Human epidermal Langerhans cells express integrins of the beta 1 subfamily

Fibroblasts as confederates of the immune system

Fibroblastic stromal cells are as diverse, in origin and function, as the niches they fashion in the mammalian body. This cellular variety impacts the spectrum of responses elicited by the immune system. Fibroblast influence on the immune system keeps evolving our perspective on fibroblast roles and functions beyond just a passive structural part of organs. This review discusses the foundations of fibroblastic stromal-immune crosstalk, under the scope of stromal heterogeneity as a basis for tissue-specific tutoring of the immune system. Focusing on the skin as a relevant immunological organ, we detail the complex interactions between distinct fibroblast populations and immune cells that occur during homeostasis, injury repair, scarring, and disease. We further review the relevance of fibroblastic stromal cell heterogeneity and how this heterogeneity is central to regulate the immune system from its inception during embryonic development into adulthood.

Ultraviolet B radiation suppresses Langerhans cell migration in the dermis by down-regulation of alpha4 integrin

BACKGROUND/PURPOSE

Ultraviolet B (UVB) radiation affects the migration and function of epidermal Langerhans cells (LC) and causes immunosuppression of contact hypersensitivity. It is known that LC leaves the epidermis after exposure to UVB. To know the behavior of LC in the dermis after UVB radiation, we studied the effect of UVB radiation on the expression of integrin families on freshly isolated or cultured murine LC. We also examined whether UVB radiation affects the migration of LC to secondary lymphoid tissue chemokine (SLC/6Ckine).

METHODS

Integrin expressions of murine LC cultured in epidermal cell suspension were analyzed using flowcytometry. We used murine LC sorted flowcytometrically for binding assay to extracellular matrix and for migration assay to chemokine. Skin explant assay and immnohistochemical staining for 'cords formation' were performed as previously described.

RESULTS

Twenty and 40 mJ/cm2 of UVB radiation down-regulated the expression of alpha4 integrin on 24 h-cultured LC, but not that of alpha6, beta1, or beta4 integrin. The number of cultured LC adhered to fibronectin, a ligand for alpha4 integrin, was decreased after UVB irradiation, while that to laminin, a ligand for alpha6 integrin, was not influenced. UVB radiation reduced the number of migrating LC to SLC. Furthermore, skin sheet explant experiments showed that UVB radiation inhibited the 'cords' formation in dermal vessels of the 48 h-cultured skin.

CONCLUSIONS

These data suggest that UVB radiation may suppress the migration of LC from the dermis to lymphatic vessels. UVB radiation may downregulate the adherence of LC to dermal fibronectin and migration to SLC, and consequently suppress the migration of LC from the UVB-irradiated dermis to lymphatics.

Alpha 6 integrins are required for Langerhans cell migration from the epidermis

Topical exposure of mice to chemical allergens results in the migration of epidermal Langerhans cells (LCs) from the skin and their accumulation as immunostimulatory dendritic cells (DCs) in draining lymph nodes. Epidermal cell-derived cytokines have been implicated in the maturation and migration of LCs, but the adhesion molecules that regulate LC migration have not been studied. We hypothesized that integrin-mediated interactions with extracellular matrix components of the skin and lymph node may regulate LC/DC migration. We found that alpha 6 integrins and alpha 4 integrins were differentially expressed by epidermal LCs and lymph node DCs. A majority of LCs (70%) expressed the alpha 6 integrin subunit, whereas DCs did not express alpha 6 integrins. In contrast, the alpha 4 integrin subunit was expressed at high levels on DCs but at much lower levels on LCs. The anti-alpha 6 integrin antibody, GoH3, which blocks binding to laminin, completely prevented the spontaneous migration of LCs from skin explants in vitro and the rapid migration of LCs from mouse ear skin induced after intradermal administration of TNF-alpha in vivo. GoH3 also reduced the accumulation of DCs in draining lymph nodes by a maximum of 70% after topical administration of the chemical allergen oxazolone. LCs remaining in the epidermis in the presence of GoH3 adopted a rounded morphology, rather than the interdigitating appearance typical of LCs in naive skin, suggesting that the cells had detached from neighboring keratinocytes and withdrawn cellular processes in preparation for migration, but were unable to leave the epidermis. The anti-alpha 4 integrin antibody PS/2, which blocks binding to fibronectin, had no effect on LC migration from the epidermis either in vitro or in vivo, or on the accumulation of DCs in draining lymph nodes after oxazolone application. RGD-containing peptides were also without effect on LC migration from skin explants. These results identify an important role for alpha 6 integrins in the migration of LC from the epidermis to the draining lymph node by regulating access across the epidermal basement membrane. In contrast, alpha 4 integrins, or other integrin-dependent interactions with fibronectin that are mediated by the RGD recognition sequence, did not influence LC migration from the epidermis. In addition, alpha 4 integrins did not affect the accumulation of LCs as DCs in draining lymph nodes.

