Human dermal dendritic cells process and present soluble protein antigens

Developmental events and cellular changes occurred during esophageal development of quail embryos

The current study focused on the histogenesis of the esophagus in quail embryos. Formation of the gut tube occurred on the 4th day of incubation. Development of the muscular layers occurred in a sequential manner; the inner circular layer on the 7th day, the outer longitudinal layer on the 8th day and the muscularis mucosae on the 9th day. Glandular development began on the 13th day of incubation. The epithelium was pseudostratified columnar that consisted of mucous cells, dendritic cells, and keratinocyte precursors. Epithelial stratification occurred on the 15th day of incubation. We used Mallory trichrome, Weigert-Van Gieson, and Gomori silver stains to visualize fibrous components. Scanned samples showed formation of endoderm and mesoderm on the 5th day of incubation. A layer of myoblasts developed on the 8th day of incubation. Formation of mucosal folds, which contained glandular openings, occurred on the 14th to 17th days of incubation. On the 5th to 8th days of incubation, CD34 and vascular endothelial growth factor (VEGF) positive-mesodermal cells, and telocytes (TCs) were detected. On the 15th day of incubation, CD34 and VEGF positive-telocytes, and fibroblasts, were identified. The current study described the correlations between functional morphology and evolutionary biology.

Immuno-informatics analysis and expression of a novel multi-domain antigen as a vaccine candidate against glioblastoma

Glioblastoma multiform is the most common of primary malignant brain tumors in adults. Currently, surgical resection of the tumor mass, followed by adjuvant radiotherapy and chemotherapy are standard treatments for glioblastoma multiform but so far are not effective treatments. Thus, the development of a vaccine, as a safe and efficient strategy for prophylactic or therapeutic purposes against glioblastoma multiform is very necessary. The present study aimed to design the multi-domain vaccine for glioblastoma multiform. An in silico approach was used to select the most potent domains of proteins to induce the host's B- and T-cell immune response against glioblastoma multiform. IL-13Rα-2 (amino acid positions 27-144), TNC (amino acid positions 1900-2100), and PTPRZ-1(amino acid positions 731-884) were found to have potent inducible immune responses. So, we considered them for fusing with a linker A(EAAAK)₃A to construct the multi-domain recombinant vaccine. The immuno-informatics analysis of the designed recombinant vaccine construct was performed to evaluate its efficacy. Although the designed recombinant vaccine construct did not show allergen property, its antigenicity was estimated at 0.78. The Physico-chemical properties of the recombinant vaccine construct were characterized and revealed the potency of the vaccine candidate. Then its secondary and tertiary structures, mRNA structure, molecular docking, and immune simulation were predicted using bioinformatics tools. Next, the designed recombinant vaccine construct was synthesized, and cloned into the pET28a vector and expressed in E. coli BL21. Besides, the circular dichroism spectroscopy was utilized for the investigation of the secondary structure changes of the recombinant vaccine construct. The results of the verification assessment of the recombinant vaccine construct expression indicated that in silico analysis was relatively accurate, and relatively change occurred on the protein secondary structure. In our future plan, the vaccine candidate that was confirmed by in silico tools should be validated by further in vitro and in vivo experimental studies.

Mosquito Saliva Reshapes Alphavirus Infection and Immunopathogenesis

Alphaviruses are transmitted to humans via bites of infected mosquitoes. Although alphaviruses have caused a wide range of outbreaks and crippling disease, the availability of licensed vaccines or antiviral therapies remains limited. Mosquito vectors such as Aedes and Culex are the main culprits in the transmission of alphaviruses. This review explores how mosquito saliva may promote alphavirus infection. Identifying the roles of mosquito-derived factors in alphavirus pathogenesis will generate novel tools to circumvent and control mosquito-borne alphavirus infections in humans.

Paracoccidioides brasiliensis interacts with dermal dendritic cells and keratinocytes in human skin and oral mucosa lesions

Paracoccidioidomycosis (PCM) is a systemic disease caused by the fungus Paracoccidioides brasiliensis and Paracoccidioides lutzii. In PCM the skin and oral mucosa are often affected. Dendritic cells and keratinocytes of the integument play a role in innate and adaptive immune response against pathogens, due to their function as antigen presenting cells. Aiming to verify the interaction of P. brasiliensis with these cell populations, we studied 52 skin and 47 oral mucosa samples taken from patients with proven diagnosis of PCM. The biopsies were subjected to immunohistochemical and/or immunofluorescence staining with anti-factor XIIIa (marker of dermal dendrocytes), anti-CD207 (marker of mature Langerhans cells), anti-pan cytokeratins (AE1-AE3) and anti-P. brasiliensis antibodies. Analyses with confocal laser microscopy were also performed for better visualization of the interaction between keratinocytes and the fungi. In sum, 42% of oral mucosa samples displayed yeast forms in Factor XIIIa dermal dendrocytes cytoplasm. Langerhans cells in skin and oral mucosa samples did not show yeast cells in their cytoplasm. In sum, 54% of skin and 60% of mucosal samples displayed yeast cells in the cytoplasm of keratinocytes. The parasitism of keratinocytes may represent a possible mechanism of evasion of the fungus to local immune mechanisms. Factor XIIIa dendrocytes and keratinocytes may be acting as antigen-presenting cells to fulfill the probably impaired function of Langerhans cells in skin and oral mucosa of human PCM.

Functional Diversity of Human Dendritic Cells

At the crossroad between innate and adaptive immunity are the dendritic Cells (DCs), a "novel cell type." discovered in 1973 by Ralph Steinman. Although not entirely appreciated at first, it is clear that they play a critical role as specialized antigen-presenting cells and essential mediators in shaping immune reactivity and tolerance. Dendritic cells are now recognized as a heterogeneous group of cells in terms of cell-surface markers, anatomic location, and function adapted to protect against an array of pathogens and conditions. Importantly, these subsets are also unique to each species. While significant progress has been made on the identification and function of mouse DC subsets, much less is known about human cells. Here we review the fascinating biology of human skin DCs and describe tolerogenic principles that are critical in maintaining immune homeostasis and for controlling inflammation, as well as mechanisms that are fundamental to confer immunity. We surmise that these principles could be applied to DCs across organs, and could be harnessed for the treatment of various human autoimmune, inflammatory diseases, as well as cancer. Importantly, to leverage the relevance of basic research to the clinical setting, it is first necessary to determine the functional homology between mouse and human DCs. We discuss practical steps towards this aim.

