Autophagy links antimicrobial activity with antigen presentation in Langerhans cells

DC, through the uptake, processing, and presentation of antigen, are responsible for activation of T cell responses to defend the host against infection, yet it is not known if they can directly kill invading bacteria. Here, we studied in human leprosy, how Langerhans cells (LC), specialized DC, contribute to host defense against bacterial infection. IFN-γ treatment of LC isolated from human epidermis and infected with Mycobacterium leprae (M. leprae) activated an antimicrobial activity, which was dependent on the upregulation of the antimicrobial peptide cathelicidin and induction of autophagy. IFN-γ induction of autophagy promoted fusion of phagosomes containing M. leprae with lysosomes and the delivery of cathelicidin to the intracellular compartment containing the pathogen. Autophagy enhanced the ability of M. leprae-infected LC to present antigen to CD1a-restricted T cells. The frequency of IFN-γ labeling and LC containing both cathelicidin and autophagic vesicles was greater in the self-healing lesions vs. progressive lesions, thus correlating with the effectiveness of host defense against the pathogen. These data indicate that autophagy links the ability of DC to kill and degrade an invading pathogen, ensuring cell survival from the infection while facilitating presentation of microbial antigens to resident T cells.

Dysbiosis and Staphylococcus aureus Colonization Drives Inflammation in Atopic Dermatitis

Staphylococcus aureus skin colonization is universal in atopic dermatitis and common in cancer patients treated with epidermal growth factor receptor inhibitors. However, the causal relationship of dysbiosis and eczema has yet to be clarified. Herein, we demonstrate that Adam17(fl/fl)Sox9-(Cre) mice, generated to model ADAM17-deficiency in human, developed eczematous dermatitis with naturally occurring dysbiosis, similar to that observed in atopic dermatitis. Corynebacterium mastitidis, S. aureus, and Corynebacterium bovis sequentially emerged during the onset of eczematous dermatitis, and antibiotics specific for these bacterial species almost completely reversed dysbiosis and eliminated skin inflammation. Whereas S. aureus prominently drove eczema formation, C. bovis induced robust T helper 2 cell responses. Langerhans cells were required for eliciting immune responses against S. aureus inoculation. These results characterize differential contributions of dysbiotic flora during eczema formation, and highlight the microbiota-host immunity axis as a possible target for future therapeutics in eczematous dermatitis.

Mast Cells Have a Pivotal Role in TNF-Independent Lymph Node Hypertrophy and the Mobilization of Langerhans Cells in Response to Bacterial Peptidoglycan

Peptidoglycan (PGN) from Gram-positive bacteria, activates multiple immune effector cells. PGN-induced lymph node (LN) hypertrophy and dendritic cell mobilization in vivo were investigated following PGN injection into the skin. Both LN activation and the migration of Langerhans cells (LCs) to draining LNs were dependent on the presence of mast cells as demonstrated using mast cell deficient W/W(v) mice. However, these responses did not require TLR2, TLR4, or MYD88. TNF-deficient mice exhibited normal increases in LN cellularity but significantly reduced LC migration. In contrast, responses to IgE-mediated mast cell activation were highly TNF dependent. Complement component C3-deficient mice showed decreased LN hypertrophy and abrogated LC migration in response to PGN. These data demonstrate a critical role for mast cells and complement in LN responses to PGN and illustrate a novel TNF-independent mechanism whereby mast cells participate in the initiation of immunity.

Skin-derived dendritic cells acquire and degrade the scrapie agent following in vitro exposure

The accumulation of the scrapie agent in lymphoid tissues following inoculation via the skin is critical for efficient neuroinvasion, but how the agent is initially transported from the skin to the draining lymph node is not known. Langerhans cells (LCs) are specialized antigen-presenting cells that continually sample their microenvironment within the epidermis and transport captured antigens to draining lymph nodes. We considered LCs probable candidates to acquire and transport the scrapie agent after inoculation via the skin. XS106 cells are dendritic cells (DCs) isolated from mouse epidermis with characteristics of mature LC cells. To investigate the potential interaction of LCs with the scrapie agent XS106 cells were exposed to the scrapie agent in vitro. We show that XS106 cells rapidly acquire the scrapie agent following in vitro exposure. In addition, XS106 cells partially degrade the scrapie agent following extended cultivation. These data suggest that LCs might acquire and degrade the scrapie agent after inoculation via the skin, but data from additional experiments demonstrate that this ability could be lost in the presence of lipopolysaccharide or other immunostimulatory molecules. Our studies also imply that LCs would not undergo maturation following uptake of the scrapie agent in the skin, as the expression of surface antigens associated with LC maturation were unaltered following exposure. In conclusion, although LCs or DCs have the potential to acquire the scrapie agent within the epidermis our data suggest it is unlikely that they become activated and stimulated to transport the agent to the draining lymph node.

Antigen distribution and antigen-presenting cells in skin biopsies of human chromoblastomycosis

BACKGROUND

Chromoblastomycosis is a chronic, suppurative, granulomatous mycosis usually confined to skin and subcutaneous tissues. The host defense mechanisms in chromoblastomycosis have not been extensively investigated. The purpose of the present study was to determine the distribution and pathways of the fungal antigen(s) and the possible role of the different immunocompetent cells in antigen processing in skin lesions.

