The phenotypic spectrum of histiocytosis X cells

The distribution of immunomodulatory cells in the lungs of patients with idiopathic pulmonary fibrosis

We have characterized the immune system involvement in the disease processes of idiopathic pulmonary fibrosis in novel ways. To do so, we analyzed lung tissue from 21 cases of idiopathic pulmonary fibrosis and 21 (non-fibrotic, non-cancerous) controls for immune cell and inflammation-related markers. The immunohistochemical analysis of the tissue was grouped by patterns of severity in disease pathology. There were significantly greater numbers of CD68(+) and CD80(+) cells and significantly fewer CD3(+), CD4(+), and CD45RO(+) cells in areas of relatively (histologically) normal lung in biopsy samples from idiopathic pulmonary fibrosis patients compared with controls. In zones of active disease, characterized by epithelial cell regeneration and fibrosis, there were significantly more cells expressing CD4, CD8, CD20, CD68, CD80, chemokine receptor 6 (CCR6), S100, IL-17, tumor necrosis factor-α, and retinoic acid-related orphan receptors compared with histologically normal lung areas from idiopathic pulmonary fibrosis patients. Inflammation was implicated in these active regions by the cells that expressed retinoid orphan receptor-α, -β, and -γ, CCR6, and IL-17. The regenerating epithelial cells predominantly expressed these pro-inflammatory molecules, as evidenced by co-expression analyses with epithelial cytokeratins. Macrophages in pseudo-alveoli and CD3(+) T cells in the fibrotic interstitium also expressed IL-17. Co-expression of IL-17 with retinoid orphan receptors and epithelial cytoskeletal proteins, CD68, and CD3 in epithelial cells, macrophages, and T-cells, respectively, confirmed the production of IL-17 by these cell types. There was little staining for forkhead box p3, CD56, or CD34 in any idiopathic pulmonary fibrosis lung regions. The fibrotic regions had fewer immune cells overall. In summary, our study shows participation of innate and adaptive mononuclear cells in active-disease regions of idiopathic pulmonary fibrosis lung, where the regenerating epithelial cells appear to propagate inflammation. The regenerative mechanisms become skewed to ultimately result in lethal, fibrotic restriction of lung function.

Differentiation of Langerhans cells in Langerhans cell histiocytosis

Langerhans cell histiocytosis (LCH) consists of lesions composed of cells with a dendritic Langerhans cell (LC) phenotype. The clinical course of LCH ranges from spontaneous resolution to a chronic and sometimes lethal disease. We studied 25 patients with various clinical forms of the disease. In bone and chronic lesions, LCH cells had immature phenotype and function. They coexpressed LC antigens CD1a and Langerin together with monocyte antigens CD68 and CD14. Class II antigens were intracellular and LCH cells almost never expressed CD83 or CD86 or dendritic cell (DC)-Lamp, despite their CD40 expression. Consistently, LCH cells sorted from bone lesions (eosinophilic granuloma) poorly stimulated allogeneic T-cell proliferation in vitro. Strikingly, however, in vitro treatment with CD40L induced the expression of membrane class II and CD86 and strongly increased LCH cell allostimulatory activity to a level similar to that of mature DCs. Numerous interleukin-10-positive (IL-10(+)), Langerin(-), and CD68(+) macrophages were found within bone and lymph node lesions. In patients with self-healing and/or isolated cutaneous disease, LCH cells had a more mature phenotype. LCH cells were frequently CD14(-) and CD86(+), and macrophages were rare or absent, as were IL-10-expressing cells. We conclude that LCH cells in the bone and/or chronic forms of the disease accumulate within the tissues in an immature state and that most probably result from extrinsic signals and may be induced to differentiate toward mature DCs after CD40 triggering. Drugs that enhance the in vivo maturation of these immature DCs, or that induce their death, may be of therapeutic benefit.

Ear involvement in childhood Langerhans' cell histiocytosis

BACKGROUND

Ear involvement (EI) in Langerhans' cell histiocytosis (LCH) occurs quite often. We reviewed the Italian pediatric population of 251 children with LCH diagnosed between 1982 and 1995, focusing on EI, to highlight the prevalence, the clinical presentation, the outcome during follow-up, and the prognostic impact of otologic LCH.

METHODS

EI was defined by chronic otorrhea and/or mastoid infiltration, external auditory meatus lesions, and middle/internal EI. The age at diagnosis, sex, system involved, organ dysfunction, treatment, disease control, and outcome were recorded.

