Langerhans' cells of the normal human pilosebaceous system. An electron microscopic investigation

Inflammatory features of frontal fibrosing alopecia

INTRODUCTION

Frontal fibrosing alopecia (FFA) is a cicatricial alopecia typically occurring in postmenopausal women. The etiology and pathophysiology of FFA is poorly understood but thought to be immune mediated. This study aims to further explore the extent of fibrosis and the inflammatory microenvironment by characterizing Langerhans cells (LCs), helper T cells, cytotoxic T cells and B cells near hair follicles in FFA.

METHODS

Eleven paraffin-embedded tissues from patients with a clinical and histopathologic diagnosis of FFA were selected for immunohistochemical studies using CD3, CD4, CD8, CD1a and CD20. The lymphocytes and LCs were counted around involved follicles. The CD4/CD8 T-lymphocyte ratios were calculated and compared to the CD4/CD8 T-lymphocyte ratios in uninvolved areas.

RESULTS

On histopathologic review, at least 35% of follicles in each case were affected by the disease with concentric perifollicular fibrosis and a perifollicular lichenoid lymphocytic infiltrate around the infundibuloisthmic portion of the hair follicle. There was an increase of perifollicular LCs (mean of 18, SD of 5.5) and intrafollicular LCs (mean of 14, SD of 4.3) in involved follicles compared to uninvolved follicles (P < .0001). The involved follicles also showed a relative decrease in the CD4/CD8 ratio indicating increased numbers of CD8+ T cells; a finding distinct from the CD4-predominant population in uninvolved follicles (P < .0001).

CONCLUSION

The inflammatory features of FFA show a CD8-biased T-cell infiltrate with increased numbers of LCs in the infundibuloisthmic region. The increased LCs may represent an aberrant immune reaction promoting a CD8+ T-cell response.

Human hair greying is linked to a specific depletion of hair follicle melanocytes affecting both the bulb and the outer root sheath

BACKGROUND

Although hair greying is a very common phenomenon characterized by loss of pigment in the hair shaft, the events that cause and control natural hair whitening with age in humans are still unclear.

OBJECTIVES

To decipher the origin of natural hair whitening.

METHODS

Human hair melanocytes were immunohistochemically characterized at different stages of whitening.

RESULTS

Loss of hair shaft melanin was found to be associated with a decrease in both bulb melanin content and bulb melanocyte population. Although few melanocytes were present in the bulbs of grey hair, they still expressed tyrosinase and tyrosinase-related protein-1, synthesized and transferred melanins to cortical keratinocytes as seen by the presence of melanin granules. In white hair bulbs, no melanocytes could be detected either with pMel-17 or vimentin labelling. Pigmented hair follicles are known to contain inactive melanocytes in the outer root sheath (ORS), and grey and white hairs were also found to contain some of these quiescent melanocytes. However, their population was decreased compared with pigmented hair follicles, ranging from small to nil. This depletion of melanocytes in the different areas of white hairs was detected throughout the hair cycle, namely at telogen and early anagen stages. In contrast, the infundibulum and sebaceous gland of both pigmented and white hairs showed a similar distribution of melanocytes. Furthermore, other distinct cell populations located in the ORS, namely putative stem cells, Merkel cells and Langerhans cells were equivalently identified in pigmented and white hairs.

CONCLUSIONS

Thus, hair greying appears to be a consequence of an overall and specific depletion of bulb and ORS melanocytes of human hair.

Spatial relationship between Merkel cells and Langerhans cells in human hair follicles

The distributions of Merkel cells and Langerhans cells within human hair follicles have been reported. However, there has been no description of the relationship between Merkel cells and Langerhans cells, which were discovered by 19th century German pathologists. Merkel cells and Langerhans cells share some similar characteristics such as the localization of human hair follicles, a close association with peripheral nerves and the expression of several neuropeptides. Merkel cells were stained with CK20 or CAM5.2, while Langerhans cells were stained with CD1a or S-100 protein. We thus immunohistochemically confirmed the preferential localization of Merkel cells and Langerhans cells in normal human hair follicles. Using a double staining technique, two- and three-dimensional observations demonstrated that a small proportion of Merkel cells were closely contacted with Langerhans cells below the sebaceous gland level, presumably indicating the bulge area. Merkel cells and Langerhans cells connected directly or approached each dendrite within the basal layer of the outer root sheath. For the first time, we demonstrated a close anatomical relationship between Merkel cells and Langerhans cells within the bulge area of human hair follicles where follicular stem cells may be present. These morphological observations suggest a functional interaction between follicular Merkel cells and Langerhans cells. We herein hypothesize that Merkel cells communicate with Langerhans cells by characteristic dendrites in which some neuropeptides or cytokines may be stored.

