Uptake, intracellular transport and degradation of exogenous protein by Langerhans cells. An electron microscopic-cytochemical study using peroxidase as tracer substance

Langerhans Cell Granule as Phagocytic Organelle

In recent years the epidermal Langerhans cell has been considered to belong to histiocytic rather than melanocytic lineage. However, the functional significance of the Langerhans cell granule, which has also been called Bribeck's granule or racket body, has not been settled. In this study, 0.1 ml of horseradish peroxidase solution (25 mg in 1.0 ml normal saline) was injected intradermally into six sites on the back of a normal adult guinea pig. The injected sites were biopsied at 10, 30, 60, 120, 180 and 300 minutes and later at 22, 120 and 142 hours. The epidermis was minced with sharp razor blades into 1 mm blocks and fixed in 5% glutaraldehyde in 0.1 M cacodylate buffer (pH 7.2) for 3 hours at 4°C. After overnight rinse in the same buffer, tissue blocks were minced again into smaller pieces to facilitate the penetration of benzidine and hydrogen peroxide. Benzidine reaction was done according to the method of Schneeberger-Keeley and Karnowsky.

New topical treatment of vulvodynia based on the pathogenetic role of cross talk between nociceptors, immunocompetent cells, and epithelial cells

Topical treatments of localized neuropathic pain syndromes in general are mostly neglected, mainly due to the fact that most pain physicians expect that a topical formulation needs to result in a transdermal delivery of the active compounds. On the basis of the practical experience, this study brings forth a new, somewhat neglected element of the vulvodynia pathogenesis: the cross talk between the nerve endings of nociceptors, the adjacent immunocompetent cells, and vaginal epithelial cells. Insight into this cross talk during a pathogenic condition supports the treatment of vulvodynia with topical (compounded) creams. Vulvodynia was successfully treated with an analgesic cream consisting of baclofen 5% together with the autacoid palmitoylethanolamide 1%, an endogenous anti-inflammatory compound. In this review, data is presented to substantiate the rationale behind developing and prescribing topical products for localized pain states such as vulvodynia. Most chronic inflammatory disorders are based on a network pathogenesis, and monotherapeutic inroads into the treatment of such disorders are obsolete.

Real-time visualization of macromolecule uptake by epidermal Langerhans cells in living animals

As a skin-resident member of the dendritic cell family, Langerhans cells (LCs) are generally regarded to function as professional antigen-presenting cells. Here we report a simple method to visualize the endocytotic activity of LCs in living animals. BALB/c mice received subcutaneous injection of FITC-conjugated dextran (DX) probes into the ear skin and were then examined under confocal microscopy. Large numbers of FITC(+) epidermal cells became detectable 12-24 hours after injection as background fluorescence signals began to disappear. Most (>90%) of the FITC(+) epidermal cells expressed Langerin, and >95% of Langerin(+) epidermal cells exhibited significant FITC signals. To assess intracellular localization, Alexa Fluor 546-conjugated DX probes were locally injected into IAβ-enhanced green fluorescent protein (EGFP) knock-in mice and Langerin-EGFP-diphtheria toxin receptor mice--three dimensional rotation images showed close association of most of the internalized DX probes with major histocompatibility complex (MHC) class II molecules, but not with Langerin molecules. These observations support the current view that LCs constantly sample surrounding materials, including harmful and innocuous antigens, at the environmental interface. Our data also validate the potential utility of the newly developed imaging approach to monitor LC function in wild-type animals.

Revisiting the tolerogenicity of epidermal Langerhans cells

Langerhans cells (LC) are unique members of the dendritic cell (DC) family residing in the epidermis of skin and mucosa. Specific autocrine and environmental factors shape the biology of LC, such as TGF-beta1, IL-10, vitamin D(3), UV light or neuropeptides, which are required for LC development but also influence their capacity to induce immunity or tolerance. Both, immunogenic and tolerogenic functions require antigen transport from the skin to the draining lymph nodes, but the LC maturation grade directs the differential outcome. In this review, we recapitulate early indications for LC tolerogenicity and oppose them to more recent findings with gene-targeted mice, which dramatically challenged some of the early results. The newly discovered Langerin(+) dermal DC subset (DDC) seems to be responsible also for many tolerogenic effects that were initially attributed to steady state migratory LC. Transfer of antigens from LC to other DC subsets as well as transport of HIV are discussed as part of the complex interactions between LC and other cells or as mechanisms of immune evasion. Finally, the first clinical trials on allergy therapies targeting skin DC in the steady state are mentioned as they may open the door to curative tolerogenic therapies.

