Cutaneous Antigen-presenting Cells Research Articles

Chikungunya Virus Envelope Protein E2 Provides a Vector for Targeted Antigen Delivery to Human Dermal CD14+ Dendritic Cells

Therapeutic modulation of human cutaneous antigen-presenting cells (APCs) that control the fate of T cells represents an interesting option for immunotherapy. Because they capture glycosylated proteins by C-type lectins, lectin-targeting antibodies have been used to specifically convey antigens to APCs (Kastenmüller et al., 2014; Romani et al., 2012; Stoitzner et al., 2014). Beyond the potential therapeutic applications, APC-targeting strategies can be harnessed to acquire fundamental knowledge about their function (Flacher et al., 2014).

Interactions of Human Dermal Dendritic Cells and Langerhans Cells Treated with Hyalomma Tick Saliva with Crimean-Congo Hemorrhagic Fever Virus.

Crimean-Congo hemorrhagic fever virus is one the most important and wide spread tick-borne viruses. Very little is known about the transmission from the tick and the early aspects of pathogenesis. Here, we generate human cutaneous antigen presenting cells—dermal dendritic cells and Langerhans cells—from umbilical cord progenitor cells. In order to mimic the environment created during tick feeding, tick salivary gland extract was generated from semi-engorged Hyalomma marginatum ticks. Our findings indicate that human dermal dendritic cells and Langerhans cells are susceptible and permissive to Crimean-Congo hemorrhagic fever virus infection, however, to different degrees. Infection leads to cell activation and cytokine/chemokine secretion, although these responses vary between the different cell types. Hyalomma marginatum salivary gland extract had minimal effect on cell responses, with some synergy with viral infection with respect to cytokine secretion. However, salivary gland extract appeared to inhibit antigen presenting cells (APCs) migration. Based on the findings here we hypothesize that human dermal dendritic cells and Langerhans cells serve as early target cells. Rather affecting Crimean-Congo hemorrhagic fever virus replication, tick saliva likely immunomodulates and inhibits migration of these APCs from the feeding site.

TLR4 acts as a death receptor for ultraviolet radiation (UVR) through IRAK-independent and FADD-dependent pathway in macrophages.

UVR-induced apoptosis in cutaneous antigen presenting cells (APC) causes systemic immune suppression and is dependent on TLR4/MyD88 signalling, but the apoptotic signalling pathways have not been defined. Macrophages pretreated with lipopolysaccharide (LPS) were unresponsive to subsequent LPS treatment, however, but were susceptible to UVR-induced apoptosis. Macrophage survival and apoptotic events after UVR were also unaffected by treatment with TLR4 antagonists, a blocking IgG or a TLR4 analog antagonist, suggesting that UVR cell death is independent of a soluble ligand. After UVR, IRAK4KDKI (catalytically inactive IRAK4) and wild-type (WT) macrophages show equivalent levels of survival, as measured by MTT assay, and apoptosis, as measured by cleaved caspase-3. Furthermore, in macrophages from both mice, UVR activated caspase-8 and PARP, while inactivating Rip3. This finding is supported by a lack of IRAK1 degradation after UVR, compared to treatment with TLR2 or TLR4 agonists. UVR induced association of MyD88 with FADD, an extrinsic apoptotic pathway protein, but not IRAK4. UVR-induced migration of FADD to the cell membrane of WT macrophages, but not MyD88-/- macrophages, was observed (confocal microscopy). Co-immunoprecipitation using an epitope-tagged MyD88 revealed that FADD, but not TRADD, was recruited to MyD88 within 30minutes of UVR exposure. UVR engages TLR4/MyD88 as a death signalling complex, rather than the classical inflammatory signalling pathway triggered by PAMP recognition of TLR4. These studies provide the rationale for the future development of topical TLR4 modulating therapies to interfere with this UVB-mediated apoptosis and the associated negative consequences of immune suppression.

