TNF and rheumatoid arthritis: Zhang et al. [123] investigated the effect of psoralen on Type II collagen-induced rat rheumatoid arthritis (RA), and found that psoralen could play an immunomodulatory role by regulating Th1/Th2 cell balance and inhibiting the release of TNF-α, IL-6 and IL-1β inflammatory factors, which would slow the progression of RA.