CD40LG and rheumatoid arthritis: Rheumatoid factors (RF), comprising IgM, IgG, and IgA class antibodies recognizing the Fc part of the IgG antibodies (though not specific for RA), anti-citrullinated protein/peptide antibodies (ACPAs, highly specific for RA) [45,46], and anti-CarP antibodies binding to carbamylated antigens [47] and other autoantibodies, are present in the sera and synovial fluids of RA patients.