CD40LG and rheumatoid arthritis: 2012). Rheumatoid factor (RF) and IgG form an immune complex that activates the complement system, thereby inducing inflammatory responses (Elberry et al. 2010). RF-IgM is the only serological indicator recognized by the American Rheumatology Association for the classification and diagnosis of RA (Hjeltnes et al. 2011), and the levels of IgG and IgM are increased in the serum of RA patients (Gińdzieńska-Sieśkiewicz et al. 2016).