Identification of immature cornified envelopes in the barrier-impaired epidermis by characterization of their hydrophobicity and antigenicities of the components

Cornified envelopes (CEs), rigid and insoluble structures in the stratum co rneum, which are assembled by crosslinking of several precursor proteins by transglutaminases, provide a hydrophobic foundation for barrier function; omega-hydroxyceramides are covalently attached to the outer surface of CE c omponents, and onto this hydrophobic assembly, lamellar layers of intercell ular lipids are organized. Morphologically irregular, fragile CEs are found in the deep layer of the stratum corneum or in certain disorders, such as psoriasis, whereas most CEs from healthy subjects are rigid and polygonal. We have established a staining method to characterize such fragile CEs as i mmature and less hydrophobic CEs, and employed it to examine regional diffe rences in the properties of CEs, especially in relation to the barrier func tion of the skin. CEs from the outermost stratum corneum of the trunk and e xtremities of healthy subjects were relatively uniform in morphology with l arger shape, and were homogeneous in hydrophobicity as judged from the use of an environment-sensitive fluorescent dye, Nile red. However, CEs from th e face were strikingly heterogeneous, and consisted of both rigid and fragi le CEs. Rigid CEs were Nile red-positive and little stained by anti-involuc rin. In contrast, fragile CEs were Nile red-negative but strongly stained w ith anti-involucrin, as detected by indirect immunofluorescence. Thus, CEs from the face were stained with Nile red or involucrin in a mutually exclus ive manner. Fragile CEs were stained with antibodies against other CE compo nents, including loricrin, envoplakin, filaggrin, and isopeptides. Such fra gile, involucrin-positive CEs were detected not only in the face, but also in the deep layer of the stratum corneum of the arm. In addition, experimen tal barrier disruption resulted in the appearance of involcurin-positive CE s in the outermost stratum corneum. These results suggest that involucrin-p ositive, fragile CEs an immature and less hydrophobic, and that their occur rence is closely related to impairment of the barrier function of the skin.