Depletion of cutaneous macrophages and dendritic cells promotes growth of basal cell carcinoma in mice

Basal cell carcinoma (BCC) belongs to the group of non-melanoma skin tumors and is the most common tumor in the western world. BCC arises due to mutations in the tumor suppressor gene Patched1 (Ptch). Analysis of the conditional Ptch knockout mouse model for BCC reveals that macrophages and dendritic cells (DC) of the skin play an important role in BCC growth restraining processes. This is based on the observation that a clodronate-liposome mediated depletion of these cells in the tumor-bearing skin results in significant BCC enlargement. The depletion of these cells does not modulate Ki67 or K10 expression, but is accompanied by a decrease in collagen-producing cells in the tumor stroma. Together, the data suggest that cutaneous macrophages and DC in the tumor microenvironment exert an antitumor effect on BCC.

Decreased CD1a(+) , CD83(+) and factor XIIIa(+) dendritic cells in cervical lymph nodes and palatine tonsils of AIDS patients

AIMS

The purpose of this study was to quantify and compare the density of dendritic cells (DCs) in cervical lymph nodes (LNs) and palatine tonsils (PTs) of AIDS and non-AIDS patients.

METHODS AND RESULTS

Factor XIIIa, CD1a and CD83 antibodies were used to identify migratory DCs by immunohistochemistry in LNs and PTs of 32 AIDS patients and 21 HIV-negative control patients. Quantification was performed by the positive pixel count analytical method. AIDS patients presented a lower density of factor XIIIa(+) cells (P < 0.001), CD1a(+) cells (P < 0.05) and CD83(+) cells (P < 0.001) in cervical LNs and PTs compared to the non-AIDS control group.

CONCLUSION

Overall depletion of DCs in lymphoid tissues of AIDS patients may be predictive of the immune system's loss of disease control.

Langerhans cells favor skin flora tolerance through limited presentation of bacterial antigens and induction of regulatory T cells

The mechanisms preventing detrimental T-cell responses against commensal skin bacteria remain elusive. Using monocyte-derived and skin-derived dendritic cells (DCs), we demonstrate that epidermal Langerhans cells (LCs), the DCs in the most superficial layer of the skin, have a poor capacity to internalize bacteria because of low expression of FcγRIIa. Furthermore, LCs show deficiency in processing and major histocompatibility complex II (MHC-II)-restricted presentation of bacterial antigens, as a result of a decreased expression of molecules involved in these functionalities. The reduced capacity to take up, process, and present bacterial antigens cannot be restored by LC activation by ectopically expressed Toll-like receptors or by cytokines. Consequently, bacteria-primed LCs poorly restimulate antibacterial memory CD4(+) T cells and inefficiently induce bacteria-specific effector CD4(+) T cells from naive T cells; however, they initiate the development of regulatory Foxp3(+)CD4(+) T cells, which are able to suppress the proliferation of autologous bystander T cells specific for the same bacteria. In contrast, dermal DCs that reside in the deeper dermal layer of the skin efficiently present bacterial antigens and provoke robust antibacterial naive and memory CD4(+) T-cell responses. In conclusion, LCs form a unique DC subset that is adapted at multiple levels for the maintenance of tolerance to bacterial skin flora.

Lymphocyte-polarized dendritic cells are highly effective in inducing tumor-specific CTLs

High activity of dendritic cells (DCs) in inducing cytotoxic T cells (CTLs) led to their application as therapeutic cancer vaccines. The ability of DCs to produce IL-12p70 is one of the key requirements for effective CTL induction and a predictive marker of their therapeutic efficacy in vivo. We have previously reported that defined cocktails of cytokines, involving TNFα and IFNγ, induce mature type-1 polarized DCs (DC1s) which produce strongly elevated levels of IL-12 and CXCL10/IP10 upon CD40 ligation compared to "standard" PGE₂-matured DCs (sDCs; matured with IL-1β, IL-6, TNFα, and PGE₂) and show higher CTL-inducing activity. Guided by our observations that DC1s can be induced by TNFα- and IFNγ-producing CD8⁺ T cells, we have tested the feasibility of using lymphocytes to generate DC1s in a clinically-compatible process, to limit the need for clinical-grade recombinant cytokines and the associated costs. CD3/CD28 activation of bulk lymphocytes expanded them and primed them for effective production of IFNγ and TNFα following restimulation. Restimulated lymphocytes, or their culture supernatants, enhanced the maturation status of immature (i)DCs, elevating their expression of CD80, CD83 and CCR7, and the ability to produce IL-12p70 and CXCL10 upon subsequent CD40 ligation. The "lymphocyte-matured" DC1s showed elevated migration in response to the lymph-node-directing chemokine, CCL21, when compared to iDCs. When loaded with antigenic peptides, supernatant-matured DCs induced much high levels of CTLs recognizing tumor-associated antigenic epitope, than PGE₂-matured DCs from the same donors. These results demonstrate the feasibility of generation of polarized DC1s using autologous lymphocytes.

CD70-CD27 interaction augments CD8+ T-cell activation by human epidermal Langerhans cells

Human cutaneous dendritic cells (DCs) from epidermal and dermal compartments exhibit functional differences in their induction of CD4+ T-cell and humoral immune responses; however, differences in the regulation of memory CD8+ T-cell responses by human skin DCs remain poorly characterized. We tested the capacity of human Langerhans cells (LCs) and dermal dendritic cells (DDCs) to induce antigen-specific cytokine production and proliferation of memory CD8+ cells. Although tumor necrosis factor-α-matured human DCs from both epidermal and dermal compartments showed efficient potential to activate CD8+ cells, LCs were constitutively more efficient than DDCs in cross-presenting CD8+ epitopes, as well as direct presentation of viral antigen to Epstein-Barr virus-specific CD8+ T cells. LCs showed greater expression of CD70, and blockade of CD70-CD27 signaling demonstrated that superiority of CD8+ activation by epidermal LC is CD70 dependent. This CD70-related activation of CD8+ cells by LCs denotes a central role of LCs in CD8+ immunity in skin, and suggests that regulation of LC CD70 expression is important in enhancing immunity against cutaneous epithelial pathogens and cancer.

Dermal dendritic cells in psoriasis, nummular dermatitis, and normal-appearing skin

BACKGROUND

The reason psoriasis (PSO) favors extensor skin is unknown. We hypothesized that PSO may involve extensor skin preferentially because of differences in the number or type of dermal dendritic cells (dDCs) between flexural and extensor skin.

