Langerhans cells: antigen presenting cells of the epidermis

Paraneoplastic neuropathies and peripheral nerve hyperexcitability disorders

Peripheral neuropathy is a common referral for patients to the neurologic clinics. Paraneoplastic neuropathies account for a small but high morbidity and mortality subgroup. Symptoms include weakness, sensory loss, sweating irregularity, blood pressure instability, severe constipation, and neuropathic pain. Neuropathy is the first presenting symptom of malignancy among many patients. The molecular and cellular oncogenic immune targets reside within cell bodies, axons, cytoplasms, or surface membranes of neural tissues. A more favorable immune treatment outcome occurs in those where the targets reside on the cell surface. Patients with antibodies binding cell surface antigens commonly have neural hyperexcitability with pain, cramps, fasciculations, and hyperhidrotic attacks (CASPR2, LGI1, and others). The antigenic targets are also commonly expressed in the central nervous system, with presenting symptoms being myelopathy, encephalopathy, and seizures with neuropathy, often masked. Pain and autonomic components typically relate to small nerve fiber involvement (nociceptive, adrenergic, enteric, and sudomotor), sometimes without nerve fiber loss but rather hyperexcitability. The specific antibodies discovered help direct cancer investigations. Among the primary axonal paraneoplastic neuropathies, pathognomonic clinical features do not exist, and testing for multiple antibodies simultaneously provides the best sensitivity in testing (AGNA1-SOX1; amphiphysin; ANNA-1-HU; ANNA-3-DACH1; CASPR2; CRMP5; LGI1; PCA2-MAP1B, and others). Performing confirmatory antibody testing using adjunct methods improves specificity. Antibody-mediated demyelinating paraneoplastic neuropathies are limited to MAG-IgM (IgM-MGUS, Waldenström's, and myeloma), with the others associated with cytokine elevations (VEGF, IL6) caused by osteosclerotic myeloma, plasmacytoma (POEMS), and rarely angiofollicular lymphoma (Castleman's). Paraneoplastic disorders have clinical overlap with other idiopathic antibody disorders, including IgG4 demyelinating nodopathies (NF155 and Contactin-1). This review summarizes the paraneoplastic neuropathies, including those with peripheral nerve hyperexcitability.

Tissue engineering strategies to bioengineer the ageing skin phenotype in vitro

Human skin ageing is a complex and heterogeneous process, which is influenced by genetically determined intrinsic factors and accelerated by cumulative exposure to extrinsic stressors. In the current world ageing demographic, there is a requirement for a bioengineered ageing skin model, to further the understanding of the intricate molecular mechanisms of skin ageing, and provide a distinct and biologically relevant platform for testing actives and formulations. There have been many recent advances in the development of skin models that recapitulate aspects of the ageing phenotype in vitro. This review encompasses the features of skin ageing, the molecular mechanisms that drive the ageing phenotype, and tissue engineering strategies that have been utilised to bioengineer ageing skin in vitro.

Efficacy of an inactivated bivalent vaccine for enterovirus 71 and coxsackievirus A16 in mice immunized intradermally

Human hand, foot, and mouth disease (HFMD), an important infectious disease in children, is caused mainly by enterovirus 71 (EV71) and coxsackievirus A16 (CA16). In this study, a bivalent inactivated EV71/CA16 vaccine is developed and evaluated in immunized BALB/c mice injected through the intradermal route. Q-RT-PCR detection of the mRNA of immune signal molecules in local epithelial tissues inoculated with the vaccine indicates activation of innate immunity, which includes upregulation of immune-related chemokines, interferons and CD molecules. Further, the finding that neutralizing antibodies and specific T cellular responses were elicited in adult mice after two immunizations with the vaccine at a 28-day interval, which endowed offspring mice to defend a viral challenge, suggests the successful induction of specific protective antiviral immunity. All these data suggest that immunization with this bivalent EV71/CA16 vaccine via the intradermal route elicits effective immunity against EV71 and CA16 infection.

A review of the effects of ageing on skin integrity and wound healing

It is well known that advancing age is a factor that affects the normal course of wound healing. The population over the age of 65 years is increasing globally, and this may be accompanied by an increase in the number of individuals experiencing delayed wound healing. There is a breadth of research to show that age-related changes in the epidermis and dermis change the skin's ability to resist damage and injury. In particular, the dermoepidermal junction becomes flattened, which predisposes the tissue to shear and friction forces. Within the dermis, alterations in the amount and structure of collagen also mean that the tissue is much more rigid. Prompt assessment of the skin to identify existing conditions as well as preventive measures is therefore essential. This article discusses the anatomy of the skin and the effects of ageing on the tissues. It also offers some guidance on skin assessment and the basics of skin care.

Engineering a Multilayered Skin Equivalent: The Importance of Endogenous Extracellular Matrix Maturation to Provide Robustness and Reproducibility

Human skin equivalents (HSEs) are a valuable tool for both academic and industrial laboratories to further the understanding of skin physiology and associated diseases. Over the last few decades, there have been many advances in the development of HSEs that successfully recapitulate the structure of human skin in vitro; however a main limitation is variability due to the use of complex protocols and exogenous extracellular matrix (ECM) proteins. We have developed a robust and unique full-thickness skin equivalent that is highly reproducible due to the use of a consistent scaffold, commercially available cells, and defined low-serum media. The Alvetex^® scaffold technology allows fibroblasts to produce their own endogenous ECM proteins within the scaffold, which alleviates the need for exogenous collagen, and supports the differentiation and stratification of the epidermis. Our full-thickness skin equivalent is generated using a detailed step-by-step protocol, which sequentially forms the multilayered structure of human skin in vitro. This model can be adapted for many downstream applications such as disease modeling and testing of active compounds for cosmetics.

Regulation of T helper cell responses during antigen presentation by norepinephrine-exposed endothelial cells

Dermal blood vessels and regional lymph nodes are innervated by sympathetic nerves and, under stress, sympathetic nerves release norepinephrine (NE). Exposure of primary murine dermal microvascular endothelial cells (pDMECs) to NE followed by co-culture with Langerhans cells (LCs), responsive CD4+ T-cells and antigen resulted in modulation of CD4+ T-cell responses. NE-treatment of pDMECs induced increased production of interleukin (IL)-6 and IL-17A while down-regulating interferon (IFN)-γ and IL-22 release. This effect did not require contact between pDMECs and LCs or T-cells and depended upon pDMEC production of IL-6. The presence of NE-treated pDMECs increased the proportion of CD4+ T-cells expressing intracellular IL-17A and increased IL-17A mRNA while decreasing the proportion of IFN-γ- or IL-22-expressing CD4+ T-cells and mRNA levels for those cytokines. Retinoic acid receptor-related orphan receptor gamma (ROR-γt) mRNA was significantly increased in CD4+ T-cells while T-box transcription factor (T-bet) mRNA was decreased. Intradermal administration of NE prior to hapten immunization at the injection site produced a similar bias in draining lymph node CD4+ T-cells towards IL-17A and away from IFN-γ and IL-22 production. Under stress, release of NE may have significant regulatory effects on the outcome of antigen presentation through actions on ECs with enhancement of inflammatory skin disorders involving IL-17/T helper type 17 (Th17) cells.

