Reappearance of CD1a antigenic sites after endocytosis on human Langerhans cells evidenced by immunogoldrelabeling

Langerhans cell sarcoma involving skin and showing epidermotropism: A comprehensive review

Langerhans cell sarcoma (LCS) is rare and aggressive; patients have an overall survival rate of less than 50%. We present a 62-year-old man with a history of superficial spreading melanoma of the upper back with sentinel lymph node metastasis, Langerhans cell histiocytosis, and LCS. The patient presented with erythematous papules and scaly areas on his face, neck, arms, chest, abdomen, and legs. A skin biopsy revealed a proliferation of large neoplastic cells involving the dermis and with epidermotropism. These cells had atypical bean-shaped nuclei, with ample cytoplasm and abundant mitotic figures including atypical forms. Immunohistochemical studies showed the tumor to be diffusely positive for CD1a, S100 protein, and langerin (CD207) and negative for melanocytic markers. Some tumor cells were positive for cyclin D1. A diagnosis of LCS involving the skin was established. The present study is a very unusual case of LCS showing epidermotropism. The patient's history of metastatic melanoma posed additional challenges for diagnosis, underlying the need of immunophenotyping in these cases. Consensus for optimal standard therapy has not been established in LCS, and thus, early recognition is important since these neoplasms tend to recur and metastasize. LCS in skin is discussed and published cases are comprehensively reviewed.

Phage display generation of a novel human anti-CD1A monoclonal antibody with potent cytolytic activity

CD1A is a cell surface protein expressed on Langerhans cells and cortical thymocytes that could potentially be used as an immunotherapeutic target in Langerhans Cell Histiocytosis (LCH), the cortical subtype of T-cell acute lymphocytic leukaemia (T-ALL) and other CD1A-positive tumours. The monoclonal antibody (mAb) CR2113 was selected from a panel of six fully human mAbs isolated from a semi-synthetic phage display library, based on specificity and avidity against cells expressing CD1 antigen variants. CR2113 recognized CD1A in T-ALL cell lines and patient samples. Confocal microscopy revealed that the CR2113-CD1A complex was internalized at 37°C. Furthermore, while CR2113 induced moderate complement-dependent cytotoxicity (CDC), potent antibody-dependent cell cytotoxicity (ADCC) activity was observed against CD1A expressing cell lines as well as T-ALL cell lines and T-ALL patient samples. In vivo experiments showed that CR2113 as a naked antibody has modest but specific anti-tumour activity against CD1A-expressing tumours. CR2113 is a high-affinity human anti-CD1A mAb with significant ADCC activity. These properties make CR2113 a candidate for clinical diagnostic imaging and therapeutic targeting of LCH as well as potential use in other clinical applications.

The class 6 semaphorin SEMA6A is induced by interferon-gamma and defines an activation status of langerhans cells observed in pathological situations

Originally implicated in axon guidance, semaphorins represent a large family of molecules that are now known to be expressed in the immune system. Among different semaphorins tested by reverse transcriptase-polymerase chain reaction in human immune cells, the expression of class 6 transmembrane semaphorin SEMA6A was restricted to dendritic cells (DCs). Using in-house generated monoclonal antibodies, SEMA6A expression appeared further restricted to Langerhans cells (LCs). In vivo, SEMA6A mRNA was expressed in freshly isolated skin LCs but SEMA6A protein was not detectable on normal skin and tonsillar epithelium. Of interest, SEMA6A protein was strongly expressed on skin and bone LCs and on LCs in draining lymph nodes from patients with LC histiocytosis or dermatopathic lymphadenitis, respectively, representing two inflammatory conditions in which LCs display an immature DC-LAMP(low), CD83(low), and CCR7+ phenotype. SEMA6A expression was low in resting LCs generated in vitro and was enhanced by interferon (IFN)-gamma but not by interleukin-4, interleukin-10, IFN-alpha/beta, or lipopolysaccharide. Most IFN-gamma-induced SEMA6A-positive cells remained immature with low CD83 and DC-LAMP/CD208 expression, but they expressed CCR7 and responded to macrophage inflammatory protein-3beta (MIP-3beta/CCL19). The expression of SEMA6A, for which the ligand and function remain unknown, may therefore identify an alternative IFN-gamma-dependent activation status of LCs in vivo.