Epidermal Langerhans' cells in children with primary T-cell immune deficiencies

Dendritic cells are the major antigen-presenting cells, especially for naive T lymphocytes; it is conceivable therefore that their absence or dysfunction may induce an immune deficiency (ID). Few data are available, however, concerning dendritic cells in human primary ID. Langerhans' cells (LC) are intraepidermal dendritic cells which express specific markers and may therefore be studied by immunohistochemistry on paraffin-embedded skin samples. Skin samples of nine children with primary ID were studied and compared with five age-matched controls. LC were present within the epidermis of two children with X-linked severe combined ID, a condition related to the lack of the common gamma-chain of interleukin-2 (IL-2), IL-4, IL-7, IL-9, and IL-15 receptors. LC were also present in skin samples of a child with Omenn syndrome and in three children with combined ID. By contrast, no LC were detected in the skin samples of two children with alymphocytosis and of a child with reticular dysgenesis, a condition characterized by the absence of peripheral blood leukocytes.

Langerhans' cells produce type IV collagenase (MMP-9) following epicutaneous stimulation with haptens

For initiation of the contact hypersensitivity response, epidermal Langerhans' cells (LC) migrate from the epidermis to draining nodes via afferent lymphatics by passing through the basement membrane. In this study, we examined production of matrix metalloproteinases (MMPs) in LC-enriched epidermal cells to clarify the type of enzymes involved in LC transmigration through the basement membrane. Using gelatine enzymography and immunoblotting analysis, 95,000 MW type IV collagenase (MMP-9) was found to be produced by LC-enriched epidermal cells. Analysis of the kinetics of MMP-9 expression showed that its production was induced within 6 hr after application of 2,4,6-trinitrochlorobenzene (TNCB), substantially increased between 12 hr and 24 hr, and then decreased to the normal level by 7 to 10 days. Other haptens, such as 2,4-dinitrochlorobenzene and 2,4-dinitrofluorobenzene, also induced MMP-9 expression. Fluoroescence-activated cell sorter analysis revealed that LC were one of the major cell types to express MMP-9 in response to TNCB. In addition, highly enriched LC from sensitized skin were shown to express strong gelatinolytic activity. These results indicate that LC by themselves, as well as other epidermal cells, are capable of producing MMP-9, and suggest that MMP-9 may contribute to proteolysis associated with transmigration of LC in the induction phase of contact dermatitis.

Expression of the antigen recognized by mAb GB36 in normal skin and in skin tumours

GB36, a mouse monoclonal antibody (mAb) raised against an epithelial antigen of the human trophoblast, reacts with the epithelial basement membrane of chorionic villi; it does not react with the invasive extravillous cytotrophoblast. Expression and characterization of the antigen of GB36 (designated GBA36) were investigated in normal keratinocytes by immunoprecipitation, immunofluorescence and immunoelectron microscopic studies. Immunoprecipitation experiments demonstrated that the proteins identified on keratinocytes by mAb GB36 and a rat mAb anti-integrin alpha 6 (GoH3) were the same. Using immunofluorescence and immunoelectron microscopic methods, GBA36 was localized on the cell membrane facing the epithelial basal lamina of basal keratinocytes. GBA36 distribution in benign and malignant skin tumours was evaluated by immunostaining methods (immunofluorescence and immunoperoxidase). Analysis of tumours revealed that whereas benign epithelial tumours and intradermal naevi displayed high levels of GBA36, the expression of this antigen decreased progressively in spinocellular and basal cell carcinomas, and in cutaneous melanomas in relation to invasiveness. During cell transformation, GBA36 undergoes quantitative alterations, and expression is down-regulated. Although the functional relevance of these changes remains unknown, the correlation of decreased GBA36 expression with tumour progression may indicate a role for altered integrin expression in tissue invasion by human skin carcinoma and melanoma.

