The RNA content of nucleolar bodies is related to their size - a cytochemical study on human monocytes and lymphocytes in blood smears and blood cytospins.

The present study was undertaken to pro- vide more information on the relationship between the nucleolar size and RNA density. Mature mono- cytes circulating in human peripheral blood ap- peared to be very convenient for such study because they contain multiple nucleoli of various sizes in one and the same nucleus. In addition, nucleoli without perinucleolar chromatin represented by nucleolar bodies are easy to be visualized by a simple cyto- chemical procedure for RNA demonstration. The di- ameter and density of NoBs in specimens stained for RNA were determined by computer-assisted meas- urements of individual cells. According to the results, the nucleolar RNA content was apparently related to the nucleolar size because the RNA density of small and large NoBs was practically the same. In addi- tion, the diameter measurements also indicated that one or two of several NoBs in one nucleus were dom- inant - larger - than the others. It should also be mentioned that the diameter and RNA density of NoBs were studied in monocytes in peripheral blood smears regardless of their limited number. Addition- al study on lymphocytes indicated that the prepara- tion procedure of smears modified both diameter and density of the measured parameters less than the preparation of cytospins as demonstrated by lower variability of the resulting values. Thus, the observed differences between smears and cytospins also indi- cated that the specimen preparation procedures should always be considered during evaluation of the nucleolar size or staining intensity of nucleoli or cy- toplasm due to the presence of RNA.