Although it has been clinically shown that the signature cytokine interleukin 17A (IL-17A) produced by Th17 cells does not significantly correlate with the severity of depression, Th17 cells are involved in the gut-brain axis to mediate the stress response, possibly by promoting neuroinflammation, microglia, and astrocyte activation thereby neuronal damage triggering depressive symptoms. This evidence concerns the gene IL17A and depressive symptom measurement.