Immunostimulatory capabilities of highly enriched Langerhans cells in vitro

Human Epidermal Langerhans Cells Express the Immunoregulatory Enzyme Indoleamine 2,3-Dioxygenase

Langerhans cells (LC) are a special subset of dendritic cells integrating cutaneous immunity. The study of LC function is of major interest not only for efforts of vaccine design and immunotherapy but also for gaining an insight into the pathogenesis of immune-mediated cutaneous diseases and neoplasias. Recently, defined antigen-presenting cells were described that express indoleamine 2,3-dioxygenase (IDO) and inhibit T cell proliferation in vitro and in vivo. Here, we show that stimulation with interferon-gamma (IFN-gamma) induces the expression of functionally active IDO in highly purified human epidermal LC. The induction of IDO after stimulation of LC with IFN-gamma seems to follow a defined kinetic with rapid upregulation followed by a downregulation after about 24 h of culture. Accordingly, proliferation of T cells induced by anti-CD3 antibodies was modulated by supernatants of IFN-gamma-activated human epidermal LC. Importantly, downregulation of T cell proliferation by supernatants of 24 h IFN-gamma-activated LC was prevented by inhibition of IDO. These results indicate that LC not only have the capacity to stimulate but also to inhibit T cells, and suggest that LC possess an immunoregulatory function in promoting T cell tolerance by production of IDO.

Milestones in the research on skin epidermal Langerhans/dendritic cells (LCs/DCs) from the discovery of Paul Langerhans 1868-1989

Almost 100 years elapsed after the discovery of dendritic cells in the human skin epithelium by Paul Langerhans in 1868 until the initiation of research on those cells was reinitiated. The present paper provides the milestones in the research on Langerhans/dendritic cells (LCs/DCs) between 1960 and 1989. This historical review will explain how researchers gradually discovered the role of the bone marrow-derived dendritic cells in the immune response. The paper is an appendix to the manuscript entitled: "Immunological and regulatory functions of uninfected and infected immature and mature subtypes of dendritic cells" (Virus Genes 26: 119-130, 2003).

In vitro evaluation of the sensitization potential of weak contact allergens using langerhans-like dendritic cells and autologous T cells

Contact hypersensitivity is a major public health concern in most industrial countries, which is why predictive tests which could identify potential allergens are needed. We have established an in vitro approach for the detection of primary immune response. This model uses Langerhans-like dendritic cells (LLDC) derived from cord blood progenitors and autologous T lymphocytes, isolated from the same blood sample. Treatment of day 12-14 LLDC, with strong haptens trinitrobenzene sulfonic acid (TNP), fluorescein isothiocyanate (FITC) or Bandrowski's base (BB), results in the proliferation of T lymphocytes, whereas weak allergens and irritants, such as sodium dodecyl sulfate (SDS) are ineffective. The use of immature (day 8) LLDC and the addition of a 48 h stage of incubation after hapten contact, result in phenotypic maturation of LLDC in addition to lymphocyte activation in all the cultures with strong haptens. The 48 h stage of incubation, results in sensitization and in some cases the induction of T cell proliferation to citronellal (1/8), coumarine (1/8) and to a prohapten p-phenylenediamine (pPDA; 2/8). The phenotype of DC after 48 h of contact with a strong hapten, becomes that of mature DC (CD83(+), CD86(+) and HLA-DR(++)). With fragrance molecules, weak haptens and prohaptens, a comparable phenotype is observed only when T lymphocytes are activated. These data suggest that the unresponsiveness observed with weak haptens, may be the consequence on an incomplete maturation of LLDC.

Cytokines and chemokines in the initiation and regulation of epidermal Langerhans cell mobilization

Langerhans cells (LC) are members of the wider family of dendritic cells. LC reside in the epidermis where they serve as sentinels of the immune system, their responsibilities being to sample the external environment for changes and challenges and to deliver information (antigen) to responsive T lymphocytes within skin draining lymph nodes. The ability of LC to migrate from the epidermis to regional lymph nodes is therefore of pivotal importance to the induction of cutaneous immune responses. The journey that LC have to make from the skin has a number of requirements. Initially it is necessary that LC disassociate themselves from surrounding keratinocytes and are liberated from other influences that encourage their retention in the epidermis. Subsequently, migrating LC must successfully traverse the basement membrane of the dermal-epidermal junction and make their way, via afferent lymphatics, to draining lymph nodes. Effective entry into lymph nodes is necessary, as is correct positioning of cells within the paracortex. There is increasing evidence that both cytokines and chemokines, and their interaction with appropriate receptors expressed by LC, orchestrate the mobilization and movement of these cells. We here consider the parts played by these molecules, and how collectively they induce and direct LC migration.