OBJECTIVE

We sought to compare dDC type and distribution in normal-appearing flexural and extensor skin, PSO, and nummular dermatitis (ND).

METHODS

Using immunohistochemical markers, the number, distribution, and type of Langerhans cells, myeloid dendritic cells (DCs), and plasmacytoid DCs was compared in normal-appearing skin, PSO, and ND.

RESULTS

Significant differences in dDC density were not identified between flexural and extensor skin, although extensor skin contained fewer CD11a(+) and CD11c(+) cells. Compared with normal-appearing skin, cells expressing CD11a, CD11c, CD123, CD303, and CD207 were increased in PSO. ND lesions showed similar increases. No significant difference between PSO and ND was evident with the exception of decreased S100A6(+) cells in PSO.

LIMITATIONS

We did not study seasonal variation in DC density or assess nonlesional skin from patients with PSO.

CONCLUSIONS

The data did not support the hypothesis that PSO favors extensor skin because of differences in DC localization. However, dDCs were significantly increased in PSO by comparison with normal-appearing skin, supporting existing evidence that they are involved in the overall pathogenesis of PSO.

Mucosal immune responses induced by transcutaneous vaccines

The skin has been investigated as a site for vaccine delivery only since the late 1990s. However, much has been discovered about the cell populations that reside in the skin, their active role in immune responses, and the fate of trans- cutaneously applied antigens. Transcutaneous immunization (TCI) is a safe, effective means of inducing immune responses against a number of pathogens. One of the most notable benefits of TCI is the induction of immune responses in both systemic and mucosal compartments. This chapter focuses on the transport of antigen into and beyond intact skin, the cutaneous sentinel cell populations that play a role in TCI, and the types of mucosal immune responses that have been generated. A number of in vivo studies in murine models have provided information about the broad responses induced by TCI. Cellular and humoral responses and protection against challenge have been noted in the gastrointestinal, reproductive, and respiratory tracts. Clinical trials have demonstrated the benefits of this vaccine delivery route in humans. As with other routes of immunization, the type of vaccine formulation and choice of adjuvant may be critical for achieving appropriate responses and can be tailored to activate specific immune-responsive cells in the skin to increase the efficacy of TCI against mucosal pathogens.

Dendritic cells in the pathogenesis of sarcoidosis

Sarcoidosis is a noncaseating granulomatous disease, likely of autoimmune etiology, that causes inflammation and tissue damage in multiple organs, most commonly the lung, but also skin, and lymph nodes. Reduced dendritic cell (DC) function in sarcoidosis peripheral blood compared with peripheral blood from control subjects suggests that blunted end organ cellular immunity may contribute to sarcoidosis pathogenesis. Successful treatment of sarcoidosis with tumor necrosis factor (TNF) inhibitors, which modulate DC maturation and migration, has also been reported. Together, these observations suggest that DCs may be important mediators of sarcoidosis immunology. This review focuses on the phenotype and function of DCs in the lung, skin, blood, and lymph node of patients with sarcoidosis. We conclude that DCs in end organs are phenotypically and functionally immature (anergic), while DCs in the lymph node are mature and polarize pathogenic Th1 T cells. The success of TNF inhibitors is thus likely secondary to inhibition of DC-mediated Th1 polarization in the lymph node.

Functional specializations of human epidermal Langerhans cells and CD14+ dermal dendritic cells

Little is known about the functional differences between the human skin myeloid dendritic cell (DC) subsets, epidermal CD207(+) Langerhans cells (LCs) and dermal CD14(+) DCs. We showed that CD14(+) DCs primed CD4(+) T cells into cells that induce naive B cells to switch isotype and become plasma cells. In contrast, LCs preferentially induced the differentiation of CD4(+) T cells secreting T helper 2 (Th2) cell cytokines and were efficient at priming and crosspriming naive CD8(+) T cells. A third DC population, CD14(-)CD207(-)CD1a(+) DC, which resides in the dermis, could activate CD8(+) T cells better than CD14(+) DCs but less efficiently than LCs. Thus, the human skin displays three DC subsets, two of which, i.e., CD14(+) DCs and LCs, display functional specializations, the preferential activation of humoral and cellular immunity, respectively.

Resident and "inflammatory" dendritic cells in human skin

Dendritic cells (DCs) are a heterogeneous group of antigen-presenting leukocytes that are important in activation of both the innate and adaptive arms of the immune system. Although there are several different DC populations in the body, DCs are globally defined by their capacity for potent antigen presentation and naive T-cell activation. In noninflamed human skin during steady state, there are three main cutaneous DC populations: epidermal Langerhans cells, dermal myeloid DCs, and dermal plasmacytoid DCs. In psoriasis, a model for cutaneous inflammation, there is an additional population of myeloid dermal DCs--"inflammatory DCs"--which appears to be critical for disease pathogenesis.

"Dermal dendritic cells" comprise two distinct populations: CD1+ dendritic cells and CD209+ macrophages

A key cell type of the resident skin immune system is the dendritic cell (DC), which in normal skin is located in two distinct microanatomical compartments: Langerhans cells (LCs), mainly in the epidermis, and dermal DCs (DDCs), in the dermis. Here, the lineage of DDCs was investigated using monoclonal antibodies and immunohistology. We provide evidence that "DDC" comprise at least two major phenotypic populations of dendritic-appearing cells, immature DC expressing CD1, CD11c and CD208; and macrophages expressing CD209, CD206, CD163, and CD68. These data suggest that dermal dendritic-appearing macrophages comprise a novel part of the innate immune response in the resident skin immune system.

Autologous glioma cell vaccine admixed with interleukin-4 gene transfected fibroblasts in the treatment of patients with malignant gliomas

Background

The prognosis for malignant gliomas remains dismal. We addressed the safety, feasibility and preliminary clinical activity of the vaccinations using autologous glioma cells and interleukin (IL)-4 gene transfected fibroblasts.

Methods

In University of Pittsburgh Cancer Institute (UPCI) protocol 95-033, adult participants with recurrent glioblastoma multiforme (GBM) or anaplastic astrocytoma (AA) received gross total resection (GTR) of the recurrent tumors, followed by two vaccinations with autologous fibroblasts retrovirally transfected with TFG-IL4-Neo-TK vector admixed with irradiated autologous glioma cells. In UPCI 99-111, adult participants with newly diagnosed GBM or AA, following GTR and radiation therapy, received two intradermal vaccinations with the TFG-IL4-Neo-TK-transfected fibroblasts admixed with type-1 dendritic cells (DC) loaded with autologous tumor lysate. The participants were evaluated for occurrence of adverse events, immune response, and clinical response by radiological imaging.

