Upjohn developed a process for the large scale production of cortisone . The oxygen atom at the 11 position in this steroid is an absolute requirement for biological activity. There are however no known natural sources for starting materials that contain that feature. The only method for preparing this drug prior to 1952 was a lengthy synthesis starting from cholic acid isolated from bile. In 1952 two Upjohn biochemists, Dury Peterson and Herb Murray announced that they were able to introduce this crucial oxygen atom by fermentation of the steroid progesterone with a common mold of the genus Rhizopus . Over the next several years a group of chemists headed by John Hogg developed a process for preparing cortisone from the soybean sterol stigmasterol . The microbiological oxygenation is a key step in this process. 
Antibody testing: If the presence of persistent antibodies is suspected, antibody testing should be performed. Antibodies may be detected and confirmed with sequential serum antibody tests. Antibodies detected early in the treatment course (., within the first six months) may be transient and may disappear with continued dosing. It is recommended that testing be repeated three months after an initial positive result to confirm that antibodies are persistent. Prescribers should consider the overall benefits and risks of Tysabri in a patient with persistent antibodies.