METHODS

The distribution of Fonsecaea pedrosoi antigen(s) in human skin was studied in 18 biopsies from 14 patients with chromoblastomycosis. A purified polyclonal immune serum raised in rabbits against metabolic antigen(s) of F. pedrosoi was used to detect yeast antigen(s) by immunohistochemical procedures. Double immunolabeling was performed with yeast antigen(s) and Langerhans' cells [labeled with anti-S100 protein monoclonal antibody (MoAb)], yeast antigen(s) and factor XIIIa+ dermal dendrocytes (immunolabeled with anti-factor XIIIa polyclonal antibody), and yeast antigen(s) and macrophages (labeled with CD 68 monoclonal antibody).

RESULTS

The F. pedrosoi antigen(s) accumulated in the skin macrophages and, in a few instances, in factor XIIIa+ dendrocytes and Langerhans' cells.

CONCLUSIONS

The data obtained suggest that chiefly macrophages, also Langerhans' cells and factor XIIIa+ dermal dendrocytes, function as antigen-presenting cells in chromoblastomycosis.

Epidermal Langerhans cells efficiently mediate CD1a-dependent presentation of microbial lipid antigens to T cells

Langerhans cells are a critical component of skin immunity, capable of capturing protein antigens in the epidermis and presenting them to specific T cells in the context of major histocompatibility complex class II molecules. Recently, a major histocompatibility complex independent pathway of lipid antigen presentation has been identified and is mediated by molecules of the CD1 family (CD1a, CD1b, CD1c, and CD1d). Because Langerhans cells are professional antigen-presenting cells and express CD1a molecules prominently, we hypothesized that Langerhans cells might play a role in T cell responses directed against not only peptide antigens but also lipid antigens. Here, we show that freshly isolated immature Langerhans cells as well as mature Langerhans cells that have migrated from the epidermis are efficient in presenting foreign microbial lipid antigens to specific T cells whereas dermal dendritic cells express much less CD1a molecules and function inefficiently. Further, we found that Langerhans cells migrating from epidermal sheets that were exposed to microbial lipid antigens expressed lipid-antigen-loaded CD1a molecules on the cell surface, resulting in activation of specific T cells. These results underscore an outstanding ability of Langerhans cells to mediate CD1a-dependent lipid antigen presentation. Thus, Langerhans-cell-mediated skin immunity may involve T cell recognition of both peptide and lipid antigens.

The histopathologic diagnosis of subclinical Johne's disease in North American bison (Bison bison)

The morphologic changes of subclinical Johne's disease in North American Bison (Bison bison) are characterized by microgranulomas composed of epithelioid macrophages and individual multinucleate giant cells of Langhans'-type occasionally containing individual cytoplasmic acid-fast bacilli compatible with Mycobacterium avium paratuberculosis. The microgranulomas are best visualized in the mesenteric lymph nodes of infected subclinical animals. Macrophages that can be confused with infection-associated epithelioid macrophages in the mesenteric lymph nodes are pigment-carrying cells from the intestinal tract. Mesenteric lymph node biopsy may be a useful diagnostic tool for detection of mild subclinical infection in individual ruminants from herds of unknown infection status. The biopsy may also be useful for Johne's disease surveillance during test-and-cull programs.

Antimicrobial activity of AmBisome and non-liposomal amphotericin B following uptake of Candida glabrata by murine epidermal Langerhans cells

The antifungal efficacy and cellular toxicity of AmBisome(R) and non-liposomal amphotericin B were compared in cultured epidermal Langerhans cells infected with Candida glabrata. Uptake of the yeast was determined by light and electron microscopy, and viability was assessed by plating dilutions of lysates from yeast-infected Langerhans cells and counting colony forming units. The Candida-infected Langerhans cells were incubated for 6, 24 or 48 h with 12.5 micro ml-1 of AmBisome or non-liposomal amphotericin B, non-drug-containing liposomes or media. Intracellular C. glabrata incubated with media or non-drug-containing liposomes showed a 2 log increase in cfu, and microscopic examination revealed budding yeast within the Langerhans cells. Both liposomal and non-liposomal amphotericin B treatment reduced intracellular growth of C. glabrata by 5 logs over 48 h of incubation. A morphometric analysis of cell ultrastructure demonstrated that AmBisome-treated Langerhans cells retained their cell architecture, but Langerhans cells treated with non-liposomal amphotericin B were characterized by the absence of intact organelles, disrupted non-granular cytoplasm and the presence of many large vacuoles. In conclusion, AmBisome was significantly less toxic for epidermal Langerhans cells than amphotericin B, but demonstrated comparable antifungal efficacy. After 48 h of drug exposure, both forms of amphotericin B effectively inhibited intracellular growth of C. glabrata, but only AmBisome did not damage the Langerhans cells.

M protein and protein F act as important determinants of cell-specific tropism of Streptococcus pyogenes in skin tissue

The pathogenic gram-positive bacterium Streptococcus pyogenes (group A streptococcus) causes numerous diseases of cutaneous tissue, each of which is initiated after the interaction of the bacterium with the cells of the epidermis. In this study, we show that different surface proteins of S. pyogenes play important roles in determining the cell-specific tropism of the bacterium in skin. Using streptococcal strains with defined mutations in the genes which encode surface proteins in combination with primary cultures of human skin and an in situ adherence assay which uses histological sections of human skin, we show that the M protein of S. pyogenes mediates the binding of the bacterium to keratinocytes, while a second streptococcal surface protein, protein F, directs the adherence of the organism to Langerhans' cells. Characterization of binding revealed that adherence was inhibited by purified streptococcal proteins and pretreatment of both host cells with the protease trypsin. Adherence was only slightly affected by the state of keratinocyte differentiation in vitro, but was considerably modulated in response to environmental conditions known to regulate expression of M protein and protein F, suggesting that the interaction between these bacterial cell-surface structures/adhesins and keratinocytes and Langerhans' cells may play an important role in streptococcal skin disease.

