The Adaptor Molecule Signaling Lymphocytic Activation Molecule-Associated Protein (SAP) Regulates IFN-γ and IL-4 Production in Vα14 Transgenic NKT Cells via Effects on GATA-3 and T-bet Expression

Abstract

NKT cells comprise a rare regulatory T cell population of limited TCR diversity, with most cells using a Vα14Jα18 TCR. These cells exhibit a critical dependence on the signaling adapter molecule, signaling lymphocytic activation molecule-associated protein (SAP), for their ontogeny, an aspect not seen in conventional αβ T cells. Prior studies demonstrate that SAP enhances TCR-induced activation of NF-κB in CD4+ T cells. Because NF-κB is required for NKT cell development, SAP might promote the ontogeny of this lineage by signaling to NF-κB. In this study, we demonstrate that forced expression of the NF-κB target gene, Bcl-xL, or inhibitory NF-κB kinase β, a catalytic subunit of the IκB kinase complex essential for NF-κB activation, fails to restore NKT cell development in sap−/− mice, suggesting that SAP mediates NKT cell development independently of NF-κB. To examine the role of SAP in NKT cell function, we generated NKT cells in sap−/− mice by expressing a transgene encoding the Vα14Jα18 component of the invariant TCR. These cells bound α-galactosylceramide-loaded CD1d tetramers, but exhibited a very immature CD24+NK1.1− phenotype. Although sap−/− tetramer-reactive cells proliferated in response to TCR activation, they did not produce appreciable levels of IL-4 or IFN-γ. The reduction in cytokine production correlated with the near absence of GATA-3 and T-bet, key transcription factors regulating cytokine expression and maturation of NKT cells. Ectopic expression of GATA-3 partially restored IL-4 production by the NKT cells. Collectively, these data suggest that by promoting GATA-3 and T-bet expression, SAP exerts control over NKT cell development and mature NKT cell cytokine production.