Cytofluorometric analysis of macrophages activated in vivo or in vitro

The relative RNA content of single macrophages was measured by cytofluorometry after differential staining of cellular DNA and RNA with the metachromatic fluorescent dye acridine orange. This method allowed the differentiation of two major groups in the adherent macrophage population differing in their RNA content. After in vivo stimulation of mice (by injection of thioglycollate medium) or guinea pigs (by injection of oil), an increasing percentage of macrophages possessing a high RNA content is recovered. In vitro stimulation of macrophage cultures with lipopolysaccharide had the same enhancing effect on cellular RNA content. Cytofluorometric measurement of RNA content may possibly become an efficient and rapid method of measuring macrophage activation.