Finally, Kanannejad and Gharesi-Fard studied unexplained male infertility in seminal plasma samples from men undergoing in vitro fertilization with 2D-PAGE, followed by mass spectrometry, and found two differentially expressed proteins clusterin (CLU) and epididymal secretory protein E1 (NPC2), which is a major component of epididymal secretion, being overexpressed, while prostate-specific antigen was downregulated in the group which succeeded in the IVF process [66]. Here, CLU is linked to male infertility.