Continued blood cell formation in spherical bodies in a long-term mouse spleen culture

During the primary culture of spleen fragments of newborn mice, a spherical body (d = circa 200 to 300 microns) as a three-dimensional cellular organization was formed. Continued production of blood cells from the spherical body was observed without changing its size for about 2 months of culture. Without growth factor, the spherical bodies produced mainly lymphocytes and macrophages. Addition of interleukin-3 enhanced their granulocyte formation, and this enhancement was observed even after a prolonged maintenance without growth factors. The spherical bodies were composed of a uniform mixture of endothelial cells and fibroblasts within the body, and cell-cell contacts between lymphocytes and fibroblasts were notable in the periphery. With prolonged culture, the spherical bodies showed a definite change in their structure by sorting two cell types and the blood cell production gradually decreased. These results suggested that a three-dimensional structure was required for the maintenance, growth, and differentiation of blood cell progenitors in the long-term spleen culture.