Does Basal Inflammation Connote Vulnerability for Depression?

The relationship between major depression and immune system functioning has increasingly been the subject of scientific inquiry, and several lines of research have pointed to the possibility of inflammatory processes playing a causal role in the development of depressive symptoms. If inflammatory processes are causal, then it is possible that basal markers of inflammation will connote vulnerability for major depression. Using a family study methodology, the present study therefore examined the relationship between depressive symptoms and markers of inflammation (specifically, C-reactive protein [CRP] and interleukin-6 [IL-6]) in 146 sibling pairs recruited from the greater Chicago community. Results showed that both CRP and IL-6 levels were stable over time and aggregated within families. There were significant positive associations between current depressive symptoms and inflammatory markers, replicating previous findings. However, familial risk analyses were inconclusive and were not able to demonstrate that CRP and IL-6 concentrations are associated with familial vulnerability for depression. Given the dynamic nature of the inflammatory system, it is possible that inflammatory stress reactivity, rather than basal levels of inflammation, is more indicative of vulnerability for depression.