Induction of tolerance to urushiol by epicutaneous application of this hapten on dinitrofluorobenzene-treated skin

Non-nuclear estrogen receptor alpha signaling promotes cardiovascular protection but not uterine or breast cancer growth in mice

Steroid hormone receptors function classically in the nucleus as transcription factors. However, recent data indicate that there are also non-nuclear subpopulations of steroid hormone receptors, including estrogen receptors (ERs), that mediate membrane-initiated signaling of unclear basis and significance. Here we have shown that an estrogen-dendrimer conjugate (EDC) that is excluded from the nucleus stimulates endothelial cell proliferation and migration via ERalpha, direct ERalpha-Galphai interaction, and endothelial NOS (eNOS) activation. Analysis of mice carrying an estrogen response element luciferase reporter, ER-regulated genes in the mouse uterus, and eNOS enzyme activation further indicated that EDC specifically targets non-nuclear processes in vivo. In mice, estradiol and EDC equally stimulated carotid artery reendothelialization in an ERalpha- and G protein-dependent manner, and both agents attenuated the development of neointimal hyperplasia following endothelial injury. In contrast, endometrial carcinoma cell growth in vitro and uterine enlargement and MCF-7 cell breast cancer xenograft growth in vivo were stimulated by estradiol but not EDC. Thus, EDC is a non-nuclear selective ER modulator (SERM) in vivo, and in mice, non-nuclear ER signaling promotes cardiovascular protection. These processes potentially could be harnessed to provide vascular benefit without increasing the risk of uterine or breast cancer.

Acquired scalp alopecia. Part II: A review

The neutrophil-associated and infiltrative scarring alopecias are reviewed including folliculitis decalvans, tufted folliculitis, dissecting cellulitis of the scalp, acne keloidalis and follicular degeneration syndrome. The management of acquired scalp alopecia is also reviewed including newer, promising therapies. More specific agents targeting components of the androgen system will make the treatment of androgenetic alopecia more rewarding. Similarly new immunomodulatory therapies show great promise for the lymphocyte-associated alopecias and include a new generation of macrolide immunosuppressives (tacrolimus, SDZ ASM 981, and SDZ 281-240), some of which appear to have good transcutaneous absorption.

Human thymic dendritic cells

ABSTRACT Human thymic dendritic cells (DC) represent a member of the bone marrow-derived dendritic cell family. They have a dendritic shape and are found in small numbers mainly at the corticomedullary border and in medullary regions of the thymus. Human thymic DC were isolated by density gradient separation, followed by treatment with CD2, CD7, CD1, and CD11b mAb and immunobeads magnetic separation. The resulting population contains 60-75% brightly HLA-DR+ cells which present the morphological characteristics of DC observed in situ. Extensive phenotypic analysis confirmed that they are of mesenchymal origin and that some express CD11a and CD54 molecules. Freshly isolated DC do not stain with a wide variety of anti-T-B and -monocyte or -macrophage mAb. However, they acquire the CD1 molecule after a few days in culture. By using a cell sorter we obtained 90-95% of purified human thymic DC. Functional studies have shown that human thymic DC are potent activators in mixed lymphocyte reactions, act as accessory cells in mitogenic thymocyte proliferation, increase the thymocyte proliferative response to a toxin signal, and produce IL-1. They also formed spontaneous physical associations with thymocytes, which raises questions about the implication of DC in differentiation and/or maturation processes of thymocytes.

High and low doses of haptens dictate whether dermal or epidermal antigen-presenting cells promote contact hypersensitivity

In the induction of contact hypersensitivity (CH) to an epicutaneously applied hapten, we have previously proposed that low doses of hapten sensitize primarily through epidermal Langerhans' cells (LC), whereas high doses rely largely on dermal antigen-presenting cells (APC). To examine this issue further, we applied either high or low doses of dinitrofluorobenzene (DNFB) epicutaneously to mice. We observed reduced LC density at the site after 12 h (nadir), which returned to normal levels at 24 h only after a low dose of hapten. When a low dose of an unrelated hapten, oxazolone, was painted on skin that had been painted 12 h previously with high dose of DNFB, oxazolone-specific CH was impaired. When grafts of whole skin, dermis alone, and epidermis alone prepared from skin painted 2 h previously with low or high doses of DNFB were placed onto naive, syngeneic mice, CH was induced by whole skin after both types of doses, by epidermis only after a low dose, and by dermis only after high dose. When epidermal cell suspensions were derivatized in vitro with low or high doses of DNFB, only cells exposed to a low dose induced proliferation of hapten-specific Tcells. Thus, only a low dose of hapten reveals the APC functions of LC without the participation of dermal APC.

