Functional and phenotypic analysis of isolated human Langerhans cells and indeterminate cells

Human dendritic cell subsets

Dendritic cells are highly adapted to their role of presenting antigen and directing immune responses. Developmental studies indicate that DCs originate independently from monocytes and tissue macrophages. Emerging evidence also suggests that distinct subsets of DCs have intrinsic differences that lead to functional specialisation in the generation of immunity. Comparative studies are now allowing many of these properties to be more fully understood in the context of human immunology.

A three-dimensional atlas of human dermal leukocytes, lymphatics, and blood vessels

Dendritic cells (DCs), macrophages (Mφ), and T cells are major components of the skin immune system, but their interstitial spatial organization is poorly characterized. Using four-channel whole-mount immunofluorescence staining of the human dermis, we demonstrated the three-dimensional distribution of CD31⁺ blood capillaries, LYVE-1⁺ lymphatics, discrete populations of CD11c⁺ myeloid DCs, FXIIIa⁺ Mφ, and lymphocytes. We showed phenotypic and morphological differences in situ between DCs and Mφ. DCs formed the first dermal cellular layer (0–20 μm beneath the dermoepidermal junction), Mφ were located deeper (40–60 μm), and CD3⁺ lymphocytes were observed throughout (0–60 μm). Below this level, DCs, T cells, and the majority of Mφ formed stable perivascular sheaths. Whole-mount imaging revealed the true extent of dermal leukocytes previously underestimated from cross-section views. The total area of apical dermis (0–30 μm) contained approximately 10-fold more myeloid DCs than the entire blood volume of an average individual. Surprisingly, <1% of dermal DCs occupied lymphatics in freshly isolated skin. Dermal DCs rapidly accumulated within lymphatics, but Mφ remained fixed in skin explants cultured ex vivo. The leukocyte architecture observed in normal skin was distorted in inflammation and disease. These studies illustrate the micro-anatomy of dermal leukocytes and provide further insights into their functional organization.

Langerhans cells in the development of skin cancer: a qualitative and quantitative comparison of cell markers in normal, acanthotic and neoplastic ovine skin

The distribution of Langerhans cells in normal, acanthotic and neoplastic ovine epithelium was examined using the enzyme marker Acetylcholinesterase (AchE) and monoclonal antibodies (MoAb) to CD1 (20.27) and MHC Class II (49.1 and 28.1) molecules. In normal skin, where Langerhans cells were regularly spaced within the basal layer, qualitative observations and direct pairwise testing showed that AChE was superior to the MoAb in detecting these cells. Significantly more (P < 0.01) dendritic cells were also detected with MoAb 49.1 than MoAb 20.27 or 28.1, suggesting differential expression of MHC Class II subsets and the presence of CD1- MHC Class II+ granule- dendritic cells in sheep analogous to indeterminate cells of man. In acanthotic skin, compared to normal skin, Langerhans cells were less numerous, irregular and more suprabasal in distribution and their morphology was occasionally swollen and indistinct. No difference was seen in the ability of AChE and MoAb in detecting Langerhans cells, however pairwise testing of markers did demonstrate that significantly more (P < 0.05) cells without dendritic processes were stained with MoAb 49.1 than with 20.27 or 28.1. In all squamous cell carcinomas examined dendritic cells that stained for AChE, CD1 or MHC Class II antigens were concentrated at the peripheral areas of neoplastic epithelium. Many dendritic cells were detected with MoAb to MHC Class II antigens, whereas CD1 and AChE positive dendritic cells were rare in tumor bearing tissue. The quantitative differences in the immunohistochemical staining of Langerhans cells between normal, acanthotic and neoplastic epithelium were consistent with ultrastructural studies. When compared with those of a newborn lamb, which had had very little exposure to antigens or ultraviolet radiation (UVR), the Langerhans cells of the aged sheep were deformed and contained far fewer Birbeck granules. The abnormalities were progressively more severe in acanthotic and neoplastic skin. These observed changes may have resulted from UVR induced damage and may be indicative of impaired function involved in the development of skin cancer.

Immunomorphological and ultrastructural characterization of Langerhans cells and a novel, inflammatory dendritic epidermal cell (IDEC) population in lesional skin of atopic eczema

We investigated epidermal cell suspensions prepared from lesional and nonlesional atopic eczema skin, other inflammatory skin conditions, and normal human skin for high-affinity IgE receptor (Fc epsilon RI) expression on dendritic CD1a cells by quantitative flow cytometric analysis. A single CD1a bright/CD1b neg/Fc epsilon RI dim/CD23 neg/CD32 dim/HLA-DR bright/CD36 neg population was found in normal skin. In contrast, lesional skin of atopic eczema and other inflammatory skin diseases harbored variable proportions of two distinct CD1a populations. Both populations exhibited typical ultrastructural features of Langerhans cells, but the second one lacked Birbeck granules and was unreactive to the Birbeck granule-specific LAG antibody. Both populations differed phenotypically: classical Langerhans cells were CD1a bright/CD1b neg/Fc epsilon RI dim/CD23 neg/CD32 dim/HLA-DR bright/CD36 dim, while the second population was CD1a dim/CD1b dim/Fc epsilon RI bright/CD23 dim/CD32 dim/HLA-DR bright/CD36 bright. The highest Fc epsilon RI expression was found on the second CD1a population in lesional atopic eczema skin. Furthermore, Fc epsilon RI expression on CD1a cells correlated significantly with the serum IgE level of the patients. Thus, a distinct population of CD1a inflammatory dendritic epidermal cells different from classical Langerhans cells appears in the epidermis of lesional skin and is subjected to specific signals leading to the upregulation of Fc epsilon RI in atopic eczema skin.