Calcitonin Gene-Related Peptide-Exposed Endothelial Cells Bias Antigen Presentation to CD4+ T Cells toward a Th17 Response

Calcitonin gene-related peptide (CGRP) is a neuropeptide with well-established immunomodulatory functions. CGRP-containing nerves innervate dermal blood vessels and lymph nodes. We examined whether CGRP regulates the outcome of Ag presentation by Langerhans cells (LCs) to T cells through actions on microvascular endothelial cells (ECs). Exposure of primary murine dermal microvascular ECs (pDMECs) to CGRP followed by coculture with LCs, responsive CD4(+) T cells and Ag resulted in increased production of IL-6 and IL-17A accompanied by inhibition of IFN-γ, IL-4, and IL-22 compared with wells containing pDMECs treated with medium alone. Physical contact between ECs and LCs or T cells was not required for this effect and, except for IL-4, we demonstrated that IL-6 production by CGRP-treated pDMECs was involved in these effects. CD4(+) cells expressing cytoplasmic IL-17A were increased, whereas cells expressing cytoplasmic IFN-γ or IL-4 were decreased by the presence of CGRP-treated pDMECs. In addition, the level of retinoic acid receptor-related orphan receptor γt mRNA was significantly increased, whereas T-bet and GATA3 expression was inhibited. Immunization at the site of intradermally administered CGRP led to a similar bias in CD4(+) T cells from draining lymph node cells toward IL-17A and away from IFN-γ. Actions of nerve-derived CGRP on ECs may have important regulatory effects on the outcome of Ag presentation with consequences for the expression of inflammatory skin disorders involving Th17 cells.

Autoimmune-mediated peripheral neuropathies and autoimmune pain

Peripheral neuropathies have diverse acquired and inherited causes. The autoimmune neuropathies represent an important category where treatment is often available. There are overlapping signs and symptoms between autoimmune neuropathies and other forms. Making a diagnosis can be challenging and first assisted by electrophysiologic and sometimes pathologic sampling, with autoimmune biomarkers providing increased assistance. Here we provide a review of the autoimmune and inflammatory neuropathies, their available biomarkers, and approaches to treatment. Also discussed is new evidence to support a mechanism of autoimmune pain.

Pituitary adenylate cyclase-activating peptide and vasoactive intestinal polypeptide bias Langerhans cell Ag presentation toward Th17 cells

Epidermal Langerhans cells (LCs) are dendritic APCs that play an important role in cutaneous immune responses. LCs are associated with epidermal nerves and the neuropeptides vasoactive intestinal polypeptide (VIP) and pituitary adenylate cyclase-activating polypeptide (PACAP) inhibit LC Ag presentation for Th1-type immune responses. Here, we examined whether PACAP or VIP modulates LC Ag presentation for induction of IL-17A-producing CD4(+) T cells. Treatment with VIP or PACAP prior to in vitro LC Ag presentation to CD4(+) T cells enhanced IL-17A, IL-6, and IL-4 production, decreased interferon (IFN)-γ and interleukin (IL)-22 release, and increased RORγt and Gata3 mRNA expression while decreasing T-bet expression. The CD4(+) T-cell population was increased in IL-17A- and IL-4-expressing cells and decreased in IFN-γ-expressing cells. Addition of anti-IL-6 mAb blocked the enhanced IL-17A production seen with LC preexposure to VIP or PACAP. Intradermal administration of VIP or PACAP prior to application of a contact sensitizer at the injection site, followed by harvesting of draining lymph node CD4(+) T cells and stimulation with anti-CD3/anti-CD28 mAbs, enhanced IL-17A and IL-4 production but reduced production of IL-22 and IFN-γ. PACAP and VIP are endogenous mediators that likely regulate immunity and immune-mediated diseases within the skin.

Langerhans cells and dendritic cells are cytotoxic towards HPV16 E6 and E7 expressing target cells

Dendritic cells (DC) can be cytotoxic towards tumor cells by means of TNF family molecules expressed on the cell surface of activated DCs. Tumor cells expressing appropriate receptors are killed by DC, generating a source of antigen to be presented to the immune system. It has not been investigated whether Langerhans cells (LC) are selectively cytotoxic to tumor cells. This is of particular interest for epithelial tumor cells that physically interact with LC in vivo. Among epithelial tumors, the oncogenic process of cervical tumors is relatively well defined by their Human Papillomavirus (HPV) mediated etiology. To study whether HPV16 E6 and E7 expressions, otherwise observed in cervical tumor cells, can sensitize normal cervical epithelial cells to DC and LC mediated killing, the E6 and E7 genes were introduced by retroviral transfection, and cells were subsequently used as targets in cytotoxicity assays. Expression of cytotoxic molecules by effector cells was measured in response to the pro-inflammatory cytokine IFN-gamma; cytotoxicity was established and concomitant expression of receptor molecules was assessed on target cells. A correlation between the shrinkage of HPV16 E6 and E7+ tumors versus DC and LC infiltration was evaluated in a murine model of cervical cancer. DC and LC proved to be equally cytotoxic towards E6 and E7 expressing cervical epithelial cells. IFN-gamma induced TRAIL expression by DC and LC, and inhibition of TRAIL partially blocked cytotoxic effects. Expression of TRAIL decoy receptors was reduced following introduction of E6 and E7 into host cells. Shrinkage of HPV16 E6 and E7 expressing tumors correlated with infiltration by S100+ DC and LC, co-localizing with apoptotic mouse tumor cells. In conclusion, DC and LC mediated killing may be exploitable for anti-tumor treatment.

Nadifloxacin downmodulates antigen-presenting functions of epidermal Langerhans cells and keratinocytes

BACKGROUND

Nadifloxacin is an anti-microbial quinolone derivative widely used for the treatment of acne as a topical agent. This drug has been suggested to have not only anti-bacterial but also anti-inflammatory actions, which may have a beneficial effect on some aspects of inflammatory acne.

OBJECTIVE

To further clarify its abilities to modulate skin immunity, we investigated whether nadifloxacin affects the hapten- and superantigen-presenting capacities of epidermal Langerhans cells (LC) and keratinocytes, respectively.

METHODS

Immune lymph node CD4+ T cells from trinitrophenyl-sensitized BALB/c mice were cocultured with LC-enriched epidermal cells (LC-EC) that were freshly isolated from syngeneic mice and derivatized with trinitrophenyl hapten in the presence or absence of nadifloxacin. Alternatively, LC-EC were preincubated with nadifloxacin (NDFX), modified with the hapten, and cultured with immune T cells. The effects of nadifloxacin on the surface molecule expression in LC and keratinocytes were also tested by flow cytometry and cellular ELISA.

RESULTS

LC-EC cultured with nadifloxacin at 10 microg/ml or more significantly suppressed the antigen-presenting function of LC for T cells. The ability of MHC class II+ keratinocytes to present a superantigen to T cells was suppressed by preincubation of keratinocytes with 30 microg/ml or more of nadifloxacin. These functional reductions in LC and keratinocytes reflected the decreased expression of MHC class II and/or costimulatory molecules.

CONCLUSION

Nadifloxacin downmodulates cutaneous immunity by interfering with the antigen-presenting ability of epidermal cells.

Anti-allergic drug olopatadine suppresses murine contact hypersensitivity and downmodulates antigen-presenting ability of epidermal Langerhans cells

Olopatadine hydrochloride is an H1-receptor-blocker but has other anti-allergic pharmacological potencies. We investigated whether olopatadine inhibits murine contact hypersensitivity, focussing on its modulatory action on epidermal Langerhans cells serving as antigen-presenting cells. While BALB/c mice were sensitized and challenged epicutaneously with hapten, they were administered intraperitoneally with olopatadine. Olopatadine at 1 or 0.2 mg/kg of weight significantly suppressed the sensitivity when injected at least once before sensitization or challenge. In olopatadine-injected mice, the ability of Langerhans cells to present hapten to primed T cells was reduced with decreased expression of MHC class II and co-stimulatory molecules. Langerhans cells exposed in vitro to 10(-5) or 10(-6) M olopatadine had less antigen-presenting activity than control, whereas neither T cell proliferation nor keratinocyte production of IL-1alpha and IP-10 was affected at these doses. These findings suggest that olopatadine downmodulates contact hypersensitivity at least partly by interfering with the antigen-presenting ability of Langerhans cells.

