There is increasing evidence suggesting the involvement of the let-7 family in inflammation and immune response.21, 22, 23 A previous study showed that the let-7 family directly inhibited IL-6 expression in breast cancer cell lines, and thereby may act as an immunorepressor.24 Let-7 is abundant in adult brain and has been implicated in neuronal proliferation and differentiation and synaptic plasticity,25, 26, 27, 28 but it is not known whether it has a role in the pathophysiology of depression. This evidence concerns the gene IL6 and breast carcinoma.