Characterization of a monoclonal antibody, RTE-21, that binds to keratohyalin granule-associated proteins in epithelial cells of human skin and thymus.

The role of skin and thymic epithelium in the promotion of T-cell activation and maturation is currently an area of great interest. In thymus, epithelium is located in the cortex, medulla, and in medullary epithelial swirls called Hassall's bodies. During studies of antigens shared by skin and thymic epithelial cells, we produced a murine monoclonal antibody (RTE-21) raised against the rat thymic epithelial cell line, IT26R21, that identified an antigen present in terminally differentiated epithelium of normal human skin and thymus. In indirect immunofluorescence studies, antibody RTE-21 identified cytoplasmic granules located in the stratum granulosum of normal human skin, Hassall's bodies of human thymus, and in a subset of cells of the IT26R21 rat thymic epithelial cell line. Moreover, the granular reactivity pattern of antibody RTE-21 in the stratum granulosum could be extracted by 1 M potassium phosphate (1 M KPO4). A 1 M KPO4 extract of epidermis containing keratohyalin granule proteins was dialyzed against distilled water, solubilized in reduced sample buffer and subjected to polyacrylamide gel electrophoresis and Western immunoblot analysis. In this assay, antibody RTE-21 recognized proteins of 70, 36, 34, and 30 kDa. Using antibody RTE-21 and indirect immunofluorescence, we demonstrated that keratohyalin granules in human thymus were localized exclusively to Hassall's bodies. These data support the notion that human thymic Hassall's bodies result from terminal differentiation of medullary thymic epithelium. Thus, antibody RTE-21 should be an important probe for the study of skin and thymic epithelial cell maturation in vitro and in vivo.

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Author Barton Ford Haynes Medicine, Duke Human Vaccine Institute