SEARCH

SEARCH BY CITATION

Keywords:

  • differentiation;
  • filaggrin;
  • keratin;
  • pilomatricoma

Abstract

  1. Top of page
  2. Abstract
  3. Background
  4. Questions addressed
  5. Experimental design
  6. Results
  7. Conclusion
  8. References

Abstract:  Pilomatricoma is believed to differentiate towards the hair matrix and hair cortex. To elucidate the origin of differentiation in pilomatricoma, we studied the expression of epithelial keratin (K) and filaggrin (filament aggregating protein) in pilomatricoma. An immunohistochemical study has been made of 53 cases of pilomatricoma using 10 monospecific anti-keratin antibodies and anti-filaggrin antibody. Basophilic cells, transitional cells and shadow cells did not react with epithelial keratins and filaggrin antibodies as well as hair matrix and hair cortex. Instead, infundibular-type epithelium was positive for K1, K10 and filaggrin. Epithelium showing trichilemmal keratinization was positive for K14 and K16. The hair bulge-like structure was positive for K19. The differentiation of pilomatricoma is diversified, and is heterogeneous in epithelial keratin and filaggrin expression. Our results for keratin and filaggrin expression suggested that pilomatricoma can differentiate not only towards hair matrix and hair cortex, but also follicular infundibulum, outer root sheath and hair bulge.


Background

  1. Top of page
  2. Abstract
  3. Background
  4. Questions addressed
  5. Experimental design
  6. Results
  7. Conclusion
  8. References

Pilomatricoma is a hair follicular-originated neoplasm that differentiates towards the hair matrix such as basophilic cells, shadow cells (1), outer root sheath (2) and any structure of the follicle with the presence of follicular germinative cells (3).

Epithelial keratins were classified into 19 subclasses (4), and keratin has been characterized genomically and a new nomenclature was adopted (5). Keratin, a marker of differentiation, is a useful tool to investigate the origin of epithelial tumors (4).

Filaggrin, a major component of keratohyaline granules, is a marker of terminal differentiation of epidermal keratinocytes (6). Keratins 1, 10 and 2 are crucial in the formation of keratin network of suprabasal keratinocytes, and filaggrin is a key epidermal protein for the formation of normal skin barier (7).

Ultrastructural and immunohistochemical study using anti-hair keratin antibodies showed that basophilic cells and shadow cells appear to correspond to the hair matrix cells and immature hair cortex cells (8,9). Recent immunohistochemical studies using human keratin showed the presence of human hair basic keratin (hHb) 1 (10) and hHb5 (1) in transitional cells in pilomatricoma, suggesting that pilomatricoma differentiates towards the hair cortex.

Questions addressed

  1. Top of page
  2. Abstract
  3. Background
  4. Questions addressed
  5. Experimental design
  6. Results
  7. Conclusion
  8. References

Does pilomatricoma differentiate towards only hair matrix and hair cortex?

Experimental design

  1. Top of page
  2. Abstract
  3. Background
  4. Questions addressed
  5. Experimental design
  6. Results
  7. Conclusion
  8. References

To determine the origin and differentiation of pilomatricoma, we studied epithelial keratin and filaggrin expression in pilomatricoma using immunohistochemical procedures. Fifty-three pilomatricoma patients were enrolled in this study. Each specimen was fixed in formalin, embedded in paraffin, and stained with haematoxylin and eosin (H&E). The anti-keratin and anti-filaggrin antibodies used in this study were as follows: 34βB4 (K1) (11), LP5K (K7) (12), LP3K (K8) (12), HP1 (K10) (13), LL002 (K14) (12), LHK15 (K15) (14), LL025 (K16) (12), E3 (K17) (12), 5D3 (K18) (12), b170 (K19) (15) and 15C10 (filaggrin) (16) (all from Novocastra Laboratories Ltd, Newcastle upon Tyne, UK). Our immunohistochemical study employed the labelled streptoavidin-biotin method (Dako, Carpentaria, CA, USA) as previously reported (17). Normal skin from the scalp acted as control specimens.

Results

  1. Top of page
  2. Abstract
  3. Background
  4. Questions addressed
  5. Experimental design
  6. Results
  7. Conclusion
  8. References

There were 21 males and 32 females. Twenty-one tumors were on the upper extremities, 16 on the face, six on the neck, four on the trunk, three on the scalp, two on the auricle and one on the lower extremity. The age of the patients ranged from 8 to 82 years (mean 31.3 years).

H&E

H&E sections showed basophilic cells, transitional cells, shadow cells, follicular germinative cells and squamoid epithelium. The squamoid epithelium is divided into three types: infundibular-type epithelium, trichilemmal keratinization-type epithelium and hair bulge-like structure. The infundibular-type keratinization epithelium was found in five cases (Fig. 1a). Trichilemmal keratinization-type epithelium was found in six cases (Fig. 2a). Adjacent to basophilic cells, hair bulge-like structure was found in three cases (Fig. 3a).

image

Figure 1.  (a) The infundibular-type keratinization with keratohyaline granules was found (H&E). (b) K1 was found in suprabasal cells in the infundibular-type epithelium with keratohyaline granules. (c) Filaggrin was expressed in superficial (granular) layers in infundibular-type epithelium.

