Lower serum levels of interleukin-6 in a population sample with symptoms of depression than in a population sample without symptoms of depression.

In this study we compared the levels of interleukin (IL)-6, IL-8, IL-10 and tumor necrosis factor-alpha (TNF-alpha) in population samples characterized by a high or low level of self-reported depression. We measured serum IL-6, IL-8, IL-10 and TNF-alpha in two cohorts which differed in scoring on the Zung Self-Rating Depression Scale (ZSDS). The group with a high score in ZSDS (average SDS index = 62.9) was called DEP (n=27), the group with a low score in ZSDS (average SDS index = 29.9) was called NDEP (n=16). The groups did not significantly differ in age, waist circumference and body mass index. For the assessment of serum cytokine levels multiplex immunoanalytic xMAP(LUMINEX) technology was used. We found lower IL-6 in the DEP group (medians; DEP 4.08 pg/ml vs. NDEP 6.11 pg/ml) on the border of statistical significance in multiple regression analysis (p=0.049). Serum levels of all other studied cytokines were not significantly different (medians; IL-8: DEP 2.18 pg/ml vs. NDEP 2.61 pg/ml; IL-10: DEP 2.85 pg/ml vs. NDEP 2.94 pg/ml; TNF-alpha: DEP 2.32 pg/ml vs. NDEP 2.30 pg/ml). These results are in contradiction to the prevailing opinion that pro-inflammatory cytokine levels are elevated in people with symptoms of depression.