CD180 is a cell surface molecule consisting of extracellular leucine-rich repeats (LRR) and a short cytoplasmic tail. The extracellular LRR is associated with a molecule called MD-1 and form the cell surface receptor complex, RP105/MD-1. It belongs to the family of pathogen receptors, Toll-like receptors (TLR). RP105/MD1, by working in concert with TLR4, controls B cell recognition and signaling of lipopolysaccharide (LPS), a membrane constituent of Gram-negative bacteria