Langerhans cells and chemical allergy

Epidermal Langerhans cells (LCs) play a pivotal role in the induction of cutaneous immune responses, including those provoked by chemical allergens. The delivery by LCs of allergen to draining lymph nodes requires cell migration from the skin, a process that is dependent upon the availability of epidermal cytokines -particularly TNF-alpha and IL-1beta. Here we consider the ways in which these cytokines interact with LCs to both induce and regulate their mobilization in response to skin sensitization. In addition, the effects of these cytokines on both the selectivity of LC migration from the skin and protection of LCs from cell death are considered. Finally, the possible counter-regulatory activity of other cutaneous cytokines and the influence of LCs on the development of selective T lymphocyte responses are explored.

Evaluation of the capacity of dendritic cells derived from cord blood CD34+ precursors to present haptens to unsensitized autologous T cells in vitro

Langerhans cells play a key role in contact hypersensitivity reactions. The application of haptens on the skin leads to many modifications of these cells, including the increase of major histocompatibility complex II expression, allogeneic stimulation potency, and migration towards lymph nodes to activate T cells. Moreover, it has been shown that Langerhans cells cultured in vitro are able to prime naive T cells in response to hapten contact. From CD34+ progenitors present in cord blood, we generated dendritic cells of which some presented the phenotypic markers of Langerhans cells. We show that these cells are able to sensitize syngeneic naive (CD45RA+) T cells to haptens such as trinitrophenyl conjugate of trinitrobenzene sulfonic acid (TNP) and fluoroscein isothiocyanate. The response to TNP is higher than to fluoroscein isothiocyanate, whereas sodium dodecyl sulfate, an irritant molecule used as a control, never caused this effect. Phenotypic analysis of cellular suspensions and experiments of cell sorting lead to the conclusion that only CD1a+ cells are able to induce a primary response of syngeneic T cells to TNP or fluoroscein isothiocyanate. Furthermore, we have shown a close relationship between the differentiation state of dendritic cells and their ability to prime T lymphocytes. Dendritic cells are able to present haptens in an efficient manner between day 10 and 14 of culturing CD34+ progenitors, whereas they were efficient in presenting alloantigens from day 6 until after day 20. This dissociation suggests the need of an active metabolic process for hapten presentation in the direct treatment of dendritic cells with haptens. This model of hapten presentation was used for a panel of fragrance molecules and other molecules considered as weaker haptens than TNP and fluoroscein isothiocyanate.

The local lymph node assay: a viable alternative to currently accepted skin sensitization tests

The prospective identification of skin sensitizing chemicals is a vital prerequisite for their proper risk management. Traditionally this has been achieved largely by the conduct of guinea pig assays such as the maximization and Buehler tests. These methods are recommended by the Organisation for Economic Cooperation and Development (OECD) and are required by the European Union (EU) for the evaluation of new substances. However, a novel mechanistically based method, the local lymph node assay (LLNA), has been the focus of substantial validation activity in recent years. This material is reviewed in this paper. It is shown that the LLNA has been validated successfully by five interlaboratory assessments as well as by comparisons with guinea pig tests and human data. The method also offers clear advantages to the user in terms of objectivity, time and cost, and delivers important animal welfare benefits. In consequence, it is recommended that the LLNA be formally adopted by the OECD in Guideline 406 and accepted by the EU and US EPA as a method suitable for the classification of the skin sensitizing potential of chemicals.

Oral mucosal Langerhans' cells

Langerhans' cells (LC) are dendritic, antigen-presenting cells present within the epithelium of skin and mucosa, including that of the oral cavity. This article reviews the literature on the phenotypic and functional features of oral mucosal Langerhans' cells, and speculates on other aspects by extrapolating from data on their epidermal counterparts.

Cytokines and regulation of allergic sensitization to chemicals

Sensitization to chemicals and the elicitation of allergic reactions results from the stimulation of specific immune responses. Adaptive immunity is orchestrated by cytokines, a family of inducible glycoproteins that influence in many ways the behaviour of, and interaction between, cells which mediate immune and inflammatory responses. In this article the role of cytokines in the development of cutaneous immune responses to chemical allergens and in directing the quality of immune responses provoked by such materials is discussed.

