MUC1 and systemic sclerosis: In this subpopulation, there was a moderate negative correlation between serum KL-6 levels and ΔppFVC in the rituximab group (r = −0.495) and a strong negative correlation in the placebo group (r = −0.768; Fig. 4), suggesting that serum KL-6 elevation indicates a good candidate for rituximab in SSc-ILD patients with serum CRP levels <0.055 mg/dl.