Antigen-presenting cells, including Langerhans cells, veiled cells and interdigitating cells

The accessory functions attributed to macrophages, such as antigen presentation, are probably carried out by specialized, marrow-derived cells which always have Ia antigen on their surfaces. These cells are not actively phagocytic, but are mainly engaged in engulfing large volumes on fluid. They are found in the epidermis as sessile cells, the Langerhans cells, but some re-enter the dermis and appear in afferent lymph as actively moving, veiled cells. Here they are joined by other veiled cells which have differentiated in the dermis: both populations then enter the draining lymph node. A similar process of differentiation probably occurs in other specialized tissues leading to the formation of cells that enter the afferent lymph and become veiled cells. In the lymph node, veiled cells localize in the paracortex or T-dependent area and later differentiate into another sessile cell type, the interdigitating cell. The life-style of this family of cells appears to be well-adapted for the transport of antigen into the paracortex, an area from which free antigen is largely excluded, and it seems likely that T-cell activation is triggered by the arrival of veiled cells bearing a new antigen on their surfaces.

Processing and presentation of type II collagen, a fibrillar autoantigen, by H-2q antigen-presenting cells

Native type II collagen (CII) is a high molecular-weight fibrillar molecule which induces a chronic polyarthritis in mice expressing the H-2q haplotype. The present study was initiated to analyze the processing and the presentation of this nonglobular protein by H-2q antigen-presenting cells (APC). Efficiency of presentation was assessed by the ability of antigen-pulsed APC to activate collagen-specific CD4+ T cell hybridomas. Fixation of APC or the presence of chloroquine completely blocked the reactivity of the T cell hybrids to native, denatured and cyanogen bromide (CB) degraded CII, thus indicating the requirement of intracellular processing for adequate presentation of CII peptides to T cells. In the presence of various processing inhibitors (brefeldin A, leupeptin and N-tosyl-L-phenylalanine chloromethylketone) stimulation of T hybrids by CII-pulsed APC was reduced, pointing to the need of newly synthesized class II molecules, the use of several intracellular compartments and the implications of different proteases in the generation of CII peptides. Peritoneal macrophages and, to a lesser extent, total spleen cells, presented native and denatured CII with higher efficiency than purified splenic dendritic cells, naive or even immune B cells from CII-primed mice. In contrast, these dendritic and B cells were fully competent to present intact ovalbumin to a specific T cell hybrid. The stimulation by dendritic cells and immune B cells was greater when CB peptides of CII were added instead of the native molecule. Similarly, the cleavage of CII was an absolute requirement for its presentation by epidermal cells and B cell lymphomas to the T cell hybridomas. Taken together, these findings emphasize the crucial role of intracellular processing for recognition of soluble CII, similar to most antigens. However, in contrast to ovalbumin, the size and fibrillar nature of the native CII molecule influences its capture by the APC, thus limiting the type of APC able to present this antigen.

Epithelial expression of HLA class II antigens and Fc gamma receptors in patients with adult periodontitis

The distribution of HLA class II (DR, DP, DQ) and Fc gamma R (I, II, III) was analyzed in the epithelia of patients with advanced marginal periodontitis using cryostat sections incubated with monoclonal antibodies (MoAb) against the Langerhans cell (LC) (CD1a) and various subtypes of HLA class II and Fc gamma R, and the indirect immunofluorescence technique. In the oral gingival epithelium (OGE), LC were concentrated subjacent to the connective tissue papillae, while in the pocket epithelium (PE), they were most abundant at the gingival margin. HLA-DP, DQ, and DR stained LC in both OGE and PE. HLA-DQ+ LC were significantly fewer than DP+ and DR+ LC. HLA-DR also stained keratinocytes (KC) in the whole extension of both OGE and PE. HLA-DP was also observed on KC, but not HLA-DQ. Fc gamma R II stained both LC and focal areas of KC. In PE FC gamma R II+ LC were concentrated near the bottom of the pocket, while in the OGE, they were concentrated at the gingival margin. Fc gamma R III was present only on KC, especially in the basal and suprabasal layer. The results indicate that the epithelial cells are actively involved in the development and maintenance of the inflammation of periodontal disease.

