Since RFs can be measured in sera from RA patients and as the concentration of IgG in serum is roughly 5–10 times higher than the concentration of IgM and IgA [1], an apparent paradox is how the RFs can circulate in blood of patients with rheumatoid diseases alongside their antigen (IgG) in large amounts without reacting with it and being cleared from the circulation. Here, CD40LG is linked to rheumatoid arthritis.