A contribution to the incidence of nucleoli in normal human blood monocytes

Normal blood monocytes were studied in blood donors to provide more information on the presence of nucleoli and nucleolar types in these cells.

Nucleoli in monocytes were visualized using cytochemical procedures that detect RNA and characteristic nucleolar proteins, i.e. nucleophosmin, nucleolin, fibrillarin and AgNOR proteins, in peripheral blood smears.

Nucleoli were detected in all blood monocytes. The nucleolar coefficient (number of nucleoli per cell) was 2.6 and no differences were found between men and women. Concerning the incidence of nucleolar types, monocytes from both male and female blood donors possessed mainly only inactive micronucleoli characteristic of mature or advanced maturation stages of blood cells; however, 16-20% of monocytes also contained functionally dominant ring-shaped nucleoli, which reflect a reversible decrease of rRNA transcription and in blood cells are intermediate stages between actively transcribing large nucleoli in highly immature cells and inactive micronucleoli in terminal nucleolated maturation stages. Monocytes containing large nucleoli with a relatively uniform distribution of RNA characteristic of immature or stimulated blood cells were rare (< 2%).

Nucleoli are present in all normal blood monocytes. The incidence of the main nucleolar types represents a very convenient complementary marker for evaluating the maturation and possibly the stimulated state of these cells.