Agar extract induces release of granulocyte colony-stimulating activity from human peripheral leukocytes

Water-soluble components of crude bacto-agar are known to be mitogenic for mouse B lymphocytes. We examined the effects of aqueous agar extract in liquid cultures of human peripheral leukocytes. In comparison with phytohemagglutinin (PHA), agar extract had only weak mitogenic activity. However, it was almost as effective as PHA in promoting the release of granulocyte colony-stimulating activity (G-CSA) into the supernatant medium. This activity was assayed in methyl cellulose cultures of non-plastic-adherent human bone marrow cells. The results provide information on the mechanism of G-CSA release in cultures of agar-immobilized human leukocytes, and serve as a reminder that crude agar is not a completely inert culture constituent.