Lipopolysaccharides, from S. marcescens (Serratia marcescens), are endotoxins derived from the bacterium Serratia marcescens, functioning as TLR-4 activators and classified as S type LPS. These compounds activate the immune system through pathogen-associated molecular patterns (PAMPs) and stimulate the secretion of chemokines. They feature a typical tripartite structure consisting of the O-antigen, core oligosaccharide, and Lipid A. Lipopolysaccharides from S. marcescens promote NF-κB activation in mouse cells via Toll-like receptor (TLR4)/MD-2 pathways. Additionally, these lipopolysaccharides can induce apoptosis in host immune cells, thereby suppressing the host's innate immunity.