Use of the fluorescence-activated cell sorter to quantitate and enrich for subpopulations of human skin cells

A variety of immunologic staining techniques were compared in a quantitative study of antigen expression by human epidermal cells. Virtually all nucleated epidermal cells express beta 2-microglobulin, which is associated with HLA-A, -B, and -C antigens, whereas only about 4% expressed T6, an antigen expressed by Langerhans cells but not other cells in the skin. With the fluorescence-activated cell sorter (FACS), epidermal cell suspensions were selectively enriched 10- to 15-fold for T6-positive Langerhans cells. An average of 6.5% of cells were specifically stained by anti-HLA-DR antibody. When dispersed cells stained with anti-DR plus peroxidase were examined with the technique of immunoelectron microscopy, only mononuclear leukocytes (probably Langerhans cells) were stained. After separating HLA-DR positive skin cells with the FACS, the DR-positive population but not the DR-negative population stimulated proliferation of allogeneic responder lymphocytes, indicating that sorted cells are metabolically active. We conclude that HLA-DR antigen is not expressed by keratinocytes in normal human skin cell suspensions and that the FACS can be used to selectively enrich or deplete skin cell suspensions of antigenically distinct subpopulations such as Langerhans cells.     

Purification and in vitro growth of human epidermal basal keratinocytes using a monoclonal antibody

We have made a new monoclonal antibody, EL-2, and used it with an immunorosetting procedure combined with Ficoll-Hypaque gradient centrifugation to purify and culture basal keratinocytes. Immunofluorescence of cell suspensions and immunoperoxidase staining of tissue sections demonstrate that EL-2 reacts with malignant cell lines, activated lymphocytes and monocytes, and basal keratinocytes. Sequential immunoprecipitation studies demonstrate that monoclonal antibodies EL-2 and 4F2 detect the same membrane protein. However, we have extended previous studies by making the new observation that both EL-2 and 4F2 react with cultured melanocytes. Basal keratinocytes were purified from single-cell epidermal suspensions by incubation with EL-2 followed by rosetting with rabbit antimouse IgG antibodies covalently linked to bovine red blood cells. Rosetting (basal) keratinocytes were separated from EL-2 negative cells by Ficoll gradient centrifugation. We obtained basal keratinocyte populations of greater than 90% purity as assessed by reactivity with EL-2 and another basal keratinocyte-specific monoclonal antibody, HCl. Langerhans cell, fibroblast, and melanocyte contamination was negligible. Cultures of basal keratinocytes were enriched in EL-2-reactive cells throughout the entire 19 days of culture studied. EL-2 is being used to characterize disorders of keratinocyte proliferation; EL-2 reacted with both squamous and basal cell carcinomas. EL-2 stained only the basal layer of lesional skin from patients with psoriasis, pityriasis rubra pilaris, and Darier's disease. Purification of basal keratinocytes will be important in biochemical and functional studies of normal skin and in establishing long-term keratinocyte lines from normal cells.     

Distribution of metallothionein in normal and pathological human skin

The expression and distribution of metallothionein (MT) in frozen sections of normal and pathological human skin was studied using the monoclonal antibody L2E3 directed against MT derived from human fetal liver. Immunohistochemical staining of normal fetal and adult skin revealed strong reactivity in basal keratinocytes of epidermis and outer hair root sheath, hair matrix cells and the secretory coil, but not the exocrine portion of eccrine glands; myoepithelial cells around apocrine sweat glands were similarly stained. In epidermal hyperplasia, variable numbers of suprabasal keratinocytes were stained, whereas in interface dermatitis, interrupted staining was found in the basal layer. Weak or scattered staining was observed in squamous tumours, whereas basal cell carcinomas did not show consistent staining. The distribution of MT in normal skin was in line with the germinative role of basal keratinocytes and hair matrix cells, whereas its distribution in hyperplastic epidermis was in line with experimental animal data, and reflected the increase in the germinative pool in these conditions. It is concluded that monoclonal antibody L2E3 may serve as a valuable immunohistochemical marker in diagnostic cutaneous pathology since it labels basal keratinocytes selectively, and since it discriminates between eccrine and apocrine sweat glands.     

