For example, proteomic research suggests that the serum levels of c-reaction protein (CRP), inter-alpha-trypsin inhibitor heavy chain H4 (ITIH4), serum amyloid A1 (SAA1), and angiopoietin-like 3 (ANGPTL3) are significantly higher in patients with depression than in healthy controls. Here, ITIH4 is linked to major depressive disorder.