The antibody MR1-2 reacts with the extra-cellular part of the TNF-RI. It also reacts with the soluble receptor. TNF-RI is present on most cell types and is considered to play a prominent role in cell stimulation by TNF-alpha: Induction of cytotoxicity and other functions are mediated largely via TNF-RI. The antibody cross reacts with rhesus and cynomolgus natural TNF-RI.