Increase in RNA and glycogen but not in DNA in developing human macrophages proven by integrating microdensitometry

In order to quantitate DNA, RNA and glycogen contents of developing macrophages, blood monocytes were obtained from 19 healthy human subjects and examined after 0, 2, 4 and 6 days of suspension culture. Cytochemical staining was carried out by standard methods using Feulgen, cuprolinic blue and PAS. All specimens from all subjects were stained at the same time. Examination was carried out in an integrating microdensitometer, the staining intensities of individual cells being measured at appropriate wavelengths. Over the 6 days of culture, highly significant increases took place in RNA and glycogen, but no significant change was found in DNA content. These findings are taken to indicate that increased protein synthesis and the building up of fuel reserves are features of macrophage development but that S phase DNA replication does not occur.