CCR4 and rheumatoid arthritis: However, this is not sufficient for the suppression of inflammation, so there are many proinflammatory mechanisms, such as CCL22, which is increased in both synovial fluid and serum of patients with RA, and may bind Treg cells CCR4 suppresses the number of Treg cells through the signal transducer and activator of transcription 5 (STAT5) signaling pathway (57).