RESULTS

EI was noted at presentation in 34 children (13. 5%). They had a younger age at diagnosis (p=.0013) and near totality of multisystem disease (93.8% of patients with EI). Among patients with multisystem disease, children with EI seemed to have a higher risk of poor response and a higher percentage of second line treatment (p=.003).

CONCLUSIONS

EI seems to identify patients with a particular disease behavior, which requires a more accurate evaluation at diagnosis, staging and treatment, and a strict follow-up, considering the possibility of an unfavorable outcome.

Diagnostic and therapeutic evaluation of an anti-Langerhans cell histiocytosis monoclonal antibody (NA1/34) in a new xenograft model

Scintigraphy using monoclonal antibodies has been suggested as a possible adjunct to conventional staging techniques for the routine staging and diagnosis of Langerhans cell histiocytosis. In this study we have developed a model for Langerhans cell histiocytosis comprising a CD1a-positive subcutaneous xenograft in the flanks of nude (nu/nu) mice. The anti-CD1a murine monoclonal antibody NA1/34 was investigated for its potential both as an imaging and as a therapeutic targeting agent in this model. Biodistribution with NA1/34 compared with irrelevant isotype-matched monoclonal antibody demonstrated specific accumulation within the xenografts of 10.0%id per g (percentage injected dose per gram) and 3.3%id per g at 48 h postinjection, respectively. NA1/34 displayed no specific accumulation to CD1a-negative xenografts. F(ab')2 fragments of NA1/34 displayed a faster clearance time of 19.6 h compared with the intact antibody, 122.4 h, resulting in a more rapid maximum xenograft uptake time of 5 h compared with 48 h postinjection for the intact antibody. Although the overall xenograft/tissue ratio for the F(ab')2 was at no time greater than that for the intact antibody, the F(ab')2 did display dramatically greater xenograft/blood ratios, reaching 19:1 at 120 h postinjection Xenograft regression using single doses of 350 microCi and 500 microCi 131I-labeled NA1/34 significantly (p < 0.001) delayed xenograft progression compared with control nonirradiated xenografts, with average delays of 3.2 and 5.7 times the control, respectively. This study suggests that the anti-CD1a monoclonal antibody, NA1/34, offers advantages in the prognosis and staging of Langerhans cell histiocytosis, in a human setting. We discuss the advantages of radioimmunoscintigraphy over conventional differential diagnostic techniques. The potential for the future radioimmunotherapy of Langerhans cell histiocytosis is also discussed.

Expression of the monoclonal antibody HECA-452 defined E-selectin ligands in Langerhans cell histiocytosis

The cutaneous lymphocyte associated antigen (CLA) recognized by the monoclonal antibody (moAb) HECA-452 plays a major role in the homing of lymphocyte subpopulations to the skin by binding to E-selectin on dermal microvessels. The factors responsible for the immigration of Langerhans cells (LC) and their precursors into the skin are still unknown, but because normal resting LC are also capable of expressing CLA, the antigen was proposed as a candidate LC-homing structure. To gain insight into these mechanisms, the expression of HECA-452 on neoplastic LC within and outside the skin was investigated in paraffin-embedded sections from 44 patients with localized and disseminated forms of Langerhans cell histiocytosis (LCH) presenting with proliferating cells positive for CD45, CD1a, S100 and HLA-DR. Irrespective of the clinical presentation or the type of organ involved, HECA-452 positive LC were detected in all biopsies tested (range 5->90%). The most prominent HECA-452 reactivity was observed in skin lesions and in areas with accumulations of eosinophilic granulocytes. Our data provide evidence for heterogeneous expression of sLex/sLea structures in various stages of activated and/or differentiated LCH cells. Remarkably, CLA-antigen expression on LCH-cells was not restricted to cutaneous sites. In view of recent findings on the expression of HECA-452 on resting epidermal LC, our data are compatible with the view that local cytokine production by keratinocytes or cells from the surrounding infiltrate induce and/or modulate CLA expression on LC in both cutaneous and extra-cutaneous sites.

