XBiotech Inc. has started treating the first patient in a phase II clinical study to evaluate Natrunix as a new treatment for Arthritis. The study is double-blind, placebo-controlled, and randomized. Natrunix is a monoclonal antibody that neutralizes the action of interleukin-1, a potent inflammation-causing substance. The study will enroll approximately 210 subjects into three different arms. All subjects will receive methotrexate and be randomized to receive either one of two doses of Natrunix or placebo.