Transcription factor activator protein (AP-) 1, a homo- or heterodimer of proteins of the JUN/FOS-proto-oncogene families including JUN, JUNB, JUND, and FOS, appears to be strongly involved in pro-inflammatory and pro-destructive processes in patients with RA and OA [6,7,8,9]. Here, JUNB is linked to rheumatoid arthritis.