Responsiveness of Serum C-Reactive Protein, Interleukin-17A, and Interleukin-17F Levels to Ustekinumab in Psoriatic Arthritis: Lessons From Two Phase III, Multicenter, Double-Blind, Placebo-Controlled Trials.

Baseline serum IL-23/IL-17 levels correlated with skin, but not joint, disease activity, suggesting tissue-specific variation. However, neither baseline Th17-associated cytokine levels nor CRP level were predictive of therapeutic response to ustekinumab in the skin or joints, despite rapid reductions in their levels following ustekinumab therapy.