CD46 is a transmembrane protein also known as complement membrane cofactor protein, MCP, and measles virus receptor. It is widely expressed on leukocytes, platelets, epithelial cells and fibroblasts. Multiple isoforms of CD46 have been reported with molecular weights ranging from 45-75 kD; CD46 binds complement components C3b and C4b and has also been reported to play a role in T cell regulation. In addition to the complement components, CD46 has been shown to interact with moesin, c-Src, tetraspanin 4, c-Yes, and integrin beta1. CD46 is also known to be a cellular receptor for human measles virus and human herpes virus-6. Defects in CD46 have been associated with hemolytic-uremic syndrome. The MEM-258 antibody has been shown to be useful for flow cytometry, Western blotting, and immunoprecipitation.