Phagocytosis of antigens by Langerhans cells in vitro

Dendritic cells (DC) isolated from lymphoid tissues are generally thought to be nonphagocytic in culture. It has therefore been unclear how these cells could acquire particulate antigens such as microorganisms for initiation of primary immune responses. Lymphoid DC derive in part from cells that have migrated from nonlymphoid tissues, such as Langerhans cells (LC) of skin. The ability of LC to internalize a variety of particles was studied by electron, ultraviolet, phase, and differential interference contrast microscopy, and by two-color flow cytometry. Freshly isolated LC in epidermal cell suspensions phagocytosed the yeast cell wall derivative zymosan, intact Saccharomyces cerevisiae, representatives of two genera of Gram-positive bacteria, Corynebacterium parvum and Staphylococcus aureus, as well as 0.5-3.5-microns latex microspheres. During maturation in culture, the phagocytic activity of these cells was markedly reduced. Likewise, freshly isolated splenic DC were more phagocytic than cultured DC for two types of particle examined, zymosan and latex beads. Unlike macrophages, LC did not bind or internalize sheep erythrocytes before or after opsonization with immunoglobulin G or complement, and did not internalize colloidal carbon. The receptors mediating zymosan uptake by LC were examined. For this particle, C57BL/6 LC were considerably more phagocytic than BALB/c LC and exhibited a reproducible increase in phagocytic activity after 6 h of culture followed by a decline, whereas this initial rise did not occur for BALB/c LC. These differential kinetics of uptake were reflected in the pattern of zymosan binding at 4 degrees C, and endocytosis of the soluble tracer fluorescein isothiocyanate-mannose-bovine serum albumin at 37 degrees C. Zymosan uptake by LC from both strains of mice was inhibited in the presence of mannan or beta-glucan, although to different extents, but not by antibodies specific for CR3 (CD11b/CD18). These data indicate that zymosan uptake by LC can be mediated by a mannose/beta-glucan receptor(s) that is differentially expressed in the two strains of mice and that is downregulated during maturation of LC in culture.

The inter-relation between inflammation and epidermal proliferation in normal skin following epicutaneous application of leukotriene-B4--an immunohistochemical study

Topical application of leukotriene-B4 (LTB4) on normal skin has been used as an in-vivo model to investigate cutaneous inflammation and epidermal proliferation, which are important phenomena in the pathogenesis of psoriasis. The aim of the present investigation is to further elucidate the interrelation between inflammation and epidermal proliferation, using specific monoclonal antibodies as markers for the different cell types involved. Aliquots of LTB4 were applied on the upperarms of eight healthy volunteers. After LTB4-application, biopsies were taken at consecutive time intervals. On frozen sections, epidermal proliferation was assessed by Ks8.12-(keratin 16) and Ki-67-binding (cycling cells), inflammation was characterized using anti-elastase (PMN), T11 (T-lymphocytes), pan-B (B-lymphocytes), WT 14 (CD14-positive cells) and OKT 6 (Langerhans cells). New observations were that the density of CD14-positive cells was increased even at 8 h and decreased slightly at 72 h. A striking rearrangement of Langerhans cells was seen in close vicinity to intra-epidermal accumulations of PMN. Remarkably an increased density of these cells in the dermis at 72 h was seen and a decrease in the epidermis. In line with previous studies, the accumulation of PMN reached a maximum 24 h after LTB4-challenge. The identity of the mononuclear infiltrate cells which have been reported 48-72 h after LTB4 proved to be T-lymphocytes. No B-lymphocytes were observed. Ki-67-positive nuclei were maximally increased 72 h after LTB4-application, which implies that recruitment of cycling cells is of relevance for the LTB4-induced proliferation in vivo. The hyperproliferation-related keratin 16 was expressed inconsistently in the suprabasal compartment.(ABSTRACT TRUNCATED AT 250 WORDS)

