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Background Human Langerhans cells (LCs) reside in foreskin and vaginal mucosa and are the first immune cells to interact with HIV-1 during sexual transmission. LCs capture HIV-1 through the C-type lectin receptor langerin, which routes the virus into Birbeck granules (BGs), thereby preventing HIV-1 infection. BGs are langerin-positive organelles exclusively present in LCs, however, their origin and function are unknown. Results Here, we not only show that langerin and caveolin-1 co-localize at the cell membrane and in vesicles but also that BGs are langerin/caveolin-1-positive vesicles are linked to the lysosomal degradation pathway in LCs. Moreover, inhibition of caveolar endocytosis in primary LCs abrogated HIV-1 sequestering into langerin+ caveolar structures. Notably, both inhibition of caveolar uptake and silencing of caveolar structure protein caveolin-1 resulted in increased HIV-1 integration and subsequent infection. In contrast, inhibition of clathrin-mediated endocytosis did not affect HIV-1 integration, even though HIV-1 uptake was decreased, suggesting that clathrin-mediated endocytosis is not involved in HIV-1 restriction in LCs. Conclusions Thus, our data strongly indicate that BGs belong to the caveolar endocytosis pathway and that caveolin-1 mediated HIV-1 uptake is an intrinsic restriction mechanism present in human LCs that prevents HIV-1 infection. Harnessing this particular internalization pathway has the potential to facilitate strategies to combat HIV-1 transmission. Electronic supplementary material The online version of this article (doi:10.1186/s12977-014-0123-7) contains supplementary material, which is available to authorized users.

Juvenile xanthogranuloma (JXG) is considered to represent a lesion originating from histiocytes. Three cases of deeply located JXG and one case of cutaneous JXG were studied. One case with extensive mesenteric involvement presented with hypercalcemia and one case with liver involvement had hypergammaglobulinemia. Immunohistochemistry, electron microscopy, karyotyping, and DNA flow cytometry were used to determine the phenotype of the cells involved and to find further clues as to the histogenesis of these lesions. Immunohistochemically, all lesions studied expressed the CD1a antigen but showed no labeling for S-100 protein. The cells did not contain Birbeck granules. From these data it is suggested that the cells involved are of indeterminate dermal histiocyte lineage and that occurrence of deep located lesions of JXG may be due to migration of CD1 a-positive histiocytes.

Langerhans cells (LCs) in the skin are a first line of defense against pathogens but also play an essential role in skin homeostasis. Their exclusive expression of the C-type lectin receptor Langerin makes them prominent candidates for immunotherapy. For vaccine testing, an easily accessible cell platform would be desirable as an alternative to the time-consuming purification of LCs from human skin. Here, we present such a model and demonstrate that monocytes in the presence of GM-CSF, TGF-β1, and the Notch ligand DLL4 differentiate within 3 days into CD1a+Langerin+cells containing Birbeck granules. RNA sequencing of these monocyte-derived LCs (moLCs) confirmed gene expression of LC-related molecules, pattern recognition receptors, and enhanced expression of genes involved in the antigen-presenting machinery. On the protein level, moLCs showed low expression of costimulatory molecules but prominent expression of C-type lectin receptors. MoLCs can be matured, secrete IL-12p70 and TNF-α, and stimulate proliferation and cytokine production in allogeneic CD4+ and CD8+ T cells. In regard to vaccine testing, a recently characterized glycomimetic Langerin ligand conjugated to liposomes demonstrated specific and fast internalization into moLCs. Hence, these short-term in vitro‒generated moLCs represent an interesting tool to screen LC-based vaccines in the future.

It is well established by in vivo and in vitro studies that dendritic cells (DCs) originate from hematopoietic progenitor cells. However, the presumed intermediate of Birbeck granule (BG)+ Langerhans cells (LCs) has not been detected in cultures derived from bone marrow or peripheral blood progenitor cells (PBPCs), thus contrasting with the data obtained with cord blood. We show here that large numbers of BG+ LCs can be generated from human CD34+ PBPCs in vitro, when granulocyte-macrophage colony-stimulating factor and interleukin-4, potent promotors of LC/DC differentiation, are combined with a cocktail of early acting hematopoietic growth factors. LCs were found to emerge from CD33+CD11b+CD14-progenitor cells that they share with the monocytic lineage. During culture, these cells exhibited a sequence of dramatic morphologic changes, starting with a major increase in granularity followed by an increase in size herein exceeding that of all peripheral blood cells. At the same time, CD1a and major histocompatibility complex class II expression were upregulated and virtually all CD1a++ cells were BG+ by electron microscopy. With prolonged culture, CD1a was downregulated on a major population of cells, paralleled by a loss of BG and an increase of CD4, CD25, and CD80 expression that may correspond to the maturation of epidermal LC in vitro. However, these cells were consistently CD5- and did not exhibit changes in the CD45-isoform expression during culture. The availability of large numbers of these highly purified BG+ LCs and mature DCs allows for specific analysis of these subpopulations and provides a source of potent antigen-presenting cells from individual patients for vaccination protocols against infectious or tumor-associated antigens.