Quantitation by competitive PCR of HIV-1 proviral DNA in epidermal Langerhans cells of HIV-infected patients

Langerhans cells (LC) belong to the dendritic cell family and represent the principal antigen presenting cells populating squamous epithelia. We have reported the presence of human immunodeficiency virus Type 1 (HIV-1) proviral DNA and RNA in purified LC from the epidermis of seropositive patients. The aim of this study was to quantify HIV-1 proviral DNA in LC of infected patients using a competitive polymerase chain reaction (PCR) assay. Bulk epidermal cell (EC) suspensions were obtained from the skin of nine AIDS patients and six seronegative subjects. Purified LC and LC-depleted EC were prepared by immunomagnetic separation using an anti-CD1a monoclonal antibody. LC preparations did not contain T cells, as assessed by reverse transcription PCR analysis of the T cell receptor beta-chain gene (C region). In addition, no CD14+ cells could be detected in LC fractions by immunostaining of cytospin preparations. To quantify HIV-1 DNA, a new competitive PCR system was devised using SK145/150 as primers (gag) and a competitor plasmid DNA with a modified sequence (209 instead of 142 bp). The number of HIV-1 DNA copies found in the LC of AIDS patients ranged from 107 to 3,645/10(5) LC. In contrast, LC-depleted EC from the same subjects were all negative. The results indicate that in AIDS patients the frequency of infected LC is comparable to that reported for peripheral blood CD4+ T cells.

Streptococcal adherence to Langerhans cells: a possible step in the pathogenesis of streptococcal pharyngitis

Group A streptococci are nonmotile and have no structures that would enable them to penetrate submucosally into the pharynx. We have postulated that they adhere to host pharyngeal mucosal cells called Langerhans cells that are motile and could transport them into deeper tissues. We used a microscopic assay to assess the adherence of streptococci to cells from normal pharyngeal scrapings after the cells and bacteria were incubated in vitro. Langerhans cells were identified by immunofluorescent staining for the CD1a antigen. Nonstaining cells were considered to be keratinocytes. Of the 2279 cells examined from 9 subjects, 92.6% were keratinocytes and 7.4% were Langerhans cells. Only 1.8% of the 2111 keratinocytes had > 50 bacteria attached in this assay, while 76.2% of the 168 Langerhans cells had > 50 attached bacteria. Thus, under the conditions of this study, group A streptococci adhere preferentially to Langerhans cells from the pharynx. Adherence to these motile cells may provide a mechanism through which pathogenic streptococci may be transported into submucosal tissues.

Electron microscopy of Langerhans cells and Borrelia burgdorferi in Lyme disease patients

To investigate dermal and epidermal involvement in the presence of Borrelia burgdorferi and to analyze the role of Langerhans cells and keratinocytes, 14 cases of erythema chronicum migrans and two controls were studied by means of electron microscopy, using negative staining and sectioning techniques. Using immunoelectron microscopy and histochemistry, positive results for B. burgdorferi were disclosed in 5 cases of erythema chronicum migrans and 3 cases of neuroborreliosis which were confirmed by cultivation. We cultured 4 stains of B. burgdorferi from the skin, 1 from blood and 2 from cerebrospinal fluid in BSK medium. Near to the centre of erythema chronicum migrans with focal necrosis were both a dissolved basal membrane and keratinocyte desmosomes surrounding damaged B. burgdorferi cells in the epidermis. Markedly oedematous keratinocytes and Langerhans cells with B. burgdorferi were released into lymphocyte infiltrates. At the periphery of all erythema chronicum migrans lesions, keratinocytes were well preserved while all dendritic cells seemed to be vacuolated. Above foci of B. burgdorferi located perivascular or among collagen fibers, Langerhans cells were frequent and more granulated. The possible role of Langerhans cells in the identification and elimination of B. burgdorferi is discussed.

Langerhans cells in oral mucosa of rhesus monkeys before and after infection by simian retrovirus-1 and simian immunodeficiency virus

To study the influence of experimental infection with simian retrovirus-1 and simian immunodeficiency virus on the number and distribution of Langerhans cells in oral mucosa of rhesus monkeys, 10 monkeys were intravenously inoculated with simian retrovirus-1, 7 with simian immunodeficiency virus, and 2 were mock-inoculated. Biopsies were taken from gingiva and cheek pouch before infection and at 1 (simian immunodeficiency virus group only), 4, and 7 months after infection. Langerhans cells were detected in frozen sections by immunohistochemistry with monoclonal antibodies Leu-6 and HLA-DR. The mean number of Langerhans cells per surface millimeter and square millimeter of epithelium was calculated under blind conditions. The results showed no statistically significant differences in the number or distribution of Langerhans cells in the three groups at the various time points of examination. Similarly, no differences were detected within any group over the observation period. Thus systemic infection of rhesus monkeys with either simian retrovirus-1 or simian immunodeficiency virus does not lead to a significant change in the number of Langerhans cells in oral mucosal epithelium.

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.

Corneal Langerhans cell dynamics after herpes simplex virus reactivation

PURPOSE

The authors investigated the progressive changes in the distribution of corneal Langerhans cells (LC) after reactivation of latent herpes simplex virus type 1 (HSV-1) in mice.

METHODS

After corneal inoculation of National Institutes of Health inbred mice with HSV-1 and the establishment of latency, viral reactivation was induced by irradiating the ocular surface with 250 mJ/cm2 of ultraviolet B (UV-B) light.