Dynamic nature and function of epidermal Langerhans cells in vivo and in vitro: a review, with emphasis on human Langerhans cells

Epidermal Langerhans cells (LC) are Birbeck granule-containing bone-marrow-derived cells, which are located mainly in the suprabasal layer of the epidermis. They can be readily identified by their strong expression of CD1a and MHC class II molecules. In addition to these 'classical' properties, an extensive phenotypic profile of normal human LC, summarized in this review, is now available. The powerful capacity of LC to activate T lymphocytes is clearly documented and, to date, LC are recognized as the prominent antigen-presenting cells of the skin immune system. They are generally believed to pick up antigens encountered in the epidermis and to migrate subsequently from the epidermis to the skin-draining lymph nodes. Upon arrival in the paracortex of lymph nodes, the antigen-laden LC transform into interdigitating cells and they present antigen to naive T lymphocytes in a MHC class II-restricted fashion; this results in the generation of antigen-specific immune responses. It has also been demonstrated that transformation of LC into interdigitating cells occurs when LC are cultured in vitro. Both in vivo and in vitro studies have indicated that properties of LC, such as phenotype, morphology and the stimulatory potential to activate T lymphocytes, are dependent on the local microenvironment in which the LC reside. The essential role of LC in the induction of contact allergic skin reactions and skin transplant rejection is well established.

Subpopulation of murine epidermal Langerhans cells identified by lectin-binding sites

Lectin-binding profiles of epidermal Langerhans cells (LCs) were investigated in three strains of mice using immunofluorescence procedures. Three lectin-binding profiles were observed in each strain of mice. Most epidermal LCs reacted with concanavalin A (Con A) and Ricinus communis agglutinin 1 (RCA-1), whereas none reacted with Dolichos biflorus agglutinin (DBA). Peanut agglutinin (PNA) and wheat germ agglutinin (WGA) reacted with some of the epidermal LCs. These binding profiles were similar from site to site of the body in all strains of mice. We also investigated the lectin-binding profiles of epidermal Ia positive (Ia+) cells migrating into the grafted skin up to 165 days after transplantation. BALB/c (H-2d) murine skin was grafted onto the back of (C3H/He x BALB/c)F1 (H-2k x H-2d) mice. The percentages of migrating I-A+ epidermal cells reactive with PNA and WGA were different from those of the normal epidermis soon after grafting and reached a normal level at 43 days after grafting. Our results demonstrated that there is a heterogeneous population of epidermal LCs defined by lectin-binding profiles.

Antigen presentation in patients with recrudescent orofacial herpes simplex virus infections

Recovery from epidermal herpes simplex virus (HSV) infection depends primarily on development of an effective cell-mediated immune response, possibly generated following antigen (Ag) presentation by epidermal cells (EC). The ability of EC to present HSV Ag was investigated in 12 subjects with occasional recrudescent facial HSV infections. All had circulating HSV specific antibodies and cell-mediated immunity to the virus. Peripheral blood mononuclear cell suspensions, depleted of antigen presenting cells (APC) by glass adherence and then enriched for T cells by adsorption on nylon wool columns, did not proliferate in response to HSV Ag. Both EC suspensions, prepared from suction blister roofs, and glass-adherent peripheral blood mononuclear cells (AC) preincubated with ultraviolet-inactivated HSV, reconstituted the T-cell proliferative response to HSV. EC were more efficient than AC at presenting HSV Ag to T cells. Depletion of CD1+ cells from EC suspensions by cell sorting reduced their ability to present HSV Ag and augmentation of CD1+ cell numbers supplemented it. Preincubation of EC or AC with monoclonal antibodies to major histocompatibility complex class II antigens DP, DQ or DR, blocked the lymphoproliferative response to HSV Ag. Evidence was obtained that cells co-ordinately expressing products of the DP, DQ and DR loci are involved in presentation of HSV Ag by both EC and AC.