Induction of low zone tolerance to contact allergens in mice does not require functional Langerhans cells

Epidermal Langerhans cells are known to be the major controlling element in the development of contact hypersensitivity. Haptenic molecules permeating the skin are taken up locally by Langerhans cells and then presented to T lymphocytes in the regional lymph nodes. Despite the presence of functional Langerhans cells, however, subsensitizing doses of hapten applied epicutaneously induce tolerance. We examined epidermal Langerhans cells at the site of contact with picryl chloride or oxazolone in BALB/c and C57B1/6 mice with regard to their responding to either subsensitizing or sensitizing doses of allergen. Subsensitizing doses did not interfere with the membranous adenosine triphosphatase system on Langerhans cells, known to relate to functional readiness of the cell. Accordingly, on electron microscopy the ultrastructure of Langerhans cells was found to be like that in untreated skin. In contrast, sensitizing doses caused a significant depletion of adenosine triphosphatase-positive Langerhans cells, and electron microscopy revealed marked cellular activation of Langerhans cells, with enlarged nuclei and increased numbers of mitochondria and Birbeck granules. Furthermore, subsensitizing doses induced tolerance regardless of whether Langerhans cells were functionally intact or had their function blocked arbitrarily. Blocking was achieved either by preceding ultraviolet B irradiation at the site of application or by painting of a sensitizer before painting another sensitizer on the same site. Moreover, not even surgical removal of the site within minutes after painting could prevent the induction of tolerance. The data suggest that subsensitizing doses of contact allergens painted on normal murine skin bypass involvement of epidermal Langerhans cells.

The endothelium in early experimental contact hypersensitivity of the oral mucosa. Leukocyte-binding properties and ultrastructure

Contact hypersensitivity is characterized by an early and specific diapedesis of mononuclear cells into the site of antigenic challenge. In order to study the functional and ultrastructural properties of the endothelium involved in the recruitment of leukocytes, Sprague-Dawley rats were skin sensitized to DNFB; and this was followed by challenge of the oral mucosa. In vitro binding of peripheral blood mononuclear cells to high endothelial venules in lymph nodes was highly specific but no affinity of peripheral blood mononuclear cells to the vessels was observed in normal oral mucosa or in early contact hypersensitivity. However, 10 days after repeated DNFB challenge, occasional vessels bound overlaid peripheral blood mononuclear cells. Ultrastructurally, we identified migration of mononuclear cells through small venules three h after challenge. The vessels involved, however, did not display morphological signs of activation reminiscent of high endothelial venules in lymph nodes. Mast cell degranulation was evident as early as 30 min after challenge, and a possible mechanism for mast cell-mediated leukocyte recruitment is discussed.

ATPase and morphologic changes in Langerhans cells induced by epicutaneous application of a sensitizing dose of DNFB

We have previously described an ATPase Langerhans cell (LC) staining technique allowing progression from light to electron microscope observation. Using this technique we have studied, following epicutaneous application of a sensitizing dose of a hapten, 2,4-dinitro-1-fluorobenzene (DNFB), the fate of the epidermal LC located in the sensitization zone. We wanted to know, under the light microscope, if the density and/or morphology of the LC are modified by such a treatment and, under the electron microscope, what are the ultrastructural changes accompanying the possible light microscope modifications. Under the light microscope, the observation of LC during the 5 d necessary for the development of contact sensitivity to DNFB shows that their number drops in the course of the first 24 h to normalize again 3 d later. Under the electron microscope, observations over the first 24 h revealed that LC remained in the epidermis, but were ATPase-negative. The disappearance of the membrane ATPase activity took place while the LC presented an increased number of coated pits, coated vesicles, endosomes, and lysosome organelles which characterize, at the ultrastructural level, the process of receptor-mediated endocytosis (RME). Following RME, many Birbeck granules (BG) appeared in the cytoplasm. Thus, epicutaneous application of DNFB leads to an endocytic activation of LC. However, the ligand(s) and/or the cell-surface components, which probably internalize during the RME process, remain unknown.

Human epidermal Langerhans cells cointernalize by receptor-mediated endocytosis "nonclassical" major histocompatibility complex class I molecules (T6 antigens) and class II molecules (HLA-DR antigens)

HLA-DR and T6 surface antigens are expressed only by Langerhans cells and indeterminate cells in normal human epidermis. We have previously demonstrated that T6 antigens are internalized in Langerhans cells and indeterminate cells by receptor-mediated endocytosis. This process is induced by the binding of BL6, a monoclonal antibody directed against T6 antigens. In the present study, using a monoclonal antibody directed against HLA-DR antigens, on human epidermal cells in suspension, we show that the surface HLA-DR antigens are also internalized by receptor-mediated endocytosis in Langerhans and indeterminate cells. Moreover, using immunogold double labeling, we demonstrate that T6 and HLA-DR antigens are internalized through common coated regions of the membrane of Langerhans or indeterminate cells. The receptor-mediated endocytosis that is induced involves coated pits and vesicles, receptosomes, lysosomes, and also, in Langerhans cells, the Birbeck granules. Thus, T6 antigens, which are considered to be "unusual" or "nonclassical" major histocompatibility complex class I molecules, and the major histocompatibility complex class II molecules, HLA-DR, are internalized in Langerhans and indeterminate cells through common receptor-mediated endocytosis organelles.

Contact dermatitis. A review

In recent years, there has been a dramatic rise in our understanding of contact dermatitis. This paper is a review of our knowledge of the mechanisms involved in contact dermatitis and related phenomena, the investigation of these events and the emergence of significant new allergens during the last 5 years.