Leydig cells nonspecifically suppress lymphoproliferation in vitro: implications for the testis as an immunologically privileged site.

We have studied the influence of mouse testis cells on unstimulated lymphoproliferation; on allogeneic mixed lymphocyte reaction; and on concanavalin A-stimulated, phytohemagglutinin-stimulated, or lipopolysaccaride-stimulated responses in vitro. Co-culture with highly enriched irradiated (2000 R) Leydig cells (LC) led in each case to a considerable reduction of 3H TdR uptake. Prolonged tissue graft survival times suggest that the testis is an immunologically privileged site. This may be explained by an immune-suppressive function of LC in vivo. LC are also capable of selectively binding lymphoid and myeloid cells to their surface. This capacity, accompanied by a suppression of immune reactivity in situ, may play a role in cases of testicular relapse observed in acute leukemia.