Changes in Lymphocyte and Langerhans Cell Populations in Allergic and Irritant Contact Dermatitis

We observed in situ changes in lymphocyte subpopulations and Langerhans cells during allergic and irritant contact dermatitis using immunohistochemical staining methods with monoclonal antibodies to cell surface antigens. In both types of contact dermatitis, there was a perivascular infiltrate of T lymphocytes, with helper/inducer T cells predominating. B cells were absent, and natural killer cells were absent or sparse. During the course of allergic contact dermatitis, Langerhans cells showed a striking sequential change in location, with the cells first in the epidermis, then perivascularly in the dermis (days 1-14), and returning to the epidermis (days 14-21). In irritant contact dermatitis, the Langerhans cells were initially identified in the epidermis and then appeared diffusely in the dermis (days 1-2). The numbers in the dermis then decreased abruptly (day 4). They were again identified in normal numbers in the epidermis (day 21). The response of Langerhans cells appears to be different between allergic and irritant contact dermatitis.     

The interaction between Langerhans cells and CD4+ T cells.

The human skin is increasingly exposed to haptens and environmental protein antigens. Because Langerhans cells represent the outermost network of MHC class II+ antigen presenting cells in mammalians, we investigated their interaction with CD4+ T cells. Hapten-modified Langerhans cells induced proliferation and IL-2 production in naive resting CD4+ T cells. T cells activated in this manner and subsequently cultured with IL-2 mediated contact sensitivity in vivo and produced IL-2 but no IL-4 upon restimulation in vitro. Thus they corresponded to Th1 cells. Repeated stimulation with Langerhans cells induced a modulation of the lymphokine pattern: IL-2- and IL-4-producing Th0-like cells were identified after 3 to 4 rounds of restimulation; after > 5 rounds, Th2-like cells with an IL-4+IL-2- pattern and the capacity for inducing IgE synthesis in B cells was identified. Th2 cells were also recently found to mediate inflammatory tissue lesions containing a cellular infiltrate. This demonstrates that Langerhans cells may activate resting CD4+ T cells, Th1-, Th0- and Th2-like cells. It further shows that Langerhans cells may promote the differentiation of postthymic CD4+ T cells into subsets with distinct immune functions: Th1 cells which have the potential to mediate inflammatory reactions such as allergic contact sensitivity and Th2 cells which may be responsible for abnormalities associated with atopic dermatitis, such as elevated IgE and inflammatory skin lesions containing a cellular infiltrate.     

Contact dermatitis sparing the eruption of herpes zoster and its periphery

A 63-year-old male developed allergic contact dermatitis with antibiotic ointment applied to the skin eruptions of herpes zoster. From the result of patch test, fradiomycin sulfate contained in the ointment was identified as the contact sensitizing antigen. Strangely, this contact dermatitis was confined to the area surrounding the sores, sparing the lesions and their periphery. We postulated that a decrease in Langerhans cell activity in the herpes zoster lesions and their peripheral area was primarily responsible for this phenomenon, since an important role of Langerhans cells in host defence against herpes virus infection has recently been demonstrated.     

CD1d‐dependent,iNKT‐cell cytotoxicity against keratinocytes in allergic contact dermatitis

Conventional CD8+ T‐lymphocytes are thought to be major effector cells in allergic contact dermatitis (ACD). However, previous work has demonstrated a significant population of invariant natural killer T‐cells (iNKT‐cells) in the elicitation phase of ACD. In this study, we investigate whether iNKT‐cells have the capacity to serve as effector lymphocytes in ACD. Using in situ staining of skin biopsy specimens from ACD lesions, we observed intra‐epidermal iNKT‐cells. Presence of these cells provides the possibility of interactions with keratinocytes (KC), Langerhans cells (LC) and CD1d‐bearing antigen‐presenting cells (APC). Investigation into gene expression profiles of cytotoxic effector molecules in seven different cases of ACD found that the expression of perforin and granzymes A, B and K were significantly elevated in ACD relative to paired clinically normal skin. Immunostaining of ACD skin biopsy specimens revealed that these cytotoxic granules indeed localized to iNKT‐cells. Studies of antigen presentation of KC to iNKT‐cells show that these epithelial cells do not activate the expression of cytotoxicity effector genes in resting iNKT‐cells, but had the capacity to serve as targets for activated iNKT‐cells, which was dependent on CD1d expression. Mature LC were not able to present glycolipids to iNKT‐cells and did not up‐regulate CD1d in vitro to a variety of maturational stimuli or in vivo during ACD. These data suggest that iNKT‐cells can serve as effector cells during human ACD and provide the rationale for developing inhibitory glycolipids as therapeutic agents for ACD.     