Functional defect in cells involved in Langerhans cell histiocytosis

The characteristic cell type involved in Langerhans cell histiocytosis, 'LCH cells', express most of the enzyme histochemical and immunocytochemical markers of normal epidermal Langerhans cells. It is not known, however, whether these LCH cells express the functional characteristics of normal epidermal Langerhans cells. We studied the alloantigen-presenting activity of LCH cells derived from lesional sites of three patients with the disease. Lesional cells expressing the CD1a molecule were enriched using either fluorescein-activated cell sorting or negative selection with indirect immunomagnetic beads, and functional activity was assessed using the 6-day primary allogeneic mixed-cell reaction. Compared to epidermal Langerhans cells from healthy controls, LCH cells showed minimal alloantigen-presenting activity on a per-cell basis. The diminished activity was not reversed by exogenous prostaglandin synthetase inhibitor or recombinant human IL-1 beta. This study confirms our previous report of a child, with fatal multisystem Langerhans cell histiocytosis suggesting that this disease represents a condition in which functionally defective cells of Langerhans cell phenotype accumulate and/or proliferate in various tissues. We postulate that the functional defect is a primary defect of these LCH cells that have acquired an as-yet-undetermined biological insult(s).

An adult case of histiocytosis X with a vulvar ulcer and multiple bone lesions

A 62-year-old female with histiocytosis X presented with a vulvar ulcer. Multiple osteolytic lesions were later detected. Histological examination of the ulcerated skin showed diffuse proliferation of histiocytic cells with folded nuclei and pale eosinophilic cytoplasm. Immunohistochemistry revealed S100 protein and vimentin as well as CD1a, CD4, and HLA-DR antigens in the proliferating cells. Electron microscopy demonstrated Birbeck granules in the cytoplasm of the cells. The patient was successfully treated by complete surgical excision of the ulcer followed by radiotherapy for recurrent vulvar erythema.

Langerhans cell histiocytosis presenting as a varicelliform eruption over the entire skin

A boy with skin eruptions resembling varicella and specific for Langerhans cell histiocytosis (LCH) is reported. At his initial visit when he was four months old, vesiculopustular lesions were present over the entire body; these had first appeared on the third day post partus. Histopathological, immunohistochemical, and electron microscopical examination confirmed the Langerhans cell phenotype and Birbeck granules in the responsible cells. He also had hydronephrosis, recurrent fever, and cutaneous bacterial infections. His parents refused further medical treatment and he died of diarrhea with cachexia about two years later. LCH may present diagnostic difficulties by manifesting as a skin eruption which resembles varicella.

CD68 positive epidermal dendritic cells

In a pilot study designed to investigate immunopathologic events in the evolution of cutaneous lesions in pemphigus foliaceus, we found that in this condition the epidermis is replete with CD68+ dendritic cells. The present study was designed to investigate the nature of this novel intraepidermal CD68+ cell population. For that purpose lesional skin of five patients with PF and, for comparison, of patients with another acantholytic autoimmune disease, pemphigus vulgaris, were examined using a panel of monoclonal antibodies in a three-step immunoperoxidase technique, in an immunofluorescence double-labeling technique, and by immunoelectron microscopy. We found epidermal CD1a+ Langerhans cells significantly decreased in pemphigus foliaceus compared to pemphigus vulgaris, but pemphigus foliaceus and not pemphigus vulgaris epidermis harbored large amounts of bone marrow-derived (CD45+) cells that expressed CD68, HLA-DR, and beta 2-integrin antigens, the most pronounced expression being observed for CD11c and CD18. These epidermal CD68+ cells were of dendritic shape, were CD1a-, and lacked Birbeck granules (BG); however, a small portion of CD68+ cells was also CD1a+ and exhibited BG as revealed by immunoelectron microscopy. These findings demonstrate that in certain conditions, i.e., in pemphigus foliaceus but not in pemphigus vulgaris, there is a shift from CD1a+/CD68- epidermal Langerhans cells towards CD1a-/CD68+ dendritic epidermal cells. The detection of a small number of CD1a+/CD68+/BG+ dendritic epidermal cells may identify these cells as a link between the CD1a+/CD68+/BG+ Langerhans cells and the CD1a-/CD68+/BG- cell population and suggests that these cells represent a transitional form of myelomonocytic cells during their phenotypic and morphologic transformation into resident epidermal Langerhans cells.

