Forms of epithelial differentiation of draining sinus in acne inversa (hidradenitis suppurativa)

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1 British Journal of Dermatology 1999; 141: 231±239. Forms of epithelial differentiation of draining sinus in acne inversa (hidradenitis suppurativa) H.KURZEN, E.G.JUNG,* W.HARTSCHUH,² I.MOLL,³ W.W.FRANKE AND R.MOLL Division of Cell Biology, German Cancer Research Centre, Heidelberg, Germany *Department of Dermatology, Mannheim Medical School, University of Heidelberg, Voûstraûe 2, Heidelberg, Germany ²Department of Dermatology, University of Heidelberg, Germany ³Department of Dermatology, University of Hamburg, Germany Institute of Pathology, Martin-Luther-University Halle-Wittenberg, Halle (Saale), Germany Accepted for publication 5 March 1999 Summary The draining sinus is a late complication of several forms of severe acne, leading to extensive, periodically in amed lesions that are undermined by a system of stulas, supposed to be of follicular origin. We investigated the expression of various cytokeratins (CKs) and desmosomal proteins in the draining sinus of acne inversa (hidradenitis suppurativa) using monoclonal antibodies in immunohistochemistry on paraf n-embedded sections. We were able to de ne three different phenotypes of strati ed squamous epithelia covering the sinus tracts. Type I epithelium was cornifying and characterized by the presence of CK 10, desmogleins 1±3 and desmocollins 1±3 in an epidermislike pattern. Type II epithelium was non-cornifying, negative for CK 10 and positive for CK 13. It was negative for desmocollin 1 but strongly immunopositive for desmoglein 1 suprabasally and for desmoglein 2 in the basal cells. Type III epithelium was non-cornifying and strongly in amed. It was marked by the presence of CK 7, CK 19 and desmoglein 2 and the absence of CK 10, desmoglein 1 and desmocollin 1. In both type II and III epithelium, desmoglein 3, desmocollin 2 and desmocollin 3 showed an inverted staining pattern as compared with normal epidermis and type I epithelium. Desmoglein 2 and CK 5/14 always remained restricted to the basal cell layer. Antibodies against CK 6 and CK 13/15/16 were immunopositive in all three phenotypes and CK 17 was predominantly immunolocalized to suprabasal layers of type II and III epithelium. The three phenotypes are characterized as pathological strati ed squamous epithelia re ecting the dynamic process of in ammation, proliferation and strati cation taking place in acne inversa. Key words: acne inversa, cytoskeleton, desmosome, epidermis, hidradenitis suppurativa, in ammation, squamous epithelium Acne inversa, also known as hidradenitis suppurativa and acne tetrade, 1±3 like acne vulgaris, is believed to be caused by follicular obstruction. Bacterial infection results in a rupture of the follicular canal and subsequent granulating in ammation. 4 The draining sinus is a late complication of acne inversa, leading to extensive, periodically in amed lesions that are undermined by a system of stulas. They extend predominantly into the dermis in a leaf-like pattern and are lined by a variably thickened strati ed epithelium. Surrounding collagenous or fatty tissue does not appear to be compressed, suggesting in ltrative rather than expansive growth. 5±7 Correspondence: Dr med H.Kurzen, Department of Dermatology, University of Heidelberg, Voûstr.2, Heidelberg, Germany. hjalmar_kurzen@med.uni-heidelberg.de q 1999 British Association of Dermatologists Cytokeratins (CKs), the main components of the epithelial intermediate lament cytoskeleton, are wellestablished differentiation markers of epithelial cells. 8± 15 Desmosomes are adhesive intercellular junctions that connect the CKs to the cell membrane. Desmogleins (Dsgs) and desmocollins (Dscs) are the main desmosomal transmembrane proteins. They belong to the cadherin family of calcium-dependent cell adhesion molecules. Three different isoforms of Dsg and Dsc, termed Dsg1±3 and Dsc1±3, can be distinguished. Their cytoplasmic portions are associated with a variety of plaque proteins, including common ones such as desmoplakin (DP) I and plakoglobin (PG), and also cell type-speci c ones such as DP II and plakophilin (PP) 1 and 2. 16±21 The desmosomal cadherins show a differentiation-speci c expression in epithelia and can 231