403 Specific targeting of cutaneous antigen-presenting cells by Chikungunya virus envelope protein E2

403 Specific targeting of cutaneous antigen-presenting cells by Chikungunya virus envelope protein E2

Phenotypic and Functional Properties of Human Steady State CD14+ and CD1a+ Antigen Presenting Cells and Epidermal Langerhans Cells.

Cutaneous antigen presenting cells (APCs) are critical for the induction and regulation of skin immune responses. The human skin contains phenotypically and functionally distinct APCs subsets that are present at two separated locations. While CD1ahigh LCs form a dense network in the epidermis, the CD14+ and CD1a+ APCs reside in the dermal compartment. A better understanding of the biology of human skin APC subsets is necessary for the improvement of vaccine strategies that use the skin as administration route. In particular, progress in the characterization of uptake and activatory receptors will certainly improve APC-targeting strategies in vaccination. Here we performed a detailed analysis of the expression and function of glycan-binding and pattern-recognition receptors in skin APC subsets. The results demonstrate that under steady state conditions human CD1a+ dermal dendritic cells (DCs) were phenotypically most mature as measured by the expression of CD83 and CD86, whereas the CD14+ cells showed a higher expression of the CLRs DC-SIGN, mannose receptor and DCIR and had potent antigen uptake capacity. Furthermore, steady state LCs showed superior antigen cross-presentation as compared to the dermal APC subsets. Our results also demonstrate that the TLR3 ligand polyribosinic-polyribocytidylic acid (pI:C) was the most potent stimulator of cytokine production by both LCs and dDCs. These studies warrant further exploration of human CD1a+ dDCs and LCs as target cells for cancer vaccination to induce anti-tumor immune responses.

Atopic Dermatitis and Disease Severity Are the Main Risk Factors for Food Sensitization in Exclusively Breastfed Infants

Filaggrin (FLG) loss-of-function skin barrier gene mutations are associated with atopic dermatitis (AD) and transepidermal water loss (TEWL). We investigated whether FLG mutation inheritance, skin barrier impairment, and AD also predispose to allergic sensitization to foods. Six hundred and nineteen exclusively breastfed infants were recruited at 3 months of age and examined for AD and disease severity (SCORing Atopic Dermatitis (SCORAD)), and screened for the common FLG mutations. TEWL was measured on unaffected forearm skin. In addition, skin prick testing was performed to six study foods (cow's milk, egg, cod, wheat, sesame, and peanut). Children with AD were significantly more likely to be sensitized (adjusted odds ratio (OR)=6.18, 95% confidence interval (CI): 2.94-12.98, P<0.001), but this effect was independent of FLG mutation carriage, TEWL, and AD phenotype (flexural vs. non-flexural). There was also a strong association between food sensitization and AD severity (adjusted ORSCORAD<20=3.91, 95% CI: 1.70-9.00, P=0.001 vs. adjusted ORSCORAD20=25.60, 95% CI: 9.03-72.57, P<0.001). Equally, there was a positive association between AD and sensitization with individual foods (adjusted ORegg=9.48, 95% CI: 3.77-23.83, P<0.001; adjusted ORcow's milk=9.11, 95% CI: 2.27-36.59, P=0.002; adjusted ORpeanut=4.09, 95% CI: 1.00-16.76, P=0.05). AD is the main skin-related risk factor for food sensitization in young infants. In exclusively breastfed children, this suggests that allergic sensitization to foods can be mediated by cutaneous antigen-presenting cells.

