Abstract
Cytokeratin (CK) expression was investigated, by means of immunocytochemistry, in the hamster thymic epithelium during ontogeny, as well as in primary cultures and upon glucocorticoid hormone treatment in vivo. As compared to the distribution pattern of distinct monoclonal antibody-defined cytokeratins in the normal adult thymus, CK modulation was evidenced in the three situations studied. During thymus ontogeny, both cytokeratins of simple lining epithelia, as CK8 and CK18, as well as the CK1/CK10 pair (typical marker of terminal stage of keratinization), were expressed since early stages of thymus development. They were located in the central region of thymic lobules preceding the cortical-medullary distinctions. This differed from what had been previously shown for mouse thymus ontogeny, revealing that the interspecific diversity in the distribution pattern of thymic cytokeratins occurred early in fetal life. A modulation of CK expression was also detected when hamster thymic epithelial cells (TEC) were led to grow in culture, with a down-regulation of CK19 contrasting with an enhancement of CK18 expression. This diverged from the maintenance of the in situ pattern when human TEC were cultured. Last, in vivo hydrocortisone treatment, known to increase the numbers of KL1+ cells in the mouse thymus medulla, promoted a cortical expression of the CK1/CK10 pair in the hamster thymus. Taken together, our findings demonstrate a continuous plasticity of the thymic epithelium, at least regarding cytokeratin expression, and enlarge the concept of interspecific diversity of intrathymic CK distribution in conditions as morphogenesis, in vitro system, and responsiveness to glucocorticoid hormone treatment.
Highlights
Studies on thymocyte differentiation are often carried out on fetal specimens or in vitro, providing important information for the role of the thymic microenvironment in this process
Concerning the thymic epithelium, we evidenced the expression of cytokeratins both of simple and stratified epithelia, as well as an interspecific diversity in the distribution of these intermediate filament proteins. These results suggested that the thymic epithelium is complex and unique, and that the general classification of epithelial tissues based on their CK expression patterns cannot be applied to the thymus (Meireles de Souza et al, 1993)
We addressed the question concerning thymic epithelial cell (TEC) differentiation and CK expression, using the hamster model during thymic ontogeny, primary TEC cultures, and following hydrocortisone treatment, the latter known to augment KL1defined CK expression in the mouse thymus (Savino et al, 1988)
Summary
Studies on thymocyte differentiation are often carried out on fetal specimens or in vitro, providing important information for the role of the thymic microenvironment in this process. No specific functional subset was isolated so far, despite the several TEC lines produced (Itoh, 1979; Nieburgs et al, 1985; Potworowski et al, 1986; Mizutani et al, 1987; Naquet et al, 1989) These markers reveal a close antigenic similarity between the thymic epithelium and epidermis (Haynes, 1984; Lobach et al, 1985; Schmitt et al, 1987), suggesting that TEC heterogeneity could be a reflex of their type of differentiation, as demonstrated for the epidermis.
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
