Description: The RP/14 monoclonal antibody reacts with mouse CD180 (RP105). This 105 kDa type I transmembrane molecule is a member of the TLR family of proteins characterized by an extracellular domain with leucine-rich repeats and a cytoplasmic domain with homology to the type I IL-1 receptor. RP105 physically associates with another molecule called MD-1 and is expressed on mature B cells, monocytes/macrophages and dendritic cells. Ligation of RP105 with RP/14 protects B cells from irradiation- or dexamethasone-induced apoptosis, and drives them to proliferate. B cells activated by RP105-ligation arrest their growth and undergo apoptosis when the antigen receptor is engaged. The RP105/MD-1 complex in concert with TLR4 mediates B cell recognition and signaling of LPS. Thus, RP105 is a signal transduction molecule and plays a role in regulation of B cell growth and death.