Expression of ICAM-3 on human epidermal dendritic cells

Three counter-receptors for LFA-1 of the immunoglobulin family have been discovered: ICAM-1, ICAM-2, and ICAM-3. Despite their homologies, their patterns of expression suggest specialized roles. The finding that ICAM-3 is much better expressed than other LFA-1 ligands on monocytes and resting T cells, and that this discovery may be important in the initiation of immune responses prompted us to search for the expression of ICAM-3 by human epidermal Langerhans cells (LC). Six out of eight different ICAM-3 monoclonal antibodies were found to be reactive with epidermal LC. Immunoelectron-microscopy staining revealed that 100% of freshly-isolated, typical Birbeck granules containing LC expressed ICAM-3. After one day and three days of culture, 100% of LC still expressed ICAM-3, but the staining intensity was decreased by 58% and 76% respectively. Immunoprecipitation of 125I surface-labeled LC with anti-ICAM-3 antibodies revealed a polypeptide with apparent M(r) of 122,000-125,000. To determine whether ICAM-3 was involved in LC function, mixed epidermal cell-lymphocyte reactions were performed with freshly isolated LC in the presence of various concentrations of different anti-ICAM-3 antibodies. Among the different antibodies tested, HP2/19 and CBR-IC3/1 were found to partially block the reaction in a dose-dependent manner, suggesting that ICAM-3 represents a new molecule involved in the initiation of the immune response driven by epidermal LC.

Foot and mouth disease virus replication in bovine skin Langerhans cells under in vitro conditions detected by RT-PCR

The replication of foot and mouth disease virus (FMDV) was studied in isolated bovine skin Langerhans cells (LC), in keratinocytes from epidermal cell suspension, and in migrating LC obtained from cultured bovine epidermal sheets in vitro. Viral RNA replication in infected cells was determined by the reverse transcriptase-polymerase chain reaction (RT-PCR) of the negative FMDV RNA strand and by the plaque forming assay of FMDV. It was established that bovine skin LC, keratinocytes, and migratory bovine LC infected with FMDV strain 01 Geshur supported virus replication. This RT-PCR method to detect the negative strand of FMDV RNA in migratory bovine skin LC may be useful for determining FMD virus replication in tissue cells.

An analysis of the role of skin Langerhans cells (LC) in the cytoplasmic processing of HIV-1 peptides after "peplotion" transepidermal transfer and HLA class I presentation to CD8+ CTLs--an approach to immunization of humans

Skin Langerhans cells (LC) are antigen-presenting cells capable of expressing MHC class I and class II molecules on the plasma membrane. This molecular activity was reviewed to combine the knowledge of peptide presentation by MHC and HLA class I and class II molecules to prime CD8+ cytotoxic T cells (CTLs) and CD4+ T helper cells, respectively. The possible utilization of the skin dendritic cells for the development of antiviral CTLs and antibodies by synthetic peptides modeled according to the motifs of peptides that naturally interact with the peptide binding grooves of the various HLA haplotypes is discussed and evaluated. It may be possible that the introduction of synthetic viral peptides with motifs to fit the HLA class I haplotypes of a human population to the skin dendritic cells will prime selectively the cellular or the humoral immune responses. This approach may provide a new vaccination technique that applies synthetic virus peptides as vaccines for the immunization of humans. The neuropeptide CGRP interacts with LC and modulates antigen presentation.