Prospects for Vaccines for Allergic and Other Immunologic Skin Disorders

The human skin hosts a variety of immune response-associated components that together form the skin immune system. Any abnormality in the functioning of the skin immune system leads to a variety of dermatologic complications, including dermatitis, psoriasis, and eczema. Exposure to antigens/allergens can lead to allergic skin disorders such as atopic dermatitis, urticaria, and allergic contact dermatitis. Recent investigations have provided new insights into the immunologic processes leading to the development of skin diseases. T cells play a central role in the activation and regulation of immune responses by recognizing antigen and inducing cytokine production. Despite advances in the understanding of the immunologic events leading to the development of skin diseases, no effective prevention measure exists. Current therapeutic treatments are based on either alleviating the symptoms or suppressing the immune system with immunosuppressive drugs. Allergen-specific immunotherapy is expected to induce specific T cells that abolish allergen-induced proliferation of T helper cells, as well as their cytokine production. Recent approaches using recombinant protein, polycytosine guanine oligonucleotides, and plasmid DNA for vaccination suggest the possibility of protection against these skin disorders. The involvement of T cells in psoriasis indicates that the development of a T-cell receptor peptide vaccine may be beneficial. Dendritic cell-based vaccines using tolerogenic dendritic cells that can induce T-cell tolerance have been shown to be useful in dealing with autoimmune disorders and allergic conditions. In the light of these developments, this article presents the current status and prospects of developing vaccines for allergic and other immunologic skin disorders.     

Common pathogenetic pathways in allergic and irritant contact dermatitis.

Despite their different pathogeneses, allergic and irritant contact dermatitis show a remarkable similarity with respect to clinical appearance, histology, and immunohistology. To further analyze this apparent contradiction, our study was designed to meticulously compare cellular infiltrates in irritant and allergic patch-test reactions by immunostaining with a broad panel of monoclonal antibodies. For this purpose, skin biopsies from allergic and irritant patch-test reactions of similar inflammatory degree were obtained from the same probands. We found that after 72 h both types of reaction were characterized by an identical dermal infiltrate consisting mainly of memory T cells, many of which were activated, and macrophages. Dermal and epidermal Langerhans cell density and HLA--DR expression of keratinocytes were also virtually identical. Our results show that antigen recognition by specific memory T cells as well as irritants can finally induce the same pattern of inflammation, including activation of T cells obviously independent of exogenous antigen.     

Antigen-presenting cells and keratinocytes express interleukin-12 in allergic contact dermatitis

Interleukin‐12 (IL‐12) has previously been suggested as playing a major rôle in the activation of cytotoxic lymphocytes. Recent reports indicate that cytotoxic CD8+ cells are critically involved in the elicitation phase of contact hypersensitivity reactions. In this study, the in situ expression of IL‐12 was investigated in normal human skin and in allergic contact dermatitis by immunohistochemistry. Skin biopsy specimens were obtained from allergic patch test reactions after 3 days, and from normal skin in 8 subjects. In contrast to normal skin, a strong enhancement of IL‐12 immunoreactivity was observed in the mononuclear cell infiltrate of allergic contact dermatitis. IL‐12 immunoreactivity was mainly located in the cytoplasm of dermal dendritic cells and macrophages as well as of some Langerhans cells. IL‐12‐positive cells were often found in close apposition to lymphocytes. Furthermore, positive immunostaining was also detected in keratinocytes at sites of marked exocytosis and spongiosis in the epidermis. In conclusion, the enhanced in situ expression of IL‐12 may contribute to the activation of cytotoxic lymphocytes and thereby represent an important factor in the pathogenesis of contact hypersensitivity reactions in humans.     