Catecholamines inhibit the antigen-presenting capability of epidermal Langerhans cells

The sympathetic nervous system modulates immune function at a number of levels. Within the epidermis, APCs (Langerhans cells (LC)) are frequently anatomically associated with peripheral nerves. Furthermore, some neuropeptides have been shown to regulate LC Ag-presenting function. We explored the expression of adrenergic receptors (AR) in murine LC and assessed their functional role on Ag presentation and modulation of cutaneous immune responses. Both purified LC and the LC-like cell lines XS52-4D and XS106 expressed mRNA for the ARs alpha(1A) and beta(2). XS106 cells and purified LC also expressed beta(1)-AR mRNA. Treatment of murine epidermal cell preparations with epinephrine (EPI) or norepinephrine inhibited Ag presentation in vitro. Furthermore, pretreatment of epidermal cells with EPI or norepinephrine in vitro suppressed the ability of these cells to present Ag for elicitation of delayed-type hypersensitivity in previously immunized mice. This effect was blocked by use of the beta(2)-adrenergic antagonist ICI 118,551 but not by the alpha-antagonist phentolamine. Local intradermal injection of EPI inhibited the induction of contact hypersensitivity to epicutaneously administered haptens. Surprisingly, injection of EPI at a distant site also suppressed induction of contact hypersensitivity. Thus, catecholamines may have both local and systemic effects. We conclude that specific ARs are expressed on LC and that signaling through these receptors can decrease epidermal immune reactions.

The imidazoquinolines, imiquimod and R-848, induce functional, but not phenotypic, maturation of human epidermal Langerhans' cells

Imiquimod (R-837) and its more potent derivative (R-848) are imidazoquinolines that have adjuvant activity in cultured human mononuclear cells. Its mechanism of action on epidermal antigen-presenting cells is not known. The purpose of the present investigation was to determine whether imiquimod and R-848 affect human epidermal Langerhans' cells' (LC) in vitro maturation. Pulse incubations (6-16 h) of cultured unfractionated epidermal cells or highly enriched LC suspensions with either imiquimod or R-848 (0. 05-5.0 microg/ml of culture medium) reproducibly enhanced their ability to induce T-cell proliferation in a primary mixed lymphocyte reaction. There was a 30 to 300% increase in T-lymphocyte proliferation induced by either imiquimod- or R-848-treated LC when compared to control, untreated LC. IFN-gamma secretion by T-lymphocytes stimulated by imiquimod- or R-848-treated LC was increased compared to control, untreated LC. After a 6-h incubation, phenotypic analysis of control-, imiquimod-, or R-848-treated LC indicated that such antigen-presenting cells were in an "intermediate" state of maturation (CD1a(+), HLA-DR, DP, DQ(bright+), CD40(low+), CD86(high+), and CD80(low+)). RNase protection assays demonstrated that either imiquimod or R-848 treatments increased steady-state transcripts encoding for IL-12 p40, IL-1beta, TNF-alpha, and IL-1 receptor antagonist by LC. These data indicate that imiquimod and R-848 dissociate the functional maturation (cytokine-mediated) and phenotypic maturation of epidermal LC. These data warrant further exploration for the use of imidazoquinoline-treated LC or other DC subsets for processing and presentation of viral peptides to Th-lymphocytes as a novel vaccine strategy to induce protective antiviral responses.

Murine Langerhans Cells Cultured Under Serum-Free Conditions Mature into Potent Stimulators of Primary Immune Responses In Vitro and In Vivo

The ability of Ag-pulsed dendritic cells (DC) to induce primary immune responses has led them to be used for vaccination purposes. However, irrelevant Ags (e.g., FCS) can also be taken up by DC during their isolation and culture and then presented in vivo. To circumvent this, we have established a serum-free (SF) culture system. Murine epidermal cell (EC) suspensions were prepared with and without FCS and cultured for 3 days either in SF or FCS-containing medium. In spite of the lower Langerhans cell (LC) yields under SF conditions, both SF- and FCS-cultured LC (SF-cLC, FCS-cLC) underwent a similar maturation process, as evidenced by a similar increase in the cell surface expression of MHC class II and of costimulatory molecules. The further observation that SF-EC cultures elaborated comparable amounts of granulocyte-macrophage (GM)-CSF as FCS-cultured EC, but were relatively impaired in their IL-1α and TNF-α production, supports the role of GM-CSF in LC maturation and, less so, in LC survival. Functionally, freshly isolated SF-LC compared with FCS-LC in their Ag-processing capacity. Three-day-cultured SF-LC were as potent stimulators of polyclonal T cell responses and of the primary allogeneic MLR as FCS-cLC, but were relatively poor activators of naive, syngeneic CD4+ T cells. In vivo, hapten-modified SF-cLC induced a contact hypersensitivity response similar in magnitude and kinetics to that evoked by FCS-cLC. Our data show that, in the absence of serum and exogenous cytokines, LC mature into potent activators of T cell responses and could thus be a valuable cellular source for DC-based immunotherapy.

Antigen-presenting cell function of epidermal cells activated by hapten application

Exposure to haptens initiates a series of immune and inflammatory reactions that cause migration of epidermal Langerhans cells (LC) to draining lymph nodes, antigen processing, and presentation to T cells. In the present study, the antigen-presenting cell (APC) function of epidermal cells (EC) following hapten application was determined using a cell transfer system. This function of EC in inducing contact sensitivity (CS) in the recipient mice appeared as early as 6 h after hapten painting, and reached its maximum at 24 h. The amount of hapten on EC did not correlate with the function, i.e. the amount retained on the cells was greatest immediately after hapten painting and decreased over time. Several experiments were performed to identify the cell type responsible for the APC function. Through immunomagnetic bead separation, the APC function was detected in Ia- EC, as well as in unfractionated EC from hapten-painted mice. A purified population of Ia+ cells (LC) induced CS with much less efficiency than unseparated cells. Depletion of LC by anti-Ia monoclonal antibody (mAb) and complement-mediated lysis did not impair the APC function, whereas it was reduced by the depletion of Thy-1+ cells by anti-Thy-1 mAb and complement-mediated lysis. Moreover, adherent cells that were harvested from a 48-h culture of EC obtained from hapten-painted skin, and were free of contaminating LC and gamma omega T cells, had a strong capacity to induce CS. These findings indicate that keratinocytes (KC) acquire APC function as well as LC, with hapten application. Phenotypically increased expression of intercellular adhesion molecule-1 (ICAM-1) and Thy-1 on EC was observed following hapten application, whereas expression of Ia and B7/BB1 was unaltered. The APC function of EC from hapten-painted skin was dependent on ICAM-1 and Thy-1 expression, as the mAbs for these molecules reduced the capacity to induce CS. These results suggest that hapten application induces not only LC but also KC to mature functionally and become potent APCs, and that these KC exert the APC function complementarily at local sites following the migration of LC with potent APC function to the draining lymph node.