Human thymic dendritic cell-thymocyte association: ultrastructural cell phenotype analysis

In rodent thymus, associations between dendritic cells (DC) and thymocytes have been suggested to be implicated in differentiation and/or maturation processes. In this study, we report intimate associations formed between human thymic DC and thymocytes in culture and we analyze their ultrastructural cell phenotype. Observations by phase contrast microscopy showed that DC present long and thin dendrites and bind many thymocytes. Transmission (TEM) and scanning electron microscopy (SEM) revealed that both cellular populations were in close connection and tight membrane contact could be observed. The phenotype of DC and attached thymocytes was characterized with a series of monoclonal antibodies by protein A-gold TEM and SEM immunolabelings. Quantitative evaluation of immunolabeling (number of gold granules/microns of cellular membrane) suggests the presence of two subpopulations of CD1+ thymic DC (strong and weak), whereas this discrepancy is not observed in DR+ and CD4+ DC populations. On the other hand, the majority of thymocytes bound to DC strongly express the CD1, CD4, CD8 and CD2 antigens and weakly the CD3 antigen, indicating that they represent double-positive immature thymocytes. Uniform distribution of DC and thymocytes membrane antigens was confirmed with a backscattered SEM study. This morphological and immunolabeling TEM and SEM analysis demonstrates that human thymic DC may form associations with CD4+CD8+CD3weak thymocytes and raises questions about their physiological relationship.

Flow cytometric analysis and sorting of HLA-DR+CD1+ Langerhans cells

There is a considerable need for reliable methods for enumeration and enrichment of Langerhans cells (LCs), since they continue to be the subject of intensive investigation in normal and diseased skin. It has been claimed that standard labelling with either anti-HLA-DR or OKT6 antibodies alone may fail to identify potentially important subsets of LCs with the phenotypes HLA-DR+CD1- and HLA-DR-CD1+. We report here on flow cytometric analysis of suction blister-derived normal epidermal cell (EC) suspensions, double stained with phycoerythrin-conjugated anti-HLA-DR and fluoresceinated OKT6. In seven separate experiments, no evidence for the existence of either HLA-DR+CDI- or HLA-DR-CDI+ ECs was obtained. We found that HLA-DR+CDI+LCs, which constituted a mean of 2.5% (+/- 0.3 SEM) of all ECs, could be readily identified on the basis of fluorescence, and that their light scatter characteristics were those of moderately sized cells of low granularity. We further describe our method for flow cytometric enrichment of such HLA-DR+CDi+ LCs for functional studies, based on selection on both fluorescence and light scatter criteria. Enrichment is to greater than 90% purity, and the method is applicable to the small number of ECs (approximately 1 x 10(6] obtained from a suction blister.

Flow cytometrically-sorted residual HLA-DR+T6+ Langerhans cells in topical steroid-treated human skin express normal amounts of HLA-DR and CD1a/T6 antigens and exhibit normal alloantigen-presenting capacity

Topical corticosteroids decrease the number of HLA-DR+T6+ Langerhans cells (LCs) and the antigen-presenting capacity of epidermal cells (ECs). We have investigated the properties of residual HLA-DR+T6+ LCs in steroid-treated human skin. Flow cytometric analysis revealed that clobetasol propionate 0.05% applied twice daily for 7 d reduced the percentage of HLA-DR+T6+ LCs in EC suspensions to 46% of control (from a mean percentage +/- sem of 2.49 +/- 0.30 in control skin to 1.15 +/- 0.22 in steroid-treated skin), but did not significantly alter the relative amounts of HLA-DR and CD1a/T6 antigens per individual HLA-DR+T6+ cell. HLA-DR+T6- and HLA-DR-T6+ cells were not detected in either group. Steroid therapy significantly decreased the allostimulatory capacity of unsorted ECs. By contrast, in parallel experiments in which the same EC suspensions were greatly enriched (85% to 90%) for HLA-DR+T6+ LCs by flow cytometric sorting, the allostimulatory capacity of purified LCs from steroid-treated skin was not significantly different from control. Residual HLA-DR+T6+ LCs, which preserve their antigenic markers and alloantigen-presenting function, may be relatively unaffected because they have only recently immigrated into the epidermis, or they may represent a subgroup of steroid-resistant LCs. Alternatively, given the dose response relationship between topical steroid potency and decrease in HLA-DR+T6+ LC numbers, the apparent steroid resistance of residual HLA-DR+T6+ LCs may reflect heterogenity in the density of expression of LC steroid receptors.

Simultaneous colloidal gold immunoelectronmicroscopy labeling of CD1a, HLA-DR, and CD4 surface antigens of human epidermal Langerhans cells

The simultaneous demonstration of three surface antigens of Langerhans cells (LC) within LC-enriched fresh epidermal cell suspensions from normal human skin was achieved, by means of a triple immunogold (IG) staining, using commercially available monoclonal antibodies (moAb) and immunoreagents, in a simple pre-embedding immunoelectronmicroscopy (IEM) procedure. As a result, suspended LC were triple-stained as follows: gold particles of 40 nm revealed the CD1 a antigen; gold particles of 20 nm revealed the HLA-DR antigen; and gold particles of 5 nm revealed the CD4 antigen. All the observed epidermal Birbeck granule-bearing LC were triple IG stained, thus simultaneously expressing the three surface differentiation antigens, which are therefore different from but coexisting with each other. The present investigation assesses the constant simultaneous expression by Birbeck granules bearing LC of not only CD1a and HLA-DR antigens, but also CD4 antigen. The occurrence is therefore excluded of both CD1a-positive HLA-DR-negative LC subpopulation and CD4-negative LC subpopulation, presumably due to the different sensitivity of the various procedures performed. The hypothetical occurrence of CD4-positive, CD1a-, and/or HLA-DR-negative LC subpopulations is ruled out. This study reaffirms indeed the high specificity and sensitivity of the IG-IEM method for a precise detection of the cell surface antigens of LC, and states the suitability of the IG labeling even for accurate multiple IEM stainings of LC.

