Effects of tryptophan depletion and catecholamine depletion on immune parameters in patients with seasonal affective disorder in remission with light therapy

Background Altered immunologic parameters are found in symptomatic depressed patients relative to remitted depressed patients and healthy controls. We investigated whether tryptophan depletion and catecholamine depletion induce alterations in immunologic parameters in patients with seasonal affective disorder remitted on light therapy, and whether these changes are associated with changes in mood. Methods Remitted patients with seasonal affective disorder underwent tryptophan depletion, catecholamine depletion, and sham depletion in a prospective randomized, double-blind crossover design. Measures of depression, plasma levels of tryptophan and catecholamine metabolites, and plasma levels of cytokines (sIL-4, IL-6, neopterin, sTNF-R1 and sTNF-R2) were obtained at baseline, and 7, 24, and 30 hours after monoamine depletion. Results Tryptophan depletion decreased plasma total and free tryptophan levels; catecholamine depletion decreased plasma 3-methoxy-4-hydroxyphenylethyleneglycol and homovanillic acid levels. Tryptophan depletion and catecholamine depletion, but not sham depletion, induced a transient exacerbation of depressive symptoms (p< .001); plasma neopterin levels increased during tryptophan depletion and catecholamine depletion (p< .05). Tryptophan depletion and catecholamine depletion induced a transient reduction of plasma sIL-4 levels (p< .05). A significant correlation was found between sIL-4R levels and depression ratings after tryptophan depletion (r = −.61, p< .05). Conclusions The monoamine depletion-induced alterations of humoral and cellular immunity suggest a potential role of immunologic parameters in the pathophysiology of seasonal affective disorder; however, the results must be considered preliminary and require further study.