Abstract
Mosaicism of normal and chromosomally aberrant cells was detected in 14 of 20 spleens from adult New Zealand Black (NZB) mice reared under conventional conditions, a strain that spontaneously develops autoimmunity and lymphoreticular malignancy. No abnormalities were found in marrows from these same animals or in spleens from NZB mice younger than 3 months. The prevalence of chromosomal aberrations was significantly higher in spleens from NZB mice than in spleens from the two other strains studied-SJL/J, which has high frequency of reticulum cell neoplasia and paraproteinemia but no autoimmunity, and BALB/c, which has essentially no autoimmunity and only a low incidence of generalized lymphoid neoplasms and plasmacytomas in ageing animals. Causes for the chromosomal abnormalities in NZB mice are considered in terms of other features in these mice-immunoproliferation, autoimmunity, and the presence of murine leukemia ("C"-type) virus particles.