RESUMO
Toll-like receptor (TLR) 2 on antigen-presenting cells (APCs) enables these cells to recognize peptidoglycan-embedded lipopeptides and glycopolymers in the Staphylococcus aureus cell wall and mount an inflammatory response to this microbe. TLR2 signalling can also modulate immunity to S. aureus by inducing an interleukin (IL)-10 response in APCs. What determines the balance between proinflammatory and modulatory responses to S. aureus is unknown. We show that the modulatory IL-10 response preferentially occurs upon CD14- and CD36-independent TLR2 signaling, triggering PI3K activation, and is restricted to monocytes and monocyte-derived macrophages (MΦs). In contrast, monocyte-derived dendritic cells (DCs) produce mostly IL-12 and IL-23. The differential APC polarization induced by staphylococcal peptidoglycan translates into differential T helper responses: MΦs primarily trigger IL-10 and weak IL-17 responses, whereas DCs trigger a robust Th1/Th17 response. Exploitation of TLR2 signalling plasticity by S. aureus may explain the wide range of outcomes of human encounters with this microbe.
Assuntos
Imunidade Adaptativa , Interleucina-10/imunologia , Peptidoglicano/imunologia , Staphylococcus aureus/imunologia , Células Th1/imunologia , Células Th17/imunologia , Elafina/metabolismo , Humanos , Macrófagos/imunologia , Monócitos/imunologia , Receptor 2 Toll-Like/imunologiaRESUMO
The catalytic subunit of the serine/threonine phosphatase 2A (PP2A) can interact with the cytoplasmic tail of CTLA-4. However, the molecular basis and the biological significance of this interaction are unknown. In this study, we report that the regulatory subunit of PP2A (PP2AA) also interacts with the cytoplasmic tail of CTLA-4. Interestingly, TCR ligation induces tyrosine phosphorylation of PP2AA and its dissociation from CTLA-4 when coligated. The association between PP2AA and CTLA-4 involves a conserved three-lysine motif in the juxtamembrane portion of the cytoplasmic tail of CTLA-4. Mutations of these lysine residues prevent the binding of PP2AA and enhance the inhibition of IL-2 gene transcription by CTLA-4, indicating that PP2A represses CTLA-4 function. Our data imply that the lysine-rich motif in CTLA-4 may be used to identify small molecules that block its binding to PP2A and act as agonists for CTLA-4 function.
Assuntos
Antígenos de Diferenciação/fisiologia , Regulação para Baixo/imunologia , Imunoconjugados , Imunossupressores/antagonistas & inibidores , Imunossupressores/farmacologia , Fosfoproteínas Fosfatases/fisiologia , Abatacepte , Motivos de Aminoácidos/genética , Animais , Antígenos CD , Antígenos de Diferenciação/genética , Antígenos de Diferenciação/metabolismo , Antígenos de Diferenciação/farmacologia , Antígeno CTLA-4 , Linhagem Celular Transformada , Citoplasma/genética , Citoplasma/imunologia , Citoplasma/metabolismo , Regulação para Baixo/genética , Humanos , Imunossupressores/metabolismo , Células Jurkat , Ligantes , Ativação Linfocitária/genética , Lisina/genética , Lisina/metabolismo , Camundongos , Mutagênese Sítio-Dirigida , Fosfoproteínas Fosfatases/metabolismo , Fosforilação , Ligação Proteica/genética , Ligação Proteica/imunologia , Proteína Fosfatase 2 , Estrutura Terciária de Proteína/genética , Receptores de Antígenos de Linfócitos T/imunologia , Receptores de Antígenos de Linfócitos T/metabolismo , Linfócitos T/imunologiaRESUMO
T cell activation through the T cell receptor (TCR) involves partitioning of receptors into discrete membrane compartments known as lipid rafts, and the formation of an immunological synapse (IS) between the T cell and antigen-presenting cell (APC). Compartmentalization of negative regulators of T cell activation such as cytotoxic T lymphocyte-associated antigen-4 (CTLA-4) is unknown. Recent crystal structures of B7-ligated CTLA-4 suggest that it may form lattices within the IS which could explain the mechanism of action of this molecule. Here, we show that after T cell stimulation, CTLA-4 coclusters with the TCR and the lipid raft ganglioside GM1 within the IS. Using subcellular fractionation, we show that most lipid raft-associated CTLA-4 is on the T cell surface. Such compartmentalization is dependent on the cytoplasmic tail of CTLA-4 and can be forced with a glycosylphosphatidylinositol-anchor in CTLA-4. The level of CTLA-4 within lipid rafts increases under conditions of APC-dependent TCR-CTLA-4 coligation and T cell inactivation. However, raft localization, although necessary for inhibition of T cell activation, is not sufficient for CTLA-4-mediated negative signaling. These data demonstrate that CTLA-4 within lipid rafts migrates to the IS where it can potentially form lattice structures and inhibit T cell activation.