Impulse cytophotometry in psoriasis

There seems to be no general agreement in the literature regarding cell cycle parameters in psoriasis; the mitotic duration is reported to be lengthened (Fisher & Wells, 1968) or shortened (Weinstein & Frost, 1968), the DNA synthesis time doubled (Pullmann, Lennartz & Steigleder, 1974; Born & Kalkoff, 1969)5 or halved (Weinstein & Frost, 1968), the Gi time shortened by a factor of 10 (Weinstein, 1972) or by a factor of 2 (PuUmann et al., 1974). Some of these disagreements might be due to variations in the maturity of the psoriatic lesions and inter-individual variations, while others are certainly caused by pitfalls in the methods being used. Another problem is that until recently cell kinetic studies have been very time consuming. We describe here the apphcation of a rapid method for the analysis of cell kinetic parameters (up to 1000 cells/s) and some preliminary results obtained with it in the kinetics of psoriasis. The instrument used is a pulse cytophotometer (PCP) (Gohde & Dittrich, 1971; Lancet editorial, 1975). Cytophotometers measure light intensities as a function of cell characteristics. In pulse cytophotometry single cells are transported through the field of a microscope-photometer. In our study we made an epidermal cell suspension from skin biopsies (4inm diameter punch) by treating them with i % trypsin solution for 30 min at 37°C. The cells were fixed in absolute ethanol and stained with ethidixmi bromide, a fiuorescent dye which stains DNA quantitatively. Each cell produces a fiuorescent signal, the intensity of which is proportional to the amount of DNA per cell. The signals are electronically processed and classified into 128 intensity catagories to produce a DNA histogram. Fig. I (A) and (B) gives examples of such a DNA histogram from normal and psoriatic skin respectively. In Fig. i(A) 64,355 ^nd in Fig. (B) 83,699 cells were measured. The area under the major peak (channel number 30) represents cells which contain the 2n amount of DNA (cells in Gj); cells in G2 and mitosis contain 4n DNA and consequently one can find them around the double channel number. The region in between contains cells in various stages of DNA synthesis (S phase). With a simple arithmetical calculation one can find the percentages of the cells in each phase of the cell cycle. Table i gives the percentages of the cells in the various phases of the cycle and therefore the relative lengths of the phases, if we asstime that there is an asynchronous distribution of the germinative population over the cell cycle. These values have to be corrected since not all the epidermal population is proliferative. The cells of the stratum spinosum, for instance, also contain the 2n amoimt of DNA. One should therefore know the ratio proliferative/nonproliferative cells, or one could attempt to fractionate the cells into two populations. The former problem can be tackled by measuring two parameters with the PCP (e.g. DNA and RNA or DNA and protein) since one might expect different ratios of DNA/RNA or DNA/protein in the differentiated skin layers compared to the basal layer. The absolute time length of the different phases could be determined by synchronization procedures in vivo or in vitro. Even without these modifications the method already seems to be very promising