A PROTEIN that could aggregate Sertoli cells in vitro was purified to homogeneity from ram rete testis fluid by Fritz and collaborators in 1983]. This protein also elicited the clustering of erythrocytes and other cell types from different species and was christened clusterin. It is one of the most abundant glycoproteins secreted by Sertoli cells into seminiferous tubules. At about the same time, Griswold and collaborators 2 analysed by twodimensional gel electrophoresis all major glycoproteins secreted by cultured rat Sertoli cells. The genes encoding some of these were later cloned in order to study their role and importance for the development of germinal cells. The cDNA-derived protein sequence for rat sulfated glycoprotein 2 (SGP-2) and protein sequencing of the purified sheep clusterin revealed them as species homologues 3A.

The human homologue of clusterin was isolated in 1988, and subsequently cloned 6, 7 and characterized as a novel inhibitor of the terminal cytolytic reaction of the complement cascadeE The inhibitor binds specifically to nascent terminal complement complexes assembled from the components C5-C9 in whole serum and was tentatively designated SP-40,407 and cytolysis inhibitor (CLI) E Like vitronectin (formerly called