Processing and presentation of intact hen egg-white lysozyme by dendritic cells

Dendritic cells in lymphoid tissues are of key importance as highly specialized antigen-presenting cells for the induction of T lymphocyte responses. Conflicting results have been published regarding antigen processing of intact proteins by dendritic cells. We now report that highly purified dendritic cells isolated from H-2k mouse spleens very efficiently generated immunogenic fragments of intact hen egg-white lysozyme (HEL) protein to present to an I-Ak-restricted T hybridoma cell line, specific for HEL peptide 46-61. Dendritic cells required 100 times less HEL protein than lipopolysaccharide-induced B cell blasts for effective presentation. Uptake of 125I-labeled HEL protein by dendritic cells and inhibition of presentation of HEL protein by chloroquine treatment was observed. This indicates an endocytotic process and the involvement of acidified compartments. Since the supernatant of dendritic cells, that were incubated with intact HEL protein, contained immunogenic fragments, further evidence for processing of HEL protein by dendritic cells was obtained. When HEL protein was covalently coupled to beads, dendritic cells were not able to ingest these beads, but could still process HEL protein for presentation. This suggests cell surface processing of HEL protein, although internalization of HEL protein released from the beads cannot be excluded. Taken together, these data show that H-2k dendritic cells are capable of processing and presenting intact HEL protein.

Cytomembrane-derived Birbeck granules transport horseradish peroxidase to the endosomal compartment in the human Langerhans cells

It has been previously shown that the cytomembrane of human Langerhans cells (LC) has the capacity to fold upon itself, thereby forming Birbeck granules (BG), which then internalize. I confirmed this by exposing LC in vitro to horseradish peroxidase (HRP) at +8 degrees C and +37 degrees C. On incubation at +37 degrees C the label appeared not only in BG, but also in tubular structures and vesicles of different shapes and sizes. Interconnections between these labeled endosomal structures were common. The LC cytomembrane could form BG at +8 degrees C and, moreover, the BG was the only organelle that was labeled and internalized at this temperature. Thus, cytomembrane-derived BG are endocytotic in nature and link the exterior of the cell and the endosomal compartment. The membrane interlinking of the BG may eventually dissolve and the BG then transform into an endosomal vesicle.

Birbeck granules or Birbeck junctions? Intercellular "zipperlike" lattice junctions in eosinophilic granuloma of bone

Three cases of eosinophilic granuloma of bone exhibited intercellular attachments between histiocytes, with a pentalaminar structure identical to that seen in nearby intracellular Birbeck granules (BG). It is proposed that the term "lattice junction" be coined to describe this organelle, which seems to be expressed only by cells of monocytic-histiocytic lineage. While this finding confirms the ability of the surface membrane to form such structures, it does not necessarily preclude other intracytoplasmic sites of origin for some BG. The previously suggested role of BG in membrane storage and regulation is reiterated as a supportable model for their function.

Accumulation of membrane-bound melanosomes occurs in Langerhans cells of patients with the Leopard syndrome

The Langerhans cells in the lentigines of four patients with the Leopard syndrome contained large membrane bound accumulations of melanin granules. Giant melanosomes were only seen in two patients. The patients had no immune-based symptoms relating to their lentigines. The Leopard Syndrome, also known as multiple lentigines syndrome, progressive cardiomyopathic lentiginosis, lentiginosis profusa syndrome and the cardiocutaneous syndrome, refers to an inherited abnormality of the skin, often associated with cardiomyopathy. The aetiology of the condition is so far unknown and the penetrance is variable. Here we describe electron microscopical findings of large accumulations of melanin within Langerhans cells.

