Psoriatic lesional keratinocytes promote the maturation of human monocyte-derived Langerhans cells

CD1a-mediated immunity from a molecular perspective

Human CD1a is a non-polymorphic glycoprotein that presents lipid antigens to T cells. The most obvious role of CD1a is associated with its expression on Langerhans cells in epidermis, where it is involved in responses to pathogens. Antigen-specific T cells are believed to co-recognise CD1a presenting bacterial antigens such as species of lipopeptides from Mycobacterium tuberculosis. Further, human skin contains large amount of endogenous lipids that can activate distinct subsets of CD1a-restricted autoreactive T cells, mostly belonging to the αβ lineage, which are abundant in human blood and skin and are important for skin homeostasis in healthy individuals. CD1a and CD1a-restricted T cells have been linked to certain autoimmune conditions such as psoriasis, atopic dermatitis and contact hypersensitivity becoming a potential candidate for clinical interventions. A significant progress has been made in the last twenty years towards our understanding of the molecular processes that orchestrate CD1a-lipid binding, antigen presentation and mechanism of CD1a recognition by αβ and γδ T cells. This review summarises the recent developments within the field of CD1a-mediated immunity from a molecular perspective.

Tissue microenvironment initiates an immune response to structural components of Staphylococcus aureus

Cell-to-cell communication in skin participates to the maintenance of homeostatic responses to foreign substances. Certain strains of Staphylococcus (S) aureus are vicious pathogens that cause deleterious effects in host cells and tissues. Both secreted toxins and structural components of S. aureus trigger an immune response, though how S. aureus stimulates host immune responses is poorly understood. We explored here how keratinocytes and fibroblasts initiate the first steps of an immune response by activating dendritic cells (DCs) through recognition of structural components of S. aureus. We treated monocyte-derived Langerhans cells (moLCs) and monocyte-derived DCs (moDCs) with conditioned media from keratinocytes (K-CM) and fibroblasts (F-CM) treated with heat-killed S. aureus (HKSA) respectively, or directly with HKSA. Immune and inflammatory responses from keratinocytes, fibroblasts, moLCs and moDCs were assessed by analysis of cell surface markers and cytokine production using flow cytometry, real-time PCR and ELISA assays. K-CM and F-CM increased the expression of CD86 and HLA-DR on moLCs and moDCs, in association with a specific cytokine profile. K-CM upregulated TNFA, IL-1B and GM-CSF mRNA expression in moLCs, while F-CM upregulated IL-12 and downregulated TNFA and TGFB mRNA expression in moDCs. Additionally, F-CM attenuated the induction of an inflammatory profile in monocytes. The recognition of structural components from S. aureus by cutaneous microenvironment induces the activation and the expression of specific cytokines from LCs and DCs.

No impairment of monocyte-derived Langerhans cell phenotype or function in early-onset psoriasis

Background

Migration of epidermal Langerhans cells (LCs) in response to the cytokines interleukin (IL)-1β and tumour necrosis factor (TNF)-α is impaired in uninvolved skin of patients with early-onset psoriasis.

Aim

To investigate whether this impairment is a reflection of a systemic defect in dendritic cells (DCs), using an established model of monocyte-derived LC-like cells (mLCs).

Methods

CD14+ monocytes isolated from both patients with psoriasis and healthy control volunteers were cultured in a cytokine cocktail for 5 days to promote their differentiation into mLCs, then stimulated for 24 h with TNF-α, IL-1β (both 100 ng/mL) or medium alone. Cellular surface protein expression was quantified by flow cytometry, and the ability of cells to migrate to media supplemented with C-C motif ligand (CCL)19 was assessed using a Transwell migration assay. The cytokine and chemokine content of supernatants was analysed by cytokine array.

Results

CD14+ cells acquired an LC-like phenotype with high expression of CD1a and major histocompatibility complex (MHC) class II. There were no differences in the expression of activation markers or in the secretion of cytokines by mLCs isolated from patients with psoriasis and those isolated from healthy controls. Moreover, mLCs isolated from both groups displayed comparable ability to migrate in vitro.

