REACTIONS OF LEYDIG-CELLS AND BLOOD-VESSELS TO LYMPHOBLASTIC-LEUKEMIAIN THE RAT TESTIS

The testis is the third common site of relapse in childhood acute lymp hoblastic leukemia (ALL). Despite the apparent clinical importance of testicular relapse, its pathogenesis is still unknown. The studies wit h an animal model of ALL have shown that many testicular factors are a ble to control the intratesticular infiltration and proliferation of l eukemic lymphoblasts during the untreated course of ALL. In the presen t study, the ultrastructure of rat testicular interstitium infiltrated by leukemic lymphoblasts was studied in two groups of rats transplant ed with rat T cell leukemia in early and late puberty. In both groups most of the leukemic cells infiltrating testicular interstitium were t otally or partly enveloped by one or more Leydig cells, and the endoth elial cells of capillaries, arterioles and venules were hypertrophic. The Leydig cells of the younger experimental group were by nuclear and cytoplasmic ultrastructure similar to the undifferentiated Leydig cel ls normally seen on the third postnatal week. The results suggest that Leydig cells bind leukemic lymphoblasts on their surface in vivo as a lso previously observed in vitro, and that ALL may disturb the puberta l maturation of Leydig cells. The occlusion of arterial and capillary lumina by folds of hypertrophic endothelial cells together with adhere d leukemic lymphoblasts may impair the circulation of leukemic testes.