Epidermal and mucosal dendritic cells and HIV1 infection

The major modes of HIV1 transmission involve circumstances and behavior that promote exchange of blood or body fluids containing HIV virus and/or HIV infected cells. In the second group, semen, vaginal secretions, exudates and occasionally saliva have been documented as sources of transmission. If the skin, protected by the horny layer, does not seem easily infected, the mucous membrane and especially the vaginal, rectal or oral mucosa are the main sites of HIV entry in absence of lesions. In mucosa, a well identified population of dendritic cells may be considered as the first target of HIV1: the Langerhans cells. Originated from the bone marrow, the 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 antigenpresenting cells through a specific cooperation with CD4+ lymphocytes after migration to the proximal lymph nodes. As HIV1-susceptible 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 is clearly demonstrated that LC may be infected in HIV1 seropositive patients. Recently in vitro, experimental infection of Langerhans cells was reproduced using a co-culture assay with HIV1 infected cells. Recent data obtained with transgenic mice containing HIV1 gene underline the key role of Langerhans cells in the pathogenesis process of HIV infection.

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.

Mast cell degranulation upregulates alpha 6 integrins on epidermal Langerhans cells

The expression of the alpha 6 beta 4 and alpha 6 beta 1 integrins on epidermal Langerhans cells (LC) before and after mast cell degranulation was studied in cultured human neonatal foreskin by immunohistochemistry. Twenty-four hours after addition of mast cell secretagogues, morphine sulfate, or substance P, solitary mid-epidermal cells showed staining for the integrin subunits alpha 6, beta 4, and beta 1. This expression was not observed in cultured control explants, and immunostained cells were confirmed to be non-epithelial, dendritic cells by immuno-electron microscopy. The identity of these cells as LC was further established by coincident staining for alpha 6 and CD1a using double immunofluorescence labeling. Addition of tumor necrosis factor-alpha (TNF alpha), the predominant cytokine in mast cell granules, also induced LC to express alpha 6 integrins. Furthermore, preincubation of skin organ cultures with anti-TNF alpha antibodies or the mast cell inhibitor cromolyn sodium abrogated the ability to induce alpha 6 integrins on LC consequent to experimental mast cell degranulation by substance P. These data implicate a role for mast cell-derived TNF alpha in the regulation of the integrins alpha 6 beta 4 and alpha 6 beta 1 on LC. These findings may have important implications relevant to mechanisms for spatial localization of LC within the cutaneous compartments during immune responses.

Role of Langerhans cells and other dendritic cells in viral diseases

Langerhans cells are part of a vast system of potent antigen-presenting cells known under the name of dendritic cells. During the last decade, much has been learned on dendritic cell involvement in the immune response to infectious diseases. This review briefly summarizes our current understanding of the role played by Langerhans cells and other dendritic cells in the pathogenesis of DNA and RNA virus infections. These data may form the basis for the development of innovative approaches in the diagnosis, prevention, and treatment of viral diseases.

Up-regulation of alpha 4 integrin on activated Langerhans cells: analysis of adhesion molecules on Langerhans cells relating to their migration from skin to draining lymph nodes

After hapten application, epidermal Langerhans cells migrate into the regional lymph nodes through dermal lymphatics. Recently, we have demonstrated that some of them take the phenotypic and functional characteristics similar to those of in vitro cultured Langerhans cells, before disappearing from the epidermis. To analyze the mechanisms underlying the migration of Langerhans cells, we studied the expression of several adhesion molecules on freshly isolated LC and cultured LC. Pgp-1 (CD44), intercellular adhesion molecule 1, and alpha 4 integrin were strongly expressed on cultured Langerhans cells. Among them, only alpha 4 integrin was strongly up-regulated by cultured Langerhans cells, because its expression by freshly isolated Langerhans cells was very weak. This up-regulation of alpha 4 integrin was also observed on in vivo activated Langerhans cells in the epidermis and draining lymph nodes after hapten application. These data suggest a possible role played by VLA-4 in the migration of Langerhans cells from the epidermis into the regional lymph nodes after hapten application.