Immunopathological and ultrastructural findings in human allergic and irritant contact dermatitis

The histopathological features of allergic contact dermatitis were compared with those of irritant contact dermatitis in a group of 17 subjects. Each patient received simultaneous patch tests of a known allergen and a standardized irritant (benzalkonium chloride). The cellular changes occurring between 3 h and 7 days after patch test application were studied by light and electron microscopy and immunocytochemistry. No differences were observed between the induced allergic contact dermatitis (ACD) and the irritant contact dermatitis (ICD), either in the responding cell types or the sequence of cellular events. Both reactions showed a predominantly T lymphocyte infiltrate with no polymorphonuclear leukocyte involvement. Apposition of Langerhans cells to lymphocytes in the epidermis was seen in both types of response. Considerable variability in the intensity of reaction to irritant and allergen occurred within individuals. There was no statistically significant difference between the intensity of the reactions to the irritant and the allergen.     

Fibronectin in the skin of patients with allergic dermatitis

In the skin of healthy subjects linear deposits were found of fibronectin at the dermoepidermal junction and in the walls of blood vessels, and reticular deposits in the papillary and reticular layers of the skin. In the epidermis of 12 out of 51 patients with allergic contact dermatitis fibronectin deposits were found in relation to Langerhans cells and keratinocytes. This was not observed in the epidermis in healthy subjects. The authors suggest that fibronectin on the surface of Langerhans cells and keratinocytes may play a role in antigen presentation.     

Allergic contact dermatitis to basic red 46 occurring in an HIV-positive patient

A 41-year-old HIV-positive man presented with a 2-month history of a generalized pruritic rash, which had started on his feet. Patch testing made a diagnosis of allergic contact dermatitis to the textile dye basic red 46, likely to have been present in his dark-blue-coloured socks. Complete resolution of his symptoms occurred with avoidance of these socks. The patient had developed allergic contact dermatitis with a low CD4 T lymphocyte count of 361 cells/microl (normal range 410-1545 cells/microl). This raised the question of the level of CD4 count necessary for an individual to develop allergic contact dermatitis to an allergen, given its role in delayed hypersensitivity. It was concluded that a low CD4 count as a result of HIV infection does not decrease the ability of an individual to develop allergic contact dermatitis. Whereas the effector role in delayed type 4 hypersensitivity reactions is mediated by CD4 T lymphocytes, in allergic contact dermatitis it appears that CD4 T lymphocytes have the suppressor role, with CD8 T lymphocytes having the effector role.     

Mechanisms of resolution of allergic contact dermatitis

Photoallergic and allergic contact dermatitis are examples of type IV hypersensitivity reactions that involve T cell-mediated immune responses against haptens that come into contact with the skin. These two types of allergies differ in that for routine contact allergens, the hapten is usually a chemically reactive species that readily couples to host proteins; for photoallergic reactions, UV light (320–400 nm) is necessary to generate (“photoactivate”) the chemically reactive hapten. From this point on, both photoallergic and allergic contact dermatitis are likely to proceed along the same pathways. For both types of cutaneous delayed-type hypersensitivity, there are naturally occurring mechanisms that terminate this type of T cell-mediated inflammation (tolerance induction). An important tolerance mechanism in the skin involves the induction of T-cell clonal anergy by “amateur” antigen-presenting cells such as keratinocytes. Advances in the understanding of the molecular pathways of T-cell activation and inactivation by antigen-presenting cells have identified critical signaling molecules such as B7/BB-1 antigen. The overexpression of these signaling molecules by the keratinocytes of transgenic mice disrupts the normal kinetics of resolution of murine contact hypersensitivity. These animals have prolonged contact hypersensitivity reactions that resemble some chronic dermatologic conditions in humans. This animal model may be a useful tool to better understand chronic allergic and photoallergic contact dermatitis.     

In situ immunological characterization of the infiltrating cells in positive patch tests

Skin biopsies from positive allergic patch tests were analysed by immunoenzymatic labelling of frozen sections with monoclonal antibodies. In seventeen patients the cellular infiltrate consisted of T cells admixed with Langerhans cells/indeterminate cells, but in two patients there were also many B lymphocytes. The B cells were accompanied by dendritic reticulum cells forming B-cell follicles, indistinguishable from those of normal and hyperplastic lymph nodes. There was no correlation between these two immunohistological staining patterns and the sensitizing antigen, the extent of local reaction or the time from epicutaneous application of allergen to examination (2 to 16 days). The ratio between T-helper and T-suppressor cells varied considerably, and showed no correlation with these variables. In all patients the infiltrating T cells expressed HLA-DR antigen. Transferrin receptors were identified on the infiltrating T cells in biopsies from nine patients. These data indicate activation of T cells in the infiltrate from positive patch tests, and support the functional significance of Langerhans cells in the initiation and maintenance of cutaneous contact allergy. An involvement of B cells and B-cell accessory cells in the pathogenesis of contact allergic reactions is also suggested. The presence of dendritic reticulum cells in skin infiltrates from positive patch tests may reflect a functional implication of the skin in the development of B-cell memory.     