In vivo reprogramming of UV radiation–induced regulatory T-cell migration to inhibit the elicitation of contact hypersensitivity

Regulatory T (Treg) cells induced by UV radiation (UVR) inhibit only the induction and not the elicitation of contact hypersensitivity (CHS) because they migrate into the lymph nodes but not the skin. The tissue-homing receptor expression and migratory behavior of Treg cells can be altered by means of invitro coincubation with skin-derived antigen-presenting cells. On this invitro treatment, Treg cells migrate into the skin and thus inhibit the elicitation of CHS. We attempted to determine whether Treg cells can be induced by UVR in sensitized mice and manipulated entirely invivo in such a way that they suppress the elicitation of immune responses. Treg cells were induced by applying contact allergens onto UV-exposed skin in wild-type, langerin diphtheria toxin receptor knock-in, or depletion of Treg cell transgenic mice. UVR-induced Treg cells inhibit the elicitation of CHS in sensitized mice when stimulated by means of an antigen-specific boost through the skin. This requires cutaneous antigen-presenting cells that alter the migratory behavior of Treg cells and drive them out of the lymph nodes into the skin. The indication is that antigen-specific Treg cells can be induced in sensitized hosts and manipulated in such a way that they suppress the elicitation of specific immune reactions. Because this is achieved entirely invivo without invasive interventions, our findings might have important implications for strategies aiming to induce and use Treg cells in a therapeutic setting.

Nanoparticle-Based Targeting of Vaccine Compounds to Skin Antigen-Presenting Cells By Hair Follicles and their Transport in Mice

Particle-based drug delivery systems target active compounds to the hair follicle and may result in a better penetration and higher efficiency of compound uptake by skin resident cells. As previously proposed, such delivery systems could be important tools for vaccine delivery. In this study, we investigated the penetration of solid fluorescent 40 or 200 nm polystyrene nanoparticles (NPs) as well as virus particles in murine skin to further investigate the efficacy of transcutaneously (TC) applied particulate vaccine delivery route. We demonstrated that 40 and 200 nm NPs and modified vaccinia Ankara (MVA) expressing the green-fluorescent protein penetrated deeply into hair follicles and were internalized by perifollicular antigen-presenting cells (APCs). Fibered-based confocal microscopy analyses allowed visualizing in vivo particle penetration along the follicular duct, diffusion into the surrounding tissue, uptake by APCs and transport to the draining lymph nodes. The application of small particles, such as ovalbumin coding DNA or MVA, induced both humoral and cellular immune responses. Furthermore, TC applied MVA induced protection against vaccinia virus challenge. Our results strengthen the concept of TC targeting of cutaneous APCs by hair follicles and will contribute to the development of advanced vaccination protocols using NPs or viral vectors.

Mesenchymal Stem Cells and Fibroblasts Have Similar Immunoregulatory Properties In Vitro but Distinct Gene Expression Profiles: Implications for Cellular Therapy.

Bone marrow mesenchymal stem cells (MSC) have potent immunosuppressive properties and are being evaluated in human trials of graft versus host disease (GVHD). The nature of their suppressive capacity is not well understood but attributed to their stem cell function. Evidence that adult stromal cells such as fibroblasts (Fb) also modulate T cell functions has important implications for immunoregulation and cellular therapy. We have investigated the phenomenon of MSC-mediated immunosuppression by comparing MSC with Fb of different origins in in vitro assays of T cell suppression and modulation. We have then isolated RNA from paired samples of dermal Fb and MSC from 6 healthy volunteers for comparative gene expression studies. Adherent Fb were isolated from digested dermis, synovium and lung. MSC were obtained from BM aspirate. Fb from the dermis, lung and synovium possess potent immunomodulatory properties. Fb suppress allogeneic T cell activation by autologously derived cutaneous antigen presenting cells and other stimulators. Fb-mediated suppression through soluble factors is dependent on IFNγ from activated T cells. IFNγ induces indoleamine-2, 3, dioxygenase in Fb with accelerated tryptophan metabolism being partly responsible for suppressing T cell proliferation. T cell suppression is reversible and exposure to stromal cells during activation reprogrammes T cells, increasing secretion of interleukin-4 2.3 fold, interleukin-10 4.3 fold and interleukin-13 15 fold (means of 4 experiments) upon restimulation. Increased Th2 polarization by stromal cells is associated with amelioration of pathological changes in an in vitro human GVHD model. Our findings also show that Fb from different sources are indistinguishable from MSC with respect to morphology, phenotype, growth and differentiation capacity in vitro. Clonogenicity (ratio of CFU to CD73+CD45- cells) of Fb and MSC are similar (range 0.2 to 0.46 CFU/cell) proving that the immunosuppressive effects of Fb from adult tissues are not due to the expansion of rare ‘stem' cells. Using paired isolates of dermal Fb and MSC to control for inter-individual variation, we were able to define consistent differences in gene expression. Microarray assays were performed using a Human Genome Focus Affymetrix array and analysed with GeneSpring GX. 143 of 9600 probesets showed reproducible differences in transcript levels between dermal Fb and MSC. Probesets upregulated in MSC include genes encoding immunomodulatory mediators: vascular endothelial growth factor (7 fold), hydroxysteroid 17β dehydrogenase (10 fold) and jagged1 (5 fold); extracellular adhesion molecules: proteoglycan1 (264 fold), vascular cell adhesion molecule (175 fold), transglutaminase (67 fold) and procollagen (8 fold); and developmental regulators in the Hedgehog and Wnt signalling pathways. Our findings are further evidence that immunosuppression is a generic property of Fb isolated from several sources and not restricted to MSC. We have for the first time identified a differential expression profile of MSC compared with Fb. These differences may not confer unique in vivo immunosuppressive properties and the potential of Fb as an alternative source of cellular therapy remains untested.