Class II major histocompatibility complex molecules of murine dendritic cells: synthesis, sialylation of invariant chain, and antigen processing capacity are down-regulated upon culture

Dendritic cells (DCs), such as Langerhans cells (LCs) of the epidermis and the DCs of lymphoid organs such as spleen, are potent antigen presenting cells. DCs express high levels of major histocompatibility complex (MHC) class II molecules, but, partly because of the low numbers of primary DCs in any tissue, there has been no detailed study of the biochemistry of their class II molecules. This information may be needed to help explain recent findings that DCs process native protein antigens when freshly isolated from epidermis and spleen. Processing ceases during culture, yet a strong accessory function for activating resting T cells develops. We studied immunoprecipitates of DC class II and invariant chain (Ii) molecules by two-dimensional gel electrophoresis. We found that (i) freshly isolated LCs synthesize large amounts of class II and Ii polypeptides; (ii) Ii molecules that are known to be involved in antigen processing display an unusually large number of sialic acids in fresh LCs; (iii) with culture, class II and Ii synthesis decreases dramatically and has virtually ceased at 3 days; and (iv) the turnover of class II in pulse/chase experiments is slow, being undetectable over a 12- to 32-hr culture period, whereas the turnover of Ii is rapid. We conclude that MHC class II molecules of DCs do not seem to be qualitatively unique. However, the regulation of class II and Ii expression is distinctive in that biosynthesis proceeds vigorously for a short period of time and the newly synthesized class II remains stably on the cell surface, whereas Ii turns over rapidly. This may enable DCs to process and retain antigens in the peripheral tissues such as skin and migrate to the lymphoid organs to activate T cells there.

Antigen processing by epidermal Langerhans cells correlates with the level of biosynthesis of major histocompatibility complex class II molecules and expression of invariant chain

Two prior studies with a small number of T cell lines have shown that the presentation of native protein antigens by epidermal Langerhans cells (LC) is regulated. When freshly isolated, LC are efficient antigen-presenting cells (APC), but after a period of culture LC are inefficient or even inactive. The deficit in culture seems to be a selective loss in antigen processing, since cultured LC are otherwise rich in major histocompatibility complex (MHC) class II products and are active APC for alloantigens and mitogens, which do not require processing. We have extended the analysis by studying presentation to bulk populations of primed lymph node and a T-T hybrid. Only freshly isolated LC can be pulsed with the protein antigens myoglobin and conalbumin, but once pulsed, antigen is retained in an immunogenic form for at least 2 d. The acquisition of antigen, presumably as MHC-peptide complexes, is inhibited if the fresh LC are exposed to foreign protein in the presence of chloroquine or cycloheximide. The latter, in contrast, improves the efficacy of antigen pulsing in anti-Ig-stimulated B blasts. In additional studies of mechanism, we noted that both fresh and cultured LC endocytose similar amounts of an antigen, rhodamineovalbumin, into perinuclear granules. However, freshly isolated LC synthesize high levels class II MHC molecules and express higher amounts of the class II-associated invariant chain. Fresh LC are at least 5-10 times more active than many other cells types in the level of biosynthesis of MHC class II products. These findings provide a physiologic model in which newly synthesized MHC class II molecules appear to be the principal vehicle for effective antigen processing by APC of the dendritic cell lineage. Another APC, the B lymphoblast, does not appear to require newly synthesized MHC class II molecules for presentation.

Interstitial dendritic cells

Interstitial dendritic cells (IDC) were first identified in the interstitium of non-lymphoid organs as leucocytes which stained intensely with anti-MHC class II antibodies. These cells have been identified in several species including man, and can be distinguished from tissue macrophages by their immunological phenotype and cytochemical and functional characteristics. IDC appear to be closely related to lymphoid dendritic cells (DC), and have the capacity to bind antigen and stimulate T lymphocyte responses. It seems probable that they represent a stage of nonlymphoid dendritic cell differentiation necessary for antigen surveillance, similar to the Langerhans cell of the skin. Exposure to antigen appears to induce migration of these cells into adjacent lymphatics and subsequent localization in the interfollicular areas of lymph node, where the DC present processed antigen to activate a primary T cell response. The IDC has been identified as the passenger leucocyte within organ allografts which contributes substantially to graft immunogenicity, so that eradication of donor organ IDC improves organ graft survival.