Immunopathology of the human hair follicle

Although patients are told that, in many instances, their hair loss is precipitated by stress, they are certainly stressed and saddened by their alopecia. They would be elated with the ability to regrow their hair. Ideally, therapy would be specific and targeted at the cascade of inflammatory, cytokine-mediated, and mesenchymal events which lead to hair loss. Such is the case with infectious folliculitides: Pityrosporum folliculitis is cleared with antifungal agents, bacterial folliculitis is cleared with antibiotics, and herpetic folliculitis is treated with antiviral agents. Future studies of the hair follicle will perhaps unlock the mechanisms that drive and maintain normal hair growth. Until that time scientists will, no doubt, continue to be fascinated by the intricate developmental and immunologic mechanisms that drive this micro-organ of the skin.

A possible role for Langerhans cells in the removal of melanin from early catagen hair follicles

Hair pigmentation is coupled to the hair follicle growth cycle. A common feature of catagen is the translocation of melanin from the matrix to the dermal papilla of the hair follicle. However, the mechanism whereby this pigment, not incorporated into the hair shaft, is removed from the hair bulb during early catagen is poorly understood. Routine ultrastructural examination of four normal scalp specimens revealed a rare hair follicle in early catagen. Close study of the hair bulb of this catagen follicle revealed a Langerhans cell in the process of transferring pigment from the matrix to the dermal papilla. This cell also contained numerous characteristic Langerhans granules (LG) (also known as Birbeck granules). Interestingly, these granules were intimately associated with melanosomes: so intimate, in fact, that melanosomes appeared to have been endocytosed by LG. This unique demonstration of removal of hair follicle melanin by Langerhans cells during early catagen and of pigment uptake by Langerhans cells by endocytosis into LG, suggests one way by which 'unused' pigment can be removed from the hair follicle during catagen.

Distribution of Langerhans cells in human hair follicle

Using immunohistochemical techniques, we mapped and quantified the distribution of Langerhans cells (LCs) within the follicular epithelium of normal human skin in serial horizontal sections. Ten skin biopsies from disparate, disease-free sites from individuals of various skin types were stained with antibody to CD1a. LCs concentrated in the infundibular epithelium (x=16.16 cells), including the follicular bulge, and extended into the germinative sebaceous epithelium (x=8.84). In contrast, rare LCs (x=1.06) were observed in the follicular epithelium below the entry of sebaceous glands into the follicle. LCs were absent in bulbar epithelium. This infundibulocentric distribution of LCs corresponds to the pattern of follicular inflammation in the scarring folliculitides of lupus erythematosus and lichen planopilaris, as well as allogeneic graft versus host reaction and infundibulofolliculitis of atopy. Follicular LCs may act as the trigger and/or target for these T cell-mediated inflammatory processes.

Anatomic distribution of melanocytes in normal nail unit: an immunohistochemical investigation

