Morphology and quantitative composition of hematopoietic cells in murine bone marrow and spleen of healthy subjects

Laboratory mice play an outstanding role in modeling human development and disease. In contrast to human leukemia, the spleen is involved in almost all cases, and the bone marrow is only variably involved in murine models. Although mice have been used for medical research for over 100 years, there are only few reports with a small number of cases looking at morphology and quantitative composition of murine hematopoietic cells in the bone marrow of non-transplanted animals of most strains. To our knowledge, there is not even a single report describing the splenogram in C57BL/6J mice, one of the most commonly used strains for medical research. The present study illustrates the morphology of the hematopoietic cells in the bone marrow and spleen of non-treated C57BL/6J mice and establishes the murine myelogram from the largest healthy C57BL/6J cohort reported to date. Furthermore, we present the first murine splenogram described for C57BL/6J mice. Our study supports the acceptance of the presence of >5 % blast cells as providing clear evidence of abnormality in bone marrow like in humans. In addition, we are the first to show <1 % blast cells in the normal spleen. Interestingly, classical dysplastic changes were rare in normal healthy mice. Our study of the bone marrow and spleen of healthy non-transplanted animals provides reference ranges of each cell type and for the myeloid/erythroid ratio, which can be used to interpret preclinical gene therapy data, leukemogenesis, and hematopoiesis studies, and may improve the quality of such analyses.