Cell membranes as sources of granulocyte colony stimulating activities

Subcellular localization of factors associated with stimulation of granulocyte progenitors (CFU-c) to form colonies in vitro was investigated. Human peripheral blood leukocytes were fractionated into three subcellular fractions. After solubilization with sodium dodecyl sulfate, fractions were assessed for ability to stimulate colony formation by CFU-c. The fraction containing cell membranes proved to be the richest source of stimulating factors. Apparent molecular weights for these factors as determined by gel filtration were equivalent to those obtained for factors from purified peripheral leukocyte conditioned medium. The results suggest that at least some granulocyte colony-stimulating factors should be regarded as membrane-active agents.