INS and depressive disorder: The current body of literature features data on a wide variety of possible biomarkers linked to depressive disorders in both adults (interferon-γ, monocyte chemotactic protein-1, macrophage inflammatory protein-1α, matrix metalloproteinase-2, tumor necrosis factor-α, hepatocyte growth factor, insulin polypeptides, pregnancy-associated plasma protein A) and adolescence (interleukin-6) [31,32,33].