Human psoriatic epidermis and scales were demonstrated to contain two antigenically separate cysteine proteinase inhibitors, one acidic with an isoelectric point of 4.7-5.0 (ACPI) and one neutral with an isoelectric point of 6.0-6.5 (NCPI), while normal epidermis contains only ACPI. The total papain (cysteine proteinase) inhibiting activity of the psoriatic epidermis as calculated per mg protein was higher than that in normal epidermis. Both ACPI and NCPI were localized immunocytochemically, mainly in the highest spinous cell layers with less activity in the parakeratotic cells and lower layers of spinous cells. Basal cells were essentially negative.
Monocytes were separated from human peripheral blood and allowed to attach to culture flasks, after which the content and production of a number of cysteine proteinase inhibitors was assayed. These were: a low molecular weight (MW 12000) acid cysteine proteinase inhibitor (ACPI); a low-molecular weight inhibitor of the same size with neutral pH (NCPI), and alpha-cysteine proteinase inhibitor with a molecular weight around 90 000 (alpha-CPI). Only NCPI was detectable in the cultures at the beginning of the incubation, and it was synthesized and released into the incubation mixture during the incubation, especially if the cells were stimulated with silica. The amount of NCPI contained in and released from the cells was drastically decreased by puromycin. Immunoblots after cell electrophoresis in polyacrylamide gel revealed only one molecular form of NCPI with a molecular weight of 12 000 both in the cells and in the culture medium. No ACPI or alpha-CPI could be detected.
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