H-2z homozygous New Zealand mice as a model for B-cell chronic lymphocytic leukemia: elevated bcl-2 expression in CD5 B cells at premalignant and malignant stages.

In New Zealand mice, the major histocompatibility complex (MHC) controls the development of both autoimmune disease and B cell chronic lymphocytic leukemia (B-CLL). While H-2d/H-2z heterozygosity acts as one major predisposing genetic element for autoimmune disease, H-2z/H-2z homozygosity acts as an element for B-CLL. In the H-2z/H-2z homozygotes, there was an age-dependent increase in frequencies of CD5 B cells in the blood and spleen, and such CD5 B cells showed oligoclonal to monoclonal expansion, giving rise to B-CLL. B-CLL cells from these mice had surface phenotypes typical of CD5 B lineage cells, and expressed high levels of proto-oncogene bcl-2. Elevated bcl-2 expression was also observed in premalignant B cells in the aged mice, thereby suggesting that apoptosis-resistant, long-surviving CD5 B cells with a self-renewal capacity form the basis of malignant transformation. This model not only provides clues for analyzing multiple steps of genetic alterations involved in the generation of B-CLL, but also sheds light on the correlation between B-CLL and autoimmune disease.