TNF and major depressive disorder: In particular, tumor necrosis factor alpha (TNFα), interleukin-2 (IL-2), interleukin-6 (IL-6), interleukin-13 (IL-13), interleukin-18 (IL-18), C-reactive protein (CRP), chemokine-2 (CCL2), and chemokine-11 (CCL11) are elevated in depression based on multiple meta-analyses (68, 71, 73).