Expression of the 43 kDa papain inhibitor during human fetal skin development

The presence of the 43 kDa papain inhibitor protein in the skin of 40 fetuses with the gestational age varying from 9 to 40 weeks was studied. Immunohistochemistry showed the first evidence of the 43 kDa papain inhibitor in the acral parts, mostly in the nail bed, at the 14th week when the epidermis in all other sites was not stained. Staining of the follicular infundibulum as well as some parts of the uppermost epidermis and keratin layer was observed from 17 to 40 weeks. The staining was most intensive at 20-30 weeks gestational age, and later the intensity gradually decreased so that in the full-term newborn the 43 kDa papain inhibitor was hardly detectable or absent. It was concluded that the 43 kDa papain inhibitor is present in fetal skin at the stage of stratification (9-14 weeks) only in the nail region and its volar surroundings. It appears at the stage of interfollicular keratinization (14-24 weeks) in the uppermost epidermis, especially in the appendical openings and its amount seems the decrease during the stage of interfollicular keratinization (24 weeks--full-term). The expression of 43 kDa inhibitor protein is temporally related to that of filaggrin.