Xanthoma disseminatum: a rare condition with non-X, non-lipid cutaneous histiocytopathy

We describe a 35-year-old man with cutaneous, mucosal, pulmonary, and bone involvement of xanthoma disseminatum. The 7-year course of the disease and the results of light and electron microscopic and immunocytochemical examinations are presented.

Effects of topical corticosteroid therapy on Langerhans cell antigen presenting function in human skin

We have investigated the mechanisms by which topical corticosteroids modulate cutaneous immune reactions in man. Volunteers applied clobetasone butyrate 0.05% (Eumovate; EV), betamethasone valerate 0.1% (Betnovate; BV), clobetasol propionate 0.05% (Dermovate; DV), and control vehicles twice daily to forearm skin for 7 days. Steroid therapy significantly decreased the number of HLA-DR/T6 (CD1a) positive Langerhans cells (LCs) per mm2 in suction blister-derived epidermal sheets, expressed as a mean percentage of controls, as follows: EV 69.2%; BV 67.3%; DV 37.8%. LC antigen presenting capacity was determined in the allogeneic and autologous epidermal cell-lymphocyte reactions. The LC-dependent allostimulatory capacity of epidermal cells, expressed as a mean percentage of controls, was also significantly reduced by steroid therapy: EV 45.1%; BV 41.9%; DV 23.4%. Following therapy with clobetasol propionate 0.05%, the capacity of epidermal cells to present tetanus toxoid to, and to augment concanavalin A mediated lymphocyte stimulation of, autologous lymphocytes was reduced to 33.6% and 19.7% respectively of controls. Depression of epidermal cell allostimulatory capacity was not the result of a steroid-induced decrease in the production of epidermal cell-derived thymocyte activating factor (ETAF)/interleukin 1 by keratinocytes, since it could not be reversed by addition of exogenous interleukin 1. Indomethacin, added to block any potential prostaglandin synthesis during the culture period, did not restore the allostimulatory capacity of epidermal cells from steroid-treated sites. Addition of epidermal cells from DV-treated sites depressed the capacity of control epidermal cells to stimulate lymphocytes in the allogeneic epidermal-lymphocyte reaction. Our results demonstrate that the anti-inflammatory action of topical corticosteroids in man is associated not only with a reduction in the number of HLA-DR/T6 positive LCs, but also with a marked decrease in Langerhans cell-dependent T lymphocyte activation. The effects of the different steroids on both of these parameters correlated with their potency as determined in the standard occlusive vasoconstrictor assay. Topical corticosteroids are widely used for the treatment of inflammatory skin disorders, and inhibit not only the elicitation phase, but also the induction phase, of allergic contact dermatitis reactions.(ABSTRACT TRUNCATED AT 400 WORDS)

Sequential immunophenotypic study of lymphoid infiltrate in allergic and irritant reactions

Sequential biopsies (4-72 h) of early allergic and irritant patch test reactions have been examined immunohistologically for reactivity with 19 monoclonal antibodies against antigens on lymphoid cells in order to investigate the nature/origin of the infiltrating lymphoid cells and assess their state of activation/proliferation. The composition of the infiltrates was similar in allergic and irritant reactions and consisted of T-lymphocytes of helper/inducer types in association with T-cell accessory cells, i.e., Langerhans cells and HLA-DR-positive macrophages. No differences in expression of T-cell or macrophage associated antigens were seen in early as opposed to late biopsies. In contrast, the proportion of cells positive for markers associated with activation (interleukin-2 receptor) or proliferation (transferrin receptor, the Ki-67 nuclear antigen) of lymphoid cells was found to increase with time in both types of reaction. These data substantiate the view that T-cell immune reactions are implicated in both allergic and toxic patch test lesions, and indicate that the lymphocytes in the infiltrates are activated and proliferate.

Growth and differentiation of human epidermal cultures used as auto- and allografts in humans

Human keratinocytes from small skin specimens were grown on mouse 3T3 cell feeder layers into epidermal sheets free from Langerhans cells and MHC class II antigen. These were found to be suitable for the permanent coverage of wounds when used as autografts or allografts. We report here the ultrastructural differentiation of this cultured epidermis after grafting onto autologous or allogeneic recipients. The cultured epidermis was a thin but multilayered Malpighian epithelium composed of keratinocytes at different stages of differentiation. The dermo-epidermal basement membrane was newly synthesized during the first few days following transplantation onto de-epidermized wounds. The analysis of keratins and examination of various keratinocyte membrane antigens by immunofluorescence indicated that full terminal epithelial differentiation was only achieved after in vivo transplantation of the cultured epidermis. Langerhans cells, absent in cultures, progressively colonized the grafts, while melanocytes, not detectable in sections of the cultures, were identified among the keratinocytes 2 weeks after grafting.