Very few histologic reports describe normal melanocytes of the nail unit. Previous studies predominantly address the distal nail matrix melanocytes; we found no review of nail-bed melanocytes in the literature. The proximal nail matrix melanocytes are difficult to identify; the cells cannot be identified by L-DOPA staining. More recently, their scarcity was confirmed by immunohistochemistry with a large panel of antibodies directed against melanocytes. We wished to detect the proximal nail matrix dormant melanocytes and compare their density and distribution with that of the other melanocytes in the distal matrix and nail bed and to establish criteria of normality that may help clarify the pathologic features of benign nevoid melanonychia in the nails of whites. A panel of five monoclonal antibodies (MoAbs), including HMB45 and TRP1 directed against antigens localized in early melanosomal vesicles, was investigated in frozen sections of six nail specimens from whites. Both vertical and horizontal sections were assessed to determine the presence of dormant melanocytes. Results showed that the proximal nail matrix melanocytes were clearly identified with MoAbs HMB45 and tyrosinase-related protein-1 (TRP-1). By contrast, melanocytes stained by MoAb against tyrosinase and L-DOPA reaction were evident, especially in the distal matrix. With MoAb TRP-1, the epithelial sheets showed counts of approximately 217+/-84/mm2 in the proximal matrix and of 132+/-34/mm2 in the distal matrix; the nail bed counts were only 45+/-25/mm2. The split epithelial sheets had 103+/-17/mm2 L-DOPA-positive melanocytes in the distal third of the matrix, but only a few of them were detected in the proximal matrix and none were noted in the nail bed. We clearly identified proximal nail melanocytes using MoAb HMB45 and TRP1. The total number of matrix melanocytes can be estimated as approximately 217/mm2. In proximal matrix, the dormant melanocytes compartment was predominant. In the distal matrix, two compartments were identified: a functionally differentiated and a dormant compartment. Contrary to classical opinion, longitudinal melanonychia originates more frequently in the distal matrix, not secondary to the larger melanocyte density but because only the distal matrix contains an active melanin synthesis compartment. Furthermore, the superficial distribution of proximal nail melanocytes in vertical sections showed a histologic feature that may simulate the pagetoid pattern of melanoma in situ.

The lunula

The lunula is the visible portion of the distal nail matrix that extends beyond the proximal nailfold. It is white, half-moon-shaped, appears by week 14 of gestation, has unique histologic features. The lunula has a primary structural role in defining the free edge of the distal nail plate. Lunular anomalies include changes in form and structure and in color. Lunular dysmorphologic features can be characterized by macrolunula, microlunula or anolunula, and nonconvex lunula. Lunular dyschromias can be confluent or spotted or can be characterized by longitudinal colored bands that traverse the lunula. Alterations in the morphologic features or color (or both) of the lunula can be an indication of either a cutaneous or a systemic disorder.

Characterization of nail matrix melanocytes with anti-PEP1, anti-PEP8, TMH-1, and HMB-45 antibodies

BACKGROUND

The normal nail matrix contains quiescent melanocytes with a peculiar arrangement and behavior.

OBJECTIVE

Our purpose was to identify nail matrix melanocytes with antibodies that recognize melanocytic cells in tissue sections.

METHODS

We used the polyclonal antibodies anti-PEP1 and anti-PEP8 and the monoclonal antibody TMH-1, which recognize melanocytic enzymes, and the monoclonal antibody HMB-45, which reacts with melanoma cells and fetal melanocytes, but not with normal adult melanocytes. Nail matrix specimens were obtained from longitudinal specimens of eight white patients with ingrown toenails. Specimens from normal adult forearm skin were used as controls.

RESULTS

All nail specimens gave similar results. Dendritic melanocytes were more numerous in the distal than in the proximal nail matrix. They were not restricted to the basal layer, but were also found in the suprabasal layers of the nail matrix epithelium. Melanocytes were seen both a single dendritic cells among the nail matrix keratinocytes and as small clusters that appeared irregularly distributed along the length of the nail matrix. Each cluster usually consisted of three to four cells.

CONCLUSION

Even if normally quiescent, nail matrix melanocytes possess the key enzymes responsible for the formation of melanin. The suprabasal location of nail matrix melanocytes may be a consequence of the distribution of adhesion molecules in the nail epithelium. In fact, in the nail matrix alpha 2, alpha 3, and beta 1 integrins are not only expressed on the basal, but also on the fourth to fifth suprabasal layers, with suprabasal expression gradually decreasing from distal to proximal matrix. The behavior of nail matrix keratinocytes may cause the peculiar arrangement and behavior of nail matrix melanocytes.

Longitudinal melanonychia (melanonychia striata): diagnosis and management

Longitudinal melanonychia presents a difficult clinical challenge because subungual melanoma must always be included in the differential diagnosis and because the cause of longitudinal melanonychia is usually not apparent. Accordingly, biopsy is often necessary to establish the cause. This review attempts to expedite management by providing suggestions for the examination of patients with this disorder. The causes of longitudinal melanonychia are enumerated and clues to arrive at the various causes are discussed. Similarities between longitudinal melanonychia and subungual melanoma are discussed in an effort to clarify their differences and similarities; clues to the diagnosis of subungual melanoma are also discussed. Various biopsy techniques applicable to longitudinal melanonychia are considered and the indications for different surgical approaches are emphasized. The importance of the pathologist in interpreting nail biopsy specimens is emphasized.

