Studies on leukemia developing spontaneously in an inbred family of rats.

This study is a continuation of our recently reported observations on leukemia and lymphomas developing spontaneously in a subline of Sprague-Dawley rats bred by brother-to-sister mating in our laboratory. The previous preliminary report described our observations made in the course of the initial 12 generations of our leukemic subline. The current study reviews the data collected during 8 additional generations and results of experimental and morphologic studies. There was no problem in transmitting the spontaneously developing leukemia by inoculation of suspensions of leukemic cells into newborn or very young suckling Sprague-Dawley rats. Attempts to transmit the disease by inoculation of cell-free, filtered leukemic extracts gave thus far positive results only in one experiment in which two of six inoculated rats developed leukemia and a third one developed an angiosarcoma on the neck. In six additional experiments, of a total of 37 rats inoculated with leukemic filtrates, none developed leukemia and 9 females developed mammary fibroadenomas. Reviews of microscopic slides of blood and of sections of lymphoid tumors, livers, spleens, kidneys, and fragments of bone marrow of the leukemic animals are discussed as well as electron microscopic studies.