Results and Discussion

In UPCI 95-033, only 2 of 6 participants received the vaccinations. Four other participants were withdrawn from the trial because of tumor progression prior to production of the cellular vaccine. However, both participants who received two vaccinations demonstrated encouraging immunological and clinical responses. Biopsies from the local vaccine sites from one participant displayed IL-4 dose-dependent infiltration of CD4⁺ as well as CD8⁺ T cells. Interferon (IFN)-γ Enzyme-Linked Immuno-SPOT (ELISPOT) assay in another human leukocyte antigen (HLA)-A2⁺ participant demonstrated systemic T-cell responses against an HLA-A2-restricted glioma-associated antigen (GAA) epitope EphA2_883–891. Moreover, both participants demonstrated clinical and radiological improvement with no evidence of allergic encephalitis, although both participants eventually succumbed with the tumor recurrence. In 99-111, 5 of 6 enrolled participants received scheduled vaccinations with no incidence of major adverse events. Monocyte-derived DCs produced high levels of IL-12 p70. Treatment was well tolerated; however, we were unable to observe detectable IFN-γ post-vaccine responses or prolonged progression-free survival in these participants.

Conclusion

Feasibility challenges inherent in the generation of a patient-specific gene transfection-based vaccine strongly suggests the need for more practical formulations that would allow for the timely administration of vaccines. Nevertheless, successful generation of type-1 DCs and preliminary safety in the current study provide a strong rationale for further efforts to develop novel glioma vaccines.

An ex vivo readout for evaluation of dendritic cell-induced autologous cytotoxic T lymphocyte responses against esophageal cancer

Esophageal cancer is a highly malignant disease that despite surgery and adjuvant therapies has an extremely poor outcome. Dendritic cell (DC) immunotherapy as a novel promising strategy could be an alternative for treating this malignancy. Effective DC-mediated immune responses can be achieved by raising cytotoxic T lymphocyte (CTL) response against multiple antigens through loading DCs with total tumor RNA. However, the efficacy of this strategy first needs to be evaluated in a pre-clinical setting. The aim of the study was to set up an ex vivo autologous human readout assay for assessing the effects of DC-mediated cytotoxic responses, using total tumor RNA as an antigen load. Biopsy specimens of seven esophageal cancer patients were used to establish primary cultures of normal and cancer cells and to obtain autologous RNA for loading DCs. Mature DCs loaded with either normal or tumor RNA were obtained and subsequently used to raise various lymphocytes populations. Apoptosis levels of the autologous cultures were measured before and after incubating the cultures with the different lymphocytes populations. The mean apoptosis levels in the tumor cell cultures, induced by lymphocytes instructed by DCs loaded with tumor RNA, significantly increased with 15.6% +/-2.9 SEM (range 3.4-24.5%, t-test, P < 0.05). Incubation of the normal cultures with the lymphocytes populations showed a mean non-significant increase in apoptosis of 0.4% +/-3.4 SEM (range -13.9 to 9.8%, t-test, P = 0.7). Here, we introduce a practical, patient-specific autologous readout assay for pre-clinical testing of DC-mediated cytotoxic responses. Additionally, we demonstrated that the use of autologous tumor RNA as a strategy for raising cytotoxic responses against multiple tumor antigens could be effective for treating esophageal cancer.

Deepening our understanding of immune sentinels in the skin

Advances in our understanding of the skin immune system have a major impact on studies of skin autoimmunity, graft-versus-host disease, inflammation, and cancer as well as on the development of novel vaccines and immunotherapy approaches. In this issue of the JCI, Zaba et al. carefully dissected the complex network of DCs and macrophages residing in normal human skin and defined novel phenotypic markers for these immunocytes (see the related article beginning on page 2517). These studies provide the basis for better insight into the role of important immune sentinels contributing to the maintenance of skin tissue homeostasis and lay the foundation for future studies of the skin immune system.

Professional antigen-presenting cells of the skin

The skin functions as an important pro-inflammatory and immune organ. Accordingly, the epidermis and dermis are highly populated by dendritic cells (DC), which are potent antigen-presenting cells (APC) with important immunostimulatory and migratory activities. Whereas the biological characteristics and immunological functions of epidermal DC known as Langernahs cells (LC) have been the focus of intense research in the past, less is known regarding their dermal counterparts named dermal dendritic cells (DDC). Although it has been widely accepted that LC are the more relevant skin-resident APC, recent experimental evidence challenges this concept and proposes a different role for these important cell populations. In this article we compile recent scientific advances regarding the function of different skin-resident DC and we try to reconcile the new observations with the previously established paradigm.

Cutaneous dendritic cells

Cutaneous dendritic cells (DC) include epidermal Langerhans cells (LC), interstitial/dermal dendritic cells (DDC), as well as plasmacytoid DC (pDC) that occur under pathological conditions. These immune cells have a spectrum of different functions with implications that extend far beyond the skin. They have the potential to internalize particulate agents and macromolecules, and display migratory properties that endow them with the unique capacity to journey between skin and draining lymph nodes where they encounter antigen-specific T lymphocytes. Herein, we will review the features of human and mouse cutaneous DC, emphasizing characteristics representative of their life-cycle stages that occur within the skin.

Loss of TLR2, TLR4, and TLR5 on Langerhans cells abolishes bacterial recognition

It is unknown whether closely related epidermal dendritic cells, Langerhans cells (LCs), and dermal dendritic cells (DDCs) have unique functions. In this study, we show that human DDCs have a broad TLR expression profile, whereas human LCs have a selective impaired expression of cell surface TLR2, TLR4, and TLR5, all involved in bacterial recognition. This distinct TLR expression profile is acquired during the TGF-beta1-driven development of LCs in vitro. Consequently, and in contrast to DDCs, LCs weakly respond to bacterial TLR2, TLR4, and TLR5 ligands in terms of cytokine production and maturation, as well as to whole Gram-positive and Gram-negative bacteria, whereas their responsiveness to viral TLR ligands and viruses is fully active and comparable to DDCs. Unresponsiveness of LCs to bacteria may be a mechanism that contributes to tolerance to bacterial commensals that colonize the skin.