Evaluation of Facial Allograft Transplantation in Humans in a Cadaver

Evaluation of Facial Allograft Transplantation in Humans in a Cadaver

Recent developments in canine atopic dermatitis: A review

Atopic dermatitis (AD) is a genetically predisposed inflammatory and pruritic allergic skin disease with characteristic clinical features. New results on the pathogenesis and therapeutic aspects are discussed in this review. IgE-mediated hypersensitivity may be involved in the largest subset of atopic patients, yet there is another subset for which such involvement cannot be documented. Alterations in epidermal barrier function, priming of cutaneous antigen-presenting cells with IgE, intrinsic keratinocyte defects, and development of autoimmunity are also factors that contribute to the primary disease. Polymorphisms in regions of the genome that are of key importance to the inflammatory response contribute to the patient's clinical picture. Secondary infections, especially with Staphylococcus and yeast organisms, strongly modify or augment the inflammatory response, which changes over time. After the treatment of secondary infections and skin inflammation the avoidance of causal allergens would prevent relapse. Another causative therapy is the variously effective allergen-specific immunotherapy. The newest treatments for canine AD (cyclosporin A and tacrolimus) are highly effective at suppressing the allergic response and comparable to treatment with glucocorticoids. Canine AD presents a substantial diagnostic and therapeutic challenge over a patient's lifetime, and no single treatment is universally effective.

40 nm, but not 750 or 1,500 nm, Nanoparticles Enter Epidermal CD1a+ Cells after Transcutaneous Application on Human Skin

Although conventional vaccines have generated major successes in the control of infectious diseases, several obstacles remain in their development against chronic diseases (HIV, tuberculosis), against which no current candidate vaccines yet ensure protection. The transcutaneous route of vaccine administration appears to be a promising approach of targeting vaccines toward antigen-presenting cells (APCs) and thus improving immune responses. We investigated the suitability of nanoparticles in this approach. We found a high density of Langerhans cells (LCs) around hair follicles that, when sorted, readily internalized all size particles. However, flow cytometry after transcutaneous application of 40, 750, or 1,500nm nanoparticles on human skin samples revealed that only 40nm particles entered epidermal LC. Fluorescence and laser scan microscopies, which were carried out to identify the penetration pathway of transcutaneously applied nanoparticles, revealed that only 40nm particles deeply penetrate into vellus hair openings and through the follicular epithelium. We conclude that 40nm nanoparticles, but not 750 or 1,500nm nanoparticles, may be efficiently used to transcutaneously deliver vaccine compounds via the hair follicle into cutaneous APCs.

