Transient Dietary Changes Modulate Inflammatory Disease Trajectory in the Lean State.

Obesity potently alters immune responses across various inflammatory contexts 1-7 . However, it is unclear whether a transient high-fat diet (HFD) can affect immune function despite minimal effects on body weight. Here, we demonstrate that a short-term HFD regimen significantly exacerbates disease severity in a model of experimental psoriasis, comparable to what is observed in obese mice on long-term HFD. We find that a critical 4-day window of HFD coinciding with disease onset is sufficient to overactivate the immune response, leading to worsened disease outcomes. Mechanistically, we identify the CD4 + T cell compartment as an essential mediator of HFD-induced disease severity. Within the compartment, we functionally validate that disease exacerbation is driven by increased differentiation of a pathogenic population of T helper 17 (T H 17) cells 8 expressing IL1R1 (interleukin-1 receptor, type I) 9 , which is triggered by localized activation of the NLRP3 (NOD-, LRR-, and pyrin domain-containing protein 3) inflammasome 10 . This brief window of HFD at disease onset leads to immune-dependent sensitization, as disease severity is increased upon a subsequent flare, despite complete recovery and under a low-fat diet (LFD) regimen. Our data indicate that transient dietary changes during the initial stages of an inflammatory event can rewire the immune milieu, profoundly influencing disease progression and inflammatory memory 11 . This phenomenon may have broad implications for conditions where obesity, and not diet itself, is considered the primary risk factor.