2 232 H.KURZEN et al. therefore serve, in addition to the CKs, as an independent system of differentiation markers. 22 As isoformspeci c antibodies have as yet been only incompletely available, information about the distribution of desmosomal cadherins in pathological epithelia is still scarce. 23±27 We examined the epithelial differentiation of draining sinus in acne inversa using monospeci c CK protein antibodies and desmosomal protein antibodies in order to study the in uence of chronic in ammation and hyperproliferation on cytoskeletal and desmosomal proteins. Materials and methods We examined skin samples from 15 patients obtained during surgical removal of chronically in amed lesions from the axilla and the groin. One part of the samples was routinely formalin- xed and paraf n-embedded, and the other part was snap-frozen in liquid nitrogen and stored at ± 70 8C until use. Only samples histopathologically diagnosed as acne inversa were used for immunohistochemistry. For most antibodies, pretreatment using microwave oven heating (three or four times, 5 min, 600 W) for some antibodies, followed by incubation with 0 001% trypsin, was necessary to restore antigen recognition from 3- to 4-mm thick paraf n sections. The following primary antibodies were used: monoclonal antibodies (MoAbs) DP 1 2±2 15 and DP 1±2 17 against DP I II, 28 PG and PG 11E4 (Dr M.J.Wheelock, Toledo, OH, U.S.A.) against PG, Dsg1E-P124 and Dsg1E-P23 against Dsg1, 22 Dsg2E-G129 and Dsg2E- G96 against Dsg2, 18 Dsg3-G194 and 5G11 against Dsg3, 22 Dsc1-U100 against Dsc1, 19 DC-Rab 36 (rabbit polyclonal) against Dsc2, 30 MoAb Dsc3-U114 against Dsc3, 19 PP1-9E7 and PP1-5C2 against PP 1, 31 PP2-150 against PP 2, 20 Ks against CK 2e (Dr L.Langbein, Heidelberg, Germany), 6B10 against CK 4, 32 AE 14 against CK 5, 33 Ks6.KA12 against CK 6, 34 OV-TL 12/30 35 and Ks7 18 against CK 7, 27 CAM 5 2 against CK 8, 36 HK9TY1 (guinea-pig polyclonal) against CK 9 (Dr L.Langbein), MoAbs K and DE-K10 against CK 10, 38 Ks8 12 against CK , 37 Ks13 1 against CK 13, 39 2D7 against CK 13, 32 LL001 against CK 14, 40 Ks17.E3 against CK 17, 41 Ks19 1 against CK 19, 42 IT-Ks20 10 against CK 20 9 and MIB 1 against Ki Sections were blocked in 10% normal horse serum in phosphate-buffered-saline (PBS). Incubation time for the primary antibody was 1 h at 37 8C and for the secondary antibody (biotinylated horse antibodies against mouse IgG and biotinylated goat antibodies against rabbit or guinea-pig IgG, all from Vector, Burlingame, CA, U.S.A.) 30 min at room temperature in a Shandon Sequenza apparatus (Shandon-Life Sciences International, Frankfurt/Main, Germany). The avidin± biotin complex method (ABC Elite kit) was used according to the manufacturer's instructions (Vector) with 3,3 0 -diaminobenzidine and H 2 O 2 being employed for the staining reactions. For control purposes, immunohistochemical stainings were performed on acetone- xed cryostat sections cut from the snap-frozen tissue specimens, employing the indirect immunoperoxidase method. 44 In the case of the Dsc MoAbs, prior to their application, sections were incubated for 30 min with 5% goat serum in PBS containing 0 2% Triton X-100 and 2% dried milk powder. Results On histological examination, the samples chosen showed different stages of sinus tract formation with variable degrees of in ammatory activity. Cornifying strati ed squamous epithelium (type I) could be distinguished from non-cornifying epithelia, the latter being either barely (type II) or strongly in amed (type III). Strongly in amed areas often bordered ulcerative epithelial defects. The epithelium close to the openings of the sinus tracts was cornifying (type I) in all specimens examined. In two cases, free hair shafts were found in the sinus and in the surrounding dermis, without apparent connection to the epithelium. In two patients, reticulate and liform downgrowths resembling Dowling±Degos disease were found. 45,46 Based on the above-mentioned histological subdivision, immunohistochemical analysis of cytoskeletal and desmosomal differentiation markers enabled de nition of three different phenotypes (types I±III) of strati ed squamous epithelia covering the sinus tracts. The results are summarized in Table 1. MoAb Ks8 60 against CK 10 (weakly also against CK 1) and MoAb DE-K10 against CK 10 strongly labelled the suprabasal and granular layers of the orthokeratotic and hyperkeratotic parts of the epithelium (type I) while the non-cornifying and in amed parts (type II and type III) remained negative (Fig. 1a). MoAbs AE 14 against CK 5 and LL001 against CK 14 stained most basal cells of the sinus tract epithelium (Fig. 2a). In some parts staining was very weak. CK 2e, CK 4 and CK 9 could not be detected at all. MoAb Ks6.KA12 against CK 6 and MoAb Ks17.E3 against CK 17 strongly stained suprabasal layers of the non-cornifying parts (types II and III)

