What immunohistochemical findings are characteristic of hidradenitis suppurativa (HS)?

Updated: Aug 30, 2019
  • Author: Marina Jovanovic, MD, PhD; Chief Editor: William D James, MD  more...
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Immunohistochemical data obtained for various cytokeratins (CKs) and the 6 desmosomal cadherins (ie, desmogleins [Dsgs] 1-3, desmocollins [Dscs] 1-3) showed 3 phenotypes of stratified squamous epithelia covering the sinus tracts in hidradenitis suppurativa: type I cornifying, type II noncornifying and moderately inflamed, and type III noncornifying and strongly inflamed. [79]

The noncornifying types II and III epithelia are characterized by the absence of the terminal differentiation markers CK10 and Dsc1 and by the strong expression of Dsg2 in the basal layer. Compared with the normal epidermis and type I epithelium, types II and III epithelia have Dsc2 and Dsg3 in all layers, whereas Dsc3 is restricted to the basal and parabasal layers. The inflammatory character of type III epithelium, as opposed to that of types I and II, is marked by the presence of CK7 and CK19 and the absence of Dsg1. [79]

All 3 types of epithelia are clearly distinct from the interfollicular epidermis because of the absence of CK2e and the presence of CKs 6, 13, 15, and 16; the presence of these proteins reflects the fact that the sinus tract epithelia have undergone the pathologically altered process of growth, differentiation, and inflammation.

CK19 is commonly found in the basal cells of noncornifying stratified squamous epithelia, such as in the outer root sheath (ORS) of the hair follicle. The strongly inflamed CK19-positive parts of the sinus epithelium show no signs of terminal squamous differentiation (ie, nuclei were present in the highest suprabasal layers, and keratohyalin granules were absent). Instead, the inflamed CK–positive parts resembled epidermal keratinocytes grown in organotypic culture, which can be induced to build a noncornifying epithelium and to express CK19 with the addition of retinoic acid to the culture medium.

In all specimens in one study, type I epithelium near the opening of the sinus showed strong similarities to the upper pilosebaceous duct from which the inflammation process seemed to emerge.

In both normal pilosebaceous duct epithelium and cornifying type I sinus epithelium, CK5 and CK14 are restricted to the basal layer, CK10 and Dsc1 antibodies label the suprabasal cells, Dsg1 and Dsg3 are present in an epidermislike pattern, and CK2e is absent.

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