The human immunodeficiency virus long terminal repeat is preferentially expressed in Langerhans cells in transgenic mice

Four lines of transgenic mice containing the HIV LTR linked to the bacterial gene encoding chloramphenicol acetyltransferase (CAT) were constructed. In each line, a characteristic tissue pattern of CAT expression was observed with detectable levels present in the eye, heart, spleen, thymus, and tail. Low levels of CAT were present in circulating lymphocytes, but CAT activity in these cells could be augmented following treatment with the mitogen phytohemagglutinin (PHA). Likewise, CAT expression was present at only low levels in circulating monocytes, but higher levels of CAT were observed in macrophages grown in the presence of various cytokines (CSF-1, GM-CSF, IL-1 alpha, IL-4, and IL-2). Furthermore, Langerhans cells recovered from skin showed higher levels of CAT activity than those observed in other cells of monocyte-macrophage lineage. These results indicate that LTR-CAT expression in cells of monocyte-macrophage lineage may increase in proportion to the degree of differentiation of these cells. These animals may be useful in the study of cell-specific determinants of LTR-directed gene activity and may serve to identify exogenous cofactors that promote the progression of HIV-related disease in vivo.

Presentation of exogenous protein antigens by dendritic cells to T cell clones. Intact protein is presented best by immature, epidermal Langerhans cells

The capacity of dendritic cells to present protein antigens has been studied with two MHC class II-restricted, myoglobin-specific, T cell clones. Spleen dendritic cells and cultured epidermal Langerhans cells (LC) presented native myoglobin weakly and often not at all. These same populations were powerful stimulators of allogeneic T cells in the primary MLR. Freshly isolated LC were in contrast very active in presenting proteins to T cell clones but were weak stimulators of the MLR. Both fresh and cultured LC could present specific peptide fragments of myoglobin to the clones. These results suggest that dendritic cells in nonlymphoid tissues like skin can act as sentinels for presenting antigens in situ, their accessory function developing in two phases. First antigens are captured and appropriately presented. Further handling of antigen then is downregulated while the cells acquire strong sensitizing activity for the growth and function of resting T lymphocytes. The potent MLR stimulating activity of cultured epidermal LC and lymphoid dendritic cells probably reflects prior handling of antigens leading to the formation of allogeneic MHC-peptide complexes.

Appearance of Birbeck granule-like structures in anti-T6 antibody-treated human epidermal Langerhans cells

We have previously demonstrated by immunogold labeling techniques that the T6 surface antigen of living human Langerhans cells (LC) of the skin is internalized by a process of receptor-mediated endocytosis (RME). Receptor-mediated endocytosis induced by the binding of the monoclonal anti-T6 antibody BL6 involves coated pits, coated vesicles, endosomes, the smooth endoplasmic reticulum, and lysosomes. After RME, gold-labeled Birbeck granules (BGs) appear in the cell center. In the present study, by modifying the experimental conditions but retaining the presence of gold-labeled BL6, we have observed (in addition to the above-mentioned gold-labeled organelles) images that appear to correspond to BG-like structures. These structures, like the intracytoplasmic BGs, are pentalaminar and gold-labeled, but they differ from the intracytoplasmic BGs by their attachment to the cell membrane, their length, the frequent presence of a coat, and by prolongation by one or more coated pits. Birbeck granule-like structures seem to result, at the ultrastructural level, from receptor ligand interactions and from modifications of the LC shape.

Different cellular reaction patterns of epidermal Langerhans cells after application of contact sensitizing, toxic, and tolerogenic compounds. A comparative ultrastructural and morphometric time-course analysis

BALB/c mice were treated with the irritants croton oil (0.5%, 20%), sodium lauryl sulfate (15%), and benzalkonium chloride (25%), the contact sensitizers 2,4-dinitrofluorobenzene (DNFB, 0.3%) and picryl chloride (PCl, 1%), and the tolerogen 2,4-dinitrothiocyanatebenzene (DNTB, 2%). All irritants used produced degenerative alterations of Langerhans cells (LCs). After application of 0.5% croton oil, however, this degeneration was preceded by an activation of the cells with increased number of mitochondria and enlargement of nuclei. The DNFB and PCl application in sensitizing doses to nonsensitized animals resulted in a cellular activation similar to that observed for 0.5% croton oil. In addition, these LCs showed enhanced adsorptive endocytosis as demonstrated by increased numbers of Birbeck granules and coated vesicles. The endocytotic activity was more pronounced in DNFB-sensitized animals. The DNTB at a concentration that induced tolerance to DNFB did not cause either cellular or endocytotic activation of LCs. These results demonstrate that the contact sensitizers DNFB and PCl induce characteristic cellular reaction patterns of LCs, which may be related to their sensitizing property.

