CD40LG and rheumatoid arthritis: IgM rheumatoid factor (RF), determined by the latex fixation test (LFT), is the most well-characterized autoantibody and is included in the America College of Rheumatology/European League Against Rheumatism classification criteria for RA and the International League of Associations for Rheumatology (ILAR) criteria for the IgM RF-positive polyarticular JIA subtype[1],[2].