IL6 and major depressive disorder: Bidirectional brain-immune relationships are marked by elevated blood levels of inflammatory cytokines (eg, IL-6, TNF-α).6,7,8 The pathophysiologic mechanisms connecting these factors is under investigation.9 Elevated inflammatory cytokines have been noted as a prelude to depressive episodes among people with major depressive disorder10,11 and are believed to contribute to mechanisms of depression onset and poorer antidepressant treatment response.12 Depression may also be associated with inflammation through health behavior relevant to cancer progression (Figure 1).