TNF and rheumatoid arthritis: In contrast, Fc fusion protein generated from the genetic linkage of effector moiety (cytokines or antibody fragments) and Fc domain (human IgG1) is believed to be effective in human therapy, as exemplified by Etanercept (Enbrel), a TNFR2-Fc fusion protein that reduces TNF in rheumatoid arthritis (RA) (19).