CD1a molecules traffic through the early recycling endosomal pathway in human Langerhans cells

In this work, we studied the localization and traffic of CD1a molecules in human epidermal Langerhans cells and the ability of these cells to stimulate CD1a-restricted T cell clones. We found that CD1a was spontaneously internalized into freshly isolated Langerhans cells, where it was rapidly distributed to the early/sorting endosomes and then to the early/recycling endosomes. In the latter compartments, CD1a colocalized with Rab11, a small GTPase known to be involved in the recycling of transmembrane proteins from early endosomes to the cell surface. In the steady state, intracellular CD1a was mainly located in Rab11+ recycling endosomal compartments. When endocytosis was blocked, intracellular CD1a moved rapidly from the early/recycling endosomes to the cell surface where it accumulated. The resultant increase in the cell surface expression of CD1a enhanced the capacity of Langerhans cells to stimulate a CD1a-restricted T cell clone. These findings are consistent with a dynamic exchange of CD1a between recycling compartments and the plasma membrane and suggest that the antigen-presenting function of CD1a depends on its traffic through the early/recycling endosomal pathway.

Macrophage inflammatory protein 3alpha is expressed at inflamed epithelial surfaces and is the most potent chemokine known in attracting Langerhans cell precursors

Dendritic cells (DCs) form a network comprising different populations that initiate and differentially regulate immune responses. Langerhans cells (LCs) represent a unique population of DCs colonizing epithelium, and we present here observations suggesting that macrophage inflammatory protein (MIP)-3alpha plays a central role in LC precursor recruitment into the epithelium during inflammation. (a) Among DC populations, MIP-3alpha was the most potent chemokine inducing the selective migration of in vitro-generated CD34(+) hematopoietic progenitor cell-derived LC precursors and skin LCs in accordance with the restricted MIP-3alpha receptor (CC chemokine receptor 6) expression to these cells. (b) MIP-3alpha was mainly produced by epithelial cells, and the migration of LC precursors induced by the supernatant of activated skin keratinocytes was completely blocked with an antibody against MIP-3alpha. (c) In vivo, MIP-3alpha was selectively produced at sites of inflammation as illustrated in tonsils and lesional psoriatic skin where MIP-3alpha upregulation appeared associated with an increase in LC turnover. (d) Finally, the secretion of MIP-3alpha was strongly upregulated by cells of epithelial origin after inflammatory stimuli (interleukin 1beta plus tumor necrosis factor alpha) or T cell signals. Results of this study suggest a major role of MIP-3alpha in epithelial colonization by LCs under inflammatory conditions and immune disorders, and might open new ways to control epithelial immunity.

Pathways for lipid antigen presentation by CD1 molecules: nowhere for intracellular pathogens to hide

A crucial feature of peptide antigen presentation by major histocompatibility complex (MHC) class I and II molecules is their differential ability to sample cytosolic and extracellular antigens. Intracellular viral infections and bacteria that are taken up in phagosomes, but then escape from the endocytic compartment efficiently, enter the class I pathway via the cytosol. In contrast, phagosome-resident bacteria yield protein antigens that are sampled deep in the endocytic compartment and presented in a vacuolar acidification-dependent pathway mediated by MHC class II molecules. Despite this potential for antigen sampling, microbes have evolved a variety of evasive mechanisms that affect peptide transport in the MHC class I pathway or blockade of endosomal acidification and inhibition of phagosome-lysosome fusion that may compromise the MHC class II pathway of antigen presentation. Thus, besides MHC class I and II, a third lineage of antigen-presenting molecules that bind lipid and glycolipid antigens rather than peptides exists and is mediated by the family of CD1 proteins. CD1 isoforms (CD1a, b, c, and d) differentially sample both recycling endosomes of the early endocytic system and late endosomes and lysosomes to which lipid antigens are differentially delivered. These CD1 pathways include vacuolar acidification-independent pathways for lipid antigen presentation. These features of presenting lipid antigens, independently monitoring various antigen-containing intracellular compartments and avoiding certain evasive techniques employed by microbes, enable CD1 molecules to provide distinct opportunities to function in host defense against the microbial world.

