MERTK and rheumatoid arthritis: While in early treatment-naive patients, MerTK expression is not related to a specific pathotype, in established active RA, following treatment with TNF inhibitors and corticosteroids, MerTK gene is significantly upregulated in synovial tissues characterised by abundant immune cells (myeloid and lymphoid) infiltration, and it positively correlates with numerous pro-inflammatory cytokines.