The distribution of cytokeratin (CK) polypeptides expressed in syringomas (12 cases) was compared with that in normal eccrine sweat ducts using immunohistochemical techniques on paraffin-embedded tissue. Intradermal and intraepidermal segments of the eccrine duct showed reactivity with an antibody to CK 1/5/10/11 in all cell layers, whereas CK19 expression was restricted to the luminal cell layer. CK14 was expressed in all cells of the eccrine duct except for the peripheral cells of the intraepidermal duct. Expression of CK5/6 was seen in the basal cells of the dermal duct and of the lower intraepidermal duct (sweat duct ridge) exclusively. Reactivity with an antibody to CK1 was found in the intermediate cells of the uppermost part of the eccrine dermal duct. In addition, this antibody gave a strong staining of the peripheral cells of the intraepidermal duct, leaving basal cells of the sweat duct ridge and luminal cells unstained. In syringoma, CK distribution was essentially comparable with that found in the uppermost part of the dermal duct and in the sweat duct ridge. Namely, ductal luminal cells expressed CK1/5/10/11, CK19, and variably CK14. Intermediate cells of ductal structures and solid nests were homogeneously stained by antibodies to CK1 and CK1/5/10/11, whereas CK14 was expressed heterogeneously. The basal or outermost layer of ductal structures and solid nests was reactive with antibodies to CK1/5/10/11, CK5/6, and CK14. With regard to CK expression, the results indicate that syringoma represents a tumor differentiating toward both the uppermost part of the dermal duct and the lower intraepidermal duct (sweat duct ridge) of the eccrine sweat gland.
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