Separate pathways for antigen presentation by CD1 molecules

The ability to sample relevant intracellular compartments is necessary for effective antigen presentation. To detect peptide antigens, MHC class I and II molecules differentially sample cytosolic and endosomal compartments. CD1 constitutes another lineage of lipid antigen-presenting molecules. We show that CD1b traffics deeply into late endosomal compartments, while CD1a is excluded from these compartments and instead traffics independently in the recycling pathway of the early endocytic system. Further, CD1b but not CD1a antigen presentation is dependent upon vesicular acidification. Since lipids and various bacteria are known to traffic differentially, either penetrating deeply into the endocytic system or following the route of recycling endosomes, these findings elucidate efficient monitoring of distinct components of the endocytic compartment by CD1 lipid antigen-presenting molecules.

Toward a Role of Dendritic Cells in the Germinal Center Reaction: Triggering of B Cell Proliferation and Isotype Switching

We have reported previously that in vitro generated dendritic cells (DC) can directly regulate B cell responses. Recently, germinal center DC (GCDC) were identified within B cell follicles. Due to their particular localization, we have tested in the present study whether GCDC could contribute to key events characteristic of the GC reaction. Our present results demonstrate that 1) ex vivo GCDC induce a dramatic GC B cell expansion upon CD40 and IL-2 activation and drive plasma cell differentiation, 2) this property is shared by GCDC and blood DC, but not by Langerhans cells, 3) IL-12 production by GCDC is critical in GC B cell expansion and differentiation, and 4) importantly, GCDC also induce IL-10-independent isotype switching toward IgG1. These observations support the novel concept that GCDC directly contribute to the germinal center reaction.

Langerhans cell (eosinophilic) granulomatosis. A clinicopathologic study encompassing 50 years

We summarize our experience with 238 cases of Langerhans cell granulomatosis (LCG), 198 of whom were followed for a median period of 10.5 years. Our patients did well unless overtreated, and no deaths were attributed to the disorder itself. The disease may appear in unifocal or multifocal form, and treatment is based on this fact. Virtually all patients recovered completely except for occasional residual orthopedic problems or residual diabetes insipidus. Several of the patients underwent subsequent pregnancies without difficulty. The granulomas primarily occur in bone, but lung, skin, and lymph nodal involvement is not uncommon. Involvement of thyroid, thymus, and other sites is rare. The hallmark of the disease is the accumulation of Langerhans cells (LCs). We review the pathology of LCG by histology, electron microscopy, and immunolabeling. LCs originally were identified in squamous epithelium, but these cells are part of the widespread system of dendritic cells. The latter cells, which arise from CD34+ progenitors, are specialized and efficient antigen-presenting cells for T-cell-mediated immunity. In LCG, however, the major associated cells are not T cells, but mature eosinophils: hence the original name eosinophilic granuloma. Confusion about terminology has been based upon the scanty and rather crude pathology reports in the original literature. The term histiocytosis X was meant to cover a spectrum of three diseases--eosinophilic granuloma, Hand-Schüller-Christian disease (HSC), and Letterer-Siwe disease (LS)--but HSC and LS have no basis in pathology and hence the terms are meaningless. The term HSC has become a synonym for multifocal eosinophilic granuloma (LCG). The term LS has been used in reporting a number of benign, malignant, or unknown conditions. We prefer the term LCG to avoid confusion with the term histiocytosis X because there is evidence that the LC is not a member of the mononuclear phagocyte system and hence not a tissue macrophage, and because the use of the term "histiocyte" has become a convenience in much of the literature when reporting incompletely understood diseases.

Structure and function of the CD1 family of MHC-like cell surface proteins

The CD1 family of proteins are structurally related to MHC class I proteins, but are only distantly related to the class I proteins or other MHC-linked class I-like proteins. Sequence comparisons indicate that the CD1 proteins have evolved into two subfamilies, those which are similar to human CD1a, b, and c and those which are similar to human CD1d. The CD1A-, B-, and C-like genes were deleted from rodents and the CD1D gene was duplicated. CD1a, b, and c are expressed by thymocytes, dendritic cells, activated monocytes, and B cells (CD1c), a tissue distribution which strongly suggests a role in antigen presentation. In contrast, CD1d and its murine homologues are expressed by many cells outside of the lymphoid and myeloid lineages. The CD1 proteins are in most cases expressed as beta 2mg-associated membrane glycoproteins, but may associate with additional proteins. CD1d is expressed on the surface of intestinal epithelial cells in a nonglycosylvated form without beta 2mg. Whether the CD1 proteins function as antigen-presenting molecules is unresolved, but it is unlikely that they present conventional peptide antigens. Strong evidence indicates that murine CD1 proteins are recognized by a population of NK1.1+, CD4+ or CD4-CD8- (double negative, DN) T cells which express an invariant TCR alpha chain. CD1d is most likely recognized by the homologous T cell population in humans. DN alpha beta T cells which recognize CD1a, b, or c have been isolated, including clones which recognize a lipid antigen from mycobacteria presented by CD1b. A third potential population of CD1 reactive cells are CD8+ T cells in the intestinal epithelium. Taken together, these observations indicate that CD1 proteins interact with several specialized populations of T cells. The precise biological functions mediated through these interactions remain to be determined.