HLA-DR-positive dendritic cells of the normal human choroid plexus: a potential reservoir of HIV in the central nervous system

In a previous study of choroid plexus (CPx) from patients with the acquired immunodeficiency syndrome (AIDS), we found a population of stromal cells infected with the human immunodeficiency virus (HIV). To determine whether these represented antigen-presenting dendritic cells, we examined the phenotype of normal human choroid plexus by light and electron microscopy (EM) and established the HIV-infected cell type by immunohistochemistry in AIDS cases with HIV-infected CPx. Monoclonal antibodies were used to detect class II major histocompatibility antigens (MHC), S-100 and S-100beta protein, lymphocytes, monocytes/macrophages, and HIV glycoprotein. A variable number of stromal cells had slightly elongated nuclei and long branching processes that were strongly immunoreactive for class II MHCs, rarely reactive for S-100 and S-100beta and immunonegative for monocyte/macrophage markers. Phagocytic activity was absent by EM and immunomarkers. They were numerous in the subepithelial region, and their processes occasionally extended toward the stromal capillaries or between the CPx epithelial cells. The HIV-infected cells were intensely immunoreactive for class II MHC markers and often displayed a dendritic morphology. These results document the presence of dendritic cells in the normal human CPx whose morphology and immunophenotype closely resemble those of DCs elsewhere in the body. They also show that these immunoreactive MHC class II cells are the cell type infected by HIV. We suggest that the functional activity of the CPx DCs is similar to that of antigen-presenting dendritic cells elsewhere in the body. This includes the potential to harbor HIV during the prolonged period of clinical latency, acting as a central nervous system reservoir of infection before the onset of AIDS.

Prolonged skin allograft survival after photodynamic therapy associated with modification of donor skin antigenicity

BACKGROUND

The ability to prolong graft survival, in some cases by depleting donor antigen-presenting cells (APCs), and the subsequent demonstration that lymphocytes stimulated by non-APCs become anergic, suggested that graft survival and tolerance induction might be achieved by manipulating donor APCs to render them incompetent. This possibility was tested in histoincompatible murine skin allograft with photodynamic therapy (PDT).

METHODS

Skin sections (C57BL/6) were exposed in vitro to low doses of benzoporphyrin derivative monoacid ring A (BPD) (verteporfin) and light (A=690+/-10 nm; low-dose PDT) before implantation on recipients (BALB/c). Furthermore, the effect of the treatment on the surface molecules of donor-derived Langerhans cells (LC) was evaluated by fluorescence-activated cell sorter analysis; the effect of treatment on the LC alloreactivity in the mixed epidermal cell lymphocyte reaction was also evaluated.

RESULTS

Pretreating skin to be grafted with low-dose PDT can significantly prolong the survival of allografts from 9.3+/-2.2 (n=42) days (control group) to 16.9+/-1.7 days (n=20; treated group). Moreover, low-dose PDT significantly down-regulated the major histocompatibility complex and costimulatory (B7) molecules (60-90% reduction) on LC, but not LC-specific endocytic receptor (DEC-205), CD45, intercellulr adhesion molecule 1, LC viabilities, and ectophosphatase activity on LC. Additionally, this treatment significantly suppressed the ability of LC to stimulate alloreactive T cells to proliferate.

CONCLUSIONS

Since engaging T cell receptors in the absence of costimulation results in suboptimal activation of T cells and ultimately anergy, it appears that the immunomodulatory effects of low-dose PDT associated with extended engraftment may depend upon decreased LC expression of major histocompatibility complex and costimulatory molecules.

Langerhans cells in the development of skin cancer: a qualitative and quantitative comparison of cell markers in normal, acanthotic and neoplastic ovine skin

The distribution of Langerhans cells in normal, acanthotic and neoplastic ovine epithelium was examined using the enzyme marker Acetylcholinesterase (AchE) and monoclonal antibodies (MoAb) to CD1 (20.27) and MHC Class II (49.1 and 28.1) molecules. In normal skin, where Langerhans cells were regularly spaced within the basal layer, qualitative observations and direct pairwise testing showed that AChE was superior to the MoAb in detecting these cells. Significantly more (P < 0.01) dendritic cells were also detected with MoAb 49.1 than MoAb 20.27 or 28.1, suggesting differential expression of MHC Class II subsets and the presence of CD1- MHC Class II+ granule- dendritic cells in sheep analogous to indeterminate cells of man. In acanthotic skin, compared to normal skin, Langerhans cells were less numerous, irregular and more suprabasal in distribution and their morphology was occasionally swollen and indistinct. No difference was seen in the ability of AChE and MoAb in detecting Langerhans cells, however pairwise testing of markers did demonstrate that significantly more (P < 0.05) cells without dendritic processes were stained with MoAb 49.1 than with 20.27 or 28.1. In all squamous cell carcinomas examined dendritic cells that stained for AChE, CD1 or MHC Class II antigens were concentrated at the peripheral areas of neoplastic epithelium. Many dendritic cells were detected with MoAb to MHC Class II antigens, whereas CD1 and AChE positive dendritic cells were rare in tumor bearing tissue. The quantitative differences in the immunohistochemical staining of Langerhans cells between normal, acanthotic and neoplastic epithelium were consistent with ultrastructural studies. When compared with those of a newborn lamb, which had had very little exposure to antigens or ultraviolet radiation (UVR), the Langerhans cells of the aged sheep were deformed and contained far fewer Birbeck granules. The abnormalities were progressively more severe in acanthotic and neoplastic skin. These observed changes may have resulted from UVR induced damage and may be indicative of impaired function involved in the development of skin cancer.

Characterization of verruciform xanthoma by in situ hybridization and immunohistochemistry

Verruciform xanthoma (VX) is a rare, benign lesion, mainly found in the oral mucosa. Histologically and ultrastructurally, the lesion is characteristic and well defined. However, the etiology of the lesion remains unclear. The purpose of the present study was to elaborate upon the pathogenesis of VX by evaluation of an additional series of oral examples for human papillomaviruses (HPV), using immunohistochemistry and in situ hybridization, and to further characterize the cellular components of VX immunohistochemically. Twelve specimens diagnosed as VX were retrospectively collected. One of the twelve specimens was positive for HPV types 6/11 by in situ hybridization. None of the twelve specimens demonstrated the presence of HPV antigen by immunohistochemistry. By immunohistochemical studies, the predominant cells in the inflammatory infiltrate were T cells. The foam cells were of monocyte/macrophage lineage. S-100-positive (Langerhans) cells were occasionally found in the suprabasal layer of the epithelium. HLA-DR-positive keratinocytes were noted at the intense inflammatory sites. Taken together, these findings suggest that an immune response may play a role, at least in part, in VX pathogenesis.

Functional expression of minor histocompatibility antigens on human peripheral blood dendritic cells and epidermal Langerhans cells

Adequate presentation and cell surface expression of foreign minor histocompatibility antigens (mHag) to allogeneic T cells can lead to graft versus-host disease (GvHD) after HLA matched bone marrow transplantation (BMT). Cells of the dendritic cell (DC) lineage, including epidermal Langerhans cells (LC), are the most potent inducers of primary alloreactive T cell responses in vivo and in vitro. To explore the possible role of peripheral blood DC and of skin derived LC in the induction of alloimmune responses against mHag, we analysed the functional expression of mHag on these professional antigen-presenting cells (APC). To this end, cytotoxic T cell (CTL) clones specific for mHag H-Y and HA-1 to HA-4 were used to demonstrate the presence of these antigens on highly purified DC and LC. Our results demonstrate that, like other cells of the hematopoietic lineage, DC and LC express all the mHag tested for. The functional expression of mHag on these potent APC suggests their involvement in the induction of mHag specific GvH directed T cell responses after allogeneic BMT.

