No abstract

Background: One of the hallmarks of the psoriatic plaque is increased epidermal proliferation. Whether this is the result of an increased recruitment of cycling epidermal cells or a decrease in cell cycle time has been a matter of debate for years. Objective: Calculating cell-kinetic information from the number of S phase cells in psoriasis by in situ hybridisation using a histone probe and the number of cycling epidermal cells by immunohistochemistry using the MIB-1 antibody. Methods: Immunohistochemistry and non-isotopic in situ hybridisation were performed on serial sections of 33 untreated psoriatic samples and 14 tacalcitol-treated samples. Results: The labelling index (number of cells in S phase/number cycling cells per millimetre length of section) in psoriatic untreated as well as in treated plaques is 16%. The amount of S phase cells in our experiment is equal compared with the number of cells in S phase as determined by BrdU incorporation. Conclusion: Using this direct approach to study cell-kinetic behaviour of psoriatic skin, we reconfirm that the psoriatic abnormality is due to a defect in the G₀–G₁ recruitment mechanism (by increased recruitment of G₀ cells), a decrease in apoptosis or an increase in the number of cell divisions in the transit-amplifying compartment, rather than a reduction in the cell cycle time.

During the last decade, novel analogues of 1alpha,25-dihydroxy vitamin D3 have been developed for the treatment of psoriasis. Recently, the efficacy of short-term treatment with the novel derivative tacalcitol (1alpha,24-dihydroxy vitamin D3) has been documented. However, data on the long-term effect of tacalcitol on psoriatic skin are sparse. In this study, we assessed the cell characteristics of the psoriatic epidermis after treatment with tacalcitol for up to 24 weeks. We investigated how long-term treatment with tacalcitol modulates the percentages of differentiated keratinocytes, inflammation cells and basal keratinocytes, and the percentage of cells in the SG2M phase in the basal cell population. From 11 patients who were treated with tacalcitol for up to 18 months, we obtained single-cell suspensions of a representative psoriatic lesion after 0, 8, 12, 18 and 24 weeks of treatment. A Psoriasis Area and Severity Index was performed at each visit as well. Cell suspensions were stained with markers for inflammation (Vim3B4), differentiation (RKSE60) and proliferation (TO-PRO-3 iodide) and analysed flow cytometrically. Clinically, patients improved significantly after 8 weeks of treatment. This clinical effect was preserved for the rest of the period of treatment with no further significant improvement. Proliferative activity also decreased significantly after 8 weeks of treatment. Proliferation did not show further significant decreases or habituation after 12, 18 and 24 weeks. For inflammation, no statistically reliable trends could be seen. Differentiation improved significantly after 8 weeks of treatment, but decreased again significantly after 12 weeks. In the period from 12 to 24 weeks, no further significant change was observed. We conclude that tacalcitol is an effective antipsoriatic drug. Prolonged treatment with tacalcitol will generally maintain improvement at the level reached after 8 weeks. Owing to the beneficial effect on both clinical state and proliferation, tacalcitol is likely to be an adequate maintenance therapy.

Double labelling can serve as a useful tool for providing information about cell kinetics in normal and hyperproliferative tissues in general, and skin in particular. We have developed a double-labelling method that combines immunohistochemistry using the monoclonal antibody MIB1 and non-isotopic in situ hybridization using either a digoxigenin-labelled RNA probe specific for histone 3 mRNA sequences or a Fluorescein-labelled oligonucleotide probe specific for histone 2b, 3, 4 mRNA sequences. Double labelling was performed on normal, tape-stripped normal skin and psoriatic skin. The three proliferation markers were also examined by single labelling. The ratio of cells in the S-phase (Ns) and the growth fraction (Ncy) was determined. In normal skin, psoriatic skin and tape-stripped normal skin after 24 h and after 48 h, we calculated that 15%, 16%, 3% and 12% of growth fraction consisted of cells in the S-phase respectively. The S-phase lasts approximately 10 h, so the cell cycle time in normal and psoriatic skin is approximately 62.5 h. At present, the MIB1/H3 digoxigenin or MIB1/H2b-H3-H4 Fluorescein double-labelling technique cannot be used routinely. Therefore, in order to understand the cell kinetic processes better, experiments are recommended to optimize these methods. From a practical point of view and for reasons of specificity and sensitivity, we prefer the Fluorescein-labelled oligonucleotide probe method.

Background: Hydrocolloid (HCD) dressings enhance the efficacy of topical corticosteroids. Objective: We wanted to evaluate the effect of calcipotriol ointment under an HCD dressing in the treatment of psoriatic plaques. Methods: In 9 psoriatic patients, we cleared one plaque using this approach and took biopsies at start, clearance and relapse. Clinical and immunohistochemical validation was assessed. Results: After an average treatment of 3.6 weeks, each lesion had cleared (apart from some residual erythema). The average remission period was 8 weeks. During this treatment, the number of cycling epidermal cells (Ki-67-positive nuclei) and the expression of keratin 14 and keratin 16 had decreased substantially. In biopsies taken from the skin immediately adjacent to the relapsing lesion, these markers remained reduced which indicated the prolonged effect of calcipotriol on epidermal differentiation. Conclusion: It is speculated that combination therapy of calcipotriol with treatments with a different mode of action such as photo(chemo)therapy, corticosteroids and cyclosporine might be worthwhile.