RESULTS

Subsequent viral replication in the cornea was followed by the migration of the LC toward the paracentral and central corneal epithelium. These areas are normally devoid of LC. The number of LC in the paracentral and central regions of the eye reached a peak at day 14 post-UV-B irradiation. After UV-B irradiation of mice latently infected with HSV-1, the development of corneal stromal opacification and neovascularization closely followed the migration of LC toward the central cornea and paralleled the influx of T-cells into the corneal stroma. This pattern was not observed in irradiated uninfected mice.

CONCLUSIONS

LC migrate centrally in the corneal epithelium after viral reactivation. There is a direct correlation between the number of LC in the cornea and the degree of persistent stromal opacification.

Direct detection of HIV-1 RNA in epidermal Langerhans cells of HIV-infected patients

Human Langerhans cells (LC) are bone marrow-derived, HLA-DR+, CD1a+, and CD4+ dendritic antigen-presenting cells found in stratified squamous epithelia. As other members of the dendritic leukocyte family, to which they belong, LC have been reported as targets for HIV-1 infection. The aim of the present study was to investigate whether HIV-1 RNA is expressed in epidermal LC of HIV-1-infected patients. Bulk epidermal cell (EC) suspensions were prepared from skin of nine recently deceased AIDS patients and 11 seronegative controls. Purified LC (94 +/- 4% HLA-DR+ cells with no CD3+ cells, as assessed by flow microfluorimetry analysis) and LC-depleted EC were obtained by immunomagnetic separation using an anti-CD1a monoclonal antibody. Samples were analyzed for the presence of HIV-1 RNA by reverse transcription of a spliced mRNA region of the tat gene, followed by polymerase chain reaction amplification. HIV-1-spliced RNA was detected in LC from 6 of 9 patients examined, whereas LC-depleted EC fractions from the same patients were all negative. The results indicate that epidermal LC from HIV-seropositive patients actively transcribe HIV-1 proviral DNA, further supporting the hypothesis that HIV productively infected LC could serve as a reservoir of the virus in the epidermis and as a source for the infection of T lymphocytes.

In vitro infection of epidermal Langerhans cells with human immunodeficiency virus type 1 (HTLV-IIIB isolate)

Human epidermal Langerhans cells (LC) isolated from normal skin were infected in vitro with human immunodeficiency virus type 1 (HIV1). To control the permissivity of LC for HIV1, cells isolated from the epidermal sheet of normal skin by trypsinization were cocultured with HIV1-carrying promonocytic cells (U937) and observed by electron microscopy. An early sign of infection occurring in the coculture was the formation of retroviral type buds from LC membrane. Different steps in the process of viral budding up to virus release into the extracellular space were observed by electron microscopy. Treatment with either coupled phorbol esters/bacterial lipopolysaccharide or a recombinant cytokine (tumour necrosis factor alpha) did not significantly enhance viral production. The ability of in vitro infected LC to transmit virus to other haematopoietic cells and the consequences of such an infection on antigen-presenting function of LC remain to be elucidated.

In vitro HIV-1 entry and replication in Langerhans cells may clarify the HIV-1 genome detection by PCR in epidermis of seropositive patients

Being dendritic antigen-presenting cells in skin and mucous membrane, Langerhans cells (LC) occur in areas at risk for inoculation by human immunodeficiency virus (HIV), and the question whether LC act as a target, reservoir, or vector for transmission of HIV has given rise to much controversy. To address this question, we first analyzed the epidermal compartment of skin from patients seropositive for HIV DNA. Second, we tested the susceptibility of each cell type normally found in this compartment to in vitro infection by HIV-1. A non-denatured DNA was obtained from epidermal sheets after a thermochemical treatment of biopsies (0.5 M ethylenediaminetetraacetic acid (EDTA), pH 7.5 at 60 degrees C for 90 seconds). Optimization of amplification of viral genome was performed with three primer pairs derived from gag, env, and pol sequences. Polymerase chain reaction (PCR) products were analyzed by Southern blot. Viral genome was found in five of 11 HIV-seropositive patients. To control the permissivity of epidermal cell population for HIV, cells isolated from the epidermal sheet of normal skin by trypsinization were co-cultured with HIV-1-carrying promonocytic cells (U937) and observed by electron microscopy. After 3-6 h of co-culture, numerous virions were either tightly bound or apparently engaged in the process of internalization through receptor-mediated endocytosis. At day 4 of co-culture, some infected LC appeared to release mature viral particles through bud formation. The in vitro HIV-1 entry and replication in LC may confirm the presence of the HIV-1 genome by PCR in epidermis of seropositive patients. The consequences of the permissivity of LC for HIV on the antigen-presenting function remain to be determined.