Fc epsilon R11/CD23 receptor distribution in patch test reactions to aeroallergens in atopic dermatitis.

There is increasing evidence that exposure to organic allergens may induce or exacerbate lesional skin in patients with atopic dermatitis. In this study, patients with atopic dermatitis were patch tested to 11 common organic allergens and to control chambers containing 0.4% phenol and 50% glycerin in 0.9% saline. In biopsies from positive patch test reactions, patch test control skin, lesional eczematous and non-lesional skin from atopic individuals, and normal skin from non-atopic volunteers, the presence and distribution of macrophages (RFD7+), dendritic cells (RFD1+), and Langerhans cells, and the expression of the low-affinity receptor for IgE (CD23) were investigated. In patch test reactions and lesional skin samples, inflammatory infiltrates of diffusely distributed macrophages (RFD7+), dendritic cells (RFD1+), T lymphocytes (RFTmix+), and Langerhans cells (CD1+) were seen, the latter being present in both the epidermis and the dermis. The numbers of Langerhans cells were reduced in the epidermis and increased in the dermis in patch test reactions and lesional skin compared to their controls. Double staining revealed a change in the distribution of CD23 antigen. In patch test control and non-lesional biopsies many macrophages and only a few Langerhans cells within the dermal infiltrates expressed this antigen. In patch test reaction and lesional skin samples, however, the proportion of CD23+ dermal Langerhans cells had increased compared to macrophages. Furthermore, in these latter samples an increased proportion of dermal CD1+ cells expressed the dendritic cell (RFD1+) marker. These results show that following antigen challenge there are marked similarities between the phenotype of the cellular infiltrate in patch test reaction and lesional skin biopsies, and also demonstrate a changing distribution of CD23 on antigen-presenting cells.     

The ICAM-3/LFA-1 interaction is critical for epidermal Langerhans cell alloantigen presentation to CD4+ T cells

Intercellular adhesion molecule (ICAM)-3 is a recently described member of the immunoglobulin superfamily and, as such, is closely related to ICAM-1 and ICAM-2. All three ICAMS are cognate for the counter-receptor lymphocyte function associated antigen-1 (LFA-L CD11a/CD18). Unlike ICAM-1 and ICAM-2. ICAM-3 is constitutively expressed at high levels on resting leucocytes. We investigated the expression and function of ICAM-3 in normal skin (n= 5), as well as its expression in psoriasis (n= 4). atopic eczema (n= 4), allergic (rhus) contact dermatitis (n=3). and cutaneous T-cell lymphoma (CTCL. n=2). Five-micrometre cryostat sections of skin were stained using monoclonal antibodies to ICAM-3 and A well characterized immunoperoxidase technique. In normal skin. ICAM-3 was expressed by all cutaneous leucocytes hut most striking was the strong expression of ICAM-3 by Langerhans cells within both epidermis and dermis. This observation was confirmed by double-labelling with CD1a and negative staining with an IgG1 isotype control. In psoriasis, atopic eczema, allergic contact dermatitis, and CTCL. ICAM-3 was co-expressed on all CD1a⁺ cells, although, in psoriasis, the intensity of ICAM-3 expression was reduced. Functional blocking experiments were performed to determine whether the observed ICAM-3 expression on Langerhans cells was functionally important in antigen presentation. CD4⁺ T cells were prepared from peripheral blood and 10⁵ CD4⁺ T cells combined with 10⁵ epidermal cells harvested from keratome biopsies of normal skin of an individual allogeneic to the T-cell donor. Addition of 50 μg anti-ICAM-3 to the co-culture resulted in a consistent (50%) reduction in degree of alloantigen presentation by Langerhans cells to T cells. Inhibition was 77% of that produced by the addition of anti-LFA-1. These data indicate that ICAM-3 is constitutively expressed by Langerhans cells and is a major ligand for LFA-1 on CD4⁺ T cells during their response to Langerhans cells. Because fresh Langerhans ceils constitutively express little ICAM-1. whereas ICAM-3 is constitutively expressed at high levels, it would appear that 1CAM-3 is the dominant functional ICAM on in situ Langerhans cells in the normal epidermis.     