Nail surgery

An update of recent surgical techniques as applied to the nail unit is presented. The procedures discussed touch on areas of internal medicine, oncology, biomechanics, trauma, podiatry, infectious disease, and genodermatoses. It is evident in reviewing the literature that a mushrooming of interest in the nail unit is taking place and that this structure has inherent importance in that it may involve all facets of health care. I hope that the reader will emerge from this chapter with a greater respect for the nail and will be stimulated to learn more about it.

Immunological and histochemical analysis of regional variations of epidermal Langerhans cells in normal human skin

Epidermal Langerhans' cells (LC) were enumerated in normal human skin from various anatomical sites using a monoclonal antibody (NA1/34) to human thymocyte antigen (HTA-1) and the standard ATPase reaction on frozen sections. The same population of cells was identified with each technique. LC densities were found to be significantly higher in hair bearing skin than in skin from the palm and sole. LC were also identified in hair follicles (where the numbers decreased from the superficial to the deep portions) and sebaceous glands but in no other adnexal structure. Normal numbers were encountered in patients who had received radiotherapy or systemic chemotherapy for malignant disease for periods of greater than two months before death. As LC are important antigen presenting cells, the variation in their density suggests that the immunological properties of normal skin may not be uniform throughout the body. This may be related to the varying anatomical distribution of some skin disorders with an immunological basis.

Melanonychia striata longitudinalis. A case report

Melanonychia strata longitudinalis is a pigmented (dark brown-tan-black) band running in the long axis of the nail. This abnormal color of the nail plate is caused by a focal increase of melanin because of increased number and/or function of normal or abnormal melanocytes in the nail matrix. Pigmented streaks in nails due to melanocytic hyperplasia are said to be so exceedingly common in black persons as to be normal and the phenomenon is benign in the majority of cases. In our white patient reported here the pigmentation is due to epithelial hyperpigmentation without melanocytic hyperplasia or evidence of malignancy, hormonal abnormality, or other adventitious influence.

Electron microscopic identification of Langerhans cells in the dermal infiltrates of mycosis fungoides

The importance of the physical interaction between epidermal Langerhans cells and malignant cells in mycosis fungoides (MF) has been stressed recently. To further evaluate this concept, electron microscopic study was carried out to identify whether or not Langerhans cells are also present in the dermal infiltrates of MF. The cells with characteristic Langerhans cell-granules were found in the dermal infiltrates, from early patch to tumor lesions of MF. No vacuolous change suggestive of cell degeneration was found in these cells. These Langerhans cells revealed only a small number of specific granules, and nuclear cleavage and chromatin pattern similar to those of malignant lymphoid cells, thus hardly differentiating 2 cell types in a low power view. Similar to epidermal MF lesions, however, a close apposition of dermal Langerhans cells with malignant lymphoid cells was seen. In one occasion, one Langerhans cell was present at the epidermodermal junction, appearing as being in the process of crossing over the basal lamina. Inasmuch as malignant cells in MF have been shown to possess the functional properties of helper T cells and receptors for Ia (immune associated antigen), expressed in the epidermis solely on Langerhans cells, our findings may further suggest that these malignant T cells bind to Langerhans cells through a "lock and key" mechanism involving membrane-bound Ia.

Langerhans' cells in a pleomorphic adenoma of submandibular salivary gland

Large numbers of round and dendritic cells similar to Langerhans' cells of normal epidermis and other epithelia were seen within a pleomorphic adenoma of the submandibular salivary gland. These cells, which were present only in areas of non-cornifying epidermoid metaplasia, exhibited Birbeck granules with isolated terminal vesicles, cytoplasmic microfilaments, microtubules, and a few poorly developed intercellular junctions.

Langerhans cells in human apocrine ducts

Electron microscopic observations revealed for the first time a few number of Langerhans cells within the intradermal apocrine duct of the normal human axillary skin. In many respects the fine structural features of Langerhans cells were noted to be identical with those described in the epidermis. Our present results suggest that Langerhans cells could be a stable and constant cellular constituent for the normal apocrine ducts. The significance of this presence of Langerhans cells remains to be investigated.