The MJ18 monoclonal antibody reacts with mouse CD276 also known as B7-H3. CD276 is a type I transmembrane protein and a member of the B7 family of co-stimulatory proteins. CD276 is expressed weakly on activated lymphocytes, macrophages, dendritic cells, nasal and airway epithelial cells, osteoblasts, and some tumor cell lines. A soluble form of CD276 is also secreted by monocytes, dendritic cells, and activated T cells. The biological role of CD276 is still under investigation however, recent studies suggest a negative regulatory role for CD276 in T cell responses. The MJ18 antibody has been shown to block CD276 when administered in vivo.