Langerhans cell distribution and keratinocyte expression of HLADR in oral lichen planus

Keratinocyte expression of the Class II major histocompatibility complex antigen HLADR, is seen in several inflammatory disorders of skin and mucosa, including lichen planus. The purpose of this study is to determine whether the distribution of Langerhans cells and their expression of CD4 in oral lichen planus is related to keratinocyte HLADR. The numbers of CD1- and CD4-positive Langerhans cells were compared in areas of keratinocyte HLADR and areas showing no expression in oral lichen planus and with normal oral mucosa. Cells were identified using an immunoalkaline phosphatase technique and numbers were expressed per mm epithelial surface length. In lichen planus, an increase both in the number of Langerhans cells and the numbers expressing CD4 were found in areas of keratinocyte HLADR expression compared with HLADR negative areas and with normal oral mucosa. There was no difference in the numbers of Langerhans cells or their expression of CD4 between HLADR-negative areas in LP and normal oral mucosa. These results show that the distribution of Langerhans cells is related to keratinocyte expression of HLADR and suggest that Langerhans cell entry may be enhanced in these areas. Whilst it is possible this enhancement is mediated by CD4/HLADR interaction, other molecules are also likely to be important in controlling Langerhans cell entry into oral mucosa.

Human epidermal Langerhans cells express beta 1 integrins that mediate their adhesion to laminin and fibronectin

Members of the beta 1 or very late antigen (VLA) integrin family represent the predominant class of integrin extracellular matrix receptors. Adhesion assays were developed for the identification of the beta 1 integrins involved in the adhesive interactions between Langerhans cells (which mainly express alpha 4 beta 1, alpha 5 beta 1, and alpha 6 beta 1) and extracellular matrix proteins. For this purpose, binding assays were performed on fibronectin-, laminin-, collagen type IV-, and collagen type I-coated plates. 59% +/- 21% of Langerhans cells (LC) specifically attached to fibronectin. Using as inhibitory probes monoclonal antibodies against the beta 1, alpha 5, and alpha 3 chains and the synthetic peptide GRGDSP resulted in a decrease of 43%, 41%, 15%, and 42% respectively of LC binding to fibronectin. 76% +/- 20% of LC specifically adhered to laminin. Anti-alpha 6 monoclonal antibody potently inhibited this adhesion, which dropped to 36%, whereas the synthetic peptide GRGDSP was ineffective. A low number of LC adhered to type I and type IV collagen (13-15%). These results indicate that alpha 5 beta 1 and alpha 6 beta 1 were the major beta 1 integrins involved in LC adhesion to fibronectin and laminin. Ultrastructural cell morphology of adherent cells was examined and showed that LC were largely spread on laminin and became tightly bound to the substrate on a large portion of membrane. On fibronectin surface, the contact between LC and substrate was smaller, thus cells could conserve their general round aspect. Moreover, LC binding to fibronectin and laminin induced a significative decrease of the Birbeck granule number. The finding that LC attach to LM and FN in vitro suggests they exist similarly in vivo. By mediating a passage through basement membrane and migration throughout the fibronectin network of the dermis, alpha 5 beta 1 and alpha 6 beta 1 could contribute to the ability of LC to migrate into and out of the epidermis.

Dynamic nature and function of epidermal Langerhans cells in vivo and in vitro: a review, with emphasis on human Langerhans cells

Epidermal Langerhans cells (LC) are Birbeck granule-containing bone-marrow-derived cells, which are located mainly in the suprabasal layer of the epidermis. They can be readily identified by their strong expression of CD1a and MHC class II molecules. In addition to these 'classical' properties, an extensive phenotypic profile of normal human LC, summarized in this review, is now available. The powerful capacity of LC to activate T lymphocytes is clearly documented and, to date, LC are recognized as the prominent antigen-presenting cells of the skin immune system. They are generally believed to pick up antigens encountered in the epidermis and to migrate subsequently from the epidermis to the skin-draining lymph nodes. Upon arrival in the paracortex of lymph nodes, the antigen-laden LC transform into interdigitating cells and they present antigen to naive T lymphocytes in a MHC class II-restricted fashion; this results in the generation of antigen-specific immune responses. It has also been demonstrated that transformation of LC into interdigitating cells occurs when LC are cultured in vitro. Both in vivo and in vitro studies have indicated that properties of LC, such as phenotype, morphology and the stimulatory potential to activate T lymphocytes, are dependent on the local microenvironment in which the LC reside. The essential role of LC in the induction of contact allergic skin reactions and skin transplant rejection is well established.

