TNF and major depressive disorder: In the pathomechanisms of fatigue and depression in MS the crucial role play proinflammatory cytokines including tumor necrosis factor α (TNFα), interleukins (IL-1a, IL-1b, IL-2, IL-6), IFN-γ released by mitogen-stimulated peripheral blood lymphocytes, and neopterin produced by macrophages upon IFN-γ stimulation (23).