Dissection of human Langerhans cells' allostimulatory function: the need for an activation step for full development of accessory function

In the present study, we analyzed the mechanism by which human Langerhans cells (LC), the dendritic cells (DC) from epidermis, support the induction of a primary allogeneic T cell response. We reported that paraformaldehyde (PF) fixation completely abrogated the stimulatory property of freshly isolated LC, although the level of major histocompatibility complex (MHC) class II antigen (Ag) expression was unaltered by the fixative. Addition of either interleukin (IL)-1 beta and/or IL-6, during the mixed epidermal cell lymphocyte reaction, failed to restore the proliferative response. By contrast, when human LC were incubated for 3 days in culture medium before fixation, they retained a low but significant allostimulatory capacity. Trypsin treatment of incubated LC before fixation did not impair their function, suggesting that stimulatory activity by fixed incubated LC did not merely reflect a repair of LC membrane after trypsin trauma suffered during epidermal cell (EC) isolation. More interestingly, we found that addition of interferon-gamma during LC incubation mediated an enhanced allostimulatory activity by the PF-fixed LC. Acquisition of allostimulatory property by in vitro activated and fixed LC did not correlate with increased MHC class II Ag expression at the cell surface. By contrast, we showed that ICAM-1 Ag expression by human LC is involved in this maturation process. Finally, we found that once human LC have been activated, IL-1 beta, but not IL-6, could serve as a costimulatory factor in the primary allogeneic T cell response. In conclusion, the data suggest that human LC accessory function is not constitutive but requires an activation step which can be provided by interferon-gamma during LC-T cell interaction.

Dendritic cells and cutaneous immune responses to chemical allergens

This article reviews the role of epidermal Langerhans cells (LC) in the development of cutaneous immune responses to chemical allergens. Following topical exposure to sensitizing chemicals, LC, many of which bear allergen, are induced to migrate from the skin, via the afferent lymphatics, to the draining lymph nodes. The phenotypic and functional changes to which LC are subject during this process and their development into active immunostimulatory cells closely resembling lymphoid dendritic cells is discussed. The migration and maturation of LC following skin sensitization is of critical importance to the effective presentation of chemical allergens to T lymphocytes and the induction of allergic responses. Evidence is reviewed which suggests that these events are initiated and regulated by epidermal cytokines. The conclusion drawn is that an early event during the induction of skin sensitization is the production by keratinocytes of cytokines which stimulate the migration of LC from the skin and which also result in the functional maturation of LC into potent antigen-presenting cells.

Stimulation of Langerhans cell migration by tumor necrosis factor alpha (TNF-alpha)

Following topical exposure of mice to skin-sensitizing chemicals, Langerhans cells (LC), many of which bear antigen, are stimulated to migrate via the afferent lymphatics to draining lymph nodes. Consistent with the acquisition of potent immunostimulatory activity, LC while in transit to lymph nodes, are subject to a functional and phenotypic maturation thought to be mediated by granulocyte/macrophage colony-stimulating factor (GM-CSF) and possibly other epidermal cytokines. An interesting question is the nature of the stimulus that initiates the migration of LC from the epidermis. We have examined the influence of intradermal tumor necrosis factor alpha (TNF-alpha), another epidermal cytokine, on the accumulation of dendritic cells (DC) in draining lymph nodes. Murine, but not human, recombinant TNF-alpha caused a rapid and concentration-dependent increase in the frequency of DC in draining nodes. The conclusion drawn is that local production of TNF-alpha provides one signal for LC migration during cutaneous immune and inflammatory responses.

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.

Cultured human Langerhans cells process and present intact protein antigens

Epidermal Langerhans cells (LC) undergo profound phenotypic and functional alterations when cultured for 2 to 3 d. To determine whether the in vitro culture of human LC modulates their capacity to process and present intact protein antigens, we compared the ability of freshly isolated LC (fLC) and cultured LC (cLC) to stimulate in vitro T-cell proliferative responses to recall antigens. We found that human fLC and cLC were able to process and present recall antigens to primed T cells, inducing significant proliferative responses. For tetanus toxoid and Candida albicans extract, T-cell proliferative responses at 6 d to antigen-pulsed fLC were slightly greater than responses to antigen-pulsed cLC. For live influenza A virus, the T-cell responses induced by antigen-pulsed cLC were comparable or slightly greater compared with fLC. Allogeneic T-cell proliferation for both LC preparations were also comparable. The exogenous pathway of antigen processing was demonstrated by chloroquine inhibition.

