Clusterin is the major secreted product of Sertoli cells and is thought to play a critical role in spermatogenesis. Clusterin was also shown to be a normal constituent of human blood.

It consists of two 40-kD chains, alpha and beta, covalently joined by disulfide bonds.

Clusterin is a member of the human complement system by directly demonstrating its presence within the S-protein-containing soluble variant of the C5b-9 complex, SC5b-9.

Clusterin is also called complement lysis inhibitor. It acts as a control mechanism of the complement cascade; specifically, it prevents the binding of a C5b-C7 complex to the membrane of the target cell and in this way inhibits complement-mediated cytolysis.

Clusterin is also involved in apoptosis regulation.

Expression in tumors

 follicular dentritic cell tumor (FDCT)