3 EPITHELIAL DIFFERENTIATION OF SINUSES IN ACNE INVERSA 233 Table 1. Staining patterns in the epidermis and the sinus epithelium of acne inversa Antigen Epidermis Type I cornifying Type II non-cornifying Type III non-cornifying, strongly in amed Desmoplakin I II Plakoglobin Plakophilin 1 Plakophilin 2 ± ± ± ± Desmoglein 1 (S, G) (S) (S) ± Desmoglein 2 (B) (B) (B) (B) Desmoglein 3 (B, P) (B, P) Desmocollin 1 (upper S, G) (upper S, G) ± ± Desmocollin 2 (B), (S) (B), (S) Desmocollin 3 (B, S), (G) (B, P), (S) (B, P) CK 2e (G) ± ± ± CK 4 ± ± ± ± CK 5 (B) (B) (B) (B) CK 6 ± 6 (S) (S) (S) CK 7 ± ± ± (S) CK 8 ± ± ± ± CK 9 ± a ± ± ± CK10 (S, G) (S, G) ± ± CK (B, S) 6 6 CK 13 ± ± ± CK 14 (B) (B) (B) (B) CK 17 ± 6 (S) (S) (S) CK 19 ± ± ± CK 20 ± ± ± ± Ki-67 / (B, P) (B, P) (B, P) CK, cytokeratin; B, basal layer; G, granular layer; P, parabasal layer; S, suprabasal layer; without indication, all layers;, strong staining;, weak staining; 6, weak or no staining; ±, no staining. a CK 9 is positive in palmoplantar epidermis. of the sinus tracts. Cornifying parts (type I) showed a variable staining (Figs 1b and 2d) correlated to the proliferation activity as indicated by staining of basal and parabasal cells with MIB 1 antibody (not shown). CK 17 immunostaining was slightly less extended than CK 6 reactivity. MoAb Ks8 12 against CK 13, 15 and 16 strongly immunolabelled the suprabasal cell layers of all parts of the sinus, while MoAb 2D7, speci c for CK 13, showed a positive reaction predominantly in the noncornifying, weakly in amed part of the sinus (type II) (Fig. 1c). Strongly in amed parts of the epithelium, which were not cornifying (type III), were intensely immunolabelled by MoAb Ks19 1 against CK 19 (Fig. 2b) and in the intermediate and uppermost layers by MoAbs OV-TL 12/30 and Ks7 18 against CK 7 (Fig. 2c). The other simple epithelial CKs, i.e. CK 8 and CK 20, remained negative in all phenotypes. Two cases showed focal accumulations of CK 8-positive and CK 20-positive Merkel cells in the sinus. The desmosomal plaque proteins DP I/II, PG and PP 1 were immunolocalized to all living layers of the sinus tract epithelium. Only in CK 19-positive parts, i.e. in non-cornifying in amed parts (type III), desmosomal staining was patchy and weak (not shown). PP 2 was not detected. Differential staining patterns were obtained for the various desmosomal cadherins. Dsg1- speci c antibodies immunostained all suprabasal cells in the hyperkeratotic parts (type I) and weakly in amed non-cornifying parts of the sinus (type II). No Dsg1 staining was seen in CK 19-positive parts (type III). Dsg2 antibodies showed only a very weak staining of the basal layer of the overlying epidermis and hyperkeratotic parts of the sinus (type I), while the non-cornifying parts (types II and III) were characterized by a strong labelling of the basal layer. MoAb 5G11 against Dsg3 immunolabelled basal and lower suprabasal layers of the hyperkeratotic parts (type I) while in the noncornifying parts (types II and III) all layers were positive (Fig. 3). Upper layers of the hyperkeratotic parts of the sinus (type I) were clearly immunopositive for MoAb Dsc1- U100 against Dsc1. The staining intensity correlated well with the degree of corni cation and was less extended than CK 10 antibody reactivity. The

4 234 H.KURZEN et al. non-cornifying parts (types II and III) were immunonegative. The Dsc2 polyclonal antibody which in normal epidermis and the hyperkeratotic parts (type I) preferentially stained desmosomes of the basal and lower suprabasal layer, extended its reactivity to all layers in the non-cornifying parts (types II and III). MoAb Dsc3- U114 against Dsc3, which labels evenly all living layers of the scalp epidermis and type I epithelium, was predominantly immunolocalized to the basal and lowest suprabasal layers in the non-cornifying parts (types II and III). The in amed areas (type III and, to a lesser extent, type II) showed an altered staining pattern for Dsc2 and Dsc3, caused by an intercellular oedema (Fig. 4). Discussion On the basis of the present results, the strati ed squamous epithelium covering the draining sinus of acne inversa can be divided into three