Langerhans cell presentation of sheep red blood cells induces antibody production

Mouse epidermal Langerhans cells (LC) were found to be capable of presenting sheep red blood cells (SRBC) to immune spleen lymphocytes, resulting in antibody production as assessed by a direct plaque cell assay. Spleen lymphocytes, prepared by removal of adherent cells, were unable to respond to SRBC in a 5-day culture; however, when co-cultured with either epidermal cells or splenic adherent cells, a response to SRBC occurred, as demonstrated by an increase in the number of antibody-producing cells. The LC were shown to be the antigen-presenting cells in these cultures, as depletion of LC via their Fc receptors abrogated the response. A similar reduction in the number of epidermal LC added to cultures likewise failed to induce antibody production. These experiments demonstrate that LC are able to present complex cellular antigens to the immune system, resulting in a B lymphocyte response.

Langerhans' cells, veiled cells, and interdigitating cells in the mouse recognized by a monoclonal antibody

An mAb, NLDC-145, is described that specifically reacts with a group of nonlymphoid dendritic cells including Langerhans cells (LC), veiled cells (VC), and interdigitating cells (IDC). The antibody does not react with precursor cells in bone marrow and blood. Macrophages are not stained by the antibody, but a subpopulation of Ia+ peritoneal exudate cells is recognized. Possible relationships of the various nonlymphoid dendritic cell (NLDC) types are discussed.

Leu-3/T4 expression on epidermal Langerhans cells in normal and diseased skin

Recent evidence exists that the expression of the Leu-3/T4 antigen is not restricted to thymus-derived lymphocytes but can also be detected on mononuclear phagocytes and epidermal Langerhans cells (LC). When searching for the presence of Leu-3/T4 antigen-bearing cells in tissue sections of a variety of inflammatory and neoplastic skin disorders, we observed quantitative and qualitative differences in the intensity of anti-Leu-3a labeling of epidermal dendritic cells. Reasoning that Leu-3/T4 expression by these cells might be a dynamic event, we compared the anti-Leu-3a LC staining pattern in clinically normal-appearing skin (CNAS) with the expression of this antigen on epidermal dendritic cells in a variety of skin disorders. For this purpose, 4-microns cryostat sections were exposed to the monoclonal anti-Leu-3a reagent and antibody binding was visualized by a sensitive 4-step immunoperoxidase technique. Within CNAS, Leu-3a+ dendritic epidermal cells were visualized at the threshold of detectability. Immunoelectron microscopic studies confirmed the LC nature of these cells. In sharp contrast to CNAS, strong and prominent anti-Leu-3a LC labeling was almost invariably encountered in biopsy specimens from patients with cutaneous T-cell lymphoma and various inflammatory conditions but not in proliferative disorders of resident skin cells. Whereas in CNAS the density of T6+ epidermal dendritic cells greatly exceeded that of anti-Leu-3a-reactive dendritic cells, these differences were less pronounced in diseased skin. Our results: confirm earlier observations that epidermal LC may bear Leu-3/T4 antigens; and in addition, suggest that the degree of Leu-3/T4 expression is regulated by signals from inflammatory cells. The induction of class II alloantigen receptors on class II alloantigen-bearing LC may represent an important regulation mechanism of antigen-presenting cell function.

The Langerhans cell granule is an adsorptive endocytic organelle

The role of Langerhans cell granules (LCG) in adsorptive endocytosis was studied by using concanavalin A (Con A) and heterologous anti-epidermal cell serum (AES) as ligands. Isolated epidermal cells were obtained by trypsinization of guinea pig skin fragments and exposed to ferritin-conjugated Con A or AES followed by ferritin-conjugated second antibody at 37 degrees C for various times up to 30 min. Langerhans cells among the treated epidermal cells were observed by electron microscopy. Shortly after the incubation, a few LCG in the cell periphery were filled with ferritin particles in the bulb portion. After prolonged incubation, ferritin-containing LCG increased in number and seemed to move to the juxtanuclear area. The granules were derived from plasma membrane invaginations that collected ferritin particles in a saclike extension at the end. Some of these invaginations were apparently of coated pit origin. The contents in the bulb of LCG seemed to be delivered finally to intracellular degradation compartments. Our findings clearly demonstrate that LCG are an adsorptive endocytic organelle.

