 12180; and Max-Delbrück-Center for Molecular Medicine, Department of Molecular Tumorgenetics and Immunogenetics, Berlin-Buch, Germany

Little is known about the dynamics of the interactions between thymocytes and other cell types, as well as the spatiotemporal distribution of thymocytes during positive selection in the microenvironment of the cortex. We used two-photon laser scanning microscopy of the mouse thymus to visualize thymocytes and dendritic cells (DCs) and to characterize their interactions in the cortex. We show that thymocytes make frequent contacts with DCs in the thymic cortex and that these associations increase when thymocytes express T cell receptors that mediate positive selection. We also show that cortical DCs and the chemokine CCL21 expression are closely associated with capillaries throughout the cortex. The overexpression of the chemokine receptor CCR7 in thymocytes results in an increase in DC-thymocyte interactions, while the loss of CCR7 in the background of a positive-selecting TCR reduces the extent of DC-thymocyte interactions. These observations identify a vasculature-associated microenvironment within the thymic cortex that promotes interactions between DCs and thymocytes that are receiving positive selection signals.

The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked advertisement in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.

¹ This work was supported research grants AI32985 and AI053039 from National Institutes of Health. T.C. is supported by fellowship from HFSP and T.A.S. is supported by Deutscher Akademischer Austauschdienst DAAD. The computational image analysis work was supported by the Bernard M. Gordon Center for Subsurface Sensing and Imaging Systems, under the Engineering Research Centers Program of the National Science Foundation (Award Number EEC-9986821), and by Rensselaer Polytechnic Institute.

² Address correspondence and reprint requests to Dr. Ellen Robey, Department of Molecular and Cell Biology, 471 Life Sciences Addition, University of California, Berkeley, CA 94720. E-mail address: erobey{at}berkeley.edu

³ Abbreviations used in this paper: DC, dendritic cell; CFP, cyan fluorescent protein; TPLSM, two-photon laser scanning microscopy; YFP, yellow fluorescent protein.

⁴ The online version of this article contains supplemental material.