Expression of neuron-specific enolase immunoreactivity by cutaneous and extracutaneous Langerhans-cell histiocytoses ("X")

The immunohistochemical expression of Neuron-Specific Enolase (NSE) and of S100 protein was studied in 10 cases of cutaneous and 19 cases of extracutaneous Langerhans cell histiocytoses (LCH), including acute/proliferative forms (cutaneous Letterer-Siwe disease) and chronic/granulomatous forms (eosinophilic granuloma, Hand-Schüller-Christian disease). Of the LCH cases, 18 (62%) exhibited detectable NSE-immunoreactivity as compared to 82.8% for S100. NSE expression was found more frequently and intensely within acute (as compared to chronic) forms of LCH. This result lends further support to the cellular unicity of LCH, but also suggests some degree of heterogeneity among LCH cells. It can be speculated that NSE-expression is correlated with the proliferation/activation state of (abnormal) Langerhans cells.

Defective alloantigen-presenting capacity of 'Langerhans cell histiocytosis cells'

The functional activity of skin cells derived from an infant who died of multisystem Langerhans cell histiocytosis (LCH) was examined. Involved and non-involved skin was obtained at postmortem examination within three hours of death; normal epidermal Langerhans cells and 'LCH cells' were separated by means of dispase digestion. The functional activity of different populations of CD1a positive cells was assessed using the conventional six day allogeneic mixed cell reaction. Compared with Langerhans cells from a healthy control, LCH cells showed minimal functional activity. However, Langerhans cells from non-involved skin showed normal and Langerhans cells overlying involved skin showed augmented functional activity. These findings suggest that LCH is a disease in which abnormal Langerhans cells accumulate and/or proliferate in various tissues but it does not affect the entire Langerhans cell population.

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.

Isolation of human immunodeficiency virus type 1 from human epidermis: virus replication and transmission studies

For a better understanding of the pathogenetic events operative in the cutaneous manifestations of human immunodeficiency virus type 1 (HIV-1) disease, we investigated whether epidermal cells (EC) from HIV-1-seronegative persons can be infected with HIV-1 and, vice versa, whether HIV-1 can be rescued from the epidermis of HIV-1-infected individuals. In a series of three experiments, we consistently found that exposure of EC from HIV-1-seronegative donors to HIV-1 led to viral replication in these cells as evidenced by the detection of HIV-1 p24 in culture fluids. Because EC had been substantially enriched for Langerhans cells (LC) before being exposed to HIV-1, it is reasonable to assume that these CD1a+/CD4+/MHC class II+ antigen-presenting cells of the epidermis represented the actual targets of infection. This assumption is further strengthened by the observation that T cell-depleted cell suspensions from Langerhans cell histiocytosis (LCH) lesions could be productively infected with HIV-1. Conversely, co-culture of epidermal sheets from HIV-1-seropositive individuals with mononuclear phagocytes (MNP) from HIV-1-seronegative donors resulted, after 3 to 5 weeks, in the detection of HIV-1 p24 in 12 of 23 cases. Immunocytochemical analysis, using a monoclonal antibody specific for p24, revealed the presence of HIV-1 in adherent MNP in three cocultures tested. In addition, cellular DNA from these cultures showed strong signals when hybridized to a HIV-1-specific DNA probe. The further finding that two isolates examined exhibited different restriction enzyme patterns indicates that they are separate entities rather than contaminants. Transmission of these isolates to MNP, B- or T-cell lines resulted in cultures strongly positive for p24 and, in the case of H9 cells, for viral particles as detected by electron microscopy. Our results therefore strongly suggest that EC not only can serve as targets for HIV-1, but also can allow efficient virus replication and transmit HIV-1 to various cell types of the hematopoietic lineage.

Precursor Langerhans cell histiocytosis. An unusual histiocytic proliferation in a patient with persistent non-Hodgkin lymphoma and terminal acute monocytic leukemia

BACKGROUND

Langerhans cell precursors are considered to be identical to their mature counterparts except for the lack of Birbeck granules. Proliferations composed of such histiocytes appear to be uncommon.

METHODS

Standard immunophenotypic, molecular genetic, and DNA content studies were used to characterize various hematopoietic disorders, including a proliferation of precursor Langerhans cells, which arose sequentially in a patient.

RESULTS

The patient studied initially had a low-grade, B-cell, non-Hodgkin lymphoma and subsequently had an unusual histiocytic proliferation (precursor Langerhans cell histiocytosis) in cutaneous and lymph node sites. The patient eventually died of acute myelogenous leukemia (FAB, M5).

CONCLUSIONS

A larger series is required to determine the significance of the precursor Langerhans cell phenotype, particularly with respect to the development of acute myelogenous leukemia.

