IFNG and rheumatoid arthritis: However, in inflamed RA synovium, these FRβ-expressing M2-macrophages can produce pro-inflammatory cytokines when exposed to either pro-inflammatory stimuli (i.e. lipo-polysaccharide (LPS) + interferon-γ (IFNγ) (19) or an RA synovial microenvironment with anti-citrullinated protein antibodies or complex IgGs (29, 30).