SSC4D (scavenger receptor cysteine-rich family member with 4 domains) is a circulating pattern recognition receptor belonging to the SRCR superfamily that functions in innate immunity and metabolic regulation. SSC4D acts as a broad-spectrum pattern recognition receptor capable of physically binding bacteria and protozoan parasites, thereby enhancing monocyte phagocytosis 1. The protein is expressed by immune cells including monocytes, macrophages, neutrophils, and B cells, as well as epithelial cells in kidney, thyroid, lung, placenta, intestine, and liver 1. Beyond immune functions, SSC4D is associated with metabolic and kidney disease pathways. Higher circulating SSC4D levels are independently associated with increased kidney stone risk (OR, 1.10-1.13), contrasting with the protective effect of uromodulin 2. SSC4D also shows strong associations with fat mass; higher plasma SSC4D correlates with increased fat mass index in population-based studies 3. Following bariatric surgery, SSC4D exhibits the highest decrease among all measured proteins at 24 months, suggesting involvement in metabolic adaptation 4. SSC4D is differentially expressed in hepatic steatosis 5 and has been implicated in epithelial-mesenchymal transition and extracellular matrix remodeling in cancer contexts 6. These findings position SSC4D as a multifunctional immune and metabolic regulator with clinical relevance to kidney stone disease, obesity, and liver disease.