Epidermal cell-derived lymphocyte differentiating factor (ELDIF) inhibits in vitro lymphoproliferative responses and interleukin 2 production

We have examined the biologic characteristics and immunologic properties of epidermal cell-derived lymphocyte differentiating factor (ELDIF), a lymphocyte differentiating factor produced by cultured human keratinocytes. The ELDIF was semipurified by a gel filtration procedure. This factor, which is distinct from prostaglandins, epidermal cell-derived thymocyte activating factor (ETAF), and the well-known thymic hormones (thymulin, thymopoietin, and thymosin alpha 1) did not exhibit any interleukin (IL)-1, IL-2, or IL-3 activity. It strongly inhibited in vitro lymphoproliferative responses of normal mouse spleen cells to phytohemagglutinin, concanavalin A, and lipopolysaccharide. This dose-dependent phenomenon was associated with a suppression of IL-2 production rather than any toxic effect. It can be concluded that ELDIF, a product of human epidermal cells, which displays in vitro T-cell differentiation and regulatory activities, could be of major importance in vivo in the control of cutaneous inflammatory reactions.

Immunohistological analysis of the lymphoid infiltrate in cutaneous malignant melanomas

The immunological phenotypes of the lymphoid cells in 39 cutaneous malignant melanomas have been investigated by staining cryostat sections with a panel of 20 monoclonal antibodies against lymphoid cells and their subsets. Staining was performed by the alkaline phosphatase: anti-alkaline phosphatase (APAAP) method in which the substrate label (red) is easily distinguishable from melanin. The lymphoid infiltrates had an essentially identical composition in all cases, consisting of T-lymphocytes associated with both Langerhans cells and HLA-DR-positive tissue macrophages. B-lymphocytes and natural killer cells were either absent or only present in low numbers. The ratio between T8 (suppressor/cytotoxic) and T4 (helper/inducer) lymphocytes varied and showed no correlation with melanoma subtype, level of invasion or magnitude of lymphocytic response. Examination for markers associated with T-cell activation and/or with cell proliferation revealed that all lesions contained HLA-DR-positive T-lymphocytes, whereas expression of the transferrin receptor and the interleukin-2 receptor (Tac-antigen) occurred mainly in melanomas with a significant inflammatory infiltrate. These data support the concept that malignant melanomas are capable of evoking autologous T-cell immune reactions.

HLA-D region antigen expression by human epidermal Langerhans cells

We have systematically examined HLA-D region antigen expression by normal human epidermal Langerhans cells with an improved double label indirect immunofluorescence technique in order to better understand the immunologic potential of this human interstitial dendritic cell type. The results of this study which differ somewhat from earlier observations strongly suggest that 100% of OKT-6-positive epidermal Langerhans cells constitutively express HLA-DQ and HLA-DP as well as HLA-DR molecules. Since HLA-DQ expression has been positively correlated with the ability to present nominal antigen, our findings would suggest the possibility that epidermal Langerhans cells, like other members of the human dendritic cell series, might be more efficient than monocytes at nominal antigen presentation since only about 50% of peripheral blood monocytes express HLA-DQ molecules.

Defined in situ enumeration of T6 and HLA-DR expressing epidermal Langerhans cells: morphologic and methodologic aspects

An essential prerequisite for the in situ enumeration of epidermal Langerhans cells (LCs) is the unequivocal identification of the desired cell type. We have examined over 250 cryostat sections of normal human skin to analyze morphologic and methodologic problems underlying the quantification of epidermal LCs, defined by anti-T6 (OKT6) and anti-HLA-DR (OKIal) immunoperoxidase staining. Our findings show that OKT6 reactivity of dendritic processes in cross-sectioned epidermis yields microscopic images which are not easy to analyze objectively. The morphology that we find leads us to categorize dendritic cells into 3 arbitrary types of T6+ LC profiles. In addition we describe criteria for the assessment of OKT6 staining patterns relating to the dendritic state of epidermal LCs. Preliminary quantitative data on this issue are discussed in relation to: epidermal thickness; the thickness of skin tissue sections; and the discrepancy between the number of T6+ and HLA-DR+ LCs. We hope that the principles outlined in this report may serve to overcome potential methodologic problems with quantitation of T6+ epidermal LCs in skin sections.

Loss of allogeneic T-cell activating ability and Langerhans cell markers in human epidermal cell cultures

Human Langerhans cells are the only epidermal cells that express the T6 and HLA-DR antigens and are responsible for the in vitro allogeneic T-cell proliferative responses in the mixed skin cell lymphocyte reaction (MSLR). To investigate the presence of Langerhans cells in normal human epidermal cell cultures, epidermal cell suspensions obtained from normal human skin specimens and from the subsequent epidermal cell cultures were analyzed by indirect immunofluorescence for the presence of T6 and HLA-DR determinants. In parallel, MSLRs were conducted with suspensions of cultured epidermal cells as stimulatory cells. These studies present evidence that when human epidermal cells are grown in culture, they loose both the ability to stimulate the proliferation of allogeneic T lymphocytes in vitro and their expression of HLA-DR and T6 antigens. The T6 antigens were lost during the first 2 weeks of culture, while HLA-DR determinants were still expressed by a small number of cells and were progressively lost through duration of cultures. The loss of HLA-DR antigens closely paralleled the progressive inability of human epidermal cells in culture to stimulate allogenic T cells in MSLR.