Infection of accessory dendritic cells by human immunodeficiency virus type 1

Many details of the pathogenesis of the human immunodeficiency virus type 1 remain to be elucidated. Details of how the virus gains entry via the mucosal surface upon sexual contact or during breast feeding remain obscure. The means by which the infection travels throughout the body as well as the nature of the major reservoirs of virus infection remains, for the most part, unknown. Recent studies raise the possibility that cells of the Langerhans/dendritic lineage play a central role in human immunodeficiency virus (HIV-1) infection and pathogenesis. It has been known for several years that veiled dendritic cells in the circulation as well as skin Langerhans are infected in people with prolonged HIV-1 infections. More recently it has been found that a large burden of viral DNA sequences is found, not only in the circulating T-cell population, but also in a population that is defined as a non-T, non-B, non-monocyte/macrophage population rich in T-helper dendritic cells. Detailed analysis of infection of primary blood-derived T-helper dendritic cells by HIV-1 shows that such cells are the most susceptible cells in the blood to infection by this virus. The cells also produce much more virus per cell than do purified populations of other blood mononuclear cells. Moreover, primary blood-derived T-helper dendritic cells are not killed by infection by HIV-1. These cells are susceptible to lymphotropic, monocyte tropic, and primary isolates of HIV-1. The sensitivity of primary blood-derived T-helper dendritic cells to infection by HIV-1 has been shown to be attributable to rapid uptake of virus particles as well as rapid synthesis of viral DNA. Subsequent steps of virus replication also occur more rapidly and more efficiently in populations of primary blood-derived T-helper dendritic cells than they do in purified preparations of blood-derived T cells and monocyte/macrophages. Studies with primates using the simian immunodeficiency virus (SIV) show that dendritic cells at the surface of sexual mucosa are rapidly infected upon exposure to high concentrations of the virus. SIV is also produced in abundance in Langerhans cells located at the surface of the sexual mucosa in animals infected for prolonged periods of time.

Effects of epidermal Langerhans cell's conditioned medium on keratinocytes: a role of Langerhans cells in cholesteatoma

Langerhans cells (LCs) are known to play an important role in the immunosurveillance system. In this study, as in others, numerous LCs were detected in the epithelial layer of acquired cholesteatoma by immunohistochemical staining. This finding suggests that cell-mediated immune responses are initiated by LCs in cholesteatoma; however, documentation concerning the microenvironment of LCs-keratinocytes in cholesteatoma is limited. Therefore, we investigated the effects of LCs on keratinocytes in vitro. To study these effects it was necessary to isolate and purify LCs. Our present study revealed that good enrichment and a high degree of purity (95%) of LCs could be obtained from neonatal rat skin using the immunomagnetic beads (Dynabeads M-450) sorting technique. These isolated LCs have the biologic activity of LCs, and Langerhans cells' conditioned medium (LCCM) stimulates DNA synthesis in thymocytes. The effect of LCCM on keratinocytes was then studied. We found that (1) LCCM stimulated DNA synthesis in keratinocytes was then studied. We found that (1) LCCM stimulated DNA synthesis in keratinocytes, but not protein synthesis, and (2) LCCM stimulated the incorporation of 3H-putrescine into keratinocytes by the activation of transglutaminase. Transglutaminase is a known marker of terminal differentiation in keratinocytes. By Western blot analysis, we identified a 17-kd immunoreactive mouse interleukin-1 alpha in LCCM. Our results imply that LCs found in cholesteatoma tissue may play an important role in stimulating both hyper-proliferation and cornification of keratinocytes; two characteristic features of cholesteatoma formation. These stimulatory effects may be due to the release of interleukin-1 or other factors by LCs.

Monocytes, dendritic cells, and Langerhans cells in human immunodeficiency virus infection

Cells of the immune system are the target of infection with HIV. CD4 + T cells latently carry much of the viral burden in the blood and ultimately are depleted by infection with HIV. In contrast, infected tissue macrophages are long-lived and may serve as a viral reservoir. They are productive of relatively greater quantities of viral message RNA and its transcriptional product, infectious virions. Viral production by both cell types is modulated by environmental cytokines, the availability of which may be modified by the virus itself or by abnormally functioning HIV-infected immune cells. Not all susceptible cells are equally infected; although this phenomenon is not well understood, it has been related in vitro to maturation or differentiation. Blood DC and LC, antigen-presenting cells bearing many similarities to cells of the monocyte-macrophage lineage, are susceptible to HIV infection in vitro. Some evidence clearly indicates that, in vivo, epidermal LC may be infected with and productive of HIV and may be depleted or phenotypically altered in the HIV-infected individual. We, and others, have been unable to substantiate these findings by routine techniques used in the identification of HIV-infected macrophages in susceptible tissues, such as the brain, lungs, and lymph nodes (in situ hybridization for HIV-specific mRNA, electron microscopy for typical viral particles, recovery of infectious virus onto target cells, immunohistochemical staining of surface proteins in tissue, and polymerase chain reaction amplification of viral DNA). Evidence for the presence of HIV within the dermis of patients is clear; however, dermis contains a great variety of cell types as well as cells from the peripheral blood. We feel strongly that were the epidermis to harbor virus to any significant degree, it would have been identified by at least some of the methods described earlier. Although it is difficult to reconcile these reported differences, it appears that LC must be infected rarely. LC from lesional and apparently normal skin of HIV-infected individuals do not serve as an important reservoir of infectious HIV. Additionally, the diverse cutaneous manifestations seen in this population cannot be attributed directly to viral presence within the lesions but are more likely to result from the multifacted immunologic disregulation occurring systemically.

Detection of HIV-1 in epidermal Langerhans cells of HIV-infected patients using the polymerase chain reaction

Langerhans cells (LC) are bone marrow-derived, HLA-DR+, CD1a+, dendritic antigen-presenting cells found in stratified squamous epithelia. Within resident epidermal cells (EC), LC are the only cells expressing the CD4 antigen and are, therefore, a possible target for human immunodeficiency virus (HIV) infection. To date, conflicting results have been reported on the in vivo infection of LC by HIV. The aim of the present study was to investigate the presence of HIV-1 proviral DNA in epidermal LC of HIV-1-infected patients. EC suspensions were prepared from clinically normal skin of nine seropositive patients. Purified LC and LC-depleted EC were obtained by immunomagnetic separation and analyzed for the presence of HIV-1 proviral DNA by the polymerase chain reaction using primer pairs from different conserved regions (env and gag) of the HIV-1 genome. HIV-1 proviral DNA was detected in LC from seven of nine patients. LC-depleted EC fractions from the same nine patients were all negative, with the exception of one case. Altogether these results demonstrate that epidermal LC are infected by HIV-1 and constitute the only resident cell type in the epidermis harboring the virus. Further studies are, however, needed to demonstrate HIV replication in LC and to elucidate the functional role of LC in this infection.