Immunity at the surface: homeostatic mechanisms of the skin immune system

The coordinated function of multiple epidermal and dermal cell populations allows the skin immune system to respond rapidly and effectively to a wide variety of insults occurring at the interface of the organism and its environment. Keratinocytes are the first line of defense in the skin immune system, and keratinocyte-derived cytokines are pivotal in mobilizing leukocytes from blood and signaling other cutaneous cells. Cytokine-mediated cellular communication also enables dermal fibroblasts and endothelial cells lining the cutaneous vasculature to participate in immune and inflammatory responses. Skin is an important site for antigen presentation, and both epidermal Langerhans cells and dermal dendritic cells play pivotal roles in T cell-mediated immune responses to antigens encountered in skin. Proinflammatory signaling pathways are necessarily balanced by a variety of regulatory pathways that help maintain the homeostatic functioning of the skin immune system.

Specific induction of cAMP in Langerhans cells by calcitonin gene-related peptide: relevance to functional effects

Epidermal Langerhans cells (LC) are associated anatomically with epidermal nerves, and a product of these nerves, calcitonin gene-related peptide (CGRP), inhibits the antigen-presenting capacity of LC and macrophages. As the CGRP receptor appears to be coupled to Gs alpha protein, which in turn activates adenylate cyclase, the ability of CGRP to induce cAMP in LC was examined and correlated with functional effects. LC were isolated from murine epidermal cells using antibodies on magnetic microspheres. Exposure to CGRP induced a significant increase in cAMP content, which could be inhibited by coculture with a truncated form of CGRP [CGRP-(8-37)] that is a specific competitive inhibitor of CGRP. Substance P and calcitonin failed to induce cAMP in LC. Although culture in CGRP reduced the ability of murine epidermal cells enriched for LC content to present pigeon cytochrome c to a responsive clone or to present antigen for elicitation of delayed-type hypersensitivity in immune mice, culture in forskolin had little or no effect on antigen presentation despite increased cAMP content of LC as much or more than that induced by CGRP. The effect of CGRP on antigen presentation in these systems could be blocked with CGRP-(8-37). CGRP inhibited the induction of B7-2 by lipopolysaccharide on peritoneal macrophages and a LC line, whereas calcitonin did not. CGRP induces specific accumulation of cAMP in LC and inhibits LC antigen-presenting function by a receptor-mediated event. However, the induction of cAMP by itself does not account for inhibition of antigen presentation. Suppression of the expression of B7-2 may be one mechanism by which CGRP inhibits antigen presentation.

Distribution of HLA class II molecules in epidermal Langerhans cells in situ

We performed immunoelectron microscopic studies to investigate the expression of HLA class II molecules in Langerhans cells (LC). In the epidermis, LC expressed class II molecules on the plasma membrane of the dendrites, resulting in a class II positive reticulo-epithelial network, but not on the surface of the cell body. In contrast, isolated LC as well as activated LC in situ displayed an even and strong expression of class II molecules on their entire cell surface. Therefore, isolation and/or activation results in redistribution and up-regulation of class II molecules on the cell surface. In addition, double-labeling experiments were carried out with monoclonal antibodies to class II antigens and to LAMP-1, CD63 and alpha-glucosidase, specific markers for organelles of the endosomal/lysosomal system. The results show expression of class II molecules on intracellular, electron-dense vesicular structures, and co-localization of class II molecules and the markers for late endosomes and early lysosomes in human LC in situ. Expression of these markers was not found on Birbeck granules, an LC-specific organelle.

Functional human epidermal Langerhans cells that lack Birbeck granules

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

Expression and function of the costimulatory molecule B7 on murine Langerhans cells: evidence for an alternative CTLA-4 ligand

We have previously shown, through transfection experiments, that the murine B7 (mB7) molecule, a ligand for the CD28 and CTLA-4 receptors, is a sufficient costimulatory signal for the antigen-specific and major histocompatibility complex (MHC)-restricted activation of murine CD4+ T lymphocytes. In addition to mB7, another ligand with affinity for CTLA-4 has been described on spleen cells. Here we report our studies on the expression and function of these molecules on murine Langerhans cells (LC). Both anti-mB7 monoclonal antibody (mAb) 16-10A1 and human CTLA4Ig (hCTLA4Ig), a chimeric fusion protein consisting of the extracellular domain of human CLTA-4 and the constant domain of human IgG1, detected antigen(s) on cultured but not freshly isolated LC. Preincubation of cultured LC with anti-mB7 mAb did not significantly affect binding of hCTLA4Ig to these cells. This result demonstrate the existence of at least one other ligand for the CLTA-4 receptor on cultured LC. Functional studies revealed that the costimulatory activity of LC was inhibited better by hCTLA4Ig than by the anti-mB7 mAb. This differential effect was seen in the case of both alloreactive and antigen-specific, syngeneic T cell responses. These findings suggest that the non-mB7-ligand for CTLA-4 is functional and participates in the induction of immune responses by LC. Importantly, even synergistic combinations of anti-mB7 mAb and hCTLA4Ig did not inhibit completely the activity of LC. These findings therefore raise the possibility that LC express other costimulatory ligands besides mB7 and related family members.

Long-term ultraviolet B-induced impairment of Langerhans cell function: an immunoelectron microscopic study

The influence of low-dose, long-term ultraviolet B (UVB) light exposure on HLA class II-positive human epidermal Langerhans cells (LC) was studied using a sensitive immunoelectron microscopic technique for the ultrastructural assessment of HLA class II expression on LC and for quantification of these cells in situ. Six healthy Caucasian volunteers participated in the experiments and received thrice weekly UVB treatments for 4 weeks. The initial dose ranged from 30 to 50 mJ/cm2 and the total dose from 600 to 3500 mJ/cm2, depending on skin type. Suction blisters and biopsies were obtained before the start of the UVB protocol and 48 h after the last UVB irradiation, and processed for the mixed epidermal cell-lymphocyte reaction (MECLR) and electronmicroscopy, respectively. The MECLR was used as a measure of the immune response. The distribution of HLA class II molecules on LC was studied by incubating ultrathin cryosections of human skin tissue with an anti-HLA class II MoAb that was conjugated to 10 nm colloidal gold. Furthermore, the number of LC was assessed ultrastructurally, when they could be recognized by their unique cytoplasmic organelle, the Birbeck granule (BG). The UVB protocol that was employed caused a marked suppression of the MECLR responses. This UVB-induced reduction of the immune response was not paralleled by changes in HLA class II expression on LC, nor in the number of epidermal LC. These findings are further support for our hypothesis that UVB-induced immune suppression in the skin is not due to a depletion of local LC.

Murine HIV-1 p24 specific T lymphocyte activation by different antigen presenting cells: B lymphocytes from immunized mice present core protein to T cells

Mice were injected with three doses of baculovirus-produced recombinant HIV-1 p24 core protein in alum adjuvant. CD4 positive T lymphocytes from immunized animals proliferated in vitro in the presence of antigen and peritoneal macrophages (Mps) or splenic dendritic cells (DCs) from non-immunized mice as antigen presenting cells (APCs). DCs were approximately three times more efficient than Mps on a cell for cell basis. No synergy was observed between Mps and DCs in this system. B lymphocytes from immunized animals also presented p24 antigen to the specific T cells. Mps did synergize with B cells to enhance the level of T lymphocyte proliferation. This may have implications for the induction of specific immune responses to pathogens after administration of single protein vaccines.

