Cell-kinetic evidence for increased recruitment of cycling epidermal cellsin psoriasis: The ratio of histone and Ki-67 antigen expression is constant

Background: One of the hallmarks of the psoriatic plaque is increased epide rmal proliferation. Whether this is the result of an increased recruitment of cycling epidermal cells or a decrease in cell cycle time has been a matt er of debate for years. Objective: Calculating cell-kinetic information fro m the number of S phase cells in psoriasis by in situ hybridisation using a histone probe and the number of cycling epidermal cells by immunohistochem istry using the MIB-1 antibody. Methods: Immunohistochemistry and non-isoto pic in situ hybridisation were performed on serial sections of 33 untreated psoriatic samples and 14 tacalcitol-treated samples. Results: The labellin g index (number of cells in S phase/number cycling cells per millimetre len gth 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 sk in, we reconfirm that the psoriatic abnormality is due to a defect in the G (0)-G(1) recruitment mechanism (by increased recruitment of G(0) 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. Copyright (C) 2000 S. Karger AG, Basel.