TNF and major depressive disorder: In contrast to earlier studies showing decreased TRP/CAA ratios in patients with depression [21], [24], [25], [26], [27] and correlations between depressive symptoms and TRP levels in IFN-γ induced depression [45], [46], we did not find any increase in TRP/CAA ratio over time and there was no association over time between SCL-90 depressive symptom scores and TRP/CAA ratio after infusion of anti-TNF-α.