Effect of lithium on stem cell and stromal cell proliferation in vitro.

Lithium is recognized as a potent stimulator of hematopoiesis both in vivo and in vitro. Previous work has suggested that this stimulation is mediated as an indirect, humoral effect by the action of lithium upon the stromal cell population. In the present study, the effects of lithium on the stromal population were investigated using a long-term liquid marrow culture model. These findings indicate that exposure of in vitro cultures to lithium results in an increase in the total cellularity and in the number of various hematopoietic progenitor cells residing within the stromal layer. A distinct morphologically recognizable cell has not been identified as the target cell responsible for the indirect stimulation of hematopoiesis by lithium. However, two candidate radioresistant stromal cells believed to be active in the production of humoral mediators of hematopoiesis did proliferate in response to lithium exposure.