Cutaneous T-cell lymphoma lesional epidermal cells activate autologous CD4+ T lymphocytes: involvement of both CD1+OKM5+ and CD1+OKM5- antigen-presenting cells

Cutaneous T-cell lymphoma is characterized by infiltration of the skin by activated CD4+ T lymphocytes. The mechanism by which these T lymphocytes achieve and maintain their activated state is unknown. Antigen-specific activation of T lymphocytes is dependent upon antigen-presenting cells which express HLA-DR class II major histocompatibility complex molecules, such as epidermal Langerhans cells. In addition to CD1+DR+ Langerhans cells, cutaneous T-cell lymphoma lesional epidermis contains major histocompatibility complex class II positive non-Langerhans cell populations, including CD1+OKM5+ bone-marrow-derived cells and DR+ keratinocytes. We asked whether any of these epidermal cell populations demonstrate capacity to activate T lymphocytes. Various numbers of epidermal cells from uninvolved and involved cutaneous T-cell lymphoma plaques were therefore used to stimulate autologous CD4+ and CD8+ T lymphocytes in the absence of exogenous antigen. Involved epidermal cells potently induced proliferation of CD4+ T lymphocytes (S.I. +/- SEM = 466 +/- 45). In contrast, uninvolved epidermal cells only induced background levels of proliferation (S.I. +/- SEM = 2 +/- 0.5, N = 8, p less than 0.01). Neither involved nor uninvolved epidermal cells were able directly to activate CD8+ lymphocytes. The capability of involved epidermal cells to activate CD4+ T lymphocytes was dependent upon CD1+DR+ leukocytes and not DR+ keratinocytes, because depletion of either HLA-DR+, CD1+ or HLe1+ epidermal cells totally abrogated the T-lymphocyte proliferation. Interestingly, on a cell per cell basis CD1+DR+ cells obtained from involved skin, demonstrated relative to CD1+DR+ cells from uninvolved skin, enhanced capacity to activate CD4+ T lymphocytes. Furthermore, CD1+OKM5+ cells from involved epidermis stimulated autologous CD4+ T lymphocytes. This indicates that a unique hitherto undescribed CD1+OKM5+ epidermal antigen-presenting cell population may participate in T-lymphocyte activation. These findings provide support for the concept that the epidermal cells in cutaneous T-cell lymphoma patients, particularly the antigen-presenting cells, may contribute significantly to the activation of CD4+ malignant and/or non-malignant inflammatory T lymphocytes within the skin.     

Immunohistochemical localization of ornithine decarboxylase in human skin

The localization of ornithine decarboxylase (ODC) in human skin and cultured keratinocytes was studied with an immuno-histochemical method. ODC was found in the epidermis, hair follicles, sweat glands and errector muscles. Irritation induced by stripping or UV-B irradiation did not change the staining pattern in the epidermis. In psoriasis, the staining was most marked at the tip of the epidermal rete ridges. In basal cell carcinoma, there was a homogeneous labelling of the tumor cells and, in squamous cell carcinoma, the labelling was strong but less homogeneous. Melanoma and dermal naevus also positively stained for ODC. Cultured human keratinocytes also showed ODC positive immunofluorescence. This technique detects the ODC antigen present rather than levels of ODC activity.     

Distribution of apoptosis-mediating Fas antigen in human skin and effects of anti-Fas monoclonal antibody on human epidermal keratinocyte and squamous cell carcinoma cell lines

