TNF and major depressive disorder: For example, some studies have detected higher levels of inflammation in MDD patients than in healthy subjects (HS), although the strength of the evidence varies according to the type of inflammatory marker (cytokine) that is examined (i.e., interleukin [IL]-1β, IL-6, interferon-γ [IFN-γ], and tumor necrosis factor α [TNF-α])12–14.