Recent advances of ultrastructural immunocytochemistry of epidermal Langerhans cells

Using electron microscopy, the immunological visualization of the membrane antigens of Langerhans cells (LC) can be performed by immunoperoxidase and immunogold techniques. The immunoperoxidase labelling permits the identification of only one antigen and the observation of qualitative variations of surface antigens. The immunogold method allows the identification of one antigen or simultaneously two or three surface antigens using gold particles of various sizes. This technique can be used to quantify the surface density of antigens on the cell membrane. The simultaneous identification of different surface antigens can be correlated with the ultrastructural characteristics of the cells. Using this technique we have recently demonstrated the existence of LC subsets in normal epidermis, and the presence of circulating T6-positive cells in normal subjects. In addition, a very low density of T4 antigenic sites on the LC membrane surface was observed. Several problems of a double-labelling immunogold technique related to steric hindrance and current artifacts are discussed.

Langerhans cell induced cytotoxic T-cell responses against normal human epidermal cell targets: in vitro studies

We investigated the role of class II MHC (HLA-DR Ia-like) antigen-bearing Langerhans cells in the in vitro generation of human alloreactive cytotoxic T lymphocytes (CTL) directed against epidermal cells (EC). Normal EC in suspensions (from reconstructive surgery specimens) and anti-DR monoclonal antibody plus complement (C')-treated EC were used to stimulate peripheral blood (PB) T cells (T cells allogeneic or autologous to EC) in a classical 6-day human mixed skin cell-lymphocyte culture reaction (MSLR). CTL responses were then tested in 51Cr release assays against cultured EC (EC grown on collagen-coated plates in parallel to MSLR). CTL responses to EC were observed only after allogeneic MSLR and when targets and EC used in MSLR were from the same donor. They were comparable in magnitude to those seen in parallel studies using PBL from the same donor as the stimulating EC as target cells. They were abolished when EC used in MSLR were depleted in class II MHC Langerhans cells (preincubation of EC suspensions with anti-DR + C'). These data show: (a) alloreactive CTL to human normal EC may be generated in MSLR, as previously shown in animals; (b) the MSLR is an in vitro model of primary immunization against EC; (c) Langerhans cells are necessary for the generation of cell-mediated cytotoxicity reactions occurring against epidermal cells.

The lymph node in mycosis fungoides: a light and electron microscopy and immunohistological study supporting the Langerhans' cell-retrovirus hypothesis

This paper describes the light and electron microscopy and monoclonal antibody findings in the lymph nodes of nine patients with mycosis fungoides. Four cases showed dermatopathic change characterized by close association between small convoluted T4 lymphocytes and T6 antigen-presenting cells (Langerhans' and indeterminate dendritic cells) in the sinuses and paracortical zones. The T4:T8 ratio was between 3 and 5:1. One case showed dermatopathic change but included large convoluted T4 lymphocytes and occasional T10 lymphocytes. The T4:T8 ratio was 4:1. The antigen-presenting cells were mostly T6 negative (interdigitating reticulum cells). One case showed extensive paracortical expansion by small and large convoluted T4 lymphocytes. The T4:T8 ratio was 20:1. Few B lymphocytes and antigen-presenting cells were present. Two cases showed partial and one case total effacement by atypical lymphoid tissue. This included small and large convoluted T4 lymphocytes and T4 immunoblasts. The T4:T8 ratios were between 30 and 40:1. The changes in their antigen-presenting cell population were complex. Langerhans' cells in one case generally failed to express T6 antigen and in two displayed histiocyte features. In one case, both immature and budding type C retrovirus-like particles were identified in Langerhans cells. One extracellular mature type C virus-like particle was identified in another case. No ultrastructural distinction could be made between similarly sized primary lysosomes and possible intracytoplasmic mature type C retrovirus particles. These findings support the hypothesis that mycosis fungoides may represent an altered dermatonodal cycle resulting from an interaction between retrovirus, Langerhans' cells and lymphocytes.

Immunogold technique applied to simultaneous identification of T6 and HLA-DR antigens on Langerhans cells by electron microscopy

A double-labeling immunogold technique in electron microscopy and specific monoclonal antibodies to surface antigens of Langerhans cells (OKT6 and BL2) were applied to assess directly the coexpression of two cell surface antigens (T6 and HLA-DR antigens) in a heterogeneous epidermal cell suspension. Electron microscopic examination of double-labeled cells revealed that all Birbeck granule-containing Langerhans cells bound OKT6 and BL2. The preparation of markers with colloidal gold particles and the procedure for double labeling are described. Several problems related to the steric hindrance and current artifacts are illustrated by micrographs and also discussed.