Epidermal Langerhans cells are not principal reservoirs of virus in HIV disease

Several reports implicate Langerhans cells of skin as susceptible targets, reservoirs, and vectors for transmission of HIV: 1) numbers of Langerhans cells in skin of HIV-infected patients were decreased about 50% of that in control skin; 2) as many as 30% of Langerhans cells in the skin of HIV-infected patients were morphologically abnormal; 3) viral particles typical for HIV were identified in or around 2 to 5% of these cells; and 4) infectious HIV was isolated from skin biopsies of infected patients. These results were consistent with similar observations of HIV-infected macrophages in such tissues as brain, lung, and lymph node. Despite these findings, other investigators find no evidence for virus infection in the epidermis of HIV-infected patients by any of several immunohistochemical or ultrastructural criteria. To address this controversy, we obtained skin from 28 HIV-seropositive subjects at various clinical stages by full thickness biopsy or suction blister. Samples were analyzed by transmission electron microscopy for presence of HIV virions, by immunofluorescent staining for viral proteins, by in situ hybridization for HIV-specific mRNA, by polymerase chain reaction amplification of virus-specific DNA, and by direct virus isolation by coculture of epidermis onto monocyte target cells. By any of these techniques, demonstration of HIV in the epidermis of infected patients was equivocal and even then, infrequent. In contrast, viral DNA was detected from the dermis of the same skin samples (26 of 28 samples). Moreover, the number and morphology of Langerhans cells in skin of infected patients were within normal limits, regardless of stage of disease. These studies in toto suggest that a role for Langerhans cells as a principal viral reservoir or vector of transmission is highly unlikely.

Trypsin-resistant gp120 receptors are upregulated on short-term cultured human epidermal Langerhans cells

The CD4 molecule is known to be the preferential receptor for the HIV1 envelope glycoprotein. Epidermal Langerhans cells (LC) are dendritic cells which express several surface antigens, among them the CD4 antigens. LC infection was suggested when these cells were seen to present buddings coincident with membrane thickening of roughly 100 nm in size. These buddings were similar in ultrastructural aspect to HIV buddings on in vitro infected promonocytic cells (U937). To clarify the exact role of CD4 molecules in LC infection induced by HIV1, we investigated the possible involvement of between native and recombinant HIV1 gp120 and the LC surface. We also assessed the expression of CD4 molecules on LC membranes dissociated by means of trypsin from their neighbouring keratinocytes. The cellular phenotype was monitored using flow cytometry. We show that human LC can bind the viral envelope protein and that this binding does not depend on CD4 protein expression. The amount of surface bound gp120 was not consistent with the amount of CD4 antigens present on LC membranes. The gp120-binding sites on LC in suspension appear to be typsin-resistant while the CD4 antigens (at least the epitopes known to bind HIV1) are trypsin-sensitive. A burst of gp120 receptor expression was detected on 1-day cultured LC while the CD4 antigens disappeared. These findings lead to the logical conclusion that the binding of gp120 is due to the presence of a LC surface molecule which is different from CD4 antigens.

Latent infection of epidermal Langerhans cells in HIV-positive individuals

Epidermal cell suspensions obtained from 3 symptom-free HIV-positive individuals were cultured and marked with monoclonal antibodies for the HIV proteins p15, p24 and gp120 in the alkaline phosphatase anti-alkaline phosphatase staining technique. For 2 individuals, cells were positive after 3 days in culture, and for the third, after 4 days. Supernatant from one of the cultures infected allogeneic peripheral blood mononuclear cells. We conclude that epidermal Langerhans cells from symptom-free HIV-positive individuals are latent-infected and are able to produce and release HIV.

Immunocompetent cells and epithelial cell modifications in molluscum contagiosum

We studied lesions of molluscum contagiosum with a panel of monoclonal antibodies to determine the phenotype of infiltrating cells and antigen modifications of infected keratinocytes. Our data indicate (1) a complete lack of immunocompetent cells in the viral lesions, and simultaneously a loss of B2-microglobulin reactivity by molluscum bodies, a cellular activation of EGF and transferrin receptors and expression of CD36 antigen of these bodies; (2) a moderate infiltrate of activated T cells and monocytes in the underlying epidermis; (3) an increase of Langerhans cell density and a CD36 expression by the surface of upper layer keratinocytes in the perilesional epidermis.

