SEROTONIN-IMMUNE INTERACTIONS IN MAJOR DEPRESSION - LOWER SERUM TRYPTOPHAN AS A MARKER OF AN IMMUNE-INFLAMMATORY RESPONSE

Serum total tryptophan and the five competing amino acids (CAA), i.e., valine, leucine, tyrosine, phenylalanine, and isoleucine were determi ned in 35 major depressed subjects of whom 27 with treatment resistant depression (TRD), and 15 normal controls. Twenty-five of the depresse d subjects had repeated measurements of the amino acids both before an d after antidepressive treatment. The following immune-inflammatory va riables were assayed in the above subjects: serum zinc (Zn), total ser um protein (TSP), albumin (Alb), transferrin (Tf), iron (Fe), high-den sity lipoprotein cholesterol (HDL-C), number of peripheral blood leuko cytes, and the CD4(+)/CD8(+) T cell (T-helper/T-suppressor) ratio. Ser um tryptophan and the tryptophan/CAA ratio were significantly lower in major depressed subjects than in normal controls. The tryptophan/CAA ratio was significantly lower in patients with TRD than in patients wi thout TRD and normal controls. There were no significant alterations i n any of the amino acids upon successful therapy. There were significa nt correlations between serum tryptophan and serum Zn, TSP, Alb, Tf, F e, and HDL-C (all positive), and number of leukocytes and the CD4(+)/C D8(+) T-cell ratio (all negative). The tryptophan/CAA ratio was signif icantly and negatively related to the number of leukocytes and the CD4 (+)/CD8(+) T-cell ratio. The results suggest that (a) TRD is character ized by lower availability of serum tryptophan; (b) the availability o f tryptophan may remain decreased despite clinical recovery; and (c) t he lower availability of tryptophan is probably a marker of the immune -inflammatory response during major depression.