Practical and theoretical issues in 1993 concerning radiation effects on the growth of normal and neoplastic hematopoietic cells.

Radiation has multiple effects on eukaryotic cells, ranging from altered gene expression and cell-cell signaling to induction of programmed cell death (i.e., apoptosis). These changes may lead to neoplastic transformation of the cell and diverse effects on differentiation and growth. The Belarusians were exposed to greater levels of radiation from the Chernobyl nuclear reactor melt-down than any other population. Medical consequences of this exposure are reviewed, focusing on the appearance of thyroid cancer and the possible increased risk of future hematologic malignancies. Since circulating hematopoietic cells must be relaced continually at high rates, the effects of ionizing radiation are reviewed at the cellular level, utilizing the hematopoietic system as a model tissue. An overview of normal hematopoiesis (as understood in 1993) is provided, and the effects of ionizing radiation on hematopoietic stem cell compartments are reviewed. Hematopoietic growth factors (i.e., cytokines) that are associated with the plasma membrane (i.e., membrane-bound cytokines), or that are released as "soluble" molecules into the microenvironment and circulation, may "protect" organisms from radiation injury and may accelerate hematopoietic recovery following radiation exposure. Cloned hematopoietic cytokines, individually or in combination, may be useful in the treatment of radiation accident victims in the future.