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Ca²⁺ Signals in CD4⁺ T Cells during Early Contacts with Antigen-Bearing Dendritic Cells in Lymph Node¹

Sindy H. Wei^*, Olga Safrina^*, Ying Yu^*, Kym R. Garrod^*, Michael D. Cahalan^2,*, and Ian Parker^*,

^* Department of Physiology and Biophysics, Center for Immunology, Department of Neurobiology and Behavior, University of California, Irvine, CA 92697

T cell activation by APC requires cytosolic Ca²⁺ ([Ca²⁺]_i) elevation. Using two-photon microscopy, we visualized Ca²⁺ signaling and motility of murine CD4⁺ T cells within lymph node (LN) explants under control, inflammatory, and immunizing conditions. Without Ag under basal noninflammatory conditions, T cells showed infrequent Ca²⁺ spikes associated with sustained slowing. Inflammation reduced velocities and Ca²⁺ spiking in the absence of specific Ag. During early Ag encounter, most T cells engaged Ag-presenting dendritic cells in clusters, and showed increased Ca²⁺ spike frequency and elevated basal [Ca²⁺]_i. These Ca²⁺ signals persisted for hours, irrespective of whether T cells were in contact with visualized dendritic cells. We propose that sustained increases in basal [Ca²⁺]_i and spiking frequency constitute a Ca²⁺ signaling modality that, integrated over hours, distinguishes immunogenic from basal state in the native lymphoid environment.

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 by National Institutes of Health Grants GM-41514 (to M.D.C.) and GM-48071 (to I.P.). S.H.W. was supported by the University of California, Irvine Medical Scientist Training Program and a fellowship from the American Heart Association.

² Address correspondence and reprint requests to Dr. Michael D. Cahalan, University of California Irvine, 275 Irvine Hall, Box 4561, Irvine, CA 92602. E-mail address: mcahalan{at}uci.edu

³ Abbreviations used in this paper: DC, dendritic cell; LN, lymph node; [Ca²⁺]_i, cytosolic Ca²⁺; pMHC, peptide MHC; HEV, high endothelial venule; BMDC, bone marrow-derived DC; DTH, delayed-type hypersensitivity; 3D, three dimensional; cyt, cytokine; Indo-1, 1-[2-amino-5-(6-carboxy-2-indolyl)phenoxy]-2-(2-amino-5-methylphenoxy)ethane-N,N,N',N'-tetraacetic acid.

⁴ The online version of this article contains supplemental material.

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