Fast antigen is a cell surface protein that mediates apoptosis. Using immunohistological, flow cytometry and electron microscopic analyses, we investigated the expression of Fas antigen on various skin tissues, and on cultured SV40-transformed human epidermal keratinocyte cell line KJD and human skin squamous cell carcinoma cell line HSC. The Fas antigen was widely distributed in skin components such as the keratinocytes in the lower portion of the epidermis, epidermal dendritic cells, endothelial cells, fibroblasts, apocrine glands, eccrine sweat glands, sebaceous glands, some normal melanocytes and infiltrating lymphoid cells. It was also strongly expressed on the keratinocytes of lichenoid eruptions seen in lupus erythematosus and lichen planus, and on the spongiotic or acanthotic epidermis seen in chronic eczema, adult T-cell leukaemia/lymphoma (ATLL) and atopic dermatitis. Its expression was closely correlated with lymphoid infiltrating cells and it was strongly expressed in lymphoid neoplastic cells, particularly ATLL cells, and fibroblasts seen in dermatofibroma. However, the antigen was not detected on basal cell epithelioma cells, some malignant melanomas or any junctional naevi. The cell lines KJD and HSC strongly expressed the Fas antigen, and crosslinking of the Fas antigen by an anti-Fas monoclonal antibody induced apoptosis of these cell lines. These results indicate that the apoptosis-mediating Fas antigen may play an important role in normal skin turnover and cell differentiation, in immune regulation of skin tumours, and in the pathogenesis of various skin diseases.     

A method for the rapid isolation of human epidermal Langerhans cells using immunomagnetic microspheres

Because Langerhans and indeterminate cells are the only epidermal cells that express the specific CD1a surface antigen T6, we have used immunomagnetic monodisperse polymer microspheres for positive selection of human epidermal Langerhans and indeterminate cells. Epidermal cells in suspension are successively incubated with a murine monoclonal anti-T6 antibody of the IgG1 subclass and then with magnetic beads coated with a sheep anti-mouse IgG1. Rosetted cells are obtained and then easily separated from the non-rosetted cells using a magnet. The two cell fractions are characterized by phase contrast microscopy, immunofluorescence, electron microscopy, and the skin cell-lymphocyte reaction. All the rosetted cells (1.5 to 5% of the total epidermal cells) express T6 antigen by indirect immunofluorescence and under the electron microscope possess all the ultrastructural characteristics of Langerhans cells. Moreover, the rosetted Langerhans cells remain functional: Under the electron microscope they internalize by receptor-mediated endocytosis gold labeled anti-T6 antibody, and in the skin cell-lymphocyte reaction they stimulate allogeneic lymphocytes. In contrast, the rosette depleted cell fraction is deprived of T6 positive cells and unable to stimulate allogeneic lymphocytes. The immunomagnetic depletion of epidermal cells is a simple and rapid method to isolate functional human Langerhans cells with good yield and high purity (97%). This technique should be of value in the study of the pharmacology of Langerhans cells and in the investigation of the interactions of Langerhans cells with keratinocytes or lymphocytes.     

Epidermal keratinocytes express the adhesion molecule intercellular adhesion molecule-1 in inflammatory dermatoses

Using indirect immunofluorescence assays on frozen tissue sections of skin from healthy subjects and subjects with inflammatory skin diseases, we found that intercellular adhesion molecule-1 (ICAM-1) was expressed in a cell surface pattern on epidermal keratinocytes at the site of lymphoid infiltration in cutaneous dermatoses. ICAM-1 was not expressed on epidermal keratinocytes in noninflamed skin. Its expression was not related solely to epidermal hyperproliferation, as hyperproliferative, tape-stripped epidermis did not express ICAM-1. We have reported previously that ICAM-1 expression on epidermal keratinocytes was upregulated by treatment with interferon gamma and that activated T lymphocytes bound to cultured epidermal keratinocytes in vitro by lymphocyte function associated-1 (LFA-1) molecules on T cells and ICAM-1 on epidermal keratinocytes. Taken together, these data suggest that upregulation of expression of ICAM-1 is an important feature of cutaneous inflammation.     

