The association between cytokines and cognitive function in patients with major depressive disorder and controls

Cognitive dysfunction is a symptom of depression (MDD). While the involvement of the immune system has long been suggested to contribute to the biological underpinnings of depression, less is known about the underpinnings of cognitive dysfunction. A recent genome-wide association study pointed to genes related to immune function to be relevant for cognitive processes in depression. However, only a few studies have explored immune proteins in blood in MDD who also suffer from cognitive dysfunction. In this study we investigate associations between cognitive impairment and cytokines using a comprehensive cognitive test battery and a broad cytokine assay.

124 patients with MDD and 69 healthy controls (HC) were recruited. To assess cognition, RBANS was used, which measures immediate and delayed memory, visual-spatial functions, language and attention. Moreover, six cytokines (IL-8, IL-1beta, IL-6, IL-10; TNF-alpha and IL-12p70) were recorded. Associations were examined by regression analyses with age, sex, education, country, group and symptom severity as covariates.

There is an exploratory tendency that higher cytokine levels (IL-1beta, IL-6, IL-8, IL-10, IL-12p70) are associated with mostly lower cognition ("language", "visual-constructional", "attention" and "total score"). After conservative, corrected interpretation, interleukins were not statistically significant associated with poorer cognitive function.

Despite a large sample, the unbalanced sample size is a limitation. For future studies, it is advisable to match participants based on age and gender.

Cognitive dysfunction could be associated with specific cytokines that underpin the contribution of the immune system, but further research is necessary.