Schistosoma mansoni: antigen-presenting cells emigrating from skin exposed to attenuated cercariae activate lymphoid cells and transfer protection in C57B1/6 mice.

C57B1/6 mice develop significant levels of protection to a challenge infection after percutaneous exposure to irradiated Schistosoma mansoni cercariae. Although some circumstantial evidence has suggested that antigen-presenting cells (APCs) within the skin play a role in priming anti-schistosomula effector mechanisms, no direct evidence has been presented. In this study, we describe efforts to directly test whether skin-resident APCs exposed to irradiated cercariae are capable of mediating responses consistent with previously proposed mechanisms associated with delayed-type hypersensitivity reactions. We demonstrate that a population of APCs emigrates from the skin after percutaneous vaccination and that these cells are able to induce proliferation of S. mansoni-specific lymphocytes. We describe our experiments conducted to confirm that proliferation is dependent on major histocompatibility complex (MHC) Class-II interactions and cell-to-cell contact between APCs and lymphocytes. Immunohistological staining of emigrating cells revealed a population of large MHC Class-II+ cells with a morphology characteristic of mature dendritic cells. On recovery and adoptive transfer into naive mice, these cells demonstrated the ability to mediate protection to a challenge infection at levels similar to those in percutaneously vaccinated controls. This confirms that cutaneous APCs can initiate anti-schistosomula effector mechanisms in C57B1/6 mice after percutaneous vaccination.

Canine Atopic Dermatitis: New Targets, New Therapies

Atopic dermatitis is a common allergic skin disease of complex etiopathogenesis in both humans and dogs. Immediate-type hypersensitivity to environmental allergens that arises as a result of environmental and genetic factors is a major part of the pathogenesis in most but not all patients. Alterations in epidermal barrier function, priming of cutaneous antigen-presenting cells with IgE, intrinsic keratinocyte defects, and even development of autoimmunity are also factors that contribute to the primary disease. Secondary factors, especially infections with Staphylococcus and yeast organisms, strongly influence the course of this skin disease. The relatively recent understanding of the complexities of atopic dermatitis has resulted in changes in diagnostic and therapeutic strategies for the disease. We now know that the best therapeutic approach is to use combinations of multiple modalities individualized for each patient over the course of his or her lifetime.

Cell surface and cytokine phenotypes of skin immunocompetent cells involved in ultraviolet-induced immunosuppression

Immunocellular migrations out of and into the skin and modulations of functional cell surface molecules on antigen-presenting cells (APCs), as well as their immunoregulatory cytokine production, are important factors involved in the mechanism of UV-induced immunosuppression and tolerance. Of particular interest here are the effects of low-dose UVB exposures that can suppress the ability of a contact sensitizer to induce contact hypersensitivity (CHS) through the site (local immunosuppression) without inducing suppression of CHS induced through skin distant to the UV exposure. Such UV-irradiated skin has many changes with respect to composition of immunocompetent cells and cytokine production. After UV exposure, Langerhans cells/dendritic cells migrate from the skin to draining lymph nodes (DLNs) as they do from contact sensitizer-applied normal skin. On the other hand, UV causes monocytic/macrophagic cells to infiltrate into the dermis and then into the epidermis; these can also be shown to be induced by contact sesitizers to migrate to DLNs. Alterations in cell surface and immunoregulatory cytokine phenotypes of the cutaneous APCs in both the skin and DLNs are critical for CHS suppression and tolerance induction. Here we describe the phenotypic changes of immunocompetent cells in UV-irradiated skin in regard to CHS suppression and tolerance and methodologies to approach this area.

Neural influences on induction of contact hypersensitivity.

