Eli Lilly and Co. has sued Biogen Idec Inc. in a London court to revoke a European patent on a potential treatment for immune-system diseases.

Biogen’s patent on the use of a class of medicines known as BAFF inhibitors to regulate the activity of a type of white blood cell is “not new” and doesn’t “involve an inventive step,” Lilly said in court papers filed in London in November.

Eli Lilly, whose top-selling schizophrenia drug Zyprexa lost its U.S. patent protection in October, is working to overcome expiring patents by investing in research. The Indianapolis-based drugmaker has new treatments for Alzheimer’s, diabetes and cancer in final-stage trials.

Biogen, the world’s largest maker of medicines for multiple sclerosis, responded in November, saying its BAFF inhibitors patent is valid. Penny Gilbert, a lawyer for the Weston, Mass.-based company, didn’t respond to a phone call Wednesday requesting comment.

Lilly lost a related patent dispute before the United Kingdom Supreme Court in November when the court ruled for Rockville, Md.-based Human Genome Sciences Inc. over another potential treatment for immune diseases. Lilly had argued Human Genome’s list of uses for the neutrokine alpha protein was too vague.

Greg Kueterman, a spokesman for Lilly, declined to comment on the Biogen litigation because the case is ongoing.