UVA Radiation Impairs Phenotypic and Functional Maturation of Human Dermal Dendritic Cells

There is now strong evidence that the ultraviolet A (UVA) part of the solar spectrum contributes to the development of skin cancers. Its effect on the skin immune system, however, has not been fully investigated. Here, we analyzed the effects of UVA radiation on dermal dendritic cells (DDC), which, in addition, provided further characterization of these cells. Dermal sheets were obtained from normal human skin and irradiated, or not, with UVA at 2 or 12 J per cm2. After a 2 d incubation, the phenotype of emigrant cells was analyzed by double immunostaining and flow cytometry. Results showed that migratory DDC were best characterized by CD1c expression and that only few cells co-expressed the Langerhans cell marker Langerin. Whereas the DC extracted from the dermis displayed an immature phenotype, emigrant DDC showed increased expression of HLA-DR and acquired co-stimulation and maturation markers. We showed here that UVA significantly decreased the number of viable emigrant DDC, a process related to increased apoptosis. Furthermore, UVA irradiation impaired the phenotypic and functional maturation of migrating DDC into potent antigen-presenting cells, in a concentration-dependent manner. The results provide further evidence that UVA are immunosuppressive and suggest an additional mechanism by which solar radiation impairs immune response.

IL-4-transfected tumor cell vaccines activate tumor-infiltrating dendritic cells and promote type-1 immunity

We previously demonstrated that IL-4 gene-transfected glioma cell vaccines induce effective therapeutic immunity in preclinical glioma models, and have initiated phase I trials of these vaccines in patients with malignant gliomas. To gain additional mechanistic insight into the efficacy of this approach, we have treated mice bearing the MCA205 (H-2(b)) or CMS-4 (H-2(d)) sarcomas. IL-12/23 p40(-/-) and IFN-gamma(-/-) mice, which were able to reject the initial inoculation of IL-4 expressing tumors, failed to mount a sustained systemic response against parental (nontransfected) tumor cells. Paracrine production of IL-4 in vaccine sites promoted the accumulation and maturation of IL-12p70-secreting tumor-infiltrating dendritic cells (TIDCs). Adoptive transfer of TIDCs isolated from vaccinated wild-type, but not IL-12/23 p40(-/-), mice were capable of promoting tumor-specific CTL responses in syngeneic recipient animals. Interestingly, both STAT4(-/-) and STAT6(-/-) mice failed to reject IL-4-transfected tumors in concert with the reduced capacity of TIDCs to produce IL-12p70 and to promote specific antitumor CTL reactivity. These results suggest that vaccines consisting of tumor cells engineered to produce the type 2 cytokine, IL-4, critically depend on type 1 immunity for their observed therapeutic efficacy.

Tapping into the influence of keratinocyte allografts and biocenosis on healing of chronic leg ulcers: split-ulcer controlled pilot study

BACKGROUND

Cultured keratinocytes may represent an alternative therapy aiming at boosting leg ulcer healing. There is no evidence-based study comparing objectively the healing rate of split-ulcer portions covered or not covered by cultured keratinocytes.

OBJECTIVE

To assess the effect of cultured keratinocytes on the healing rate of leg ulcers.

METHOD

Five applications of fresh (cela, XCELLentis, Ghent, Belgium) or frozen (CryoCeal, XCELLentis) cultured allogeneic keratinocytes were performed at weekly intervals to treat large leg ulcers (mean diameter > 5 cm) in four patients. A split-ulcer study was designed to secure a control area covered only by petrolatum gauze. Clinical, planimetric, bacteriologic, and immunohistologic assessments of the keratinocyte-treated and control parts of the ulcers were performed.

RESULTS

Compared with controls, planimetry revealed a beneficial effect afforded by cryopreserved cultured keratinocytes on the ulcer healing rate of two of four ulcers (+12 and 81%). The healing effect was obtained on the ulcers associated with the lowest bacterial load. Cultured keratinocytes did not qualitatively and quantitatively modify the ulcer biocenosis. They did not affect the number of any type of inflammatory cells present in the granulation tissue (type I dermal dendrocytes, macrophages, T lymphocytes, granulocytes). No specific side effect of cultured keratinocytes was evidenced.

CONCLUSION

In this small case series, it appears that cultured allogeneic keratinocytes may be helpful in the healing process of venous leg ulcers. However, a clean wound with reduced bacterial load seems to be the prerequisite condition for obtaining a beneficial effect.

Cytokine gene therapy for malignant glioma

Despite advances in surgical and adjuvant therapy, the prognosis for malignant gliomas remains dismal. Malignant gliomas, like other malignancies, are able to overcome host immune defences through a variety of mechanisms that have become increasingly well-characterised over the past decade. However, this 'immunologically privileged' status of the brain is not absolute. Systemic immunisation with brain-specific antigens can induce immune responses that are manifested in the CNS, such as experimental allergic encephalomyelitis. The efficacy of peripheral immunisation against brain tumours has also been demonstrated in preclinical models. Based on these observations, clinical trials of peripheral immunisations with brain tumour-derived antigens have been initiated. A limitation of this approach is that the immunological environment within brain tumours is suboptimal for functions of antitumour immune effector cells. As a means to overcome this issue, delivery of cytokine genes to the tumour site may reverse the inhibitory immunological environment of the brain tumours and enhance the efficacy of peripheral vaccine-induced immune effector cells. The brain tumour environment may also be rendered more immunologically favourable by the delivery of additional antigen-presenting cells that can provide infiltrating effector cells with secondary activation signals. Indeed, the authors' recent data indicate that the injection of intracranial tumours with dendritic cells secreting interferon-alpha enhances the efficacy of peripheral vaccinations with tumour-specific antigens by cross-priming tumour antigen-specific T cells in the cervical lymph nodes. This review highlights the recent literature on cytokine gene therapy for brain tumours, and proposes the effective use of cytokine gene delivery both at the site of vaccines (i.e., the site of antigen presentation) and within the target brain tumours (i.e., the site where the effector cells exert their antitumour immunity). Successful immunogene therapy for brain tumours requires detailed understanding of cytokine functions and the use of them at the appropriate stages/sites of the immunological milieu.

Antennapedia transduction sequence promotes anti tumour immunity to epicutaneously administered CTL epitopes

The identification of tumor antigens has spurred the development of efficient adjuvants and novel delivery systems for cancer immunotherapy. To this end, a peptide-based vaccine consisting of the Antennapedia transduction sequence (ANTP) attached to an antigenic peptide was designed to enhance per-cutaneous delivery into cells of the epidermis and dermis. Here we show that the topical application of OVA(257-264) linked to ANTP in mice onto tape-stripped skin resulted in enhanced delivery of the antigen through the skin whereas OVA(257-264) alone remained distributed uniformly on the skin surface. This delivery correlated with an increase in the CTL response against OVA. When mixed with CpG oligodinucleotides (ODN), the recombinant antigen protected mice from tumor challenge. These data provide the first indication that in vivo use of a translocation sequence can enhance delivery of therapeutic peptides and increase anti-tumor immunity through a simple and safe mechanism involving enhanced penetration of the skin barrier.