Conclusions

These data suggest that the failure of LCs to migrate in response to stimulation in patients with psoriasis is not attributable to a systemic defect in DC function, but is rather a reflection of local changes in the epidermal microenvironment.

GM-CSF and IL-4 induce dendritic cell differentiation and disrupt osteoclastogenesis through M-CSF receptor shedding by up-regulation of TNF-alpha converting enzyme (TACE)

Monocytes give rise to macrophages, osteoclasts (OCs), and dendritic cells (DCs). Macrophage colony-stimulating factor (M-CSF) and receptor activator of nuclear factor-kappaB (RANK) ligand induce OC differentiation from monocytes, whereas granulocyte-macrophage colony-stimulating factor (GM-CSF) and interleukin-4 (IL-4) trigger monocytic differentiation into DCs. However, regulatory mechanisms for the polarization of monocytic differentiation are still unclear. The present study was undertaken to clarify the mechanism of triggering the deflection of OC and DC differentiation from monocytes. GM-CSF and IL-4 abolished monocytic differentiation into OCs while inducing DC differentiation even in the presence of M-CSF and RANK ligand. GM-CSF and IL-4 in combination potently up-regulate tumor necrosis factor-alpha (TNF-alpha) converting enzyme (TACE) and activity in monocytes, causing ectodomain shedding of M-CSF receptor, resulting in the disruption of its phosphorylation by M-CSF as well as the induction of osteoclastogenesis from monocytes by M-CSF and RANK ligand. Interestingly, TACE inhibition robustly causes the resumption of the surface expression of M-CSF receptor on monocytes, facilitating M-CSF-mediated phosphorylation of M-CSF receptor and macrophage/OC differentiation while impairing GM-CSF- and IL-4-mediated DC differentiation from monocytes. These results reveal a novel proteolytic regulation of M-CSF receptor expression in monocytes to control M-CSF signaling and monocytic differentiation into macrophage/OC-lineage cells or DCs.

From laboratory to clinic: rationale for biologic therapy

Traditional systemic therapy for psoriasis is limited by either lack of efficacy or the long-term side effect profile of the medications used. Newer information about the pathophysiology of the disease has led to new perspectives on developing novel techniques for attacking psoriasis. This article discusses the pathogenesis of psoriasis, looks at the immunologic factors that contribute to forming a psoriatic plaque, reviews how novel biologic therapies are made, and explores how biologics can target each of these specific parts of the immunologic cascade.

Langerhans cell histiocytosis and juvenile xanthogranuloma. Two case reports

BACKGROUND

Histiocytoses represent a large, puzzling group of diseases which may involve the skin and other organs. At present, juvenile xanthogranuloma is the disorder most often confused with Langerhans cell histiocytosis. A complex overlap exists between juvenile xanthogranuloma and Langerhans cell histiocytosis, with lesions showing clinical and/or pathological features of both disorders.

OBSERVATIONS

We report 2 patients affected by Langerhans cell histiocytosis who, during chemotherapy, presented cutaneous lesions with clinical and histological features of juvenile xanthogranuloma. During the therapy, in both cases, histological examination of new biopsies revealed the presence of Touton giant cells in the dermis with a few histiocytic cells; immunohistochemical staining was negative for CD1a, and no Birbeck granules were seen by ultrastructural examination.

RESULTS AND CONCLUSION

A possible explanation for the link between Langerhans cell histiocytosis and juvenile xanthogranuloma regards the lineage development and the relationships of histiocytes. We suggest that chemotherapy can modify the production of cytokines by influencing the conversion or 'maturation' of pathological cells into macrophages or xanthomatous cells and fusing them to form multinucleated giant Touton cells. In our opinion, the modification of the cutaneous lesions during chemotherapy in Langerhans cell histiocytosis patients, as observed in our cases, could be a favorable prognostic factor.

