Curcumin alleviates murine ulcerative colitis by modulating Tfh-B cell crosstalk via the CD40/CD40L costimulatory pathway.

Ulcerative colitis (UC) progression is closely associated with dysregulated T follicular helper (Tfh)-B cell crosstalk, a process are centrally mediated through the CD40/CD40L costimulatory pathway. This study aimed to investigate whether curcumin (Cur) alleviates UC by regulating Tfh-B cell crosstalk via modulation of this pathway. Mice with dextran sulfate sodium (DSS)-induced UC were administered were treated with Cur for 14 consecutive days. Tfh and B cell subsets were analyzed using flow cytometry, while CD40/CD40L gene and protein expression were assessed via qRT-PCR and WB. Cellular spatial interactions were examined through immunofluorescence. Additionally, molecular docking, molecular dynamics simulations and surface plasmon resonance (SPR) were performed to evaluate Cur's binding to the CD40/CD40L complex. Cur treatment significantly reduced the disease activity index, restored colon length, ameliorated histological damage, and suppressed proinflammatory cytokines (e.g., IL-6, IL-21) as well as IgG levels. Mechanistically, Cur downregulated significantly CD40L⁺ Tfh cells and CD40⁺ B cells, and inhibited significantly key GC transcription factor Bcl-6 and plasma cell differentiation regulator Blimp-1. Molecular simulations confirmed that Cur stably binds to the CD40/CD40L interface through van der Waals forces and electrostatic complementarity, effectively blocking their interaction. The evidence from kinetic and competitive SPR assays demonstrates that Cur not only exhibits strong binding affinity by directly targeting CD40L, but also concentration-dependently blocks its interaction with CD40, resulting in significant functional inhibition of the CD40/CD40L signaling axis. Collectively, these findings demonstrate that Cur ameliorates UC by inhibiting the CD40/CD40L complex, which disrupts pathological Tfh-B cell crosstalk and ultimately restores gut immune homeostasis.