Dendritic cells in glomerulonephritis

Renal biopsies (n = 45) from patients with various forms of glomerulonephritis (GN), comprising mesangial IgA-GN (n = 25), focal glomerular sclerosis (n = 13) and acute GN (n = 7), were examined by double staining immunocytochemistry (APAAP, streptavidin-peroxidase) using unconjugated monoclonal antibodies (Ab) against--(i) the CD1b antigen expressed on dendritic cells (DCs), (ii) the invariant chain (Ii), and (iii) biotin-conjugated Ab against HLA-DR. In normal control kidneys (n = 7) without interstitial inflammation, CD1b-positive DCs were not detected. Glomerular endothelial cells and a few cells in mesangial areas showed double staining with the Ab against HLA-DR in Ii. In GN without active interstitial inflammation (n = 9), CD1b-positive DCs were not found. In biopsies with interstitial inflammation (n = 36) CD1b-positive DCs were found interspersed among other inflammatory cells. In seven of the biopsies showing IgA-GN DCs were seen in the vicinity of those glomeruli that exhibited either crescents or glomerular sclerosis with splitting of Bowman's capsule. In proximal tubular epithelial cells de novo expression of HLA-DR/Ii-chain was only seen when DCs were present. We conclude that in different forms of GN: (i) CD1b-positive DCs play an important role in the development of interstitial inflammation, and (ii) their presence may be related to the de novo coexpression of HLA-DR/Ii in tubular epithelial cells, possibly mediated through the production of interferon gamma and other cytokines.

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.

Analysis of effects of ultraviolet B radiation on induction of primary allergic reactions

Acute, low-dose exposure to UVB light reveals a genetic polymorphism in humans with respect to the ability of irradiated skin to support the induction of contact hypersensitivity (CH) to dinitrochlorobenzene (DNCB). In healthy adult caucasians, as well as in humans with deeply pigmented skin, approximately 45% fail to develop CH when DNCB is painted on UVB-irradiated skin; these individuals are termed "UVB susceptible" (UVB-S), whereas those who develop CH at the challenge site are termed "UVB resistant" (UVB-R). The UVB-S trait is characteristic of virtually all patients with biopsy-proved basal/squamous cell cancer, and may therefore be a risk factor for this disease. We have investigated the effects of UVB on expression of primary allergic reactions (PAR) in healthy caucasian and black-skinned adults, as well as patients with skin cancer. Among UVB-R caucasians, very few (less than 25%) developed PAR at site exposed to UVB, whereas among black-skinned UVB-R subjects, all displayed a PAR at the UVB irradiated site. To determine whether the lack of PAR in UVB-R caucasian subjects was systemic or local in origin, DNCB was applied to UVB-exposed buttock skin, and each individual was then challenged with dilute DNCB on forearm skin twice: 11 and 30 d thereafter. When inflammatory responses were evaluated at the original hapten application site, as well as both challenge sites, complete concordance was observed between positive challenge reactions at 30 d (UVB-R) and positive challenge reactions at 11 d, whereas only one caucasian subject displayed a PAR at 12 d. Thus, UVB-R caucasians can display CH as early as 11 d following hapten application to UVB-treated skin, indicating that their failure to display PAR is a local, rather than a systemic, effect of UVB. Because UVB-induced phototoxicity was significantly greater in caucasian than in deeply pigmented skin, it is anticipated that phototoxicity leads to rapid hapten "washout" from UVB-exposed caucasian skin. We propose that PAR usually do not occur in UVB-treated caucasian skin because insufficient hapten remains at the site to trigger a spontaneous inflammation when systemic hapten-specific immunity emerges.

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

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

T-lymphocyte-activating properties of epidermal antigen-presenting cells from normal and psoriatic skin: evidence that psoriatic epidermal antigen-presenting cells resemble cultured normal Langerhans cells

Fresh and cultured human Langerhans cells display disparate functional programs, based on their capacities to activate autologous and allogeneic T cells, and with respect to their susceptibility to inhibition by transforming growth factor-beta (TGF beta). We have compared the functional properties of epidermal antigen-presenting cells (APC) procured from uninvolved and involved skin of patients with psoriasis with fresh and cultured normal epidermal cells. Freshly obtained psoriatic epidermal APC resembled cultured normal epidermal cells in their superior capacity to activate syngeneic and allogeneic T cells; fresh normal epidermal cells failed to activate syngeneic T cells, and induced only modest proliferation among allogeneic T cells. The modest T-cell--activating properties of fresh, normal epidermal cells were not suppressed by TGF beta, whereas the T-cell--activating potential of psoriatic epidermal cells, cultured normal epidermal cells, and blood APC was inhibited approximately 50% by TGF beta. Thus, fresh psoriatic epidermal APC resemble cultured normal epidermal cells functionally. Because these properties are already evident in cells obtained from uninvolved psoriatic skin, the "cultured" functional phenotype of epidermal APC in this disease may precede the appearance of active psoriatic skin lesions. Surface marker analysis of normal and psoriatic epidermal cell suspensions revealed that virtually all of the bone marrow--derived cells in normal epidermal cell suspensions were conventional (CD1+) Langerhans cells, whereas CD1+ cells comprised only a minority of bone marrow--derived (CD45+) cells in psoriatic epidermis. It is speculated that some of the CD1-, CD45+ cells in psoriatic epidermis may be Langerhans cells that have lost their "fresh" phenotype. These data indicate that an abnormality in epidermal APC function exists in psoriatic skin--even before clinical lesions develop, and we speculate that the abnormal capacity of psoriatic epidermal APC to activate syngeneic T cells may be important in the expression of keratinocyte pathology. Because psoriatic epidermal APC functions were profoundly inhibited in vitro by treatment with cyclosporin A, the effectiveness of this drug in psoriasis may be due in part to its ability to inhibit epidermal antigen-presenting cell function in vivo.

Characterization of murine lung dendritic cells: similarities to Langerhans cells and thymic dendritic cells

Dendritic cells (DC) are potent accessory cells (AC) for the initiation of primary immune responses. Although murine lymphoid DC and Langerhans cells have been extensively characterized, DC from murine lung have been incompletely described. We isolated cells from enzyme-digested murine lungs and bronchoalveolar lavages that were potent stimulators of a primary mixed lymphocyte response (MLR). The AC had a low buoyant density, were loosely adherent and nonphagocytic. AC function was unaffected by depletion of cells expressing the splenic DC marker, 33D1. In addition, antibody and complement depletion of cells bearing the macrophage marker F4/80, or removal of phagocytic cells with silica also failed to decrease AC activity. In contrast, AC function was decreased by depletion of cells expressing the markers J11d and the low affinity interleukin 2 receptor (IL-2R), both present on thymic and skin DC. AC function was approximately equal in FcR+ and FcR- subpopulations, indicating there was heterogeneity within the AC population. Consistent with the functional data, a combined two-color immunofluorescence and latex bead uptake technique revealed that lung cells high in AC activity were enriched in brightly Ia+ dendritic-shaped cells that (a) were nonphagocytic, (b) lacked specific T and B lymphocyte markers and the macrophage marker F4/80, but (c) frequently expressed C3biR, low affinity IL-2R, FcRII, and the markers NLDC-145 and J11d. Taken together, the functional and phenotypic data suggest the lung cells that stimulate resting T cells in an MLR and that might be important in local pulmonary immune responses are DC that bear functional and phenotypic similarity to other tissues DC, such as Langerhans cells and thymic DC.