Human epidermal cell-induced generation of alloreactive cytotoxic T-lymphocyte responses against epidermal cells. Requirement for DR-positive Langerhans cells

Human epidermal cells act as stimulators in the mixed-skin cell lymphocyte culture reaction (MSLR). To analyse the generation in MSLR of alloreactive cytotoxic T lymphocytes (CTL) in cell-mediated cytolysis of human epidermal cells. a phenomenon suggested by various observations of skin inflammatory processes in vivo, 18-h 51Cr-release assays against epidermal cells cultivated on collagen-coated plates (epidermal cells autologous to the stimulator cells in MSLR) were conducted after allogenic human MSLR. To analyse the role of human Langerhans cells and related epidermal dendritic cells, which are the only cells expressing the DR-Ia-like (class II) antigens in normal epidermis and in suspensions of normal epidermal cells, MSLR and CTL assays were conducted with, as stimulator cells, suspensions of normal human epidermal cells as controls, and, in parallel, suspensions of epidermal cells after preincubation with anti-class II monoclonal antibody and complement. The generation of alloreactive CTL to epidermal cells occurred only after allogenic MSLR and when targets and stimulator cells were from the same donor; it was abolished when epidermal cell suspensions used in MSLR were depleted in HLA-DR-expressing cells. These findings demonstrate that an epidermal cell-induced generation of cell-mediated cytotoxicity to human epidermal cells may occur in vitro. Langerhans cells and other class II antigen-expressing epidermal cells (dendritic indeterminate cells) are necessary for an optimal in vitro sensitization in MSLR and the subsequent generation of alloreactive CTL towards epidermal cells in man.

The semi-quantitative distribution of T4 and T6 surface antigens on human Langerhans cells

We have used indirect immunogold electron microscopy to compare the respective density of cell membrane determinants revealed by OKT6 and OKT4 monoclonal antibodies on normal human Langerhans cells (LC): 12.9 +/- 3.5 gold granules were noted per cell section on OKT4-positive LC whereas 236.8 +/- 23.5 granules were counted per cell section on OKT6-reactive cells. These results confirm that human LC react with OKT4 antibody and they demonstrate a marked quantitative difference on LC surface between the antigenic determinants recognized by OKT6 and OKT4 antibodies.

Human Langerhans cells in epidermal cell culture, in vitro skin explants and skin grafts onto "nude" mice

In order to find a model system which best preserves human Langerhans cells (LC) outside of the human body, three possibilities were examined: epidermal cell culture, skin explants, and skin grafts onto "nude" mice. Using OKT-6 and anti-HLA-DR monoclonal antibodies, we quantified LC in epidermal sheets or epidermal cell cultures. All observations were carried out over a period of 4 weeks. We found that under epidermal cell culture conditions, LC rapidly disappeared, to the extent that after 10 days only rare HLA-DR-positive cells could be observed. In contrast, in the presence of intact dermis (explants and grafts), 60%-80% of the original number of LC, morphologically unchanged, dendritic and OKT-6 and HLA-DR-positive, were seen. These findings suggest that human LC are either a long-lived cell population or else can proliferate locally. The systems studied may be a useful tool for future investigation of LC function.

In vitro studies of epidermal antigen-presenting cells. The mixed skin lymphocyte reaction: an in vitro model for the generation of alloreactive cytotoxic T cells by human epidermal cells

Langerhans cells and indeterminate cells are the unique antigen-presenting epidermal cells participating in human lympho-epidermal interactions. They bear class II HLA-DR molecules, can substitute for macrophages in antigen presentation, induce a T-cell proliferative response to antigens and haptens in sensitized donors, and are necessary for alloantigen T-cell activation and generation of alloreactive cytotoxic T cells in vitro. Indirect immunofluorescence and immunogold electron microscopy on class II positive epidermal cell enriched suspensions (panning, FACS) indicated two populations of DR-positive epidermal cells: strongly DR-positive cells (25-30, 8% of positive epidermal cells) and faintly DR-positive cells, with a density of surface DR sites of respectively 5 X 10(5) and 1 X 10(5). Most Langerhans cells are among this second group while indeterminate cells are usually strongly DR-positive. OKT6-labelled cells were only typical Langerhans cells.

Quantitative evaluation of two distinct cell populations expressing HLA-DR antigens in normal human epidermis

HLA-DR antigens are expressed only by Langerhans cells (LC) and indeterminate cells (IC) in normal human epidermis. Indirect immunofluorescence and ultrastructural immunogold labelling were used to study the HLA-DR expression by means of two anti-DR monoclonal antibodies (MCA). Freshly dispersed DR-positive epidermal cells expressed different densities of DR antigens on their membrane surface. Approximately 25% of DR-positive cells were strongly labelled by anti-DR-MCA and 75% were weakly stained. After 18 h in complete culture medium before labelling no significant difference in these percentages was observed. The lymphoid-like LC-enriched cells obtained by Ficoll-Hypaque centrifugation also had two populations of DR-positive cells: strongly labelled cells (30.8%) and weakly labelled cells (69.2%). DR-positive cells may be divided into two types according to the density of DR sites on their cell membrane: (I) type DR+ shows weak surface labelling by gold particles (8.8 +/- 3.0 gold particles/micron) and has cytoplasmic Birbeck granules, identifying such cells as typical Langerhans cells; (2) type DR shows strong membrane immunogold labelling (38.9 +/- 4.6 gold particles/micron) and may or may not contain Birbeck granules. The gold particles bound to the cell membrane were used to quantify the number of HLA-DR sites expressed on each cell type: 1 X 10(5) sites on DR+ cells and 5 X 10(5) on DR cells.