different phenotypes with characteristic features concerning both morphology and marker proteins: type I, cornifying with orthokeratotic and parahyperkeratotic parts, and characterized by the presence of CK 10, Dsg1±3 and Dsc1±3 in an almost epidermis-like pattern; type II: non-cornifying and moderately in amed, negative for CK 10 and positive for CK 13, and negative for Dsc1 but strongly immunopositive for Dsg1 suprabasally and Dsg2 in the basal cells; and type III: non-cornifying and strongly in amed, and marked by the presence of CK 7, CK 19 and Dsg2 and the absence of CK 10, Dsg1 and Dsc1. An intercellular oedema leading to an altered staining pattern of antidesmosomal antibodies and a strong in ltration with leucocytes are indicators of the highly in ammatory process. The non-cornifying character of type II and III epithelia as opposed to type I is underlined by the absence of the terminal differentiation markers CK 10 and Dsc1, and by the strong expression of Dsg2 in the basal layer. Dsg3, Dsc2 and Dsc3 show an inverted staining pattern as compared with normal epidermis Figure 1. The three different phenotypes of pathologically altered epithelium covering the draining sinus in acne inversa. (a) Antibody DE-K10 against cytokeratin (CK) 10 stains orthokeratotic to parahyperkeratotic parts designated type I. (b) Parallel section to (a), stained with Ks6.KA12 against CK 6. Both phenotypes I and II are labelled. (c) CK 13 is predominantly positive in type II epithelium. Note the lack of corni cation and moderate in ammatory activity in the positive parts. (d) Transition from type II to type III is marked by the sudden onset of CK 19 immunoreactivity and strong in ammatory reaction. D, dermis; L, lumen of the sinus. Bars: a±c, 200 mm; d, 100 mm.

5 EPITHELIAL DIFFERENTIATION OF SINUSES IN ACNE INVERSA 235 Figure 2. Important cytokeratin (CK) patterns. (a) Transition from type I to type II. CK 14, as marked by antibody LL001, remains restricted to the basal and parabasal layer like in the epidermis, although the staining intensity is weaker. (b) CK 19-positive type III epithelium. Note the in ammatory in ltrate in the dermis and the epithelium. (c) The upper intermediate layer of type III epithelium is immunopositive for antibody OV-TL 12/30, which speci cally reacts with CK 7. Dotted line denotes level of the basement membrane. (d) The suprabasal layers of type III epithelium react strongly with antibody Ks17.E3 against CK 17. D, dermis; L, lumen of the sinus. Bars: a, b, d, 50 mm; c, 100 mm. in type II and III epithelia, i.e. Dsc2 and Dsg3 are present in all layers while Dsc3 is restricted to the basal and parabasal layer. In normal epidermis and type I epithelium, the opposite pattern is present. The in ammatory character of type III epithelium as opposed to type I and II is marked by the presence of CK 7 and 19 and the absence of Dsg1. All three types are clearly distinct from interfollicular epidermis because of the absence of CK 2e and the presence of CK 6 and CK 13/15/16. Although there are similarities in the CK patterns with several other normal strati ed squamous epithelia 47 and in some aspects also with fetal epidermis, 48 there is in no case complete accordance, re ecting the fact that sinus tract epithelia have undergone pathologically altered differentiation programmes. The three phenotypes were not in all cases sharply de ned, and transitional stages were often found. This re ects the dynamic and pathologically altered processes of growth and in ammation in the sinus epithelia. A similar situation was reported previously in in ammatory processes of the human gingiva. As in the draining sinus of acne inversa, the strongly in amed parts of the gingiva were reported to be marked by an upregulation of CK 19 and downregulation of CK 1/10. 49,50 Unlike in the gingiva, we found in all CK 19- positive sinus epithelia also a variably strong reaction for CK 7 in the intermediate and uppermost cell layers. This difference, however, might be due to different sensitivities of the particular CK 7 antibodies used. We were not able to demonstrate a positive reaction for CK 4, even though our antibody, 6B10, reacted strongly in positive controls and the usual type I CK partner of CK 4, CK 13, was found to be expressed in type II epithelium. CK 19 is commonly found in simple epithelia, the basal cells of non-cornifying strati ed squamous epithelia like in the oral cavity, in the outer root sheath of the hair follicle and in different carcinomas. 