A study of older women found that those with major depression had about double the amount of the immune peptide LL‑37 in their blood compared to non‑depressed peers, even though other common inflammation markers (CRP, white‑blood cells) were unchanged.

Cathelicidin LL-37 is a small cationic that plays an important role in antimicrobial defense, as it kills a broad spectrum of infectious agents by disrupting their membranes, including gram-positive and gram-negative bacteria, some viruses and fungi; and it neutralizes activity of bacterial endotoxins. Moreover, cathelicidin LL-37 exerts proinflammatory effect, while numerous reports indicate the role of inflammation in the development of depression. The purpose of this study was to evaluate the circulating levels of cathelicidin LL-37 in elderly depressed patients. Thirty-nine elderly (age ≥ 60 years) women with major depressive disorder and thirty-eight non-depressed elderly (age ≥ 60 years) women were included into the study. The mean serum cathelicidin LL-37 concentration in patients with depression and in healthy subjects were 2.40 ± 3.00ng/mL and 1.17 ± 3.04ng/mL, respectively, and the difference was statistically significant. No significant differences between mean serum CRP level and WBC count in MDD patients and control group were documented. There were no correlations between LL-37 level and age, BMI, GDS score, CRP level or WBC count. It can be assumed that elevated serum LL-37 levels in depressed patients may reflect inflammatory activation associated with depression.