CFD (complement factor D) is a serine protease that serves as the rate-limiting enzyme in the alternative complement pathway, a critical component of innate immunity 1. CFD cleaves factor B when complexed with complement C3b, thereby activating the C3 convertase and initiating complement cascade amplification that leads to pathogen elimination and immune signaling 1. Beyond its classical immune function, CFD exhibits diverse tissue-specific roles. In skeletal muscle, CFD expression in fibro/adipogenic progenitor cells promotes intramuscular adipogenesis through NAB2-mediated transcriptional regulation, with CFD levels serving as predictive biomarkers for intramuscular fat accumulation 2. In pulmonary hypertension, intracellular CFD drives metabolic reprogramming and proinflammatory responses in vascular fibroblasts, contributing to disease pathogenesis 3. CFD also plays roles in cancer progression, where CFD-positive inflammatory cancer-associated fibroblasts promote colorectal cancer liver metastasis via SFRP1-FGFR2-HIF1 signaling 4. Therapeutically, CFD represents a promising target, as demonstrated by long-acting anti-CFD antibodies that protected against COVID-19-associated endotheliopathy and complement-mediated vascular damage in both organoid and primate models 1. These findings highlight CFD's expanding roles beyond complement activation in metabolism, tissue remodeling, and disease pathogenesis.