Marta Gazal, Karen Jansen, Luciano D. Souza, Jean P. Oses, Pedro V. Magalhães, Ricardo Pinheiro, Gabriele Ghisleni, Luciana Quevedo, Manuella P. Kaster, Flávio Kapczinski, Ricardo A. da Silva

To investigate peripheral levels of interleukin-10 (IL-10) in patients with major depressive disorder (MDD) and bipolar disorder (BD) and evaluate the relationship between IL-10, age of disease onset, and duration of illness. Case-control study nested in a population-based cohort of 231 individuals (age 18-24 years) living in Pelotas, state of Rio Grande do Sul, Brazil. Participants were screened for psychopathology using the Mini-International Neuropsychiatric Interview (MINI) and the Structured Clinical Interview for DSM-IV (SCID-I). Serum IL-10 was measured using commercially available immunoassay kits. Peripheral levels of IL-10 were not significantly different in individuals with MDD or BD as compared to controls. However, higher IL-10 levels were found in MDD patients with a later disease onset as compared with controls or early-onset patients. In addition, IL-10 levels correlated negatively with illness duration in the MDD group. In the BD group, age of onset and duration of illness did not correlate with IL-10 levels. Higher levels of IL-10 are correlated with late onset of MDD symptoms. Moreover, levels of this cytokine might decrease with disease progression, suggesting that an anti-inflammatory balance may be involved in the onset of depressive symptoms and disease progression in susceptible individuals.