Factor-XIIIa-positive dendrocytes in drug-induced toxic epidermal necrolysis (Lyell's syndrome): paradoxical activation in skin and rarefaction in lymph nodes

BACKGROUND

Drug-induced toxic epidermal necrolysis (TEN) is a rare life-threatening disease characterized by the extensive destruction of the epidermis contrasting with the discreteness of lymphoid cell infiltration. The precise pathomechanism of the disease remains unclear.

METHODS

Skin specimens and peripheral and thoracic lymph nodes (LNs) were collected from 2 TEN patients. They were examined by conventional histology and immunohistochemistry using antibodies directed to factor XIIIa (dermal dendrocytes), CD1a (Langerhans cells), CD15 (granulocytes), CD20 (B lymphocytes), CD45RO (activated T lymphocytes), CD68 (macrophages) and the proliferation marker Ki-67. LNs from patients with mycosis fungoides, from subjects dead from acute cardiac failure or traumatic injuries, as well as metastasis-free sentinel LNs of cutaneous melanoma served as positive and negative controls.

RESULTS

TEN LNs showed absence of germinal centers but a moderate hyperplasia of the paracortical T cell zone. Immunohistochemistry did not reveal any distinctive aspect in LN cellular densities between TEN and other control conditions except for the factor-XIIIa+ dendritic cells which were dramatically reduced in numbers in TEN LNs. This rarefaction in LNs contrasted with the great number of these cells in the skin of the same patients.

CONCLUSION

The structure of TEN LNs rules out the involvement of an antibody-mediated response. As dendritic factor-XIIIa+ cells are involved in most cutaneous T-cell-mediated responses, their depletion in TEN LNs could explain the sparse lymphoid cell infiltrate in lesional TEN skin.

Recruitment of immature plasmacytoid dendritic cells (plasmacytoid monocytes) and myeloid dendritic cells in primary cutaneous melanomas

The present study has analysed the distribution and phenotype of dendritic cells (DCs) in primary cutaneous melanomas and sentinel lymph nodes by immunohistochemistry. In primary melanomas, an increase of DCs was found in the epidermis and the peritumoural area. Intraepidermal DCs were mostly CD1a(+)/Langerin(+) Langerhans cells. Peritumoural DCs included a large population of DC-SIGN(+)/mannose-receptor(+)/CD1a(-) DCs, a small subset of CD1a(+) DCs, and, remarkably, plasmacytoid monocytes/plasmacytoid DCs (PM/PDCs). The PM/PDCs, most likely recruited by SDF-1 secreted by melanoma cells, produced type I interferon (IFN-I), but the expression of the IFN-alpha inducible protein MxA was extremely variable and very limited in the majority of cases. All DC subsets were predominantly immature. The peritumoural area also contained a minor subset of mature CD1a(+) DCs. However, the small amount of local interleukin (IL)-12 p40 mRNA and the naïve phenotype of 20-50% of peritumoural T-lymphocytes are consistent with poor T-cell stimulation or erroneous recruitment. In sentinel lymph nodes, notable expansion of mature CD1a(+)/Langerin(+) DCs was observed. The paucity of intratumoural DCs and the predominant immature phenotype of peritumoural dermal DCs indicate defective maturation of primary cutaneous melanoma-associated DCs, resulting in lack of T-cell priming. These results may explain why melanoma cells grow despite the presence of infiltrating immune cells.

Os histiócitos e as histiocitoses não Langerhans em dermatologia

Atualmente, os histiócitos não são mais compreendidos como células únicas, mas como um grupo heterogêneo de células com o mesmo aspecto histológico, mas com características e funções distintas entre si. Várias doenças proliferativas de histiócitos, conhecidas como histiocitoses, são descritas. Tais doenças são raras, e seu estudo costuma ser difícil. Este artigo objetiva simplificar o entendimento desse grupo de doenças, adequando-o a esse novo paradigma da heterogeneidade dos histiócitos.

Correlation of factor XIIIa+ dermal dendrocytes with paracoccidioidomycosis skin lesions

We demonstrated and quantified by immunohistochemistry the factor XIIIa+ dermal dendrocytes (FXIIIa+ DD) in paracoccidioidomycosis skin lesions. Sixty-one biopsies were classified according to the tissue response in well-organized granulomas (group 1), poorly organized granulomas (group 2) and samples showing both kinds of granuloma (group 3). Ten biopsies from normal skin were used as controls. In order to verify the internalization of Paracoccidioides brasiliensis antigens by FXIIIa+ DD, we performed a double immunostaining technique. FXIIIa+ DD were hypertrophied with prominent dendrites and their number in the test groups was higher than in the control group, especially in the dermal papillae. P. brasiliensis yeasts were seen within the cytoplasm of FXIIIa+ DD in 40% of the immunostained biopsies. We could correlate these findings with the probable role of FXIIIa+ DD as antigen-presenting cells in the pathogenesis of skin lesions in paracoccidioidomycosis.

IL-1beta is essential for langerhans cell activation and antigen delivery to the lymph nodes during contact sensitization: evidence for a dermal source of IL-1beta

IL-1beta(-/-) mice manifest an impaired contact hypersensitivity response to the hapten trinitrochlorobenzene, with the principle defect expressed during the sensitization phase of this response. Following application of hapten to the skin, epidermal Langerhans cells of IL-1beta(-/-) mice failed to demonstrate the classical phenotype of activation. In addition, the delivery of epicutaneously applied fluorescein isothiocyanate to draining lymph nodes was decreased in IL-1beta(-/-) mice. Hapten delivery to draining lymph nodes could be restored by intradermal injection of recombinant IL-1beta. Reconstitution of lethally irradiated IL-1beta(-/-) mice by transfer of wild-type bone marrow restored hapten-stimulated IL-1beta mRNA expression, demonstrating that IL-1beta production was dependent on bone marrow-derived cells. In wild-type skin, IL-1beta expression was upregulated in a time- and dose-dependent fashion following hapten application. Interestingly, prominent IL-1beta expressing cells were found in the dermis, suggesting that dermal cells may contribute significantly to the contact hypersensitivity response.

