Diverse xenotropic virus expressions in two NZB mouse breeding lines that differ in chromosome breakage

Two breeding lines of the NZB/BI mouse strain, which was originated from Bielschowsky's stock and maintained as a conventional inbred colony since 1963, were developed by selective matings according to chromosome breakage incidence in bone marrow cells. These breeding lines were used because they represent an interesting experimental model, since they differ in the manifestations of the autoimmune process and the incidence of lymphomas. The present study showed that embryos from both breeding lines differed in the expression of the xenotropic type C RNA virus, characteristic of NZB mice. All 17 cultures initiated with embryos from the line showing high chromosome breakage (HB) had positive reverse transcriptase (RT) reactions after cocultivation with an indicator cell line (SIRC). On the contrary, only 3 of the 22 embryos from the line showing low chromosome breakage (LB) had RT activity at late passages (7-10). The chromosome studies done on these embryo cultures showed highly significant differences in the chromosome breakage incidence for the 2 breeding lines [10.6 and 20.5% of cells with aberrations for LB and HB embryos, respectively (P less than 0.001)].