In vitro effect of UV radiation on immune function and membrane markers of human Langerhans cells

Human Langerhans cells (LC) are located in the epidermal tissue which is naturally accessible to UV irradiation. They may be the first immunocompetent cells exposed to its effect. In the present study, the epidermal tissue was dissociated with trypsin, and epidermal cell (EC) suspensions, which contain keratinocytes, melanocytes, and LC were irradiated with UVB (10 or 20 mJ/cm2). After irradiation LC retained their surface determinants: T-6 and HLA-Dr. In addition, their number did not decrease during 3 days of culture following UVB exposure as compared with nonirradiated EC cultured in parallel. On the contrary, UV irradiation of EC resulted in decreased lymphocyte-stimulating ability in a mixed skin cell-lymphocyte culture reaction (MSLR). EC used directly after irradiation in MSLR induced about half the lymphocyte response compared to nonirradiated EC. After 24-h culture, the irradiated EC did not produce any lymphocyte response, whereas the 48-h cultures showed a slight lymphocyte stimulation. At 72 h the cultures from irradiated and nonirradiated EC showed similar responses in MSLR. The doses of UV radiation which decreased MSLR responses did not affect EC viability and did not significantly reduce their DNA content. It is suggested that under the experimental conditions used in this study the defect induced by UV irradiation was essentially functional and was the result of the transient inhibition of the antigen processing function of LC rather than of an alteration in membrane antigen expression (T-6 and HLA-Dr).

Enrichment of human epidermal Langerhans dendritic cells

Langerhans cells (LC) were enriched from a human epidermal cell (EC) suspension by a rosette-forming technique. First EC were sensitized with the monoclonal antibody OKT6, and then they were mixed with ox erythrocytes (ORBC) coated with affinity-purified rabbit IgG anti-mouse IgG antibodies. Rosette-forming LC were then separated from non-rosetting EC by means of Percoll flotation. After hypotonic lysis of the ORBC, the cells obtained had a viability greater than 90%, and 67-98% of the viable cells were OKT6-positive. In functional studies the enriched cells were strongly stimulatory for allogeneic lymphocytes and were able to function as antigen-presenting cells for the T-cell response to the soluble antigen purified protein derivative.

Role of HLA-DR bearing Langerhans and epidermal indeterminate cells in the in vitro generation of alloreactive cytotoxic T cells in man

Human epidermal cells (EC) act as stimulator cells in the mixed-skin cell lymphocyte culture reaction (MSLR). To analyze the role of human epidermal Langerhans cells (LC) and indeterminate cells (IC), which are the only cells expressing the DR-Ia-like antigens in normal epidermis, in the generation of alloreactive cytotoxic T lymphocytes (CTL) in cell-mediated cytolysis, 18-hr 51Cr-release assays against PBL targets (targets autologous to stimulator EC) were conducted after allogeneic human MSLR. MSLR and CTL assays were conducted with, as stimulator cells, suspensions of normal human EC as controls, and EC after: (1) preincubation with anti-HLA-DR or OKT6 (specific for LC in EC suspension) monoclonal antibodies; (2) panning, a monolayer technique used to deplete EC suspensions in OKT6 or DR-positive cells. The generation of alloreactive CTL was found to occur only after allogeneic MSLR and when targets and stimulator cells were from the same donor; it was reduced by EC incubation: cytotoxic activity 26.66 +/- 3.84 (controls); 8.8 +/- 3.6 and 7.7 +/- 3.7 (EC incubated with OKT6 or anti-DR, respectively); it was reduced or abolished when the EC used in MSLR were depleted in OKT6 or DR-positive cells by panning. These findings demonstrate that human LC and IC are necessary for an optimal in vitro sensitization in MSLR and the subsequent in vitro generation of alloreactive CTL in man.

Ultrastructural immunogold labelling of human Langerhans cells enriched epidermal cell suspension

Colloidal gold particles are well suited as markers in electron microscopy. Indirect immunogold staining was used to identify cell membrane antigens defined by monoclonal antibodies OKT6 and BL6 on human Langerhans cells (LC) in suspensions. Isolated epidermal cells were obtained by skin trypsinization and enriched or depleted in OKT6 positive on BL6 positive LC using the panning method: incubation of OKT6 or BL6 preincubated cells on immunoglobulin coated dishes. Indirect immunogold staining was then performed after prefixation in 2% paraformaldehyde. In LC enriched suspensions, only LC exhibited a specific membrane labelling with OKT6 or BL6 recognized by the presence of small evently distributed gold granules. Neither Birbeck granules, nor other cytoplasmic organelles, were labelled. No other epidermal cells were found positive. In LC depleted suspensions, no labelling was observed. Immunogold labelling on LC enriched suspensions after panning is now in progress for the qualitative evaluation and the quantitative analysis of cell surface constituents and antigens expressed by human dendritic epidermal cells.