Tumor incidence and development of autoimmune hemolytic anemia in two breeding lines of the NZB mouse strain that differ in chromosome breakage.

Increased chromosome breakage observed in NZB mice was studied. Breeding experiments with mice selected according to breakage frequencies provided evidence that the proportion of mice with high breakage (HB) and low breakage (LB) figures in the progeny depends on the phenotype of the parents. Selective breeding for the "chromosome breakage" characteristic was successful and resulted in the separation of a breeding line with LB incidence. However, the selection could not be continued beyond the fourth generation for the mice with HB incidence because of lethal factors. Comparative studies of HB mice from the HB line and LB mice from the LB line showed significant differences for tumor incidence and positivity of the Coombs' test.