Contact hypersensitivity (CH)-induction begins when cutaneous antigen-presenting cells (APC) capture hapten that has been applied epicutaneously, and the process prepares hapten for presentation to T-cells. APCs are functionally plastic, are influenced by the microenvironment in which they reside, and their functional properties have a profound effect on the phenotype of the hapten-specific T-cells that they activate. Ultraviolet B radiation (UVR) distorts the cutaneous microenvironment, thereby altering local APC function, and changing the immune outcome from sensitization to unresponsiveness. Although UVR induces keratinocytes to produce TNF alpha and IL-10 (cytokines that have been implicated in failed CH-induction and tolerance, respectively, after UVR), dermal mast cells turn out to be the source of these immunomodulatory cytokines. Mast cell degranulation is triggered by CGRP released from UVR-exposed cutaneous nerve termini. Even in normal skin, cutaneous nerves influence the immune response to haptens. Substance P released from cutaneous nerves acts as an adjuvant, raising the immunogenicity of epicutaneously applied haptens. Thus, the nerves and the neuropeptides that these processes release contribute to the cutaneous microenvironment. By altering APC function, cutaneous nerves can dictate the quality and the quantity of immune responses to antigens of the skin.

In Human Skin, UVB Initiates Early Induction of IL-10 Over IL-12 Preferentially in the Expanding Dermal Monocytic/Macrophagic Population

In contrast to Langerhans cells, which make interleukin (IL)-12, differentiated macrophages that infiltrate the epidermis 72 h after ultraviolet B (UV) irradiation potently produce IL-10 mRNA and secrete IL-10 protein. We asked whether differentiated UV macrophages in the epidermis acquired their activated, IL-10hi status as a result of entering the epidermis or as a result of encountering UV-induced changes in the dermal microenvironment. In this study, sequential section immunostaining directly showed dynamic and reciprocal changes of infiltrating CD11b+ macrophages and CD1a+ Langerhans cell loss in human epidermis and dermis after in vivo UV exposure in relation to the microanatomic localization of newly appearing dermal cells that stain for IL-10 mRNA by in situ hybridization. Using quantitative reverse transcriptase polymerase chain reaction on purified dermal cell subsets, the first significant rise in IL-10 mRNA occurred 6 h after UV in the dermal CD11b+ (CD1-, 3-, 24-, 56-) monocytic/macrophagic population. Significant induction of IL-10 mRNA 24 h post-UV was limited to the CD11b+ CD1- subset (p = 0.006). The fold increase of IL-10 mRNA relative to 0 h by the CD11b+ dermal monocytic/macrophagic population peaked at 24-48 h and tapered thereafter. Intense IL-10 production by macrophages in the epidermis appeared to follow dermal changes, with maximum production at 72 h, indicating migration/activation of this population from the dermis, and the remainder of dermal cells, depleted of monocyte/macrophages and Langerhans cell-like antigen-presenting cells, showed no increase in IL-10 at any time point post-UV. IL-10 protein-producing CD11b+ macrophages in the dermis were also documented by flow cytometry. IL-12 mRNA was differentially regulated from IL-10 after UV, in that IL-12 was consistently downregulated in the CD11b+ monocytic/macrophagic population (p < 0.0002). Taken together, monocytic/macrophagic cells with high IL-10 and low IL-12 expression initially appear in the dermis as early as 6 h, and then appear in the epidermis, implicating the dermis as the primary site of activation/signaling for IL-10 upregulation in cutaneous antigen-presenting cells.

The inhibition of antigen-presenting activity of dendritic cells resulting from UV irradiation of murine skin is restored by in vitro photorepair of cyclobutane pyrimidine dimers.

