In-hospital levels of C-reactive protein and IL-6 predict post-operative depressive symptoms among patients undergoing total knee replacement surgery

Behavioral changes observed following immune system activation are similar to many of the hallmark symptoms of major depressive disorder (MDD), including appetite change, lethargy, fatigue, negative mood and anhedonia. Acute phase proteins, such as interleukin-6 (IL-6) and C-reactive protein (CRP) have been implicated in the production of sickness behavior, and research has revealed significant differences in the levels of these acute phase proteins between depressed and non-depressed individuals. The current study examined whether early post-operative IL-6 and CRP levels predicted subsequent depressive symptoms in 110 patients undergoing total knee replacement surgery (TKR). In-hospital levels of IL-6 and CRP predicted depressive symptoms at three-months following surgery, as indicated by significant main effects and a significant interaction term. Specifically, lower levels of in-hospital CRP and higher levels of IL-6 in-hospital predicted more depressive symptoms three-months following surgery. The finding that levels of acute phase proteins soon after surgery predict subsequent depressive symptoms, if replicated, extends prior research on the relationships between IL-6, CRP, and depression. Further, this predictive relationship suggests the possibility of early identification of individuals at risk for the subsequent development of post-operative depression.