Immune-inflammatory markers in patients with seasonal affective disorder: effects of light therapy

Background: There is increasing evidence that an activation of the immune-i nflammatory system is involved in the pathophysiology of depressive disorde rs. The purposes of this study were to (1) compare immune-inflammatory mark ers in patients with seasonal affective disorder (SAD) with those in matche d normal controls; and (2) examine the effects of light therapy on the immu ne-inflammatory markers in patients with SAD. Methods: Plasma concentration s of interleukin-6 (IL-6), soluble n-6 receptor (sIL-6R) and soluble IL-2 r eceptor (sIL-2R) were measured in 15 patients with SAD and 15 age- and sex- matched normal controls. Of the 15 patients, 14 had repeated blood sampling for these variables following 2 weeks of light therapy. Results: We found that patients with SAD had significantly increased IL-6 levels compared to normal controls (P < 0.0005). There was a trend toward increased sLL-2R in patients with SAD (P = 0.09). There was no significant difference in sIL-6R level between the two diagnostic groups (P = 0.18), but the product term ( IL-6xsIL-6R) was significantly higher in patients with SAD than that in nor mal control controls (P < 0.0003). Furthermore, all 14 patients who complet ed the study improved with 2 weeks of light therapy and nine of them (64%) had 50% reduction in score of the Hamilton Depression Rating Scale-SAD vers ion post-treatment compared to baseline. However, the initially increased i mmune markers in SAD patients were not significantly altered by the therape utic light therapy. Limitations: This study was limited to a small sample s ize and other immune inflammatory markers should be measured for further ev idence of immune activation in seasonal depression. Conclusions: Our result s of increased IL-6, IL-6xsIL-6R, and sIL-2R in patients with SAD suggest a n activation of the immune-inflammatory system in winter depression, which is not altered by 2 weeks of successful light therapy. (C) 2001 Elsevier Sc ience B.V. All rights reserved.