Annular lichen planus: study of the cellular mechanisms of annularity

Annular lichen planus is a rare, unique subtype of lichen planus. We report a 34-year-old Japanese male who had multiple, dark red to purple, annular macules with slightly raised borders. Histopathological examination of a skin biopsy specimen from the peripheral region of the macule showed the typical features of lichen planus. Immunohistochemical stainings revealed that a number of CD1a-positive, S-100-protein-positive Langerhans cells were present at the border zone of the annular lesion and most of the infiltrating cells were CD4-positive, CD8-negative lymphocytes. Conversely, inside the annular lesion, the number of Langerhans cells was decreased, and an equal number of CD4-positive cells and CD8-positive cells was present in the sparse infiltration. These results suggest that activation of Langerhans cells initiated a lichenoid tissue reaction but a subsequent depletion of Langerhans cells suppressed the lymphocyte infiltration. These sequential events might be involved in the formation of the unique annular structure in this condition.

In situ Expression of CD40 and CD40 Ligand in Psoriasis

BACKGROUND

The interaction between CD40 and CD40 ligand (CD40L) provides a signal that contributes to the initiation of cellular immune responses. However, little information on the in vivo expression of CD40 and CD40L in cutaneous inflammation has been reported.

OBJECTIVE

To investigate the potential role of CD40-mediated signals in the pathogenesis of psoriasis.

MATERIALS AND METHODS

In situ CD40 and CD40L expression was examined immunohistochemically in different stages of psoriatic lesions: fully developed and initial pinpoint.

RESULTS

In normal skin, faintly positive immunoreactivity for CD40 was seen in the basal keratinocytes and dermal endothelial cells. These showed almost the same intensity as that seen in psoriatic lesional skin. In the dermal infiltrates of psoriatic lesions, CD40 was intensely expressed and some of these positive cells appeared to be dendritic in shape. Whereas CD40 expression was observed almost in all specimens of psoriatic lesions, the expression of CD40L was predominantly detected in the initial pinpoint lesions of psoriasis. These seemed to be distributed close to CD40-positive cells.

CONCLUSION

These results suggested that CD40L-triggered signals could be involved in the early stage of psoriatic lesion formation.

Histometric assessment of psoriatic plaques treated by vitamin D3 derivatives

BACKGROUND

Psoriasis is an immunogenetic disorder. Factor XIIIa+ dermal dendrocytes (DD) are part of the pathobiological changes in the plaque type of the disease.

OBJECTIVE

The present study aimed at comparing the effect of 3 vitamin D(3) derivatives on the epidermis, microvasculature and DD in psoriasis.

METHOD

Twenty men suffering from chronic plaques of psoriasis on the trunk were enrolled in this study. They applied twice a day for 3 weeks calcipotriol, tacalcitol and calcitriol, each to one plaque. Another similar lesion received petrolatum as a placebo treatment. Skin biopsies were taken at entry and at completion of the 3-week treatment phase. Immunohistochemistry was performed using the lectin of Ulex europaeus and an antibody to factor XIIIa. Computerized image analysis served to measure the stratum Malpighii area, the microvasculature area and the DD numerical density in the papillary dermis.

RESULTS

At entry in the study, the 4 test sites were indistinguishable with regard to the stratum Malpighii area, the papillary microvasculature area and the papillary DD density. The 3 histometric parameters appeared correlated with each other. At completion of the 3-week treatment phase, the 3 vitamin D derivatives had decreased the size of the stratum Malpighii. In addition, calcitriol had also reduced the DD density in the papillary dermis. No other significant changes were yielded.

CONCLUSION

As assessed by histometry, the psoriatic epidermis responded to a short treatment using the 3 vitamin D derivatives. The better result compared to the control site was achieved by calcitriol. DD appeared to be most controlled by the same drug. The microvasculature did not appear to be decreased at the 3-week time point in treatment.