Langerhans cells and epithelial cell modifications in cervical intraepithelial neoplasia: correlation with human papillomavirus infection

The study of a series of 18 cervical intraepithelial neoplasia (CIN) grade II and III was aimed at determining the distribution and phenotype of immunocompetent cells (Langerhans cells, T and NK cells) and the alteration in the expression of EGF receptors and beta 2-microglobulin in correlation with human papillomavirus (HPV) infection (viral antigen and DNA typing with biotinylated probes). These lesions were characterized by a reduced number of Langerhans cells and a dense infiltrate. HPV infection did not induce HLA-DR expression in the infected epithelial cells. We observed an enhanced expression of epidermal growth factor (EGF) receptors by epithelial cells and a reduced beta 2-microglobulin reactivity by both epithelial and immunocompetent cells. Most of CIN showed foci of infected cells. No significant differences were observed in immunological markers of CIN harboring benign HPV 6/11 DNA or oncogenic HPV 16/18 DNA. Viral antigen was not detected in these lesions. These changes in the epithelial cells of CIN and their microenvironment associated to the lack of HLA-DR expression in the infected cells hamper the squamous epithelial cells to function as antigen presenting cells. This may facilitate a decrease in the immunological surveillance and may contribute to the severity of such lesions.

Cutaneous T-cell lymphoma lesional epidermal cells activate autologous CD4+ T lymphocytes: involvement of both CD1+OKM5+ and CD1+OKM5- antigen-presenting cells

Cutaneous T-cell lymphoma is characterized by infiltration of the skin by activated CD4+ T lymphocytes. The mechanism by which these T lymphocytes achieve and maintain their activated state is unknown. Antigen-specific activation of T lymphocytes is dependent upon antigen-presenting cells which express HLA-DR class II major histocompatibility complex molecules, such as epidermal Langerhans cells. In addition to CD1+DR+ Langerhans cells, cutaneous T-cell lymphoma lesional epidermis contains major histocompatibility complex class II positive non-Langerhans cell populations, including CD1+OKM5+ bone-marrow-derived cells and DR+ keratinocytes. We asked whether any of these epidermal cell populations demonstrate capacity to activate T lymphocytes. Various numbers of epidermal cells from uninvolved and involved cutaneous T-cell lymphoma plaques were therefore used to stimulate autologous CD4+ and CD8+ T lymphocytes in the absence of exogenous antigen. Involved epidermal cells potently induced proliferation of CD4+ T lymphocytes (S.I. +/- SEM = 466 +/- 45). In contrast, uninvolved epidermal cells only induced background levels of proliferation (S.I. +/- SEM = 2 +/- 0.5, N = 8, p less than 0.01). Neither involved nor uninvolved epidermal cells were able directly to activate CD8+ lymphocytes. The capability of involved epidermal cells to activate CD4+ T lymphocytes was dependent upon CD1+DR+ leukocytes and not DR+ keratinocytes, because depletion of either HLA-DR+, CD1+ or HLe1+ epidermal cells totally abrogated the T-lymphocyte proliferation. Interestingly, on a cell per cell basis CD1+DR+ cells obtained from involved skin, demonstrated relative to CD1+DR+ cells from uninvolved skin, enhanced capacity to activate CD4+ T lymphocytes. Furthermore, CD1+OKM5+ cells from involved epidermis stimulated autologous CD4+ T lymphocytes. This indicates that a unique hitherto undescribed CD1+OKM5+ epidermal antigen-presenting cell population may participate in T-lymphocyte activation. These findings provide support for the concept that the epidermal cells in cutaneous T-cell lymphoma patients, particularly the antigen-presenting cells, may contribute significantly to the activation of CD4+ malignant and/or non-malignant inflammatory T lymphocytes within the skin.

Interstitial dendritic cells

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

An ultraviolet B radiation protocol for complete depletion of human epidermal Langerhans cells

We report an ultraviolet B (UVB) protocol that achieves essentially complete depletion of Langerhans cells (LC) from human skin, while leaving the skin clinically intact. Sixteen human volunteers of skin types II and III were exposed to 144 mJ/cm2 of UVB each day for 4 successive days, on a 2-cm-diameter circle of buttock skin. In each case the irradiated skin showed redness and mild edema but no vesiculation or ulceration. One hour after the last exposure a 4-mm punch biopsy was taken from the center of the irradiated site. The epidermal sheet from each sample was separated and exposed to CD-1 antibody (12 samples) or HLA-DR antibody (4 samples) and the density of LC was assessed by immunofluorescence light microscopy. In each case the epidermal LC population was severely depleted to less than 20 cells/mm2, from a baseline of approximately 565 cells/mm2, and in many cases no morphologically normal LC remained. This simple protocol thus provides intact human skin completely depleted of LC. Such skin will provide an appropriate model for the in vivo study of the immune function in human skin deprived of its epidermal antigen-presenting capacity.

Regional variation in Langerhans cell distribution and density in normal human oral mucosa determined using monoclonal antibodies against CD1, HLADR, HLADQ and HLADP

The distribution, density and activation of Langerhans cells (LC) has been established in biopsies of normal human buccal mucosa, hard palate, lateral border and dorsum of tongue, floor of mouth and lip taken from sudden death post mortems. LC were identified in cryostat sections with monoclonal antibodies against CD1, HLADR, HLADQ and HLADP using an immunoalkaline phosphatase technique. The use of post mortem material was validated by comparison with biopsies taken from volunteers. LC were predominantly situated in the basal and immediately suprabasal layers of the epithelium. In floor of mouth, lip, lateral border and dorsum of tongue the cells were found along the length of the epithelium. In buccal mucosa, although LC showed fundamentally a similar distribution, a tendency to cluster around the connective tissue papillae was also noted. In hard palate LC were found parallel to the surface in the mid zone of the epithelium. No evidence of LC free areas was found. Dorsum of tongue had the highest density of LC per mm epithelial surface length (28.3 cells per mm) which was significantly greater (P less than 0.05) than buccal mucosa (25.2) which in turn had significantly more cells (P less than 0.05) than lip (22.4). The lowest density of LC was found in lateral border of tongue (17.6), hard palate (17.6) and floor of mouth (16.7). These sites had significantly fewer cells than lip, buccal mucosa and dorsum of tongue (P less than 0.05). Class II MHC molecules are necessary for antigen presentation and in all sites except buccal mucosa there was no significant difference between the number of cells expressing CD1, HLADR, HLADQ and HLADP.(ABSTRACT TRUNCATED AT 250 WORDS)

Optimization of an in vitro lymphocyte blastogenesis assay for predictive assessment of immunologic responsiveness to contact sensitizers

Current methods for the predictive and diagnostic assessment of contact sensitization rely on the visual scoring of skin reactions. Predictive animal tests, generally using guinea pigs, require a relatively large number of animals to produce a sufficient database for interpreting skin reaction scores. In vitro assays have the potential of being more quantitative than skin testing and, if so, would require fewer animals. However, although in vitro assays are commonly used to study the cellular immune response to strong contact sensitizers, there has been little effort to validate them for predictive assessment purposes. We have optimized an in vitro lymphocyte blastogenesis assay for detecting the response of mouse lymphocytes to strong contact sensitizers with the eventual objective of applying this assay to moderate and weak sensitizers as well. Lymph node lymphocytes from mice sensitized to the strong contact allergens, dinitrochlorobenzene (DNCB), dinitrofluorobenzene (DNFB), or trinitrochlorobenzene (TNCB), responded [greater than or equal to 12,000 counts per minute (CPM) above background] when cultured with water soluble chemical analogues, di- or trinitrobenzene sulfonic acid (DNBS or TNBS). However, the strong sensitizer, oxazolone (OXAZ), has no water soluble analogue and lymphocytes from mice sensitized to OXAZ responded poorly in vitro (less than 2000 CPM) to an ethanol-solubilized OXAZ preparation in spite of very strong in vivo sensitization (ear swelling assay). To increase the assay sensitivity, for OXAZ, we modified the antigen presentation conditions by using 1) solubilized antigen-modified adherent spleen cells, 2) dendritic cells from the draining lymph nodes of antigen painted mice, and 3) antigen-modified Langerhans cell-enriched cultured epidermal cells (EC). These approaches increased OXAZ-directed responses to greater than 7000, greater than 20,000, and greater than 100,000 CPM, respectively, under culture conditions optimized for cell density, responder: stimulator cell ratio, culture duration, and responder cell type. Our results represent a first attempt to directly modify cultured epidermal cells with OXAZ and use these cells to stimulate OXAZ-directed blastogenesis in microtiter plate cultures. This optimized assay is now under evaluation for predictive assessment of contact sensitizers relevant to occupational and consumer exposures.

