Associations of number and severity of depressive episodes with C-reactive protein and Interleukin-6.

BACKGROUND

Many researchers have found that the inflammatory process in the body and the brain may result in psychiatric disorders. Meta-analyses of cross-sectional studies have reported increase in inflammatory markers in depression. However, the direction of the association remains unclear.

AIMS

To compare the levels of C-reactive protein (CRP) and Interleukin-6 (IL-6) in depressed and healthy controls. To study the associations of these biomarkers with severity and number of depressive episodes.

METHODS

A total of 72 subjects with major depression and 60 healthy controls were studied. CRP and IL-6 were measured in all subjects.

RESULTS

No significant differences were noted between depressed patients and healthy controls with regard to CRP (p=0.29) and IL-6 (p=0.50). Those who were suffering from severe depression based on Beck's Depressive Inventory (BDI), were positively correlated with raised CRP (p=0.011) in comparison to patients with mild to moderate depression. Single and recurrent depressive disorder (RDD) were not associated with significant rise in CRP (p=0.866) and IL-6 (p=0.531).

CONCLUSIONS

Severity of depression is correlated with elevated CRP but not with IL-6. No association found between number of depressive episodes and levels of CRP and IL-6. It is possible that immune dysregulation is not generally present in depression, but might be restricted to particular subgroups of depressed patients. Several factors that could influence the depression and inflammation relationship need further investigation.