Functional dichotomy between Langerhans cells that present antigen to naive and to memory/effector T lymphocytes

The general thrust of this volume is to review the roles of accessory cells in regulating T and B lymphocytes. To that end, we have summarized the evidence that indicates the crucial role that Langerhans cells play in the induction and expression of immunity to antigens that gain access to, or arise within, skin. Langerhans cells accomplish this important goal by their abilities to (a) activate naive T cells to antigens not previously encountered by the host, and (b) activate memory/effector T cells specific for previously encountered antigens. Arguments have been advanced to support the view that the functional properties of Langerhans cells used to present antigens to naive T cells differ substantially from the properties that equip Langerhans cells to activate effector T cells. The arguments are based in part on the fact that Langerhans cells carry out these functions in two very different environments: in the epidermis, and in the draining lymph node. The arguments are also based on results of in vitro experiments that reveal distinct differences in antigen processing and presenting properties of Langerhans cells freshly obtained from mouse and human skin as compared to Langerhans cells that have been cultured in vitro for 2-3 days. We propose that freshly explanted Langerhans cells faithfully reflect the functional program of intraepidermal Langerhans cells, and are able to present antigen to memory/effector T cells that enter the epidermal compartment. To accomplish this task, epidermal LC pick up environmental antigens, process them with great efficiency, and then present them in situ, without further upregulation of "accessory" signals (cell-adhesion molecules, secretion of additional cytokines). They can carry out this function, even in the presence of TGFB--a a cytokine which is constitutively made by keratinocytes, and which we have found to profoundly inhibit antigen presentation by most other types of "professional" antigen-presenting cells. Intraepidermal Langerhans cells are also capable of carrying cutaneous antigens through the dermal epidermal junction and migrating to the draining lymph node. We further propose that cultured Langerhans cells are fated to present antigens to unprimed/naive T cells, and thereby to initiate immune responses to new cutaneous antigens. Cultured LC process antigens less efficiently than fresh cells, but their unique capacity to present antigen effectively to unprimed T cells rests chiefly on the fact that they have significantly upregulated cell surface adhesion molecules, expression of MHC molecules, and secretion of activating cytokines--the "accessory" signals that are required for arousing naive T cells.(ABSTRACT TRUNCATED AT 400 WORDS)

Isolation and culture of panning method-enriched Langerhans cells from dispase-dissociated epidermal cells of the mouse

Langerhans cells (LCs) are bone marrow-derived, Ia-positive antigen-presenting cells in the epidermis which constitute 2-4% of the total epidermal cells. We examined the usefulness of a combination of dispase treatment and the panning method for enriching and culturing mouse LCs. Trunk skin was treated with partially purified dispase (Godo Shusei, type II) to separate epidermal sheets and to dissociate epidermal cells. Suspended cells were treated with ascites or culture supernatant containing anti-Ia monoclonal antibody, and LCs were enriched by the Ia-mediated panning method. Per mouse, 3-4 X 10(5) LCs were recovered with greater than 95% purity and greater than 90% viability. Enriched LCs potently stimulated the allogeneic mixed-leukocyte reaction. Ultrastructural observations revealed that enriched LCs contained many vesicles but almost no Birbeck granules. A laminal structure, which was apparently adhesive to the surface of LCs, was observed when ascites were employed as the anti-Ia antibody. These results indicate that a combination of dispase treatment and the Ia-mediated panning method is very useful for isolating high yields of functionally mature murine Langerhans cells with high purity and viability.

Human epidermal Langerhans cells undergo profound morphologic and phenotypical changes during in vitro culture

Morphology, phenotype, and enzyme activity of highly enriched (80%) unlabeled human epidermal Langerhans cells (LC) have been studied, with emphasis on changes during a short-term culture of three days in vitro. All freshly isolated LC contained Birbeck granules and expressed high levels of CD1a, CD1c, and MHC class II molecules HLA-DR, -DP, and -DQ. They have a weak to moderate expression of RFD1, C3biR, Fc gamma R, p 150/95, MHC class I molecules HLA-ABC, and of the adhesion molecules LFA-3 and ICAM-1, whereas no expression of LFA-1 and several monocyte/macrophage markers were detected. Human LC undergo profound changes during in vitro culture. Birbeck granules, C3biR, Fc gamma R, and p 150/95 were completely lost and the expression of CD1a and CD1c was markedly decreased or lost. Expression of molecules that have essential functions in antigen presentation remained present at the same level (MHC class II molecules and ICAM-1) or was markedly enhanced (LFA-3 and MHC class I). Highly remarkable was the dramatically enhanced expression of interdigitating cell marker RFD1. The monocyte/macrophage markers initially absent remained absent and the enzyme activity initially present (including ATPase and nonspecific esterase) remained present. In conclusion, the results in this report stress rapid alterations of human LC during in vitro culture, resulting in transformation into cells that have phenotypical characteristics of potent antigen presenting cells that resemble interdigitating cells.