INCREASED NEOPTERIN AND INTERFERON-GAMMA SECRETION AND LOWER AVAILABILITY OF L-TRYPTOPHAN IN MAJOR DEPRESSION - FURTHER EVIDENCE FOR AN IMMUNE-RESPONSE

There is now some evidence that major depression may be accompanied by an immune response. The latter condition is suggested by elevated sec retion of neopterin and interferon-gamma (IFN gamma) and by lower L-tr yptophan (L-TRP) plasma levels. This study investigated the plasma lev els of neopterin, L-TRP, and the L-TRP/competing amino acids (CAA) rat io in 30 normal control subjects and 47 depressed subjects (16 minor d epressed, 13 simple major depressed, and 18 melancholic subjects), and IFN gamma secretion by mitogen-stimulated peripheral blood mononuclea r cells in 7 normal control subjects and 13 major depressed subjects. Plasma neopterin levels were significantly higher in depressed subject s than in normal controls; 61% of melancholic patients had increased n eopterin levels (greater than or equal to 7 nmol/l) with a specificity of 90%. Patients with major depression had significantly lower L-TRP and L-TRP/CAA values compared with normal control subjects. The amino acid values were significantly and negatively correlated with plasma n eopterin levels. Major depressed subjects exhibited significantly high er IFN gamma secretion than did normal control subjects. The results f urther support the hypothesis that major depression is accompanied by an immune response and that the lower L-TRP availability in that illne ss may be an epiphenomenon of immune activation.