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Interactions of Ly49 Family Receptors with MHC Class I Ligands in trans and cis¹

Léonardo Scarpellino^*, Franziska Oeschger^*, Philippe Guillaume^*, Jérôme D. Coudert, Frédéric Lévy^*, Georges Leclercq and Werner Held^2,*

^* Ludwig Institute for Cancer Research, Lausanne Branch; University of Lausanne, Epalinges, Switzerland; and Department of Clinical Chemistry, Microbiology and Immunology, Ghent, Belgium

The Ly49A NK cell receptor interacts with MHC class I (MHC-I) molecules on target cells and negatively regulates NK cell-mediated target cell lysis. We have recently shown that the MHC-I ligand-binding capacity of the Ly49A NK cell receptor is controlled by the NK cells’ own MHC-I. To see whether this property was unique to Ly49A, we have investigated the binding of soluble MHC-I multimers to the Ly49 family receptors expressed in MHC-I-deficient and -sufficient C57BL/6 mice. In this study, we confirm the binding of classical MHC-I to the inhibitory Ly49A, C and I receptors, and demonstrate that detectable MHC-I binding to MHC-I-deficient NK cells is exclusively mediated by these three receptors. We did not detect significant multimer binding to stably transfected or NK cell-expressed Ly49D, E, F, G, and H receptors. Yet, we identified the more distantly related Ly49B and Ly49Q, which are not expressed by NK cells, as two novel MHC-I receptors in mice. Furthermore, we show using MHC-I-sufficient mice that the NK cells’ own MHC-I significantly masks the Ly49A and Ly49C, but not the Ly49I receptor. Nevertheless, Ly49I was partly masked on transfected tumor cells, suggesting that the structure of Ly49I is compatible in principal with cis binding of MHC-I. Finally, masking of Ly49Q by cis MHC-I was minor, whereas masking of Ly49B was not detected. These data significantly extend the MHC-I specificity of Ly49 family receptors and show that the accessibility of most, but not all, MHC-I-binding Ly49 receptors is modulated by the expression of MHC-I in cis.

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 in part by a grant from the Swiss National Science Foundation (to W.H.).

² Address correspondence and reprint requests to Dr. Werner Held, Ludwig Institute for Cancer Research, Lausanne Branch, University of Lausanne, Chemin des Boveresses 155, 1066 Epalinges, Switzerland. E-mail address: wheld{at}isrec.unil.ch

³ Abbreviations used in this paper: MHC-I, MHC class I; ₂m, ₂-microglobulin; Tg, transgenic; VSV, vesicular stomatitis virus; MFI, mean fluorescence intensity.