Pulmonary histiocytosis X (HX) is a disorder characterized by the presence of granulomas in which Langerhans cells (LC) and lymphocytes are abundant. Although the pathogenesis of pulmonary HX remains unknown, an uncontrolled immune response initiated by LC, which are potent antigen-presenting cells in vitro, may play an important role. To further characterize LC and lymphocytes present in granulomas from these patients, we used immunohistochemical techniques and monoclonal antibodies to evaluate the surface phenotype and electron microscopy (EM) to seek evidence for close interactions between both cell types in these lesions. In all samples, HX granulomas contained large numbers of strongly positive CD1a cells in which typical Birbeck granules were identified by EM. The number of Birbeck granules in LC from HX granulomas was strikingly increased compared with that in LC in the bronchioles of normal subjects. Furthermore, unlike normal LC, essentially all LC in HX granulomas expressed CD4 antigens and were strongly positive for CD1c. Lymphocytes infiltrating HX granulomas were almost entirely CD3+ T cells and were mainly CD4 positive (CD4/CD8 ratio 3.7 +/- 1.3). These T lymphocytes expressed almost exclusively alpha/beta T cell receptors, and gamma/delta T cells were rarely observed (5% of CD3+ cells). In areas of lymphocytic infiltration, close differentiated contacts between LC and lymphocytes were observed by EM in all samples. These results demonstrate that interactions between activated LC and CD4+ T lymphocytes are prominent in early HX granulomas and support the idea that an immune response in which LC serve as accessory cells is involved in the pathogenesis of this disorder.

A case of vitiligo with inflammatory raised borders was observed electron microsocopically, resulting in an interesting view of the formation of Birbeck granules in Langerhans cells. Following the formation of larger coated vesicles, which perform adsorptive pinocytosis from the cell membrane, membrane invagination of the cell occurred shown as the tubular infolding, resulting in the observation of the characteristic Birbeck granule band pattern in its interior. This phenomenon supports the theory of Hashimoto and Tarnowski (1968) that Birbeck granules are formed from the infolding of the cell membrane. In addition, our study shows the involvement of adsorptive pinocytosis in the formation of the granules. It was suggested that when the coated Birbeck granule shifts into the cell, possibly its coat is detached and the vesicle portion forms the globule of the Birbeck granule.

Dear Editor, A 21-year-old man presented with a rapidly growing (9 cm), non-tender right flank mass with superficial excoriation and inflammation (Fig. 1a). The lesion was accompanied by rapid onset of disseminated brown papules, involving the torso, back, and limbs (Fig. 1b). Facial and axillary skins were spared, and there was no particular direction of spread. The skin patches did not coalesce or show pruritus or inflammation. There was also weight loss of 15 lb in 3 months. A positron emission tomogram scan (PET) showed FDG uptake in the right waist (SUV 5.8) and right groin (SUV 2.1) (Fig. 1c). Wide margin resection of the mass and lymph node excision was performed with clear margins. Histology of both specimens showed sheets and loose clusters of pleomorphic malignant cells infiltrating the dermis and subcutis with frequent mitosis (Fig. 1d). In view of the anaplastic morphology and unusual presentation, extensive immunophenotyping was performed. The cells were positive for CD1a, S100, and Langerin stains. They were negative for melanocytic markers (HMB45, melan-A, MITF) EMA, cytokeratin (CK, Cam 5.2, 34betaE12), actin, desmin, CD31, CD34, c-kit, B and T markers (CD20, CD79a, CD3), CD68, CD30, CD56, CD21, MPO, and ALK1. Electron microscopy for Birbeck granules was not performed. The picture was compatible with Langerhans cell sarcoma (LCS). A separate skin biopsy of a pigmented lesion on the torso showed elongated rete ridges with increased basal melanin pigmentation within keratinocytes and the tips, with no increased Langerhans cells and no evidence of malignancy or dysplasia. The lesion was compatible with common lentigo. The patient was treated with consolidation radiotherapy to the primary sites, but there was no regression of the skin lentiges. Fig. 1 a Clinical photo showing the flank mass with impending ulceration. b Widespread lentiginous lesion all over the trunk heralding the rapid growth of the malignant lesion. c PET with maximum intensity projection showing two sites of active lesions in the ... In the World Health Organization classification, LCS is the malignant end of the spectrum of benign Langerhans cell histiocytosis (LCH) [1]. The typical LCH cell is replaced by pleomorphic tumor cells in the LCS, only identifiable by phenotype or ultrastructure. Initial unifocal subcutaneous involvement is not unusual. However progressive disease, especially with multifocal dissemination, is highly fatal, despite multi-agent chemotherapy. It remains to be seen whether systemic progression may occur in our patient. Our patient demonstrated two hitherto unreported phenomena, namely paraneoplastic manifestation of LCS and acquired rampant disseminated lentigines as a new paraneoplastic dermatosis. The clinical history and histological findings do not suggest an underlying disseminated cutaneous LCH. Common paraneoplastic dermatoses (e.g., acanthocis nigricans) are well characterized and are putatively caused by neoplastic humoral secretions. Acquired melanocytic nevi are mostly related to solar exposure and are therefore localized. Recently, some cases of acral lentigines are debated to be paraneoplastic [2]. Disseminated lentigines are usually only found in familial lentiginosis syndromes (e.g., LEOPARD syndrome, Peutz–Jeghers, Carney complex, PTEN hamartoma syndrome). The neoplastic associations of these syndromes come from their primary systemic gene mutations [3]. The rapidly acquired disseminated growth of lentigines in our case is highly unusual and is somewhat induced by the abnormal aggressive transformation of the LCS cells. Skin pigmentation is usually under exquisite humoral control [4], and cutaneous Langerhans cells interact closely with melanocytes and keratinocytes [5]. It is impossible, however, to retrospectively work out the exact mechanism how the localized growth induced a systemic pigment response, since interval archival specimens are unavailable and the list of possible mediators are extensive. In any case, extirpation of the primary lesion appeared to halt further skin lesions.

