Elevated IL-6 levels in patients with atypical depression but not in patients with typical depression

Elevated levels of the proinflammatory cytokine Interleukin-6 (IL-6) are among the most consistent findings in patients with major depressive disorder (MDD). Additionally, some evidence suggests that elevated cytokine levels in patients with major depression are responsible for the development of metabolic syndrome in patients suffering from MDD. Therefore, the aim of the study was to examine the concentrations of IL-6 in specific subtypes of MDD and to investigate their relationship to metabolic factors. Twenty-four patients with typical (24) and atypical (eight) major depression according to DSM-IV criteria were studied and compared to 24 normal controls. Blood samples were collected during a stepwise glucose-clamp procedure, and IL-6 concentrations were measured by high sensitivity ELISA. IL-6 levels were elevated in patients suffering from atypical depression but not in patients with typical depression, compared to normal controls. IL-6 correlated significantly with HbA1c, insulin, waist girth, BMI, number of alcoholic drinks per week and C-reactive protein. Our data indicate that high concentrations of IL-6 during the glucose clamp may be limited to the atypical subgroup of patients with MDD.