Calcipotriol inhibits the proliferation of hyperproliferative CD29 positive keratinocytes in psoriatic epidermis in the absence of an effect on the function and number of antigen-presenting cells

The aim of this study was to elucidate some of the possible mechanisms of action of the vitamin D analogue calcipotriol in vivo . Calcipotriol is finding increasing use in the treatment of psoriasis, but the primary target cell in vivo has not yet been identified. We treated psoriatic patients and healthy volunteers with calcipotriol and placebo ointment for 4 and 7 days, and obtained epidermal cell suspensions from treated areas. Epidermal cells were cocultured with autologous T cells, isolated from peripheral blood, in the absence or the presence of a classical antigen or a superantigen. In both psoriatic and normal skin, calcipotriol treatment did not alter the capacity of epidermal antigen-presenting cells to stimulate the proliferation of autologous T cells, either in the absence or in the presence of exogenous antigen. Epidermal cell suspensions were analysed further by staining for infiltrating leucocytes (CD45+) and Langerhans cells (CD1a+). Flow cytometric analyses showed that calcipotriol did not alter the number of CD45+ cells or Langerhans cells in psoriatic skin. These results indicate that calcipotriol does not alter either the number or the function of epidermal antigen-presenting cells in psoriatic epidermis. In contrast, we found that calcipotriol significantly inhibited the proliferation of epidermal cells isolated from psoriatic skin after in vivo treatment, as determined by propidium iodide staining and flow cytometry. More specifically, we stained for CD29+ keratinocytes and found an even more significant reduction in proliferative capacity. This cell type contains the population of hyperproliferative keratinocytes in psoriatic epidermis. In conclusion, calcipotriol seems to act via an inhibitory effect on hyperproliferative basal keratinocytes of psoriatic epidermis, rather than via an effect on infiltrating leucocytes, including antigen-presenting cells.     

Altered keratin expression in benign and malignant skin diseases revealed with monoclonal antibodies

We studied keratin expression in benign epidermal skin diseases, and in Bowen's disease by using three monoclonal cytokeratin antibodies. In adult normal skin, these antibodies bind only to the follicular epithelium (PKK1), the basal keratinocytes (PKK2), or the suprabasal cells in interfollicular epidermis (KA5). Additionally, in fetal epidermis, the PKK1 antibody reacts with basal keratinocytes. In psoriasis and lichen planus, the PKK2 antibody distinctly revealed all epidermal cell layers by immunostaining. However, a negative basal cell-like layer was revealed in both lesions with the KA5 antibody. In pityriasis rubra pilaris, the basal cell layer was uniformly stained with the PKK2 antibody, but only some keratinocytes in upper cell layers showed fluorescence and, in chronic eczema, the 3-4 lowest epidermal cell layers were reactive. The PKK1 antibody did not stain interfollicular keratinocytes in any of the benign proliferative skin diseases studied. In Bowen's disease, a heterogeneous staining pattern with varying intensity among individual cells was seen with all of the antibodies used. Our results suggest different changes in keratin expression in chronic benign and malignant epidermal diseases that may reflect the mechanisms behind these changes.     

Addisonian pigmentation associated with acute lymphoblastic leukemia: A rare paraneoplastic phenomenon

Addisonian pigmentation usually presents with nonspecific symptoms and signs, which are often ignored or misdiagnosed as a sign of other more common diseases. We present a case of 12-year-old child in whom diffuse Addisonian hyperpigmentation of skin was associated with underlying acute lymphoblastic leukemia (B-type), a rare paraneoplastic phenomenon in hematological malignancies.     

Immunologic characteristics of keratins in extramammary Paget's disease

Six cases of extramammary Paget's disease were immunohistochemically investigated with several antikeratin monoclonal antibodies. Paget cells and surrounding epidermal keratinocytes were equally stained with an antikeratin monoclonal antibody, HKN-4, which recognizes a broad spectrum of keratins. However, Paget cells were clearly distinguished from the surrounding epidermal keratinocytes by HKN-2, which does not react with keratins of secretory cells but does react with keratins of ductal and myoepithelial cells of sweat glands and with epidermis and hair tissue of the normal skin. The HKN-2 did not bind to Paget cells, but the surrounding keratinocytes were positive. CK7, LE41, RGE53, and LP2K, which recognize simple epithelium-type keratins 7 (molecular weight [MW], 54,000; type II), 8 (MW, 52,500; type II), 18 (MW, 45,000; type I), and 19 (MW, 40,000; type I), respectively, stained Paget cells but not the surrounding keratinocytes. Two cases of Merkel cell carcinoma, examined as controls, showed positivity to LE41 and RGE53 but not to CK7 and LP2K. Since in the normal skin the secretory cells of sweat glands showed the same keratin expression as that of Paget cells, Paget cells of extramammary Paget's disease may be derived from or differentiate to the secretory cells of sweat glands.     

