Pro-inflammatory cytokine associated with somatic and pain symptoms in depression

More than two-thirds of depressed patients complain of somatic and pain symptoms, which are frequently regarded as a psychological reaction. Although there is a growing body of evidence showing that depression is related to immune abnormalities, few studies have investigated the association between inflammatory cytokines and somatic/pain symptoms.

Patients with depressive disorder but without any medical disorders, and age/gender/body mass index (BMI)-matched healthy subjects were enrolled. All the subjects completed the self-rating scales of the Beck Depression Inventory-II and the Depression and Somatic Symptoms Scale, which was comprised of depressive, somatic, and pain subscales. Pro-inflammatory cytokines, including C-reactive protein (CRP), interleukin-2 receptor (sIL-2R), soluble interleukin 6 receptor (sIL-6R), soluble TNF-receptors (sTNF-R), soluble P-selectin (sP-selectin), monocyte chemotactic protein-1 (MCP-1), and adiponectin, were assessed by enzyme-linked immunosorbent assays.

In all, 109 patients with depressive disorder and 126 normal controls were enrolled. The patients with depressive disorder had significantly more severe depression, somatic and pain symptoms (all p<0.001), and higher levels of sIL-2R (p<0.0001), sTNF-R (p<0.001), and sP-selectin (p=0.005) than the normal control group. Using multivariate regression analysis with controlling of age, gender, BMI, and other pro-inflammatory cytokines, sIL-2R was the most significant predictor for depressive symptoms (p<0.0001); with further controlling of severity of depressive symptom, sP-selectin was the only predictor for somatic (p=0.002) and pain (p=0.059) symptoms.

The elevated sP-selectin associated with somatic symptoms in depression, may indicate early micro-vascular changes occur subtly, and provide neurobiological evidence for somatic and pain symptom in depression.