47,51±54 The strongly in amed CK 19-positive parts of the sinus epithelium showed no signs of terminal squamous differentiation, with nuclei present in the highest suprabasal layers and absence of keratohyalin granules. Instead, they resembled epidermal keratinocytes grown in organotypic culture, which can be induced to build a non-cornifying epithelium and to express CK 19 together with CKs 4, 13 and 7, by the addition of retinoic acid to the culture medium. 55,56 It would be interesting to examine the expression of retinoic acid and retinoid X receptors in the different epithelial phenotypes of the draining sinus. Retinoids are known to induce a differentiation shift in keratinocytes which thereby acquire certain features of simple glandular epithelia. 56 Type III epithelium expressed some markers of such epithelia while keratinocyte maturation markers were reduced. This may be interpreted as a kind of metaplasia towards glandular differentiation. A previous report on the distribution of desmosomal proteins in acne vulgaris 25 showed a reduced staining intensity of Dsc3, Dsg1 and Dsg2 antibodies, while the other isoforms were not analysed. We have been able to use the complete set of isoform-speci c antibodies against all desmosomal cadherins known so far. Studies from various laboratories have shown that the different members of this family of cell±cell adhesion molecules are expressed in different characteristic patterns depending on the epithelial cell type and state of differentiation and maturation. 16,18,19,21,56 The highest complexity of desmosomal cadherins is elaborated in strati ed squamous epithelia, with Dsg1 and particularly Dsc1 being linked to the terminal differentiation of keratinocytes. Dsg2, a constituent of desmosomes of most types of epithelia, is restricted within strati ed squamous epithelia to the undifferentiated basal cells. 18 However, it is expressed more abundantly, including in suprabasal layers, in fetal

6 236 H.KURZEN et al. Figure 3. The desmoglein (Dsg) staining patterns in the different phenotypes of the sinus epithelium. (a) Dsg1 expression in type I epithelium corresponds to the epidermal pattern: the suprabasal cells are strongly immunopositive. (b) Parallel section to Figure 1(d). Dsg1 turns negative in type III epithelium, while type II is immunopositive. (c) Dsg2 expression in type I epithelium is only very weak and is always restricted to the basal layer. The staining intensity is much stronger in type II (d) and type III (e). The basal and lower suprabasal layers of type I epithelium (f) are labelled by Dsg3-speci c antibodies (5G11) while in type II (g) and type III (h) all layers are immunoreactive. B, basal layer; D, dermis; L, lumen of the sinus. Bars: a±e, 50 mm; f±h, 100 mm. strati ed epithelium of the oesophagus (I.Schwetlick et al. personal communication). This is an example of the dynamic changes in the expression patterns of desmosomal cadherins which take place during embryonic development of strati ed squamous epithelia until the mature state is reached. 21,22 In the adult, suprabasal extension of Dsg2 is also a feature of the primitive strati ed squamous epithelium seen in immature squamous metaplasia of the uterine cervix (I.Schwetlick et al. personal communication). Our nding of the restriction to the basal layer of Dsg2 even in the most altered type III sinus tract epithelium indicates that despite heavy in ammation, the degree of immaturity is not as pronounced as in early fetal stage or immature squamous metaplasia. The differential immunohistochemical data obtained for the six desmosomal cadherins allowed us to discriminate between the different epithelial subtypes and to show that not only the degree of keratinization and proliferation but also the in ammatory activity in uences the expression patterns of the Dsc and Dsg isoforms. To what extent different isoforms result in differential adhesive properties of desmosomes remains to be elucidated. 