Functional human epidermal Langerhans cells that lack Birbeck granules

Birbeck granules (BG) are cytoplasmic organelles that are only found in Langerhans cells (LC). The function of BG is still unclear, although it has been claimed that they are actively involved in receptor-mediated endocytosis and participate in the antigen-processing/presenting function of LC. We have identified a healthy white 29-year-old man whose LC completely lack the presence of BG as determined by electronmicroscopic studies. This was observed repeatedly using skin biopsy specimens taken from several places on the body during a period of 2.5 years. The absence of BG in these LG was documented further by the lack of staining with a BG-specific monoclonal antibody. Despite the complete lack of BG, LC were present in normal numbers, had all the usual morphologic characteristics, and were CD1a and human leukocyte antigen (HLA) class II positive. Two observations indicate that these BG-negative LC display normal antigen-presenting capacity. First, the individual could be sensitized by the hapten diphenylcyclopropenone. This was accompanied by a strong increase in the cell surface expression of HLA class II antigens on his LC, suggesting LC activation. Second, his epidermal cells elicited a normal positive response in an allogeneic mixed epidermal cell lymphocyte reaction. Together these observations strongly suggest that BG are not a prerequisite for normal LC function in vivo and in vitro.

Epidermal Langerhans cells and HIV-1 infection

Originating from the bone marrow, Langerhans cells migrate into the peripheral epithelia (skin, mucous membranes) and play a key role in the immune surveillance system against foreign antigens. They act as antigen-presenting cells through a specific cooperation with CD4+ lymphocytes after migration to the proximal lymph nodes. As HIV-1-permissive cells, Langerhans cells in genital or rectal mucosa may be the first infected cell type and may be the vectors of infection for CD4-positive T cells. It has been clearly demonstrated that Langerhans cells may be infected in HIV-1 sero-positive patients. Recently in vitro experimental infection of Langerhans cells was achieved using a co-culture assay with HIV-1-infected cells. Investigation into the exact role of Langerhans cells in the course of HIV-1 infection will contribute greatly to our understanding of AIDS pathogenesis.

Migration and maturation of Langerhans cells in squamous metaplasia of the rat trachea induced by vitamin A deficiency

The migration and maturation of Langerhans cells (LCs) in rat tracheal squamous metaplasia due to vitamin A deficiency were investigated immunohistochemically and electron microscopically. In the early stage of metaplasia, i.e. basal cell hyperplasia, no LCs with Birbeck granules (BGs) could be found, but there were desmosome-free cells which had the morphological characteristic of immature LCs. They were clearly different from inflammatory cells such as macrophages and lymphocytes, and were, therefore, considered to be precursors of LCs. In the stage of stratification, small numbers of Ia- and protein kinase C type II (PKCII)-positive cells were recognized. Ultrastructurally they were immature LCs with ovoid nuclei, many free ribosomes and few dendrites. The cytoplasm was dark and a few BGs and atypical granules (AGs) could be seen in the Golgi area. In the early stage of cornification, LCs with partially intended nuclei, prominent nucleoli and well-developed Golgi complexes were found. There were many BGs and AGs and structures transitional between them in the Golgi areas. In epithelium showing mature squamous metaplasia, many Ia- and PKCII-positive dendritic cells could be seen. Most of these were typical mature LCs with lobulated nuclei, clear cytoplasm and prominent dendritic processes. The number of BGs and AGs were fewer than in the LCs found in the early stage of cornification, and these granules were distributed throughout the cytoplasm. In the final stage, where the basal cells had differentiated into a flatter epithelium, few LCs could be seen.(ABSTRACT TRUNCATED AT 250 WORDS)

Studies on Langerhans cells in the tracheal squamous metaplasia of vitamin A deficient rats

LCs in the tracheal squamous metaplasia of vitamin A deficient rats were studied. The first appearance of LCs with Birbeck granules (BGs) was in the stage of stratification. The number of LCs increased along with the development of metaplasia, but decreased in number in the later stage, where basal cells also differentiate into flattened epithelium. In the area where only basal cells differentiated into flatter epithelium, without a cornified layer, LCs with BGs could also be found. These findings suggest that LCs which originate in bone marrow mature in squamous epithelium. The distribution and morphology of LCs are dependent on the state of keratinocytes, but not the presence of a cornified layer.