Download figure to PowerPoint

image

Figure 2.  (a) Trichilemmal keratinization-type epithelium without granular layers was found in squamoid epithelium (H&E). (b) K16 was expressed in trichilemmal keratinization-type epithelium without keratohyaline granules.

Download figure to PowerPoint

image

Figure 3.  (a) Adjacent to basophilic cells, hair bulge-like structure was found. (b) K19 was expressed in the outermost cells in hair bulge-like structure.

Download figure to PowerPoint

Immunohistochemical findings

Keratin and filaggrin expression in normal hair follicle and pilomatricoma is summarized in Table 1.

Table 1.   Keratin and filaggrin expression in normal hair follicle and pilomatricoma
 EpidermisNormal hair folliclePilomatricoma
InfundibulumORSIRSHair matrixHair cortexHair medullaBasophilic cellTransitional cellShadow cellSquamoid epithelium
Follicular germinative cellInfundibular-type epitheliumTrichilemmal keratinization-type epitheliumHair bulge-like structure
  1. ORS, outer root sheath; IRS, inner root sheath; sb, suprabasal; b, basal; −(+), K15 and K19 are expressed in the outermost cells in hair bulge; −∼+, K17 is expressed in infrainfundibulum.

  2. Filaggrin is expressed in granular and cornified layers in the epidermis, and in the superficial layers in infundibulum and infundibular type-epithelium.

K1+(sb)+(sb)+(sb)
K7
K8
K10+(sb)+(sb)+(sb)
K14+(b)+(b)++(b)+
K15−(+)
K16+(sb)+
K17−∼++(sb)±±
K18
K19− (+)+
Filaggrin+++
Keratin and filaggrin expression in normal skin

In normal hair follicles, epithelial keratin and filaggrin expression was described in Table 1 as previously reported (17). Neither epithelial keratins nor filaggrin were expressed in hair matrix, hair cortex, hair medulla and inner root sheath.

Keratin and filaggrin expression in pilomatricoma

Basophilic cells, transitional cells, shadow cells and follicular germinative cells were not stained for keratin and filaggrin.

Infundibular-type epithelium. K1 was found in suprabasal cells (Fig. 1b) as well as K10. K14 was expressed in basal cells. K17 was weakly expressed. K7, K8, K15, K16, K18 and K19 were not expressed. Filaggrin was expressed in superficial layers (Fig. 1c).

Trichilemmal keratinization-type epithelium. K1 and K10 were not expressed, and K14 and K16 (Fig. 2b) were expressed throughout the layers. K17 was weakly expressed. K7, K8, K15, K19 and filaggrin were not detected.

Hair bulge-like structure. Adjacent to basophilic cells, K19 was expressed in the outermost cells (Fig. 3b). The other keratins and filaggrin were not expressed.

Conclusion

  1. Top of page
  2. Abstract
  3. Background
  4. Questions addressed
  5. Experimental design
  6. Results
  7. Conclusion
  8. References

Previous immunohistochemical studies found that pilomatricoma differentiates towards the hair cortex and outer root sheath (2,18). However, pilomatricoma can enter a pathway of squamous cell differentiation with the expression of K1 and K10 in pilomatricoma (18), and transitional cells lack epithelial keratin (18). There are a few cells which co-express epithelial keratin and trichocytic keratins, and that basophilic cells appear to be devoid of detectable amounts of keratins with scarcity of cytoplasm (18).

Langbein and Schweizer (19) reported that hair matrix cells do not contain epithelial keratins, but do contain human hair-specific acidic keratin (Ha) 2 and Ha5. They stated that the middle upper cortex does not contain epithelial keratins, but does contain Ha1, 3, 4, 5, 6, 7 and 8 (19), suggesting that basophilic cells represent counterparts of the lowermost and keratin-free germinative cells of the hair matrix (19).

In this study, no epithelial keratins were expressed in basaloid cells, transitional cells, shadow cells and follicular germinative cells. Hair matrix and hair cortex are devoid of epithelial keratins. We found instead that squamoid epithelium contained abundant epithelial keratins. In infundubular-type epithelium, we found K 1, K10, K14 and filaggrin, suggesting the differentiation towards infundibulum. In trichilemmal keratinization-type epithelium, K16 and K14 were expressed in this epithelium, suggesting the differentiation towards the outer root sheath beneath the opening of the sebaceous duct. In hair bulge-like structures, K19 was detected in the outermost cells adjacent to basophilic cells. We expected these hair bulge-like structures to be follicular germinative cells, but their characteristics are different.

A previous report (2) found that basophilic cells contain K5, K8, K10, K11 and K19. The reason of different results might be that we used different anti-keratin bodies recognizing different epitopes. Moll et al. (18) found K5, K6, K14, K16, K17, and K19 by biochemical methods. Our immunohistochemical study demonstrated the presence of K1, K10, K14, K16, K17 and K19. We did not detect K15 in pilomatricoma, but did find K19. Jih et al. (14) and Kanitakis et al. (20) also reported the absence of K15 in pilomatricoma.

In conclusion, our results demonstrate that pilomatricoma can differentiate not only towards the hair matrix and hair cortex, but also the infundibulum, outer root sheath and hair bulge, suggesting that the differentiation of pilomatricoma is diversified and heterogeneous.

References

  1. Top of page
  2. Abstract
  3. Background
  4. Questions addressed
  5. Experimental design
  6. Results
  7. Conclusion
  8. References