The researchers studied the effects of methotrexate on arthritis in rats by looking at the levels of a protein called IL-6. They found that IL-6 levels in arthritic rats follow a daily pattern, increasing at night and decreasing in the morning. Giving methotrexate once a day when IL-6 levels rise or fall was more effective than giving it once a week. Rats treated this way had lower arthritis scores, less inflammation, and improved joint health compared to rats receiving weekly treatment. This suggests that timing methotrexate based on IL-6 rhythms could enhance its effectiveness in treating arthritis.