In a previous study, it was demonstrated that human Langerhans cells (LC) are preserved in human skin grafted onto a nude mouse. Moreover, although it was observed that mouse LC of the host invade skin grafts from allogeneic mouse or rat, they do not penetrate in human skin grafts. In most of the human skin equivalent systems produced in vitro, LC appear to be lost. The present study was designed to investigate whether the mouse LC will repopulate a human skin equivalent. For this purpose, two different systems of skin equivalent have been grafted onto the nude mouse. They were composed of human keratinocytes deposited on dead human dermis, or on lattice composed of human fibroblasts embedded in type I collagen. At different times after grafting, the presence of LC in the transplants was assayed either by indirect immunofluorescence or by electron microscopy. Indirect immunofluorescence was performed on frozen sections or on epidermal sheets with anti-Ia, anti- HLA-DR, or OKT6 antibodies. It was observed that, at 2 months after grafting, Ia(+) HLA-DR(-) OKT6(-) cells are present in grafted human epidermis. Moreover, LC with typical Birbeck granules are also detected by electron microscopy. It could be concluded, from this study, that mouse LC can repopulate human epidermis devoid of human LC.

To the Editor.— It was with great interest that we read the recent report by Barsky et al 1 of their patient with benign cephalic histiocytosis. In their discussion, they suggested that a patient with atypical juvenile xanthogranuloma (JXG) described by us in 1972 2 might have had benign cephalic histiocytosis rather than JXG. Certainly, the facial lesions of the two patients as depicted in the case reports bear striking resemblance to one another. Three skin biopsy specimens were obtained from our patient and studied extensively by light and electron microscopy. Light microscopy demonstrated findings typi cal of JXG, including a dense dermal infiltrate of histiocytes, foam cells, and scattered eosinophils and lymphocytes. One biopsy specimen contained a moderate number of Touton giant cells. Electron microscopy confirmed the absence of organelles characteristic of histiocytosis X (Birbeck granules) and further showed the lipid-filled macrophages and multinucleated Touton giant cells characteristic of

Effects of a range (2-50 Gy) of single doses of 250 kV X rays on epidermal Langerhans cells in vivo were quantified in groups of CBA/CaH mice. Animals were sacrificed and compared with controls on the 10th day after local irradiation of their hind feet, when Langerhans cell numbers were at a minimum. ATPase-positive Langerhans cells in sheets of footpad epidermis were counted by light microscopy and cells with Birbeck granules were enumerated by electron microscopy. Both methods revealed a dose-dependent loss of Langerhans cells after ionizing radiation. Fifty percent of the ATPase-positive cells were lost after 14.4 ± 1.3 Gy, and 50% of Birbeck granule-containing cells were lost after 17.9 ± 4.2 Gy, suggesting that differentiated epidermal Langerhans cells are radioresistant. Loss of equivalent proportions of ATPase-positive and ultrastructurally identifiable cells after a range of doses indicates that X rays do not merely alter Langerhans cell surface markers but actually deplete the epidermal populatio...