Pernio as the presenting sign of blast crisis in acute lymphoblastic leukemia

A previously healthy 5‐year‐old girl presented with acute onset of blue toes and red spots on the nose and fingers. The striking nature of these lesions, along with the finding of submandibular lymphadenopathy, prompted further evaluation. Laboratory findings were remarkable for anemia, high transaminase levels, and high blast count. Histopathologic findings were consistent with early pernio. Further examination revealed acute B‐cell lymphoblastic leukemia. Treatment of the leukemia led to resolution of the pernio.     

A surface glycoprotein complex related to the adhesive receptors of the VLA family, shared by epidermal Langerhans cells and basal keratinocytes

A murine monoclonal antibody, designated K20, was raised by immunization with a human malignant T-cell line. It reacted specifically with membrane glycoprotein complexes on early haematopoietic cells, T cells, and monocytes. In epidermis, K20 specifically reacted with Langerhans cells and basal keratinocytes, as demonstrated by double labeling experiments. Membrane immunoprecipitation analysis demonstrated that the antigen identified by K20 on lymphoid cells and epidermal cells was different. While on lymphoid cells, K20 recognized glycoprotein complexes made of a constant 130-kD subunit associated with subunits of higher molecular weight ranging from 150 to 200 kD, a complex of 105-145 kD was precipitated from Langerhans and basal cells. Metabolic labeling studies demonstrated that these proteins were synthesized by the basal cells. The antigen identified by K20 was thought to belong to the integrins, a family of cell surface receptors that play a role in cell adhesion, cell interactions, wound healing, and immune defense mechanisms. K20 is the first monoclonal antibody that specifically recognizes a membrane antigen common to Langerhans and basal cells. Additionally, K20 is the first of five reported monoclonal antibodies to have been characterized on the epidermal cells that detect antigens shared by lymphoid subpopulations and normal basal keratinocytes.     

Interleukin‐1 from epithelial cells fosters T cell‐dependent skin inflammation

Background Chronic inflammatory skin diseases such as atopic dermatitis and psoriasis are characterized by the infiltration of lymphocytes into the epidermal compartment. Several studies point to an active role of skin epithelial cells in the pathophysiology of such diseases. Objectives In this study we addressed the regulatory function of primary human keratinocytes in the interaction with autologous T cells and monocytes. Methods We used a human coculture model with keratinocytes grown from epidermal stem cells of the outer root sheath of human hair follicles and autologous T cells. Results In our coculture system we observed a high production of interferon (IFN)‐γ, but not Th2 cytokines, in the presence of superantigen or antigen‐pulsed autologous monocytes. Critical parameters for this effect were: (i) T‐cell receptor activation, (ii) an intercellular adhesion molecule‐1/lymphocyte function‐associated antigen (LFA)‐1‐dependent interaction between keratinocytes and T cells, and (iii) secretion of interleukin (IL)‐1β. Remarkably, in the presence of activated T cells, epithelial cells seemed to be a more significant source of IL‐1β than monocytes. Application of the LFA‐1 blocker efalizumab or IL‐1 receptor antagonist anakinra enabled us to suppress completely the production of IFN‐γ by T cells in the coculture. Conclusions IL‐1 secretion and the physical contact between keratinocytes and activated, infiltrating T cells may be central for the development of chronic inflammatory skin conditions.     

