Christoph Wülfing Interface accumulation of receptor/ Irina Tskvitaria-Fuller ligand couples in lymphocyte Nigel Burroughs activation: methods, mechanisms, Michael D. Sjaastad Jennifer Klem and significance John D. Schatzle Authors’ addresses Christoph Wülfing 1 , Irina Tskvitaria-Fuller 1 , Nigel Burroughs 2 , Michael D. Sjaastad 3 , Jennifer Klem 1 , John D. Schatzle 1 , 1 Center for Immunology, Departments of Cell Biology and Pathology, Program in Immunology, UT Southwestern Medical Center, Dallas, TX, USA. 2 Mathematics Institute, University of Warwick, Coventry, UK. 3 Hyseq Corporation, Sunnyvale, CA, USA. Correspondence to: Christoph Wülfing Center for Immunology and Department of Cell Biology UT Southwestern Medical Center 5323 Harry Hines Blvd Dallas, TX 75390-9093 USA Fax: π 1 214 6487331 e-mail: Christoph.Wuelfing@UTSouthwestern.edu Acknowledgments We thank D. Farrar for critical reading of the manuscript, A. Mobley for FACS support, and P. Verrett for expert technical assistance. Parts of this work were supported by grants from the NIH. Immunological Reviews 2002 Vol. 189: 64–83 Printed in Denmark. All rights reserved Copyright c Blackwell Munksgaard 2002 Immunological Reviews 0105-2896 64 Summary: Cellular interaction is vital to the activation of most lympho- cytes. At the interface between the lymphocyte and the cell that activates it, multiple receptor/ligand pairs accumulate in distinct patterns. This accumulation is intriguing, as it is likely to shape the quality of receptor signaling and thereby lymphocyte behavior. Here we address such recep- tor/ligand accumulation with an emphasis on T and natural killer (NK) cells. First, we discuss the strengths and limitations of commonly used approaches to visualize receptor/ligand accumulation. Second, we discuss two principal mechanisms of receptor and ligand translocation, diffusion and cytoskeletal transport, as understanding these mechanisms can be invaluable in the determination of the significance of receptor/ligand accumulation. We show that the extent of receptor/ligand accumulation at the Tcell/antigen presenting cell interface is dominated by diffusion for all but the lowest affinity interactions, while patterning of these recep- tors/ligands within the interface is strongly influenced by cytoskeletal transport. Third, we discuss two specific issues in lymphocyte receptor/ ligand accumulation. We review the abundant but frequently contro- versial data on Tcell receptor (TCR)/major histocompatibility complex (MHC) accumulation and suggest that central TCR/MHC accumulation is a mediator of efficient Tcell activation. In the investigation of NKcell/ target cell interactions, we characterize the often tentative NKcell/target cell couple maintenance, as it creates a major obstacle in studying recep- tor/ligand accumulation. Introduction Cell/cell contact is a key step in the activation of lymphocytes, particularly of T cells and natural killer (NK) cells. Such con- tact induces substantial cellular reorganization in the lympho- cyte. A prominent aspect of this reorganization is the accumu- lation of receptors and their ligands at the cellular interface in distinct patterns (Fig. 1A) (1–27). Receptor/ligand accumu- lation should be examined in detail, as it is likely to shape the quality of receptor signaling. This review discusses receptor/ligand accumulation in three sections. In the first part, we discuss the strengths and limi- tations of the most commonly used approaches to visualize