Phenotypic and functional outcome of human monocytes or monocyte-derived dendritic cells in a dermal equivalent

The dermis harbors a true dendritic cell population that could elicit primary allogeneic T cell responses in vitro and contact hypersensitivity reactions in vivo. The origin of dermal dendritic cells remains poorly understood, however. In this study, we analyzed the fate of monocytes or monocyte-derived dendritic cells in a dermal equivalent. Freshly isolated monocytes or monocytes cultured for 6 d with either GM-CSF/IL-4 or GM-CSF/IL-4/TGF-beta 1 (TGF-DC) were seeded in a collagen solution with normal human fibroblasts. The lattices were cultured for 7--14 d in the presence, or absence, of the exogenous cytokines, before phenotypic and functional studies were performed. Supply of exogenous cytokines allows the appearance of typical CD1a(+)/CD14(-)/CD68(low) dendritic cells with significant allostimulatory property, regardless of the cell type incorporated into the lattices. In cytokine-free conditions, monocytes and GM-CSF/IL-4-derived dendritic cells give rise to a CD1a(-)/CD14(+)/CD68(high) monocyte/macrophage population with no allostimulatory property. When incorporated into the lattices in the absence of exogenous cytokines the TGF-DC express few CD68 and FXIIIa. Interestingly, these cells do not all convert into the CD14(+)/CD1a(-) population. Indeed, a small HLA-DR(+)/CD1a(+)/CD14(-) subset was consistently found, which represents about one-third of the HLA-DR(+) cells. Moreover, TGF-DC recovered from the lattices after culture without cytokines do display a significant allostimulatory function. Thus, in the absence of exogenous cytokines, only Langerhans-cell-like dendritic cells can retain the typical dendritic cell features when inserted in a dermal environment. Taken together, these results may provide evidence supporting an epidermal origin of dermal dendritic cells.

Expression of multilectin receptors and comparative FITC-dextran uptake by human dendritic cells

Dendritic cells (DC) are potent antigen-presenting cells and understanding their mechanisms of antigen uptake is important for loading DC with antigen for immunotherapy. The multilectin receptors, DEC-205 and macrophage mannose receptor (MMR), are potential antigen-uptake receptors; therefore, we examined their expression and FITC-dextran uptake by various human DC preparations. The RT-PCR analysis detected low levels of DEC-205 mRNA in immature blood DC, Langerhans cells (LC) and immature monocyte-derived DC (Mo-DC). Its mRNA expression increased markedly upon activation, indicating that DEC-205 is an activation-associated molecule. In Mo-DC, the expression of cell-surface DEC-205 increased markedly during maturation. In blood DC, however, the cell-surface expression of DEC-205 did not change during activation, suggesting the presence of a large intracellular pool of DEC-205 or post-transcriptional regulation. Immature Mo-DC expressed abundant MMR, but its expression diminished upon maturation. Blood DC and LC did not express detectable levels of the MMR. FITC-dextran uptake by both immature and activated blood DC was 30- to 70-fold less than that of LC, immature Mo-DC and macrophages. In contrast to immature Mo-DC, the FITC-dextran uptake by LC was not inhibited effectively by mannose, an inhibitor for MMR-mediated FITC-dextran uptake. Thus, unlike Mo-DC, blood DC and LC do not use the MMR for carbohydrate-conjugated antigen uptake and alternative receptors may yet be defined on these DC. Therefore, DEC-205 may have a different specificity as an antigen uptake receptor or contribute to an alternative DC function.

Would cyclosporin A be beneficial to mitigate drug-induced toxic epidermal necrolysis?

Drug-induced toxic epidermal necrolysis (TEN) is a rare life-threatening disease whose mortality remains high. The treatment of the disease is badly settled. Several kinds of drugs have been tested, including systemic corticosteroids, cyclophosphamide, pentoxifylline and thalidomide, but without any clear-cut outcome. Cyclosporin A (CsA) has many inhibitory effects on the main cell populations involved in TEN (T lymphocytes, macrophages and keratinocytes). CsA could also act on tumor necrosis factor alpha metabolism, a cytokine which is important in TEN epidermal destruction. Moreover, apoptosis is the mechanism leading to keratinocyte death and CsA has antiapoptotic properties. CsA has already been used successfully on a limited series of TEN patients. We have reviewed the potential theoretical useful effects of CsA in TEN. We conclude that CsA could be a good candidate to reverse TEN progression.

Cytological alterations in dermal dendrocytes in vitro: evidence for transformation to a non-dendritic phenotype

Dermal dendrocytes (DDs) are bone marrow-derived cells which are abundant in normal human and murine dermis, where they are closely associated with mast cells in the perivascular space. The biological role of DDs remains enigmatic. DDs express coagulation factor XIIIa and the recently described von Willebrand factor receptor, GPIb alpha, potentially indicating a function in tissue repair and haemostasis, although participation in antigen presentation is also speculated. In healing wounds and 'fibrohistiocytic' tumours, such as dermatofibromas, DDs are often associated with non-dendritic histiocytes, some of which also express factor XIIIa (FXIIIa). We have utilized human skin organ culture to examine the effects of various biological mediators on cytological characteristics of DDs. It was found that by 24 h in organ culture, immunoreactive DDs begin to lose their dendritic shape, assuming more rounded contours. This phenomenon was accentuated by mast cell degranulation; was independent of the nature of mast cell secretagogue; and could not be reproduced by recombinant tumour necrosis factor-alpha, a cytokine known to increase FXIIIa expression in DDs. Like their dendritic precursors, non-dendritic cells expressed variable FXIIIa, CD34 and CD68 and did not express CD1a or CD45. By ultrastructure, non-dendritic cells that develop in vitro resembled non-degenerating monocytes containing occasional primary lysosomes and lipid inclusions, and like DDs, expressed fibronexus-like plaques on the cell membrane. Transition of DDs from dendritic to non-dendritic cells as a consequence of specific microenvironmental influences may provide insight into the frequent concurrence of these two cytological types in fibrohistiocytic tissue reactions and neoplasia.