Epidermal interleukin-1 is increased in cutaneous T-cell lymphoma

Interleukin-1 (IL-1) is a monocyte-derived polypeptide with immunoregulatory and proinflammatory functions. Although monocytes are the principle source of IL-1, other cells, such as keratinocytes, endothelial cells, renal mesangial cells, and neutrophils, produce a factor with IL-1 activity. The IL-1-like polypeptide produced by keratinocytes, epidermal-derived thymocyte-activating factor (ETAF), is similar on biological, biochemical, and molecular levels to monocyte-derived IL-1. Studies of IL-1 or ETAF have for the most part been undertaken using cell culture supernatants or cell lysates, and in situ localization of ETAF has not been demonstrated. Previous studies have suggested that ETAF is involved in the pathogenesis of cutaneous T-cell lymphoma (CTCL). To gain insights into the role of these cytokines in disease states, we investigated whether IL-1 could be localized in tissue sections using a direct immunofluorescence technique with a monoclonal antibody directed against IL-1. This monoclonal antibody partially inhibited ETAF activity and totally inhibited IL-1 activity in the co-stimulator assay and so could be used to detect IL-1 or ETAF. We studied skin biopsies from 10 healthy individuals, 10 patients with CTCL, and 11 patients with various inflammatory dermatoses. Intense epidermal fluorescence was demonstrated in all cases of CTCL, whereas minimal reactivity was visible in normal biopsies and the inflammatory dermatoses. Most patients with CTCL showed an intercellular pattern, while none of the normal controls or those with inflammatory dermatoses showed this pattern. An irrelevant IgM monoclonal antibody, used as a negative control, did not demonstrate epidermal staining. To further demonstrate specificity, we incubated the anti-IL-1 antibody with recombinant beta IL-1:Epidermal reactivity was completely blocked. In a separate experiment, COLO 16 cells, a squamous cell carcinoma cell line that constitutively produces ETAF, stained positively for the IL-1 antibody. We conclude that epidermal IL-1 is elevated in CTCL.     

Abnormal distribution of epidermal protein antigens in psoriatic epidermis.

The immunohistochemical distribution of the epidermal proteins filaggrin, involucrin, and cytokeratins is characteristic in normal epidermis. This distribution may change as a result of malignant transformation or abnormal differentiation. The present study was conducted to determine the patterns of reactivity of psoriatic epidermis to antibodies against various epidermal proteins and to clarify abnormal differentiation or maturation of the keratinocytes in psoriatic epidermis. Anti-human filaggrin, anti-human involucrin, and twelve kinds of anti-cytokeratin antibodies were used in this study. Cryostat or paraffin-embedded sections were stained with these antibodies by the avidin-biotin peroxidase technique. The epidermis of the noninvolved skin of patients with psoriasis vulgaris showed the distribution seen in normal skin. However, involved psoriatic skin revealed little or no reaction in the stratum corneum or in the granular layer with the anti-filaggrin antibody. Cells positively staining with anti-involucrin antibody paradoxically appeared in the lower cell layers of involved psoriatic epidermis. An anti-keratin antibody, AE1, stained suprabasal cells in involved psoriatic epidermis, although this antibody selectively stained epidermal basal cells in normal skin. The other anti-keratin antibodies, especially KL1, PKK1, and a polyclonal anti-keratin antibody, were less reactive with involved psoriatic skin than with normal skin. These observations suggest that the maturation pathway of keratinocytes in active psoriatic lesions differs qualitatively from that in normal epidermis.     

Monoclonal Antibody OKB19, Reactive with a B-Lymphoid Differentiation Antigen (CD19), Binding to Basal Layer Keratinocytes of Normal Human Skin

