Acid ceramidase regulates CD8+ T-cell exhaustion via type I interferon-mediated upregulation of PD-L1

Besides its robust antiviral activity, type I interferon (IFN-I) also exerts immunomodulatory effects and can even drive pathology during chronic viral infections. Mechanisms that regulate IFN-I induction during virus infection, thus strongly affecting the outcome of disease, remain to be defined. Here, using the lymphocytic choriomeningitis virus (LCMV) Docile strain, we identified acid ceramidase (aCDase, <i>Asah1</i>) as a critical lipid-metabolic regulator of endosomal, nucleic acid-driven IFN-I responses and disease outcome during chronic virus infection. aCDase is highly expressed in plasmacytoid dendritic cells (pDCs) and required for robust early IFN-I production. aCDase deficiency resulted in ceramide accumulation, blunting IFN-α/β induction, impairing IFN-I-dependent upregulation of programmed death-ligand 1 (PD-L1) on antigen-presenting cells and preventing the exhaustion of virus-specific CD8⁺ T cells, leading to severe immunopathology. This pathology is abrogated by CD8⁺ T-cell depletion or by adoptive transfer of IFN-I-induced PD-L1-expressing macrophages. Conversely, limiting ceramide production in acid sphingomyelinase (Asm)-deficient mice prevented ceramide accumulation, and pDCs showed accelerated IFN-I induction. Mechanistically, ceramide abundance regulated IFN-I production by altering endosomal signaling microdomains. Collectively, our findings reveal ceramide homeostasis as a key determinant of IFN-I-driven CD8⁺ T-cell exhaustion and immunopathology during chronic viral infection and highlight aCDase as a potential therapeutic target.