Immunofluorescence localization of peripheral proteins in cultured human keratinocytes

To gain preliminary data on the location of a 195 kD cell peripheral protein of epidermal keratinocytes recognized by monoclonal antibody AE11, immunofluorescence staining was carried out on cultured human epidermal cells. B11 antidesmosomal polyclonal antibody and AE3 antikeratin monoclonal antibody staining were used as comparative reference controls. Desmosomal antigens span the cell membrane and keratins constitute a family of cytoplasmic proteins. The cultured cells were systematically used either unfixed, fixed with 4% paraformaldehyde, or fixed with methanol at 4 degrees C. The former two preparations were designed to expose only the surface antigens, whereas the latter method permeated the membrane to allow cytoplasmic staining. Differences in staining patterns were observed in the basal layer as compared with the upper layers with all three antibodies. B11 antidesmosomal antibody staining was consistent in pattern after either paraformaldehyde or methanol fixation. In addition to the punctate staining along adjacent cell surfaces as shown in the basal layer, the surface planes of the upper cells exhibited parallel arrays of linear streaks, demonstrating the distribution of desmosomal proteins. Antikeratin staining by AE3 showed the typical filamentous staining in basal cells. However, a homogeneous patchy staining of suprabasal cells was observed. The presence of punctate surface staining using antikeratin antibody on paraformaldehyde fixed cells suggests leakage of keratin to the cell surface. AE11 showed stronger staining in the top cells on methanol treated cultures and a punctate surface staining of the cells fixed with paraformaldehyde. These observations provide useful preliminary information in localizing peripheral proteins in epidermal keratinocytes.