Expression and Role of Integrin Receptors in Sézary Syndrome

The potential role of integrins in the epidermotropism of the atypical lymphocytes of Sézary syndrome was studied by monitoring the expression of alpha and beta chains and their major ligands in skin biopsies and peripheral blood cells in patients at different progression stages. Most mononuclear cell integrins were also detected on infiltrating cells including the leukocyte complex CD11/CD18, alpha 4 beta 1, and their ligands, ICAM-1 and VCAM-1. Conversely, alpha 6 and beta 4 were present only in epidermal basal cells. Mononuclear infiltrates of SS were positive for both alpha 3 and alpha 5 chains, whereas in inflammatory cutaneous diseases only alpha 5 was expressed, indicating that a major feature of Sézary cells is the unique expression of alpha 3 beta 1. Significant changes of alpha 3 beta 1 were monitored in the follow-up of Sézary patients and correlated with the results of the therapy. The heterodimer alpha 1 beta 1 was absent from mononuclear cells except in one case. Among matrix molecules, laminin and type IV collagen displayed a pattern similar to that of the controls, whereas fibronectin and tenascin deposition were apparently increased. Circulating Sézary cells, both at diagnosis and during follow-up, were alpha 3 and alpha 5 negative and failed to acquire these adhesion molecules after mitogenic stimulation. We propose that the expression of alpha 3 beta 1 is a distinguishing feature of skin-infiltrating Sézary cells and may be related to their epidermotropism. It could also be adopted as an additional parameter of the progression and therapeutic stage of Sézary syndrome.

Expression of transforming growth factor type beta on human epidermal dendritic cells

Our study demonstrates that epidermal Langerhans cells (LC) of healthy human skin produce Transforming growth factor-beta (TGF-beta). This multipotent mediator might keep the immunocompetent LC in an "immature" stage, in which they are able to capture and process antigen. Development to potent antigen-presenting cells would become possible after migration from the epidermal network to the draining lymph node to stimulate (auto-)reactive T-cell clones.

Immune-associated surface markers of human keratinocytes

The results of a number of investigations have proved that human keratinocytes (HKs) possess the ability to synthesize and express cell surface moieties characteristic of effector and/or accessory cells of the immune system. The present paper summarizes the known immune cell surface features of HKs, reflecting their stage of activation and differentiation. The surface and functional characteristics of HKs suggest their monocyte/macrophage behavior, which fits in well with the presumed active involvement of HKs in the skin immune system.

Interaction of human epidermal Langerhans cells with HIV-1 viral envelope proteins (gp 120 and gp 160s) involves a receptor-mediated endocytosis independent of the CD4 T4A epitope

The CD4 molecule is known to be the preferential receptor for the HIV-1 envelope glycoprotein. Epidermal Langerhans cells are dendritic cells which express several surface antigens, among them CD4 antigens. To clarify the exact role of CD4 molecules in Langerhans cell infection induced by HIV-1, we investigated the possible involvement of the interactions between HIV-1 gp 120 or HIV-1 gp 160s (soluble gp 160) and Langerhans cell surface. We also assessed the expression of CD4 molecules on Langerhans cell membranes dissociated by means of trypsin from their neighbouring keratinocytes. The cellular phenotype was monitored using flow cytometry and quantitative immunoelectron microscopy. We reported that human Langerhans cells can bind the viral envelope proteins (gp 120 or gp 160s), and that this binding does not depend on CD4 protein expression. This binding is not blocked by anti-CD4 monoclonal antibodies. We show that a proportion of gp 120/gp 160s-receptor complexes enters Langerhans cells by a process identified as a receptor-mediated endocytosis. The amount of surface bound gp 120/gp 160s is not consistent with the amount of CD4 antigens present on Langerhans cell membranes. Gp 120/gp 160s binding sites on Langerhans cell suspensions appeared to be trypsin resistant, while CD4 antigens (at least the epitopes known to bind the HIV-1) are trypsin sensitive. A burst of gp 120 receptor expression was detected on 1-day cultured Langerhans cells while CD4 antigens disappeared. These findings lead to the most logical conclusion that binding of gp 120/gp 160s is due to the presence of a Langerhans cell surface molecule different from CD4 antigens.