57 The relationship of the sinus epithelium to the hair follicle and to apocrine glands has been a matter of debate for a long time. 2 As we have shown, its differentiation characteristics are clearly distinct from those of the normal subinfundibular outer root sheath of the hair follicle. CK 5/14 and Dsg2 always remain restricted to the basal cell layer of the sinus epithelium, while in the subinfundibular outer root sheath they are also expressed in the suprabasal cell layers. Type I epithelium, which was found close to the opening of the sinus in all specimens examined, showed strong similarities to the upper pilosebaceous duct from which the in ammatory process seems to emerge. In both normal pilosebaceous duct epithelium and cornifying type I sinus epithelium, CK 5 and CK 14 are restricted to the basal layer, CK 10 and Dsc1 antibodies label suprabasal cells, Dsg1 and Dsg3 are present in an epidermis-like pattern and CK 2e is absent. This is in agreement with the theory that acne inversa lesions are caused by follicular plugging and subsequent rupture of the follicle epithelia. 58 Residual fully keratinized hair shafts found in the dermis and the sinus lumen of several specimens could be remnants of the ruptured follicles. However, similarities in the patterns of differentiation markers are no de nite proof of a histogenetic relationship as

7 EPITHELIAL DIFFERENTIATION OF SINUSES IN ACNE INVERSA 237 modulations of cellular differentiation may occur, e.g. under environmental in uences such as in ammation. Thus, the question whether the sinus epithelium is derived from the infundibulum or the deeper hair follicle cannot be fully clari ed by analyses of such markers. The interesting point is that all three types of sinus epithelium identi ed by our marker studies apparently lack a normal counterpart and thus can be regarded as pathological phenotypes. It might be rewarding to investigate whether the presented data are of value in differentiating acne inversa lesions from other causes of stulas like Crohn's disease, which has been reported to be associated with acne inversa. 59,60 In conclusion, the epithelial lining of the draining sinus in acne inversa is heterogeneous and comprises three different phenotypes of pathologically altered strati ed squamous epithelia de ned by the expression of special combinations of CKs and desmosomal proteins. Desmosomal cadherins and CKs have proved to be useful in independently characterizing subtypes of different epithelia. Acknowledgments We thank Erika Mengel and Anke Holzbach for technical assistance, and Jutta MuÈ ller-osterholt for the photographic work. The work was supported in part by the Deutsche Forschungsgemeinschaft. References Figure 4. Differential expression of desmocollin (Dsc) genes. Dsc1 is restricted to type I epithelium (a). Dotted line denotes level of the basement membrane. Transition from type I to types II and III reveals inversion of Dsc2 and Dsc3 staining patterns: while Dsc2 is predominantly immunolocalized to the basal and lower suprabasal layers of epidermis (not shown) and type I epithelium (b), its reactivity is clearly extended to all layers in type II (c) and type III (d) epithelium, resembling very much the desmoglein 3 patterns. The Dsc3 gene is expressed evenly in all layers of the epidermis (not shown) and almost evenly in type I epithelium (e). In type II epithelium, the reactivity of the upper suprabasal layers is grossly reduced (f), while in type III epithelium only the basal and parabasal layer is Dsc3-immunopositive (g). B, basal layer; D, dermis; L, lumen of the sinus. Bars: a, d, 200 mm; b, c, e±g, 50 mm. 1 Kierland RR. Unusual pyodermas (hidrosadenitis suppurativa, acne conglobata, dissecting cellulitis of the scalp). A review. Minn Med 1951; 34: 319±41. 2 Plewig G, Kligman AM. Acne Morphogenesis and Treatment. Berlin: Springer-Verlag, Plewig G, Steger M. Acne inversa (alias acne triad, acnetetrad or hidradenitis suppurativa). In: Acne and Related Disorders (Marks R, Plewig G, eds). London: Dunitz, 1989: 345±57. 4 KuÈster W, RoÈdder-Wehrmann O, Plewig G. Acne inversa. Pathogenese und Genetik. Hautarzt 1991; 42: 2±4. 5 Jansen T, Plewig G. Classi cation of suppurative hidradenitis. Hautarzt 1994; 45: 652±3. 6 Jansen T, Lindner A, Plewig G. Abszedierende FistelgaÈnge bei Akne und Rosacea. Hautarzt 1995; 46: 417±20. 7 Jemec GBE, Hansen U. Histology of hidradenitis suppurativa. JAm Acad Dermatol 1996; 34: 994±9. 8 Moll R, Franke WW, Schiller DL et al. The catalog of human cytokeratins: patterns of expression in normal epithelia, tumors and cultured cells. Cell 1982; 31: 11±24. 9 Moll R, Lowe A, Laufer J, Franke WW. Cytokeratin 20 in human carcinomas. A new histodiagnostic marker detected by monoclonal antibodies. Am J Pathol 1992; 140: 427± Moll R. Cytokeratins as markers of differentiation in the diagnosis of epithelial tumors. Subcell Biochem 1998; 31: 205±262.