Exposing skin to UVB (280-320 nm) radiation suppresses contact hypersensitivity by a mechanism that involves an alteration in the activity of cutaneous antigen-presenting cells (APC). UV-induced DNA damage appears to be an important molecular trigger for this effect. The specific target cells in the skin that sustain DNA damage relevant to the immunosuppressive effect have yet to be identified. We tested the hypothesis that UV-induced DNA damage in the cutaneous APC was responsible for their impaired ability to present antigen after in vivo UV irradiation. Cutaneous APC were collected from the draining lymph nodes of UVB-irradiated, hapten-sensitized mice and incubated in vitro with liposomes containing a photolyase (Photosomes; Applied Genetics, Freeport, NY), which, upon absorption of photoreactivating light, splits UV-induced cyclobutane pyrimidine dimers. Photosome treatment followed by photoreactivating light reduced the number of dimer-containing APC, restored the in vivo antigen-presenting activity of the draining lymph node cells, and blocked the induction of suppressor T cells. Neither Photosomes nor photoreactivating light alone, nor photoreactivating light given before Photosomes, restored APC activity, and Photosome treatment did not reverse the impairment of APC function when isopsoralen plus UVA (320-400 nm) radiation was used instead of UVB. These controls indicate that the restoration of APC function matched the requirements of Photosome-mediated DNA repair for dimers and post-treatment photoreactivating light. These results provide compelling evidence that it is UV-induced DNA damage in cutaneous APC that leads to reduced immune function.

IgE-mediated allergen presentation via Fc epsilon RI on antigen-presenting cells.

In atopic individuals, cutaneous antigen-presenting cells (APC), i.e. Langerhans' cells (LC) and dermal dendritic cells (DDC), frequently display anti-IgE reactivity. While earlier observations suggested that this phenomenon results from the binding of (complexed) IgE to the low affinity IgE receptor (Fc epsilonRII/CD23), recent evidence exists that LC and DDC, as well as peripheral blood dendritic cells and monocytes from atopic individuals, can bind monomeric IgE via the high-affinity receptor for IgE (Fc epsilonRI). We have now found that Fc epsilonRI, both quantitatively and qualitatively, is the pivotal serum IgE-binding structure on APC of atopic individuals, that Fc epsilonRI on APC functions as allergen-focusing molecule and that allergens are more efficiently taken up, processed and presented to T cells following targeting to APC via Fc epsilonRI compared to allergen binding to APC in the conventional manner. In vivo, Fc epsilonRI-IgE-dependent allergen presentation may critically lower atopic individuals' threshold to mount allergen-specific T cell responses. This would result in the perpetuation of allergen-specific IgE production (type I reactions) and perhaps even in the occurrence of T-cell-mediated delayed-type hypersensitivity reactions in allergen-exposed tissues.

Expression of the B7/BB1 Activation Antigen and its Ligand CD28 in T-Cell-Mediated Skin Diseases

Interactions of CD28 (on T cells) with its recently identified ligand B7/BB1 (on antigen-presenting cells) have been shown to activate T cells via a major histocompatibility complex/Ag-independent "alternative" pathway, leading to an amplification of T-cell-mediated immune responses. The in vivo relevance of these molecules for cutaneous immunity is presently unknown. These findings prompted us to study the expression of B7/BB1 and CD28 in normal human skin and in selected T-cell-mediated inflammatory skin diseases. Biopsies were obtained from lesional skin of patients with allergic contact dermatitis, lichen planus, and, as control, from basal cell carcinoma and from healthy controls. Serial cryostat sections were stained with a panel of MoAbs directed against CD28, B7/BB1, CD3, CD1a, and KiM8 using immunohistochemistry (ABC technique). CD28 expression was observed in the majority of dermal and epidermal CD3+ T cells in contact dermatitis and lichen planus. In normal skin and basal cell carcinoma, CD28 was expressed only occasionally by perivascular T cells. In allergic contact dermatitis and lichen planus, B7/BB1-expression was found on dermal dendritic cells, on dermal macrophages, on Langerhans cells, focally on keratinocytes, and occasionally on dermal T cells. No B7/BB1 immunoreactivity was detected in normal skin and basal cell carcinoma. These findings indicate that T-cell-mediated skin diseases are accompanied by an influx of CD28+ T cells and an upregulation of B7/BB1 on cutaneous antigen-presenting cells, keratinocytes, and on some T cells. We speculate that "alternative" T cell-activation via the B7/CD28 pathway may contribute to the pathogenesis of these skin diseases.