CST4 and dry eye syndrome: In an investigation, it was revealed that several proteins were downregulated in both dry eye and MGD, including prolactin inducible protein (PIP), zinc-α-2-glycoprotein (AZGP1), galectin 7 (LEG7), cystatin S (CST4), actin cytoplasmic 1 (ACTB), lactotransferrin (LTF), cystatin SN (CST1), and mammaglobin-B (SG2A1) (74).