Monoclonal antibody (moAB) OKB19 reacts with CD19 antigen, which is the broadest lineage-specific surface marker on B-lymphocytes. In frozen tissue sections, using an immunohistochemical technique, the OKB19-positive cells in the basal layer were sharply demarcated from the negative suprabasal layers. In normal hair follicles, the OKB19 reactivity was also confined to one layer of the dermal side of the outer root sheath. However, this reactivity gradually disappeared in the lower areas. The inner surface of the lumina in the eccrine duct was weakly stained with OKB19. The basal keratinocytes were also stained with OKB19 in the lesional epidermis of the various dermatoses examined in this study, when the basal keratinocytes remained unaffected. Even in the hyperproliferative state of psoriasis, the OKB19 reactivity was confined to the basal layer. Several kinds of tumor cells derived from the skin were not stained with OKB19. No labeling was seen even in the basaloid cells of basal cell carcinoma, which are morphologically similar to basal keratinocytes. B4 and Leu-12, other monoclonal antibodies reacting with CD19, did not recognize any keratinocytes in the normal human skin. MoAB OKB19, therefore, reacts with an antigen present on basal keratinocytes and provides a probe for the isolation of the basal keratinocyte subpopulation. Thus, this antibody should be useful in studies of not only B-lymphocyte differentiation, but also normal and aberrant differentiation of the epidermal keratinocytes.     

Location of HLA-A,B,C antigens in dendritic cells of normal human skin: an immunoelectron microscopic study

The distribution of the major histocompatibility antigens HLA-A,B,C, (HLA) on dendritic cells of normal human skin was studied by immunoelectron microscopy and a 4-step immunoperoxidase technique utilizing monoclonal antibodies. Light microscopy revealed peripheral staining for HLA of epidermal and pilar infundibular keratinocytes. In the epidermis, the staining was present from the basal layer to the upper stratum spinosum. In the follicles below the level of the infundibulum, HLA was detected only on rare intraepithelial dendritic cells. These dendritic cells could not be identified in the epidermis due to the HLA staining of the surrounding keratinocytes. Similar cells stained diffusely with anti-T6 antibody; the keratinocytes did not. Immunoelectron microscopy demonstrated: (1) the presence of HLA staining of keratinocyte membranes from the stratum basalis to the level of the upper stratum spinosum and in the pilar infundibulum, (2) the possible absence of HLA on melanocytes, (3) the presence of focal HLA staining of the membranes of epidermal and follicular dendritic cells that contained Birbeck granules and were, therefore, Langerhans cells, (4) dendritic mononuclear cells within the follicular epithelium, which although devoid of Birbeck granules, exhibited similar reactivity with anti-HLA antibody. These findings suggest that HLA antigens are present on the membranes of Langerhans cells, but are not demonstrable on melanocytes in normal human skin.     

Localization of haptoglobin in normal human skin and some skin diseases

BACKGROUND: Haptoglobin (Hp) is an acute-phase reactant, known to be produced mainly in the liver. Haptoglobin can also be detected in the cytoplasm of normal epidermal Langerhans cells (LCs), and can prevent their functional maturation. The synthesis of Hp in skin cells has not been well studied. METHODS: We examined Hp expression at mRNA and protein levels by in situ hybridization and immunohistochemistry, respectively, in normal human skin and in the skin of patients with psoriasis, lichen planus, erythroderma, seborrheic keratosis, verruca vulgaris, basal cell carcinoma, systemic lupus erythematosus, pemphigus and bullous pemphigoid. RESULTS: (1) Haptoglobin mRNA was expressed in the epidermal keratinocytes (KCs), the epithelial cells of hair follicles, sebaceous glands and eccrine glands in normal skin and all dermatoses investigated. (2) Whereas compared with normal skin, the Hp mRNA in KCs of patients with psoriasis, lichen planus, erythroderma, seborrhoea keratosis and verruca vulgaris was significantly intensified, it was weaker in patients with systemic lupus erythematosus, pemphigus and bullous pemphigoid. (3) Haptoglobin protein only stained positively in some KCs of patients with psoriasis, lichen planus and erythroderma. (4) Although some but not all epidermal LCs were positively stained with anti-Hp antibody in normal skin and in skin samples from all patients, the ratios of Hp-positive LCs/total LCs were significantly higher in those diseases with intensified Hp mRNA in KCs. CONCLUSIONS: Skin is another extrahepatic organ where Hp can be synthesized by KCs. The expression of Hp mRNA in KCs and the Hp protein in both LCs and KCs appears to be correlated with the amount of inflammation, which might indicate that skin itself is involved in down-regulating the local inflammatory reaction by KC-synthesized Hp.