Filaggrin expression in normal and pathological skin. A marker of keratinocyte differentiation.

Filaggrin is a basic, histidine-rich protein synthesized by cells of keratinizing epithelia, that subserves major physiological functions in maturating epidermis. Its precursor, profilaggrin, constitutes a major component of kertohyalin granules. In this work the expression of profilaggrin/filaggrin was studied in 140 specimens of normal human adult and fetal skin, cultured epithelia before and after allo- and xeno-grafting, and several cases of keratinization disorders and tumours. An avidin-biotin-alkaline phosphatase technique was applied on deparaffinized tissue sections, by using a specific monoclonal antibody (AKH1) to profilaggrin/filaggrin. The results show that the expression of profilaggrin/filaggrin is variously altered in keratinization disorders, whereas in epithelial proliferations it seems to decrease with an increasing degree of dedifferentiation of the tumour. Therefore the expression of these antigens can be considered to be a sensitive marker of maturation of normal epidermis and provides a new tool for the study of differentiation of the surface epithelium in skin diseases.