8 238 H.KURZEN et al. 11 Cooper D, Schermer A, Sun TT. Classi cation of human epithelia and their neoplasms using monoclonal antibodies to keratins: strategies, applications and limitations. Lab Invest 1985; 52: 243± Smedts F, Ramaekers FCS, Troyanovsky S et al. Keratin expression in cervical cancer. Am J Pathol 1992; 141: 497± Schaafsma HE, Ramaekers FCS. Cytokeratin subtyping in normal and neoplastic epithelium: basic principles and diagnostic applications. Pathol Annu 1994; 29: 21± Fuchs E. Epidermal differentiation and keratin gene expression. Princess Takamatsu Symp 1994; 24: 290± Hughes BR, Morris C, Cunliffe WJ, Leigh IM. Keratin expression in pilosebaceous epithelia in truncal skin of acne patients. Br J Dermatol 1996; 134: 247± Koch PJ, Franke WW. Desmosomal cadherins: another growing multigene family of adhesion molecules. Curr Opin Cell Biol 1994; 6: 682±7. 17 Schmidt A, Heid HW, Schafer S et al. Desmosomes and cytoskeletal architecture in epithelial differentiation: cell type-speci c plaque components and intermediate lament anchorage. Eur J Cell Biol 1994; 65: 229± SchaÈfer S, Stumpp S, Franke WW. Immunological identi cation and characterization of the desmosomal cadherin Dsg2 in coupled and uncoupled epithelial cells and in human tissues. Differentiation 1996; 60: 99± Nuber UA, SchaÈfer S, Stehr S et al. Patterns of desmocollin synthesis in human epithelia: immunolocalization of desmocollins 1 and 3 in special epithelia and in cultured cells. Eur J Cell Biol 1996; 71: 1± Mertens C, Kuhn C, Franke WW. Plakophilins 2a and 2b: constitutive proteins of dual location in the karyoplasm and the desmosomal plaque. J Cell Biol 1996; 135: 1009± King IA, Angst BD, Hunt DM et al. Hierarchical expression of desmosomal cadherins during strati ed epithelial morphogenesis in the mouse. Differentiation 1997; 62: 83± Kurzen H, Moll I, Moll R et al. Compositionally different desmosomes in the various compartments of the human hair follicle. Differentiation 1998; 63: 295± Vilela MJ, Parrish EP, Wright DH, Garrod DR. Monoclonal antibody to desmosomal glycoprotein 1Ða new epithelial marker for diagnostic pathology. J Pathol 1987; 153: 365± Collins JE, Taylor I, Garrod DR. A study of desmosomes in colorectal carcinoma. Br J Cancer 1990; 62: 796± Knaggs HE, Hughes BR, Morris C et al. Immunohistochemical study of desmosomes in acne vulgaris. Br J Dermatol 1994; 130: 731±7. 26 Harada H, Iwatsuki K, Ohtsuka M et al. Abnormal desmoglein expression by squamous cell carcinoma cells. Acta Derm Venereol (Stockh) 1996; 76: 417± Hiraki A, Shinohara M, Ikebe T et al. Immunohistochemical staining of desmosomal components in oral squamous cell carcinomas and its association with tumour behaviour. Br J Cancer 1996; 73: 1491±7. 28 Moll R, Cowin P, Kapprell HP, Franke WW. Desmosomal proteins: new markers for identi cation and classi cation of tumors. Lab Invest 1986; 54: 4± Cowin P, Kapprell HP, Franke WW et al. Plakoglobin: a protein common to different kinds of intercellular adhering junctions. Cell 1986; 46: 1063± Demlehner M, SchaÈfer S, Grund C, Franke WW. Continual assembly of half-desmosomal structures in the absence of cell contacts and their frustrated endocytosis: a coordinated sisyphus cycle. J Cell Biol 1995; 131: 745± Heid HW, Schmidt A, Zimbelmann R et al. Cell type-speci c desmosomal plaque proteins of the plakoglobin family: plakophilin 1 (band 6 protein). Differentiation 1994; 58: 113± van Muijen GN, Ruitter DJ, Franke WW et al. Cell type heterogeneity of cytokeratin expression in complex epithelia and carcinomas as demonstrated by monoclonal antibodies speci c for cytokeratins 4 and 13. Exp Cell Res 1986; 162: 97± Lynch MH, O'Guin M, Hardy C et al. Acidic and basic hair/nail (`hard') keratins: their colocalization in upper cortical and cuticle cells of the human hair follicle and their relationship to `soft' keratins. J Cell Biol 1986; 103: 2593± Wetzels RH, Kuijpers HJ, Lane EB et al. Basal cell-speci c and hyperproliferation-related keratins in human breast cancer. Am J Pathol 1991; 138: 751± Ramaekers FCS, van Niekerk C, Poels L et al. Use of monoclonal antibodies to keratin 7 in the differential diagnosis of adenocarcinomas. Am J Pathol 1990; 136: 641± Makin CA, Bobrow LG, Bodmer WF. Monoclonal antibody to cytokeratin for use in routine histopathology. J Clin Pathol 1984; 34: 975± Huszar