Internalization of Ia molecules into Birbeck granule-like structures in murine dendritic cells

Dendritic cells isolated from the draining lymph nodes of mice sensitized epicutaneously with hapten are potent antigen-presenting cells and contain Birbeck granules and cored tubules characteristic of antigen-activated epidermal Langerhans cells. We used immunogold labeling and transmission electron microscopy to follow the internalization of Ia molecules in these antigen-presenting cells. We found that Ia molecules were internalized into Birbeck granule-like structures in the antigen-activated dendritic cells. Computer reconstruction of serial sections of the dendritic cells demonstrated that these structures span the cytoplasm from the cell membrane to the nuclear membrane and are associated with lysosomes. The internalization of Ia molecules into these structures supports the hypothesis that the Birbeck granule-like structures are derived from the cell membrane and are involved in the antigen-processing/presenting function of the dendritic cells.

HLA class II expression on human epidermal Langerhans cells in situ: upregulation during the elicitation of allergic contact dermatitis

An immunoelectron-microscopic technique was applied to investigate the localization of molecules that are involved in the elicitation of allergic contact dermatitis in human epidermal cells in situ. Langerhans cells in the epidermis of lesions showed a strongly increased cell surface expression of HLA class II molecules as compared with normal skin. In addition, a high number of intracellularly located HLA class II molecules were present in Langerhans cells of lesional epidermis, suggesting increased biosynthesis of these molecules during the elicitation process. In contrast, no differences in the expression of CD1a by Langerhans cells was observed between normal and lesional skin. Frequently, the Langerhans cells were found in close apposition to mononuclear cells, which also exhibited a strong cell surface HLA class II expression. The number of Birbeck granules that are characteristic intracellular Langerhans cells organelles was increased in lesional Langerhans cells as compared with normal-skin Langerhans cells, which may correlate with the activated state of lesional Langerhans cells. These Birbeck granules were always HLA class II or CD1a negative. The increased synthesis and expression of HLA class II molecules on the cell surface of Langerhans cells suggests a direct role for these HLA class II molecules in the elicitation process of allergic contact dermatitis.

Generalized eruptive histiocytoma

The case is reported of a 56-year-old female who over 18 months developed a symmetrical eruption of hundreds of bluish-red papules, a small number of which have spontaneously resolved. The clinical and histopathological findings were compatible with the diagnosis of generalized eruptive histiocytoma. The ultrastructural findings in this case suggest that this condition which is in the non-X group of histiocytic disorders is closely related to histiocytosis X.

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.

A potential role for CD1a molecules on human epidermal Langerhans cells in allogeneic T-cell activation

The structural similarities of CD1a molecules to major histocompatibility complex (MHC) class I antigens, as well as their expression on epidermal antigen-presenting cells suggest that CD1a molecules might be involved in the cutaneous immune response. In the present study, we investigated the effect of different anti-CD1a monoclonal antibodies (BL6, DMC1, and Na1/34) on T cell proliferation induced by allogeneic epidermal cells in vitro. A significant inhibition of the mixed skin cell-lymphocyte reaction was obtained with BL6 and DMC1 monoclonal antibodies (MoAb), which recognize the same epitope on CD1a molecule. The observed inhibition could not be related to a steric hindrance of MHC class II molecules, because Na1/34 MoAb, which reacts with another epitope on CD1a molecule, had no significant effect. BL6 and DMC1 MoAb interfered with an early event of T-cell activation, as shown by a time-course study. In the presence of these MoAb, the addition of exogenous interleukin 2 did not restore T-cell proliferation. Furthermore, the inhibitory effect of anti-CD1a MoAb was not mediated by a suppressor factor released by Langerhans cells (LC). These present data suggest that CD1a molecule may have an important function in self peptide presentation by human Langerhans cells.