Chromosome damaging agent of low molecular weight in the serum of New Zealand black mice.

Two substrains of NZB mice were developed by selective matings according to chromosome breakage frequencies in direct bone marrow preparations: HB, a line with increased chromosome breakage, and LB, a line with low or normal breakage rates. The serum of NZB mice from the HB strain contains a chromosome breaking factor that produces chromosome abnormalities in human lymphocytes. This clastogenic substance could not be detected in serum of NZB line. Nor does it exist in serum of Balb, C3H, C57 B1, Swiss, or AKR mice, in which no chromosomal breakage was observed in bone marrow. The breakage factor has a molecular weight between 1000 and 10,000 daltons.