Life table analysis and pathologic observations in male mice of a long-lived hybrid strain (Af X C57BL/6)F1.

We have utilized a long-lived (Af X C57BL/6)F1 hybrid strain of mice for a variety of aging studies. In this report we have characterized the life expectancy and pattern of spontaneous deaths in 202 mice, malignant and nonmalignant lesions in 64 male mice dying spontaneously, and organ weights and lesions in 39 male mice killed at selected ages. The maximum age observed was 41.5 months. The principal causes of death were malignant lymphoma and alveologenic neoplasms, which were present in 56.3% and 45.3%, respectively, of the mice dying spontaneously. A variety of other neoplastic and non-neoplastic lesions that are not infrequently seen in older mice were observed in these mice. Neoplasms seen in these mice that are rare in other mice included disseminated mast cell tumors in two mice and gastric adenocarcinoma in one mouse. In comparing the diseases observed in this hybrid strain with those reported for the parent strains, there was an incidence of malignant lymphoma similar to the C57BL/6 parent, an incidence of alveologenic neoplasms intermediate between the parent strains, and a markedly reduced incidence of amyloidosis. This study provides a detailed background of baseline hematologic and morphologic data in a long-lived hybrid of two commonly used strains of mice.