IL-7 and Depression: The importance of gender and blood fraction.

Interleukin 7 (IL-7) is involved in B and T cell development and differentiation. Recent work suggests IL-7 may be altered in depression; however, we have previously shown that gender and blood fraction oftentimes impacts putative biomarker relationships among those with and without Alzheimer's disease (AD). The current study examined the impact of blood fraction (serum versus plasma) and gender on the IL7 depression link in a sample of elders with and without AD. Non-fasting serum (150 AD cases 150 controls) and plasma (100 AD cases, 100 controls) IL-7 levels were assayed via electrochemiluminescence. The correlation between serum and plasma for IL-7 was 0.34. In the total sample, serum (r(2)=0.16, p=0.006) and plasma (r(2)=-0.20, p=0.007) IL-7 levels were significantly, but inversely, correlated with GDS-30 scores. When split by gender, serum IL-7 levels were significantly positively associated with GDS scores among men (r(2)=0.34, p=0.001) whereas plasma IL-7 levels (r(2)=-0.23, p=0.008) were significantly negatively associated with GDS scores among women. A logistic regression model predicting depression status (GDS30>=10) included age, gender, education, plasma, and serum IL-7 levels, found both significantly associated with depression status, but in opposite directions. Our findings support a significant link between IL-7 and depression; however, we further highlight the importance of blood fraction and gender when examining this relationship. Additionally, these findings further support the need for additional work that could lead to targeted therapeutic interventions utilizing anti-inflammatory medications for individuals with depression.