HIV I infection of dendritic cells

Dendritic cells (DC) from human peripheral blood are susceptible to productive and probably to latent infection with HIV-I. Infection of DC also occurs in vivo since in HIV-seropositive individuals Langerhans' cells of the skin and DC from peripheral blood, (in preparation) are infected. In peripheral blood 3-25% of DC, identified as large, low-density cells lacking monocyte markers, are infected as judged by in situ hybridization with an HIV probe. This contrasts with the lower proportion (< 0.2%) of other cells infected. DC exposed to HIV in vitro or in vivo fail to present other antigens or mitogens to stimulate T cells. This functional defect in infected DC is not blocked by the presence of soluble CD4 antigen and occurs in the absence of T cell infection suggesting a block at the level of the antigen-presenting cell itself. Infection, depletion and dysfunction of DC in HIV seropositive patients is already present in asymptomatic individuals and this precedes the appearance of T cell defects. We speculate that loss of functional DC may be a fundamental defect leading to a block in recruitment of resting T cells into immune responses. In contrast to the HIV-induced impairment of antigen presentation by DC, these cells were potent stimulators of responses to the HIV antigens themselves. Normal DC infected with HIV in vitro stimulated primary proliferative and cytotoxic T cell responses (in preparation). These were produced in cells from individuals expressing a range of different MHC types but the cytotoxic cells, once produced, killed autologous but not allogeneic, infected T cell blasts. Primary response to viral peptides can also be produced suggesting that this system may be useful for identifying immunogenic epitopes of HIV using cells from sero-negative, non-immunocompromised individuals.

Langerhans cell density and activity in mouse skin and lymph nodes affect herpes simplex type 1 (HSV-1) pathogenicity

Langerhans cells are epidermal antigen-presenting cells that function by taking up antigens in the skin, migrating to the lymph nodes, where they are designated interdigitating cells, and triggering the immune response. The role of interdigitating cells (IDC) was investigated in a murine model of herpes simplex virus-1 infection in the skin. The number of IDC in the lymph nodes began to increase on the first day following infection and reached a peak three days p.i. Low titers of infectious virus were recovered from the fraction of lymph node cells that consisted of 60-80% IDC at one day p.i. Lymph node cells that were obtained from mice immunized with HSV-1 proliferated in vitro in response to viral antigens but did not respond to mock antigens. When mice were immunized with HSV-1 inoculated into skin that had been depleted of Langerhans cells, this in vitro proliferative response was abolished. Thus, the present results suggest that Langerhans cells function in the immune defense of the skin against HSV-1 infection by transporting the virus to the peripheral lymph nodes where an immune response is initiated. Injection of the immunomodulator OK-432 into the footpad skin caused a local increase in the number of Langerhans cells in the epidermis and led to an increased migration of dendritic cells to the lymph nodes. Under these conditions, a decrease in HSV-1 pathogenicity was noted. These observations indicate that the pathogenicity of herpes simplex virus type 1 in the skin is affected by Langerhans cell density and activity in the epidermis and the lymph nodes.

The relationship of corneal Langerhans cells to herpes simplex antigens during dendritic keratitis

The corneal migration and topographic distribution of Langerhans cells (LC) in relation to herpes simplex virus antigens was studied during the course of dendritic keratitis in inbred mice. Corneal epithelial sheets from infected mice at selected time points were "double stained" for Ia-positive Langerhans cells and HSV antigens, using a sequential avidin biotin immunoperoxidase and glucose oxidase technique. The amount of HSV antigen was maximum at day 2 paralleling the clinical time course, with most corneal epithelium HSV antigen negative by day 8. LC were seen in peripheral corneas by day 2 and in paracentral and central cornea by day 8, with peak numbers detected between days 8 and 11 post-infection. Although HSV antigens and LC were simultaneously detected within corneal epithelium, LC were not observed in anatomic juxtaposition to HSV antigens, even after reinoculation of infected corneas with HSV on day 14 following the primary infection. These data suggest that local factors in the corneal epithelium other than HSV antigens per se may be chemotactic for LC during the course of dendritic keratitis.

Immunohistochemical study of normal skin of HIV-1-infected patients shows no evidence of infection of epidermal Langerhans cells by HIV

Langerhans cells (LC) are dendritic epidermal antigen-presenting cells expressing the surface molecule CD4, which renders them theoretical cellular targets for direct infection by the human immunodeficiency virus (HIV). To date, somewhat conflicting results have been reported concerning the in vivo infection of LC by HIV as well as the numerical alteration of these cells in the course of HIV infection. In the present work we studied clinically normal skin of a group of 44 HIV-1-seropositive patients classified according to the Centers for Disease Control (CDC) stages II (n = 14), III (n = 9), and IV (n = 21). Monoclonal antibodies (MAb) to HIV p18, p24, and gp120 and to HLA-DR and CD1a antigens (specific for LC) were applied on frozen skin sections using an amplification biotin-streptavidin-fluorescein technique. The MAb to HIV p18 cross-reacted with a cytoplasmic antigen of epidermal basal keratinocytes also present on HIV-seronegative skin specimens. No other reactivity was observed with any of the three anti-HIV MAb. The quantitative study showed that no significant correlations could be established between the number of LC (evaluated independently by HLA-DR and CD1a antigens) and the number of peripheral blood CD4+ve lymphocytes or the CDC disease stage. These results cast some doubt on the previously reported in vivo infection and numerical decrease in LC in HIV infection. The precise involvement of LC in HIV infection awaits further investigation.

The response of Langerhans cells to palatal cover plates in the rat

It is not known whether the long-term use of prosthetic or orthodontic appliances, which may be associated with fungal infections, affects Langerhans cells (LC) in the underlying mucosa. The number and distribution of LC was studied in rat palatal epithelium over a 7-day period after insertion of cover plates. Smears of cultures taken before and at the end of the experiment were examined for fungi. LC were identified in cryostat sections using an immuno-alkaline phosphatase technique to demonstrate cell surface Ia (Class II Major Histocompatibility Complex antigens). Occluding the palate predisposed to food trapping and microbial growth. Fungi were recovered from the plates of two animals but not from control or experimental animals before fitting the plates. No differences in LC numbers were found on days 1 and 3 after insertion of the plates, but a significant increase was observed on day 7. It is not known whether this change represents a true increase in LC number or an increase in Ia expression, but it is likely to be the response to an alteration in the number and/or nature of antigens penetrating the mucosa because of microbial growth and food retention.

