Identification of prekeratin by immunofluorescence staining in the differential diagnosis of tumors.

Fibrillar proteins with a role in cellular shape and motility are present in the cytoplasm of most animal cells. They vary greatly in size, organization, and reactivity according to cell type and can be separately identified by the use of recently developed monospecific antisera and indirect immunofluorescence staining. Prekeratin, a structural protein in the form of intermediate sized filaments is present exclusively in cells of epithelial origin. In the present study 41 human tumors of various organs and their normal tissue counterparts were reacted with prekeratin antiserum and examined by immunofluorescence staining in paraffin embedded sections. Prekeratin was identified in all epithelial cells of the squamous type, which gave the strongest staining reaction, and in smaller amounts in epithelial cells of other histologic types. Cells of lymphoid, melanic, neural, and connective tissue origin were not stained. Thus, combining the specificity of antiprekeratin sera with the selectivity of immunofluorescence staining resulted in a new method of identifying tissues that is applicable to the differential diagnosis of tumors.