Interrogating the role of type I interferon in the dysregulation of AhR activity in systemic lupus erythematosus

Abstract

Systemic lupus erythematosus (SLE) is an autoimmune disorder driven by aberrant B cell-helper T follicular helper (Tfh) cells and T peripheral helper (Tph) cells that promote autoantibody production by chronically active B cells. In healthy conditions, aryl hydrocarbon receptor (AhR) regulates a T helper cell phenotypic axis by suppressing the Tfh/Tph subset while promoting Th22 differentiation. In SLE patients, this axis is skewed towards the Tfh/Tph population. Type I interferon (IFN), elevated in the serum of SLE patients, can tilt the axis towards the Tfh/Tph phenotype. Both SLE patient serum and exogenous type I IFN were shown to inhibit the activation of a luciferase reporter of AhR’s DNA binding activity that is induced by TCDD, a strong AhR agonist. However, whether type I IFN mediates the AhR inhibitory effect of SLE serum remains unknown. The primary objective of this research project was to determine the necessity of type I IFN for the inhibitory effect of SLE serum on the activation of the AhR luciferase reporter. Using an IFNAR knockout AhR luciferase reporter cell line, we demonstrated that type I IFN signaling is not necessary for SLE serum to inhibit AhR luciferase reporter activation. However, we subsequently found that SLE serum and type I IFN do not reduce TCDD-induced upregulation of canonical AhR response genes. Furthermore, expression of the luc+ luciferase reporter gene remained unaltered indicating that the observed decrease in luciferase activity is not due to reduced luc+ transcription but instead due to other effects of the external treatments, making the AhR luciferase reporter an imperfect system to study AhR dysregulation in SLE. Future studies will utilize modified luciferase assays as well as alternative approaches to elucidate the effect of SLE serum on AhR signaling pathways and determine specific AhR-inhibitory serum factors.