Eosinophilic granuloma of bone and biochemical demonstration of 49-kDa CD1a molecule expression by Langerhans-cell histiocytosis

Histiocytic cells infiltrating the lesions in eosinophilic granuloma of bone as well as in cutaneous histiocytosis X were studied using a murine monoclonal antibody (MA) produced with proliferating cells from an eosinophilic granuloma of bone. This MA reacts with Langerhans cells (LC) of normal human skin or mucous membranes and with proliferating cells of eosinophilic granuloma of bone and skin lesions of Letter-Siwe disease, as shown by immunohistochemistry and immunogold labelling. As other murine MA's obtained after immunization with human cortical thymocytes, this MA immunoprecipitates the 49-kDa CD1a antigen found on human LC and thymic-cell surfaces but not its breakdown product after treatment with trypsin, as demonstrated by analysis of immunoelectron labelling, cytofluorometry and gel electrophoresis. This first production of a CD1a MA from an eosinophilic granuloma supports the concept of Langerhans-cell histiocytosis.

Langerhans cell histiocytosis masquerading as lichen aureus

We report a 13-year-old boy with localized Langerhans cell histiocytosis. The lesion was restricted to the skin of the mons pubis and clinically resembled lichen aureus. Histopathologic and electron microscopic examinations of a skin biopsy specimen of the lesion showed typical features of Langerhans cell histiocytosis. Extensive examination revealed no other organ involvement.

Langerhans cell histiocytosis of the female genital tract

Langerhans cell histiocytosis (LCH) of the female genital tract is rare. Four new cases are reported, and there is a review of the 38 cases in the literature. This disease may involve the vulva, vagina, cervix, endometrium, and ovary. Four distinct patient groups, segregated on the basis of initial presentation and subsequent anatomic extent of disease, were categorized as follows: (1) "pure" genital LCH, (2) genital LCH with subsequent multi-organ involvement, (3) oral or cutaneous LCH with subsequent genital and multi-organ involvement, and (4) diabetes insipidus with subsequent genital and multi-organ disease. Although involvement of the genital tract can occur at any age, it is most common in young adulthood. Clinically, LCH may mimic either primary neoplasia or various inflammatory lesions; the major pathologic differential diagnosis is venereal and other inflammatory diseases. The pure genital form may have a distinct nosologic position in the spectrum of LCH similar to the "pure," self-limited cutaneous histiocytosis seen in infants. There is no correlation between histologic findings and the outcome of the genital lesions. There is also no correlation between clinical presentation and/or the extent of involvement and outcome of genital lesions; complete regression, partial improvement, persistent lesions, and recurrences were seen in all four groups of patients. The treatment of genital LCH is not well defined and is highly individualized. Therapy has included surgery, radiation, topical corticosteroids, topical nitrogen mustard, systemic chemotherapy, and combination therapy; mixed results were obtained with all treatment modalities. Although no modality has been shown to yield a superior outcome, complete surgical excision is advocated as initial therapy.

Etoposide in the treatment of six children with Langerhans cell histiocytosis (histiocytosis X)

Six children received etoposide as the single agent for treatment of Langerhans cell histiocytosis (LCH; histiocytosis X). Five were less than 2 years old at diagnosis. All had multiorgan involvement; one had liver and pulmonary dysfunction. Two infants also had clinical signs of immune deficiency. Complete response was observed in five. There was no major toxicity. Although three of four evaluable patients relapsed, the drug was considered useful in moving the children from a symptomatic to an asymptomatic clinical status. Etoposide may become a "first-line" drug in the treatment of systemic LCH, especially when the side effects of steroid therapy are considered unacceptable.

Merkel cell carcinoma of the head and neck associated with Bowen's disease

The Merkel cell carcinoma occurs primarily in the skin of the head and neck, and develops in the dermis with a trabecular growth pattern. Immunohistochemistry reveals positive staining for neuron-specific enolase, neurofilaments, cytokeratin and chromogranin A. Electron microscopically, the tumor cells contain dense-core granules, spinous cytoplasmic processes, desmosomes, zonulae adherentes and paranuclear filament aggregates besides frequent mitoses, focal necroses and lymphocyte and plasma cell infiltrates. The Merkel cell carcinoma is often co-existent with other malignancies such as squamous cell carcinoma or, as in the present study, with Bowen's disease. The definite diagnosis of the Merkel cell carcinoma can be effected only by electron microscopic examination of the tumor.

