IL6 and major depressive disorder: These include but are not limited to interferon-γ (IFN-γ) and IFN-γ-induced protein 10 (IP-10) in Mycobacterium tuberculosis, which can aid in the diagnosis of disease, as well as vaccine-induced protection [3, 4]; CCL2 in HIV infection, which correlates with viral load [5]; tumour necrosis factor-α (TNF-α), interleukin (IL)-1β, and IL-6 in heart failure, which are associated with more severe disease and adverse outcome [6, 7]; and TNF-α and IL-6 in major depressive disorder, which correlate to poor antidepressant response [8, 9].