TNF and ankylosing spondylitis: In more recent study, altered kynurenine pathway metabolism was found in patients with ankylosing spondylitis and effective therapy with tumor necrosis factor-alpha (TNFα) inhibitors resulted in a decrease in kynurenine/tryptophan ratio, even though the effect of treatment on other metabolites appears to be limited (Eryavuz Onmaz et al. 2021).