Immunohistochemical study of the abnormal cells in Langerhans cell histiocytosis (histiocytosis x)

The immunophenotypic properties of the abnormal cells in routine specimens from 16 cases of Langerhans cell histiocytosis (LCH) were examined. In five cases, cryostat sections were also available. The abnormal cells expressed a similar phenotype and were positive for HLA-DR, S-100 protein, peanut agglutinin (PNA), CD1a, CD4 and several macrophage-associated markers, including CD11c, CDw32 and CD68 (the latter detectable in routine sections with antibody KP1). Staining with CD14, CD35 (C3b receptor), and CD11b (C3bi receptor) was negative with the exception of one of the cases in which a proportion of the cells showed faint positivity with CD11b. Staining for pan-T-cell (CD2, CD3, CD5) and pan-B-cell (CD19, CD22) antigens was negative in all lesions. It is concluded that LCH expresses a characteristic phenotype with some heterogeneity with regard to macrophage markers and that immunohistochemical methods in cryostat sections and routine specimens form a useful supplement to other techniques for the diagnosis of this condition.

Allogeneic bone marrow transplantation for Langerhans' cell histiocytosis

A group of proliferative diseases of the epidermal Langerhans' cells are commonly referred to as Langerhans' cell histiocytosis (LCH). A small number of the patients with this disease face an unfavorable disease course despite chemotherapy and radiation therapy. In LCH patients with a poor prognosis, allogeneic bone marrow transplantation (BMT) could be the appropriate treatment with proven antiproliferative effects and may be able to repopulate the recipient with stem cell-derived Langerhans' cells from the donor or correct the presumed underlying immunodeficiency. An LCH was diagnosed in a 15-year-old boy with multiple osteolytic lesions, anemia, and diabetes insipidus centralis. Repeated flare-ups of the disease had necessitated several courses of conventional chemotherapy including cyclophosphamide (CY), prednisolone (P), 6-mercaptopurine (6-MP), vincristine (VCR), and additional local irradiation without stable remission. Three years after first being diagnosed with LCH the patient underwent high-dose chemotherapy-radiation therapy followed by allogeneic BMT from his human lymphocyte antigen (HLA)-identical brother. Currently, he is alive and well and has been disease-free for more than 41 months after BMT.

Human normal-resting epidermal Langerhans cells do express the type 3 complement receptor

The expression of CR3 by murine-resting epidermal Langerhans cells (LC) is well established, but CR3 expression by human normal-resting epidermal LC has not yet been demonstrated. In this study, highly sensitive immunostaining techniques, such as immunogold labelling in transmission- and scanning-electron microscopy, were used on freshly isolated, LC-enriched, normal human epidermal cells. Human normal resting epidermal LC were found to be CR3+, since a low but significant number of gold granules labelled the plasma membrane of all the LC observed under transmission-electron microscopy, and all the epidermal cells showing LC morphology as observed by scanning-electron microscopy.

Cultured human Langerhans cells resemble lymphoid dendritic cells in phenotype and function

Freshly isolated murine epidermal Langerhans cells (LC) are weak stimulators of resting T cells. Upon culture their phenotype changes, their stimulatory activity increases significantly, and they come to resemble lymphoid dendritic cells. Resident murine LC, therefore, might represent a reservoir of immature dendritic cells. We have now used enzyme cytochemistry, a panel of some 80 monoclonal antibodies, and immunofluorescence microscopy or two-color flow cytometry, as well as transmission electron microscopy, to analyse the phenotype and morphology of human LC before and after 2-4 d of bulk epidermal cell culture. In addition, LC were enriched from bulk epidermal cell cultures, and their stimulatory capacity was tested in the allogeneic mixed leukocyte reaction and the oxidative mitogenesis assay. Cultured human LC resembled human lymphoid dendritic cells in morphology, phenotype, and function. Specifically, LC became non-adherent upon culture and developed sheet-like processes (so-called "veils"), decreased their surface ATP/ADP'ase activity, and lost nonspecific esterase activity. As in the mouse, surface expression of MHC class I and II antigens increased significantly, and FcII receptors were significantly reduced. Markers that are expressed by dendritic cells (like CD40) appeared on LC following culture. Cultured human LC were potent T-cell stimulators. Our findings support the view that resident human LC, like murine LC, represent immature precursors of lymphoid dendritic cells in skin-draining lymph nodes.

