A 46-year-old woman with active ankylosing spondylitis comes to the office for a follow-up examination. The use of various conventional nonsteroidal anti-inflammatory drugs has been ineffective. Sulfasalazine treatment also has not resulted in improvement. The most appropriate next step in treatment is administration of a drug that inhibits which of the following?

A) Interleukin-1
B) Interleukin-6
C) Tumor necrosis factor (TNF)-alpha
D) Transforming growth factor (TGF)-beta