IL1B and osteoarthritis: Macrophage migration inhibitory factor (MIF) has been shown to significantly stimulate the proliferation of rheumatoid arthritis FLS, with indirect IL‐1β and TNF‐α involvement.23 IL‐1 is also known to stimulate FLS proliferation.24 As macrophages are major producers of both IL‐1 and MIF, these factors may explain the influence that DH82 cells have on EFLS proliferation and this may be relevant to the synovial hyperplasia observed during osteoarthritis.