Morphologic and functional characterization of human peripheral blood T cells expressing the T cell receptor gamma/delta

The morphologic and functional characteristics of cells freshly isolated from human peripheral blood and bearing a T cell receptor (TcR) gamma/delta were analyzed. Cell preparations highly enriched for TcR gamma/delta+ cells were obtained by treatment of E rosette-forming lymphocytes with anti-CD4 and anti-CD8 monoclonal antibodies (mAb) and complement. These preparations consisted of 64-82% TcR gamma/delta+ lymphocytes, as indicated by the sum of cells reacting with the BB3 and A13 mAb which define two distinct, nonoverlapping, TcR gamma/delta+ cell subsets in the peripheral blood. TcR gamma/delta cells were able to form conjugates with the natural killer-sensitive K-562 and with the natural killer-resistant HL-60-R tumor cell lines. The cytochemical localization of lysosomal acid hydrolases showed that 95%-98% of the cells in the TcR gamma/delta+ preparations had the morphologic features of granular lymphocytes. Moreover, electron microscopy analyses showed that TcR gamma/delta+ cells had electron-dense granules dispersed in the cytoplasm and a variety of smooth vesicles, a morphology identical to that of other CD3- or CD3+ granular lymphocyte subsets. Freshly isolated TcR gamma/delta+ cells were unable to lyse K-562 and natural killer-resistant targets, such as HL-60-R and P815. However, low levels of target cell lysis were observed upon triggering of the effectors by anti-CD3 TcR mAb or by lectin. After short-term culture with interleukin 2, TcR gamma/delta+ cells acquired a strong cytolytic activity against K-562 and HL-60-R target cells in the absence of triggering stimuli, and also displayed high levels of cytolytic activity against P815 in the presence of anti-CD3/TcR mAb.

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.

DMC1: a monoclonal antibody produced from histiocytosis X cells which reacts with the native CD1a molecule of human epidermal Langerhans cells

Human epidermal Langerhans cells express two (CD1a and CD1c) of the three human thymic cell surface differentiation antigens (CD1a, CD1b, and CD1c). The first cluster of differentiation antigens (CD1) is defined by a group of monoclonal antibodies (MCA). All these MCA were obtained after immunization of mice or rats with human cortical thymocytes. OKT6 MCA (a CD1a MCA) was the first to be described as reactive with human epidermal Langerhans cells. We produced a murine MCA, called DMC1, after immunization with proliferating Langerhans cells of Eosinophilic Granuloma of the bone (Histiocytosis X). In tissues DMC1 MCA reacted with epidermal dendritic cells (Langerhans cells) in the skin and cortical thymocytes in the thymus as observed on indirect immunofluorescence. At the ultrastructural level, DMC1 MCA was specific for Birbeck granule-containing Langerhans cells and did not react with melanocyte and keratinocyte populations. The quantitative analysis of immunoelectron labeling and the cytofluorometric study showed that the intensity of labeling was inversely correlated with the concentration of trypsin used in the preparation of epidermal cell from skin samples. DMC1 MCA precipitated a protein with a relative mass of 49,000 (CD1a molecule) from lysates of iodinated epidermal Langerhans cells under reducing conditions. It recognized the original CD1a molecule (Mr 49,000) but not the membrane breakdown product of CD1a (Mr 27,000) brought about by trypsin.

The Langerhans' cells

The morphological, enzymatical, immunocytochemical and functional properties of Langerhans' cells are briefly reviewed. Langerhans' cells are located mainly in the squamous stratified epithelia, but are also present in the thymus and in superficial lymphnodes. At the ultrastructural level, they are characterized by unique cytoplasmic organelles, the Birbeck granules, whose function is still unknown. Langerhans' cells possess strong ATPase activity and are weakly positive for alpha-naphtyl acetate esterase and for acid phosphatase; they are immunoreactive for CD1a (T6), class II MHC antigens and S-100 protein. In some pathological conditions, like dermatopathic lymphadenopathy and Langerhans' cell histocytosis, Langerhans' cells also are characterized by the expression of monocyte-macrophage antigens. Langerhans' cells act as antigen-presenting cells to T lymphocytes; their functional capacity is strictly dependent on the levels of expression of class II MHC antigens. Langerhans' cells are of bone marrow origin and are derived from a circulating precursor which is probably related to the monocyte.