Human eccrine sweat gland ducts and benign and malignant eccrine poromas were studied for the expression of various cytokeratins (CK) and vimentin by applying immunoperoxidase and immunofluorescence microscopy to frozen or paraffin-embedded sections, and using two-dimensional gel electrophoresis and immunoblotting. In acrosyringia and dermal eccrine ducts, the luminal cells exhibited intense staining for CKs 1/10/11 and 19. The periluminal cell layers of acrosyringia contained CKs 1/10/11, while CK 5 was absent. In contrast, the basal cell layer of dermal ducts was only positive with the antibody against CK 5, i.e. a pattern resembling that seen in epidermal basal cells. CK 9 was detected only in keratinocytes peripherally surrounding acrosyringia. In benign poromas, gel electrophoresis revealed that CKs 5 and 14 were predominant, with CKs 6, 16 and 17 being minor components. At the immunohistochemical level CKs 1/10/11 and 19 could be further detected with varying frequency in scattered or clustered cells and/or duct-like structures. Occasionally, CK 9-positive cells were observed. Malignant poromas displayed a similar overall gel-electrophoretic pattern. Their immunohistochemical staining patterns were also similar to (albeit rather more variable than) those seen in benign poromas. Our results show that, with respect to their CK expression pattern, the majority of poroma cells resemble the basal cells of both the dermal ducts and the epidermis, while only minor and variable subpopulations acquire features present in ductal/acrosyringial luminal cells that would be indicative of poral differentiation. Thus, the matrix cells of poromas seem to be most closely related to basal cells located at the transition between the glandular epidermal ridge and dermal eccrine duct, being in no way analogous to the cells of the adult acrosyringium above the basal cell level.
