Differentiation of epithelial cells on microporous membranes

Histological and immunological characteristics of the junctional epithelium

The continuity of epithelial tissue is collapsed by tooth eruption. The junctional epithelium (JE) is attached to the tooth surface by hemidesmosomes, which constitutes the front-line defense against periodontal bacterial infection. JE constitutively expresses intercellular adhesion molecule-1 (ICAM-1), and neutrophils and lymphocytes penetrate into JE via interaction between ICAM-1 and LFA-1 expressed on the surface of these migrating cells. JE also expresses cytokines and chemokines. These functions of JE are maintained even in germ-free condition. Therefore, the constitutive expression of adhesion molecules, cytokines, and chemokines might be used not only for anti-pathogenic defense but also for maintaining the physiological homeostasis of JE. In this review, we have mainly focused on the structural and functional features of JE, and discussed the function of intraepithelial lymphocytes in JE as a front-line anti-microbial defense barrier and regulator of JE hemostasis.

IRAG working group 3. Cell function-based assays. Interagency Regulatory Alternatives Group

Cell function-based tests measure responses of cells at sublytic concentrations of test agents. The fluorescein leakage assay measures effects of substances on the barrier function of epithelial monolayers or multilayers (MDCK or NHEK cells) as in vitro models of corneal epithelial function. Two IRAG data submissions suggest that the fluorescein leakage assay shows promise as a screening test for surfactants and alcohols. The test method requires further optimization, standardization and evaluation to fully determine its utility as an in vitro ocular irritancy test. The silicon microphysiometer test measures effects of test substances on the metabolic rate of cells; although a large number of cell types have been evaluated, L929 cells have been used for irritancy screening. Three IRAG data submissions on the silicon microphysiometer test showed strong in vivo/in vitro correlations for surfactants and surfactant-based personal care and household cleaning products in a range of mild to moderate ocular irritancy. This and published information support the reproducibility of the method and its use as an ocular irritancy screening test for aqueous-soluble liquid, surfactant-based formulations.

Human epidermis reconstructed on synthetic membrane: influence of experimental conditions on terminal differentiation

Cell suspensions of human keratinocytes seeded onto cell culture inserts may undergo terminal differentiation in the absence of fibroblasts. Among the parameters that control these morphogenic events, exposure to air and the composition of the culture medium were investigated. In the latter case, three media were considered DMEM:Ham's F12, MCDB 153, and keratinocyte SFM medium at equivalent calcium (1.5 mM) and fetal calf serum (5%) concentrations. Immunochemical methods and transmission electron microscopy show that cells cultured in DMEM:Ham's F12 medium, and then raised at the air-liquid interface, form a basal layer plus suprabasal cell layers corresponding to the stratum spinosum, stratum granulosum, and stratum corneum. The suprabasal keratinocyte layers show morphologies that resemble intact skin in which cells are connected by desmosomes and contain intermediate filaments and keratohyalin-filaggrin granules. When the cultures are kept submerged, the keratinocytes show occasional keratohyalin granules and are connected by fewer desmosomes. Additionally, no proper stratum corneum is formed. In keratinocyte SFM medium and MCDB 153, cultures raised at the air-liquid interface are not able to form an epithelium of normal architecture and do not express terminal differentiation markers. Differentiation is initiated, however, since desmosomes and bundles of keratin filaments appear; on the other hand, filaggrin is not expressed even after 28 d in culture. Membrane-bound transglutaminase is expressed throughout the entire suprabasal compartment in MCDB153 and DMEM:Ham's F12 media but never appears in keratinocyte SFM medium. These studies show the relative independence of epidermal differentiation program to the composition (including the calcium concentration) of the media contacting the dermis and filling the extracellular space.(ABSTRACT TRUNCATED AT 250 WORDS)