Derivation of Langerhans cell granules from cytomembrane

OKT6 monoclonal antibody has been shown to react selectively with Langerhans cell (LC) cytomembrane in human skin. Taking advantage of this property, we examined the stainability of LC granules with OKT6 using immunoperoxidase method at the ultrastructural level. It was found that the delimiting membranes of LC granules, both attached to the cytomembrane and in the cytoplasm, were specifically stained in the epidermal sheet. These findings suggest that LC granules are derived from invagination of LC cytomembrane and retain T6 antigen. We employed two new methods: one is promotion of endocytosis by incubating the epidermal sheet in tissue culture medium with OKT6 at 4 degrees C and further incubation without OKT6 at 37 degrees C, and the other is the use of saponin to facilitate penetration of the secondary antibody through the cytomembrane of LC. In the LC cytoplasm only the delimiting membrane of the granule was stained; other membranous organelles, such as mitochondria and rough endoplasmic reticulum, did not react.

Isolation and characterization of interferon-producing reticuloendothelial cells from mouse epidermis

A homogeneous population of trypsin-resistant epidermal cells has been isolated from newborn ICR mice. These cells are characterized by adherence, receptors for Fc-IgG, ATPase activity, phagocytosis of latex particles and opsonized sheep erythrocytes, and secretion of lysozyme and interferon. The production of interferon by these cells suggests that they may be important in protection against viral infections of the skin as well as in regulation of immune responses. The ultrastructure of these trypsin-resistant epidermal cells shows striking similarity to that of reticuloendothelial cells.

Histiocytic and dendritic reticulum cells shown by a zinc iodide-osmium technique

Structures corresponding to histiocytic and dendritic reticulum cells have been shown in human tonsillar tissue, "reactive" lymph nodes and spleens by means of a zinc iodide-osmium technique. These cell types have been shown in various locations in these tissues using paraffin and resin embedded sections produced after fixation/staining of the tissue in zinc iodide-osmium. The quality of morphology attained by this procedure is much improved compared with the demonstration of the two cell types by means of alpha-naphthyl acetate esterase reactions performed on frozen sections. The zonal architecture of the lymphoid follicle is emphasised by this technique. In lymph nodes, sinus lining cells are also shown. Lymphoid cells, polymorphs, fibroblasts, and endothelial cells are negative with the zinc iodide-osmium method. In addition, interdigitating cells are not stained. The results of this procedure are compared with those with those of other methods for the demonstration of histiocytic and dendritic reticulum cells.

Coated Langerhans cell granules in histiocytosis X cells

Histiocytosis X cells (HXC) and epidermal Langerhans cells (LC) are thought to be closely related because they share morphologic features and immunologic markers. One of these common markers, the LC granule, is an acknowledged morphologic criterion for the identification of these cell types, but its function and, thus, significance are as yet unknown. In this study, we report the presence of a fuzzy coat radiating from the cytoplasmic face of the LC granule membrane in HXC. This bristly coat is indistinguishable from that of coated vesicles and pits and, thus, represents a strong morphologic clue to the function of LC granules because coated structures have been shown to be involved in the selective transport of molecules in eukaryotic cells.

The nature of Langerhans cells granules: an ultrastructural study

Langerhans cells and macrophages have been studied in both oral lichen planus lesions and histiocytosis X. Many of the macrophages in both lesions contained phagolysosomes in various stages of degradation. Some of these phagolysosomes were found to develop slender processes and very narrow extensions containing little processed phagocytosed material. These latter structures were indistinguishable from Langerhans granules and were termed Langerhans granule-like structures. There is enough evidence in the present study to suggest that typical Langerhans granules evolve from Langerhans granule-like structures and to confirm that Langerhans cells are a type of macrophage which at one stage of their development show Langerhans granules.