Distribution of MHC-II and CD1 molecules in the skin of lambs and changes during experimentally-induced contact hypersensitivity

The presentation of antigen to specific T-cell populations is a crucial event during the elicitation phase of contact hypersensitivity (CHS). Significant changes in CD4(+) T-cell and gammadelta T-cell populations occur in the skin of sheep 48h after re-exposure to dinitrochlorobenzene but the expression of antigen presentation molecules such as MHC-II and CD1 at this stage of the hypersensitivity response has not been investigated. In the present study, a panel of monoclonal antibodies recognising CD1 and MHC-II subtypes was used in combination with computer assisted morphometric analysis to estimate the distribution of antigen presentation molecules in the superficial and deep dermis of the ears of lambs during the elicitation phase of CHS. The MHC-II molecules showed predominantly a perivascular and peri-appendageal distribution in the dermis and there were scattered MHC-II(+) cells in the basal and suprabasal layers of the epidermis. The CD1w2(+) (CD1b-like) molecules were present on distinct cells that were scattered evenly through the dermis, whereas CD1w3(+) (CD1c-like) molecules were almost exclusively detected on or in close association with the vascular endothelium. There was a significant increase in the presence of MHC-DQ(+) cells in the superficial dermis of dinitrochlorobenzene-treated animals compared with both an untreated control group and a vehicle-treated control group. However, MHC-DQ/DR(+) and CD1w3(+) cells only showed a significant increase compared with the vehicle-treated control group. The present study shows that the distribution of molecules involved in antigen presentation to CD4(+) T-cells and gammadelta T-cells changes during the elicitation phase of CHS in sheep, and suggests a role for MHC-DQ molecules on antigen presenting cells. However, the changes in distribution and expression of MHC-II and CD1 subtypes argue against a prominent role for a CD1-dependent pathway for T-cell recognition in the clinical cutaneous hypersensitivity response in sheep. Based on the expression of MHC-II molecules and CD1c molecules, we also suggest a potential role for endothelial cells in antigen presentation during the clinical dermatitis reaction.

Immunological activation of dermal Langerhans cells in contact with lymphocytes in a model of human inflamed skin

Langerhans cells play an important role in the skin's immune system. Little is known, however, about the antigen-presenting capacity of Langerhans cells in the context of skin inflammation. By immunohistochemistry we investigated the phenotypic characteristics of epidermal and dermal Langerhans cells and their spatial relationship with infiltrating lymphocytes. We studied skin flaps autotransplanted to the oral cavity to fill a defect after maxillofacial cancer surgery. In 15 of 21 cases sampled for the present study, the skin flaps were severely inflamed by Candida albicans infection. In contrast to the normal skin, such inflamed skin showed a marked increase in CD1a(+) dermal Langerhans cells. Double immunohistochemistry revealed that dermal Langerhans cells abundantly expressed B7-2 (CD86), a representative costimulatory molecule, and CD83, a marker of mature dendritic cells. Furthermore, these dermal Langerhans cells were in close contact with CD4(+)/CD45RO(+) lymphocytes. This cell-to-cell contact was further visualized by immunoelectron microscopy. Langerhans cells were also observed within lymphatic vessels that were identified by the expression of vascular endothelial growth factor receptor-3. Ki-67 labeling indices were 4.2% in CD4(+) T cells and 0.8% in CD8(+) T cells within the dermis. Factor XIIIa(+) dermal dendrocytes were distributed outside the clusters of lymphocytes and were not in contact with them. Our observations indicate that dermal Langerhans cells in the inflamed skin are activated to express common phenotypes to mature dendritic cells so that they could stimulate neighboring memory CD4(+) T cells.

Differential regulation of epidermal and dermal dendritic cells by IL-12 and Flt3 ligand

An abrogation of the decline in epidermal Langerhans cell numbers above melanoma might significantly improve the efficacy of immunotherapy for melanoma treatment. Systemic Flt3 ligand (FL) administration in mice induced a significant increase in mature dendritic cells (DC) within the skin, preferentially in the dermis, whereas IL-12 promoted a significant increase of immature DC preferentially in the epidermis. Both effects were abrogated in IL-12 knockout mice. Thus, IL-12 could promote FL-induced accumulation of skin DC. The involvement of FL and IL-12 in the regulation of DC accumulation within the skin may contribute, at least in part, to the stimulation of antimelanoma immunity by FL- and IL-12-based immunotherapies. Moreover, FL and IL-12 could be used for selective in vivo generation of DC in either epidermis or dermis for experimental and clinical purposes.

Morphea limited to the superficial reticular dermis: an underrecognized histologic phenomenon

Morphea (localized scleroderma) is a disease of unknown etiology, presenting as circumscribed areas of indurated skin. Histologically, most cases of morphea feature thickened collagen bundles in the deep reticular dermis, sometimes also extending into the superficial dermis or into the subcutis. We present six cases of morphea in which typical histologic features were restricted to the superficial dermis and contrast these with 27 additional biopsies of conventional morphea seen during the same time period. Sections were stained for elastic fibers, and dermal dendritic cells were labeled with antibodies to CD34 and Factor XIIIa. All six cases showed thickened collagen bundles restricted to the superficial dermis, sparing the deep dermis and without associated evidence of lichen sclerosus et atrophicus (LSA). Dermal elastic fibers were not appreciably decreased in number. There was loss of CD34-positive dermal spindle cells in each of our six superficial examples of morphea, which was restricted to the area of altered collagen in four of the six cases. This report highlights the distinctly uncommon phenomenon of morphea presenting solely as alteration of the superficial reticular dermis, without features of LSA. The selective loss of CD34-labeled spindle cells may provide information regarding the role of these putative immune accessory cells in morphea. Recognition of this manifestation of morphea may be helpful diagnostically.

Von Willebrand factor receptor GPIb alpha is expressed by human factor XIIIa-positive dermal dendrocytes and is upregulated by mast cell degranulation

GPIb alpha, a glycoprotein component of the GPIb-IX-V complex, serves as a platelet membrane receptor that mediates adhesion to von Willebrand factor normally present in the vascular subendothelium. Recent data have demonstrated that GPIb alpha is not restricted to platelets, but is also expressed by endothelium in vitro. In this study, we describe the expression and distribution of GPIb alpha in normal adult and neonatal human skin. GPIb alpha is present, as detected by immunohistochemistry, on endothelial cells and on highly dendritic cells localized within the perivascular space, dermal-epidermal junction, and reticular dermis. By dual-labeling immunofluorescence and confocal microscopy, GPIb alpha-positive cells within the dermal interstitium are demonstrated to represent factor XIIIa-positive dermal dendrocytes. In organ cultures of neonatal human foreskin, mast cell degranulation induced by either substance P or compound 48/80 resulted in transiently increased GPIb alpha expression by dermal dendrocytes. Because the GPIb-IX-V complex plays a part in regulating hemostasis and may be important for cellular interactions with extracellular matrix molecules, these data provide additional insight into the potential function of FXIIIa-positive dermal dendrocytes in skin remodeling and repair.