HIV target cells: effect of their infection by HIV on the pathogenesis of AIDS

Pathogenesis of HIV infection and expression of retroviral proteins are gradually being elucidated. Antibody to HIV is a marker of past or present viral infection. The virus can be isolated from cultured lymphocytes of seropositive but not seronegative patients. Sero-epidemiological studies show that the majority of infected patients are asymptomatic carriers without biological sign of immune depression. Some then show immune abnormalities such as a decrease of CD4 cells in the blood; some patients present with lymphadenopathies or signs of AIDS-related complexes. Frank AIDS is a late stage of the disease. Some cofactors increase the immunodeficiency and then accelerate the passage from asymptomatic carrier to persistent generalized lymphadenopathies or AIDS by spreading the virus into target cells, susceptible T4 cells, bone marrow precursors, or brain. These AIDS patients then present with opportunistic infections and/or malignancies like Kaposi's sarcoma, lymphoma, and/or brain diseases (dementia or encephalitis).

The presence of bacteria in the oral epithelium in periodontal disease. III. Correlation with Langerhans cells

Langerhans cells (LC) are cell types found in the skin and gingiva. LC have immunological functions as phagocytic cells and as antigen-presenting cells for T and B lymphocytes. Sections from biopsies of the gingiva in cases of periodontal disease were found to have increased numbers of LC. These biopsies also contained intragingival bacteria. Serial sections of frozen specimens of human gingiva were prepared for staining. Hematoxylin and eosin were used for tissue survey, the Gram stain for assessment of bacterial invasion, anti-Leu-6 monoclonal antibody associated with peroxidase technique (PAP) to identify LC, antibacterial sera to Bacteroides gingivalis and Actinobacillus actinomycetemcomitans associated with peroxidase to specifically identify these two common periodontopathogenic bacteria. Additional positive identification of bacteria was performed by preparing the same histological section containing gram-stained particles for scanning electron microscope and transmission electron microscope LC confirmation. The results suggest that the increased number of LC seen in diseased sites of oral epithelium containing intragingival microorganisms may be one of the host immune mechanisms to penetration by bacteria.

Epidermal Langerhans cells--a target for HTLV-III/LAV infection

Langerhans cells (LC) are bone marrow-derived, Ia+, CD1+, CD4+, ATPase+ dendritic antigen-presenting cells within the human epidermis. Since the CD4 molecule has been implicated as a receptor structure for HTLV-III/LAV (human T-cell leukemia virus/lymphadenopathy-associated virus), we asked whether LC from HTLV-III/LAV-seropositive individuals display signs of HTLV-III/LAV infection. In skin biopsies from 7/40 HTLV-III/LAV-infected persons (1 asymptomatic carrier, 2 patients with acquired immunodeficiency syndrome (AIDS)-related complex and 4 patients with AIDS), LC were the only epidermal cells to react with a monoclonal antibody specific for the HTLV-III core protein p17. A varying percentage of p17+ LC were morphologically altered with blunt dendrites and poorly demarcated cellular contours. In one of these biopsies, the presence of LC-associated viral particles characteristic of HTLV-III/LAV as well as cytopathic changes in approximately one-third of the LC population were demonstrated by electron microscopy. These results strongly suggest that LC may harbor HTLV-III/LAV. The infection of LC with this retrovirus may have deleterious consequences for the immunologic functions of this cell system and may thus contribute to both the acquisition of immunodeficiency and the infectious and neoplastic complications of AIDS.

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

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

Langerhans cells at the sites of vaccinia virus inoculation

Langerhans cells in the epidermis at the sites of vaccina virus inoculation were studied with the electron microscope. The cells contained unusually increased numbers of the Langerhans cell granules. Such abnormal Langerhans cells have not been described except for in histiocytosis X. Vaccinia virus particles were found in the Langerhans cells, where they were located individually or embedded in the granular matrix or in lysosomes.

Langerhans' cells are an actual site of HIV-1 replication

Human epidermal Langerhans' cells (LC) are HLA-DR+/DQ+, CD1+, CD4+ dendritic antigen-presenting leukocytes. Based on the observation that in certain human immunodeficiency virus type 1 (HIV-1) infected individuals, LC are the only epidermal cells to react with monoclonal antibodies against HIV-1 isolate termed human T-lymphotropic virus IIIB/83 core proteins p17 and p24, we have proposed that LC can serve as a target for HIV-1. This contention was strengthened by the ultrastructural finding of HIV-1-like particles in the close proximity of LC and by the demonstration of signs of moderate to severe LC damage. Detailed electron microscopic analysis of skin and mucosal biopsies from an AIDS patient with p17/p24-positive LC now revealed not only mature HIV-1-like virions in the extracellular space surrounding LC and in intracytoplasmic LC vacuoles, but also developmental forms of HIV-1-like particles budding from LC surface membranes. Using peripheral blood derived monocytes/macrophages as targets for HIV-1 isolation, a virus isolate, designated human T-lymphotropic virus III WR-SK/86, was recovered from skin tissue from this patient by cocultivation and identified as unique by nucleic acid hybridization analysis. These findings now conclusively show that HIV-1 replicates in and is released from LC and support the concept that antigen-presenting cells (mononuclear phagocytes, LC) can serve as a reservoir for the acquired immunodeficiency syndrome virus.