IMMUNE MECHANISMS IN ATOPIC DERMATITIS: STUDIES AND HYPOTHESIS

The pathogenesis of atopic dermatitis remains uncertain. The aim of this study was to correlate blood and skin findings with respect to analysis of immunoregulatory T cells in 18 patients with severe atopic dermatitis. Circulating T lymphocytes were characterised by flow cytometry, and in situ infiltrates of acute skin lesions identified by the immunoperoxidase technique. Analysis of peripheral blood T lymphocyte sub-sets failed to reveal any difference from normal controls. Skin infiltrates were strongly positive for T11 – the pan T lymphocyte marker. The majority of these cells both in the dermis and epidermis were of the T4 helper-inducer sub-set, while a smaller proportion of cells were of the T8 suppressor- cytotoxic T cell sub-set. T6 positive Langerhans cells were markedly increased in the dermis of affected skin, compared with normal skin. The finding of increased numbers of helper-inducer T lymphocytes' in association with increased numbers of Langerhans cells, which function as antigen presenting cells, suggests a strong immunological mechanism in disease pathogenesis, and may yield knowledge both with respect to origin of skin damage and elevation of IgE.     

In situ identification of mononuclear cells in lichen planus

In this study, the in situ immunological typing of cell populations in lichen planus was attempted. T lymphocytes and suppressor/cytotoxic subsets, B lymphocytes, macrophages, immunocytes and Langerhans' cells were studied by one or more technical parameters and semiquantitative assessment of T cell populations were carried out. A critical evaluation of assays for T cell characterization was also attempted. T cells were found predominant in lichen planus infiltrate but macrophages were also many. Langerhans' cells were increased in the epidermis compared to normal skin and contact dermatitis.     

Allergic and toxic contact dermatitis: inflammatory cell subtypes in epicutaneous test reactions

Histochemical and immunohistochemical techniques were used to identify T lymphocytes, mononuclear phagocytes and plasma cells in situ from allergic and toxic epicutaneous test reactions. Intraccllular α-naphthyl acetate esterase (ANAE), endogenous peroxidase and immunoglobulin were used as markers for inflammatory cells. In allergic contact dermatitis 76 ± 7% of all cells were ANAE-positiveT lymphocytes, 13 ± 6% mononuclear phagocytes and 12 ± 6%), ANAE-negative cells. In toxic skin lesions the corresponding values were 64 ± 20%, 18 ± 15% and 18 ± 6%, respectively. There were no statistically significant differences between the allergic and toxic skin reactions. The basic reaction type in allergic and toxic contact dermatitis seems to be similar, with possibly some qualitative and quantitative differences.     

Abnormal epidermal barrier in the pathogenesis of contact dermatitis

A crucial role of the epidermal permeability barrier is obvious in contact dermatitis. An intact skin barrier prevents the penetration of harmful substances into the skin. Irritants and allergens that stay on the skin surface and come into contact with the stratum corneum only do not harm the skin. After disruption of the skin barrier, however, irritants may penetrate into the living epidermal layers, injure the keratinocyte membrane, and release cytokines, which leads to inflammation and to irritant contact dermatitis. The skin barrier is often disrupted by chronic exposure to water plus detergents, solvents, or other irritants. A disrupted barrier in irritant contact dermatitis also allows for the penetration of allergens. Allergens may come into contact with Langerhans and T cells, induce immunological reactions, and cause inflammation, which results in allergic contact dermatitis. Treatments in contact dermatitis should restore the skin barrier to prevent relapse of the disease. Topical corticosteroids, most often used in treating contact dermatitis, reduce immunological reactions and inflammation but do not lead to a complete barrier repair. Skin barrier repair is more complete after treatment with calcineurin inhibitors and bland lipid-based emollient; therefore, these preparations should be preferred for long-term treatment of contact dermatitis.