Chromatin-bound PCNA as S-phase marker in mononuclear blood cells of patients with acute lymphoblastic leukaemia or multiple myeloma

Objectives: Proliferating cell nuclear antigen (PCNA) has often been used as a marker to aid assessment of tumour growth fraction. This paper addresses the question of whether it can be used as an S-phase marker, when the non-chromatin-bound form of the protein is removed by pepsin treatment. Materials and methods: Cytofluorometric measurements were carried out after immunofluorescence staining of PCNA and counterstaining of DNA. S-phase fraction was determined with the help of windows on PCNA versus DNA scattergrams, or mathematically from DNA histograms. Results: S-phase fractions obtained using the two methods correlated well, but did not always agree, exact discrepancies depending on the mathematical model used for histogram analysis. Conclusions: Determination of S-phase fractions with the help of PCNA immunofluorescence staining is possible, and probably more reliable than calculation of S-fractions from DNA histograms. It thus offers an alternative to assays involving BrdU labelling in vivo.