Molecular mechanisms that set the stage for DC-T cell engagement.
The unsurpassed capacity of dendritic cells (DC) to prime naive T cells is thought to depend on the formation of an immunological synapse. DC-SIGN, a C-type lectin exclusively expressed at the cell surface of DC, functions as an adhesion receptor facilitating T cell binding and priming through recognition of glycosylated ICAM-3 on naive T cells. Yet, DC-SIGN also mediates binding to pathogens such as HIV by recognizing glycosylated gp120. The scope of the present study was to investigate whether DC-SIGN upon recognition of its cellular ligand and pathogenic ligand affects DC synapse formation and activation/mobilization of other adhesion receptors such as LFA-1 to the cell contact site. Using a DC-SIGN deletion mutant, we show that DC-SIGN is a constitutively active receptor that mediates ligand binding independent of signaling through the cytoplasmic domain. Surprisingly, initial binding of gp120 to DC-SIGN did not result in increased adhesion levels of LFA-1 to its ligand ICAM-1 in both immature DC and Raji-DC-SIGN cells. However, ligand binding to DC-SIGN induced recruitment of LFA-1 to the adhesion site. Moreover, we could demonstrate that activation of LFA-1 results in DC-SIGN-LFA-1 co-clustering in the cell membrane. This triggers binding of ligands to LFA-1 that are shared with DC-SIGN, such as ICAM-3, but not of ligands that are not shared with DC-SIGN, such as ICAM-1. Thus, we propose that upon ligand binding DC-SIGN recruits LFA-1 to the contact site, resulting in the formation of DC-SIGN-LFA-1 co-clusters, in which the initial DC-SIGN-mediated interactions with ligand are transient and eventually shift to more stable LFA-1-dependent interactions.
van Gisbergen
Klaas P J M
KP
Department of Molecular Cell Biology and Immunology, VU Medical Center, van der Boechorstraat 7, 1081 BT Amsterdam, The Netherlands.
Paessens
Lutz C
LC
Geijtenbeek
Teunis B H
TB
van Kooyk
Yvette
Y
D015703:Antigens, CD / Q000378:metabolism; D015815:Cell Adhesion Molecules; D045744:Cell Line, Tumor; D003713:Dendritic Cells / Q000276:immunology* / Q000378:metabolism*; D006801:Humans; D018799:Intercellular Adhesion Molecule-1 / Q000378:metabolism; D037181:Lectins, C-Type / Q000235:genetics / Q000378:metabolism; D008024:Ligands; D016169:Lymphocyte Function-Associated Antigen-1 / Q000378:metabolism; D013601:T-Lymphocytes / Q000276:immunology* / Q000378:metabolism*
D015703:Antigens, CD; D015815:Cell Adhesion Molecules; C483616:ICAM3 protein, human; D037181:Lectins, C-Type; D008024:Ligands; D016169:Lymphocyte Function-Associated Antigen-1; D018799:Intercellular Adhesion Molecule-1