Ram rete testis fluid contains a protein (clusterin) which influences cell-cell interactions in vitro.

Ram rete testis fluid is shown to elicit clustering of suspensions of Sertoli cells from testes of immature rats, TM-4 cells derived from mouse testis, and erythrocytes from several species. Details of bioassay procedures and characteristics of the phenomenon are reported. Concanavalin A and wheat germ agglutinin prevent aggregation elicited by rete testis fluid, and this inhibition is specifically prevented by alpha-methylmannoside and N-acetyl-glucosamine, respectively. Influences of rete testis fluid on cell aggregation are not dependent on exogenous calcium, but clustering is blocked by various metabolic inhibitors such as dinitrophenol. Rete testis fluid addition to mixed suspensions of erythrocytes and TM-4 cells is followed by separate aggregation of each cell types. Using aggregation of TM-4 cells suspended in simple medium at low density in rotation as a bioassy, we have determined which fractions in rete testis fluid retain activity. We have shown that a heat-stable, trypsin-sensitive protein, having an isoelectric point below pH 4.0, retains the capacity to aggregate cells. We discuss the possible functions of this protein, named clusterin, in cell interactions.