LAB/NTAL Facilitates Fungal/PAMP-induced IL-12 and IFN-γ Production by Repressing β-Catenin Activation in Dendritic Cells

Abstract

Fungal pathogens elicit cytokine responses downstream of immunoreceptor tyrosine-based activation motif (ITAM)-coupled or hemiITAM-containing receptors and TLRs. The Linker for Activation of B cells/Non-T cell Activating Linker (LAB/NTAL) encoded by Lat2, is a known regulator of ITAM-coupled receptors and TLR-associated cytokine responses. Here we demonstrate that LAB is involved in anti-fungal immunity. We show that Lat2 ^−/− mice are more susceptible to C. albicans infection than wild type (WT) mice. Dendritic cells (DCs) express LAB and we show that it is basally phosphorylated by the growth factor M-CSF or following engagement of Dectin-2, but not Dectin-1. Our data revealed a unique mechanism whereby LAB controls basal and fungal/pathogen-associated molecular patterns (PAMP)-induced nuclear β-catenin levels. This in turn is important for controlling fungal/PAMP-induced cytokine production in DCs. C. albicans- and LPS-induced IL-12 and IL-23 production was blunted in Lat2 ^−/− DCs. Accordingly, Lat2 ^−/− DCs directed reduced Th1 polarization in vitro and Lat2 ^−/− mice displayed reduced Natural Killer (NK) and T cell-mediated IFN-γ production in vivo/ex vivo. Thus our data define a novel link between LAB and β-catenin nuclear accumulation in DCs that facilitates IFN-γ responses during anti-fungal immunity. In addition, these findings are likely to be relevant to other infectious diseases that require IL-12 family cytokines and an IFN-γ response for pathogen clearance.

Author Summary

Fungal infections are a major healthcare problem and the incidence of fungal infections has increased significantly in recent years. Mortality rates are high even with treatment, highlighting the need for a better understanding of anti-fungal immunity in order to develop improved therapies. Adaptive T-helper 1 and T-helper 17 (Th1 and Th17) responses are important mediators of anti-fungal immunity. Dendritic cells express Dectin-1, Dectin-2 and Toll-like receptors, which interact with fungal pathogens to induce these adaptive immune responses. Here we identify LAB as an important facilitator of IFN-γ production by regulating β-catenin activation. Susceptibility to fungal infections is increased in the absence of LAB, in association with reduced IFN-γ production. β-catenin activation in dendritic cells inhibits the IL-12 production required for IFN-γ production. Thus targeting β-catenin therapeutically could help to promote efficient IFN-γ production in patients suffering from fungal infections. These findings are important for fungal infections and potentially for other diseases where IFN-γ production is important for disease outcome.