Effect of psoralens and ultraviolet radiation on murine dendritic epidermal cells

Monofunctional psoralens produce less phototoxicity than bifunctional psoralens after ultraviolet A (UVA) irradiation. We investigated the effect of repetitive treatments with angelicin (isopsoralen), a monofunctional psoralen, plus UVA radiation (IPUVA) on the number and morphology of dendritic epidermal cells (dEC). This effect was compared with that of 8-methoxypsoralen plus UVA radiation (PUVA), UVA alone, and UVB radiation. C3H/HeN mice were treated topically with the drugs three times/wk for 4 consecutive wk; followed each time by 1 or 2.5 J/cm2 of UVA radiation. Other groups of mice were treated with the drugs alone, UVA alone, or 0.81 J/cm2 of UVB. Epidermal sheets were stained for ATPase, Ia, and Thy-1 markers. Mice treated with PUVA and UVB exhibited severe phototoxicity, whereas no overt phototoxicity was observed in mice treated with IPUVA, UVA alone, or the drugs alone. Early during the PUVA and UVA treatments the ATPase marker was lost from dEC, followed by loss of the Ia marker; the Ia marker was lost before the ATPase marker from dEC in animals treated with IPUVA. At the end of the treatment, however, nearly total depletion of ATPase+, Ia+, and Thy-1+ dEC was observed in mice treated with PUVA and IPUVA. UVB radiation caused rapid depletion of Thy-1+ dEC as well as ATPase+ and Ia+ cells. During treatments with IPUVA, PUVA, UVA, and UVB, the Langerhans cells became rounded and lost their dendrites. These changes were quantitated by image analysis. We conclude that alterations of cutaneous immune cells can occur in the absence of overt phototoxicity, and that monofunctional and bifunctional psoralens plus low dose of UVA radiation may have different effects on dEC markers.

Functional characteristics of veiled cells from canine prenodal lymph

The surgical interruption of afferent lymphatics in the hind limb of dog leads to peripheral lymph stasis. The stagnated lymph contains large numbers of immunocompetent cells originating solely from the skin. This experimental model allows a study of the functions of the afferent skin-draining lymph cell population, the recovery and assessment of the lymphokines and other mediators liberated by these cells during the culture, and the production of anti-sera against different types of lymph cells. In the present study, we focused on the functional, morphological and cytochemical evaluation of the non-lymphoid cells, isolated from the whole lymph cell population by means of the gradient centrifugation technique. The non-lymphoid cells were large, with an irregularly-shaped nucleus and numerous cytoplasmic projections, giving them a "veiled" cell (VC) appearance. All VC were strongly positive for DLA-class II antigens and membrane-associated ATP-ase, and 60% of them exhibited the activity of non-specific esterase. In the functional assays, VC displayed the potent accessory-cell activity in the mitogen-induced response of autologous blood- and lymph-derived lymphocytes. In the mixed leukocyte cultures, VC acted as stimulators of the allogeneic and autologous lymphocyte proliferation. The high spontaneous and mitogen-induced responsiveness of the whole lymph cell population was found to be dependent on the presence of VC. The small number of VC (5% of cultured cells) was sufficient to produce the above-mentioned effects. These results indicate that VC is a cell responsible for the antigen presentation in the skin-associated immune reactions in dog, which is relevant to the observations on similar cells from the other species.

Genetic basis of ultraviolet-B effects on contact hypersensitivity

The genetic basis of the effects of ultraviolet B (UVB) radiation on the induction of contact hypersensitivity (CH) to dinitrofluorobenzene (DNFB) has been explored in genetically defined mice. It was found that acute, low-dose UVB radiation produced profound depletion of epidermal Langerhans cells (LC) at UVB-treated sites in all strains of mice tested. However, when DNFB was applied to UVB radiation sites, unresponsiveness developed in some strains of mice, but vigorous contact hypersensitivity was induced in others. The UVB-susceptible phenotype proved dominant or codominant in F1 hybrids derived from parental strains of the susceptible and UVB-resistant phenotypes. Experiments conducted in one set of F1 hybrids derived from two UVB-susceptible parental strains displayed UVB resistance, suggesting gene complementation, and showed that more than one genetic locus was involved. Segregant backcross populations, analyzed for the capacity to develop CH after UVB treatment and skin painting with DNFB, revealed that at least two, and probably three, independent genetic loci participate in determining UVB resistance. Results of experiments with H-2 congenic and recombinant mice derived from the B10 background implicated class I genes of the major histocompatibility complex as relevant genetic factors. These results indicate that there is a dissociation between the effects of UVB radiation on epidermal Langerhans cells and the capacity of a cutaneous surface to support the induction of contact hypersensitivity. The data indicate that the induction of CH to haptens is dependent on normal numbers of functional LC at the skin painting site only in some strains of mice. The data imply that in the so-called UVB-resistant strains of mice, alternative (non-Langerhans cell-dependent) mechanisms allow for the induction of CH. Several independent genetic loci, one of which appears to be H-2, govern this UVB-related effect.

Immunostimulatory capabilities of highly enriched Langerhans cells in vitro

Langerhans cells (LC) are epidermal antigen-presenting cells capable of inducing allogenic, antigen-specific, and cytotoxic T cell proliferation. Previous studies have examined the dynamics of LC maintained in vitro in crude epidermal cell (EC) suspensions in which the major cell type is the keratinocyte (KC). To avoid the confounding effects of KC and other immunoregulatory cells on LC dynamics in vitro, highly enriched murine LC (85%) were studied, through 72 h of incubation in vitro, for their ability to present alloantigen (in a primary allogenic proliferation assay) and foreign antigen (in a secondary autologous proliferation assay). The results were compared to similar studies using crude EC suspensions. Freshly prepared LC are very poor stimulators of a primary allogenic proliferation response, with a 12- to 16-fold increase in stimulatory capacity by 72 h using panned-enriched and crude EC suspensions, respectively. Similarly, freshly prepared LC are weak stimulators of a secondary autologous proliferation response, with a 2.5- to 6-fold increase in immunostimulatory capability by 72 h. The overall increased stimulatory effect observed with the crude EC suspensions compared to highly enriched LC is most likely attributed to the effect of KC on T cell proliferation, rather than to a maturation effect of KC on LC during the 72 h of in vitro incubation. Using back-scattered electron imaging, the surface density of MHC-class II molecules (Ia) increased three- to fourfold through culture, which parallels the increase in functional ability. This study demonstrates that LC in either a crude or highly enriched cell suspension mature into potent immunostimulatory cells after incubation in vitro with an increased surface expression of Ia molecules. Keratinocytes are not necessary for LC maturation in vitro, but seem to exert some stimulatory effect by enhancing lymphocyte proliferation in the functional assay system.