M, Gigi O, Moll R, Franke WW. Monoclonal antibodies to various acidic (type I) cytokeratins of strati ed epithelia. Selective markers for strati cation and squamous cell carcinomas. Differentiation 1986; 31: 141± Ivanyi D, Ansink A, Groeneveld E et al. New monoclonal antibodies recognising epidermal differentiation-associated keratins in formalin- xed, paraf n-embedded tissue. Keratin 10 expression in carcinoma of the vulva. J Pathol 1989; 59: 7± Moll R, AchtstaÈtter T, Becht E et al. Cytokeratins in normal and malignant transitional epithelium. Maintenance of expression of urothelial differentiation features in transitional cell carcinomas and bladder carcinoma cell culture lines. Am J Pathol 1988; 132: 123± Purkis PE, Steel JB, Mackenzie IC et al. Antibody markers of basal cells in complex epithelia. J Cell Sci 1990; 97: 39± Troyanovsky SM, Guelstein VI, Tchipysheva TA et al. Patterns of expression of keratin 17 in human epithelia: dependency on cell position. J Cell Sci 1989; 93: 419± Karsten U, Papsdorf G, Roloff G et al. Monoclonal anti-cytokeratin antibody from a hybridoma clone generated by electrofusion. Eur J Cancer Clin Oncol 1985; 21: 733± Gerdes J, Schwab U, Lemke H, Stein H. Production of a mouse monoclonal antibody reactive with a nuclear antigen associated with cell proliferation. Int J Cancer 1983; 31: 12± Franke WW, Moll R. Cytoskeletal components of lymphoid organs. I. Synthesis of cytokeratins 8 and 18 and desmin in subpopulations of extrafollicular reticulum cells of human lymph nodes, tonsils and spleen. Differentiation 1987; 36: 145± Fenske NA, Groover CE, Lober CW, Espinoza CG. Dowling-Degos disease, hidradenitis suppurativa, and multiple keratoacanthomas. A disorder that may be caused by a single underlying defect in pilosebaceous epithelial proliferation. J Am Acad Dermatol 1991; 24: 888± Milde P, Goerz G, Plewig G. Morbus Dowling-Degos mit ausschlieûlich genitaler Manifestation. Hautarzt 1992; 43: 369± Bosch FX, Leube RE, AchtstaÈtter T et al. Expression of simple epithelial type cytokeratins in strati ed epithelia as detected by immunolocalization and hybridization in situ. J Cell Biol 1988; 106: 1635± van Muijen GN, Warnaar SO, Ponec M. Differentiation-related changes of cytokeratin expression in cultured keratinocytes and in fetal, newborn and adult epidermis. Exp Cell Res 1987; 171: 331± 45.

9 EPITHELIAL DIFFERENTIATION OF SINUSES IN ACNE INVERSA Bosch FX, Ouhayoun JP, Bader BL et al. Extensive changes in cytokeratin expression patterns in pathologically affected human gingiva. Virch Arch B Cell Pathol 1989; 58: 59± Ouhayoun JP, Goffaux JC, Sawaf MH et al. Changes in cytokeratin expression in gingiva during in ammation. J Periodontal Res 1990; 25: 283± Gigi-Leitner O, Geiger B, Levy R, Czernobilsky B. Cytokeratin expression in squamous metaplasia of the human uterine cervix. Differentiation 1986; 31: 191± Czernobilsky B, Gat A, Evron R et al. Carcinoma of the clitoris: a histologic study with cytokeratin pro le. Int J Gynecol Pathol 1995; 14: 274±8. 53 Bartek J, Vojtesek B, Staskova Z et al. A series of 14 new monoclonal antibodies to keratins: characterization and value in diagnostic histopathology. J Pathol 1991; 164: 215± Heid HW, Moll I, Franke WW. Patterns of expression of trichocytic and epithelial cytokeratins in mammalian tissues. I. Human and bovine hair follicles. Differentiation 1988; 37: 137± Kopan R, Traska G, Fuchs E. Retinoids as important regulators of terminal differentiation: examining keratin expression in individual epidermal cells at various stages of keratinization. J Cell Biol 1987; 105: 427± Asselineau D, Darmon M. Retinoic acid provokes metaplasia of epithelium formed in vitro by adult human epidermal keratinocytes. Differentiation 1995; 58: 297± Amagai M, Karpati S, Klaus-Kovtun V et al. Extracellular domain of pemphigus vulgaris antigen (desmoglein 3) mediates weak homophilic adhesion. J Invest Dermatol 1994; 102: 402±8. 58 Yu CC, Cook MG. Hidradenitis suppurativa: a disease of follicular epithelium, rather than apocrine glands. Br J Dermatol 1990; 122: 763±9. 59 Ostlere LS, Langtry JA, Mortimer PS, Staughton RC. Hidradenitis suppurativa in Crohn's disease. Br J Dermatol 1991; 125: 384±6. 60 Attanoos RL, Appleton MA, Hughes LE et al. Granulomatous hidradenitis suppurativa and cutaneous Crohn's disease. Histopathology 1993; 23: 111±15.