Epidermal class II human lymphocyte antigen expression in atopic dermatitis: a comparison with experimental allergic contact dermatitis

Application of Staphylococcal enterotoxin B on normal and atopic skin induces up-regulation of T cells by a superantigen-mediated mechanism

BACKGROUND

The skin of patients with inflammatory skin diseases such as atopic dermatitis is frequently colonized with Staphylococcus aureus. Colonization with S aureus has been reported to exacerbate atopic dermatitis. Recent studies have demonstrated that S aureus isolated from the skin of patients with atopic dermatitis releases bacterial toxins that act as superantigens. We have previously applied the staphylococcal superantigen staphylococcal enterotoxin B (SEB) on intact human skin and found that the application led to induction of dermatitis.

OBJECTIVE

The purpose of the study was to determine whether superantigen-induced dermatitis is primarily due to a T cell-superantigen-mediated reaction or represents nonspecific cytokine-driven inflammation.

METHODS

We applied SEB, vehicle, and sodium lauryl sulfate on normal skin in healthy (n = 6) and atopic subjects (n = 6) and biopsy specimens were taken from all treated areas. The biopsy specimens from all subjects and peripheral blood from the atopic subjects were analyzed for the T-cell receptor (TCR) Vbeta repertoire with mAbs against TCR Vbeta 2, 3, 8.1, 12, 14, and 17.

RESULTS

From all subjects, both healthy and patients with atopic dermatitis, skin biopsy specimens from SEB-treated areas demonstrated selective accumulation of T cells expressing SEB-reactive TCR Vbeta 12 and 17 (P <.05). This selective up-regulation was not found in the sodium lauryl sulfate-treated areas.

CONCLUSION

Our data strongly support that superantigen-induced T-cell activation is involved in the dermatitis seen after experimental application of SEB on intact skin.

Epidermal HLA-DR and the enhancement of cutaneous reactivity to superantigenic toxins in psoriasis

Streptococcal and staphylococcal superantigens (SAg's) have been implicated in the pathogenesis of inflammatory skin diseases, but the mechanisms by which these toxins act are unknown. The present study assessed the ability of nanogram quantities of topically applied purified toxic shock syndrome toxin-1 (TSST-1), staphylococcal enterotoxin type B, and streptococcal pyrogenic enterotoxin types A and C to induce inflammatory reactions in clinically uninvolved skin of normal controls and subjects with psoriasis, atopic dermatitis, and lichen planus. These SAg's triggered a significantly greater inflammatory skin response in psoriatics than in normal control subjects or in subjects with atopic dermatitis or lichen planus. Surprisingly, skin biopsies did not exhibit the T-cell receptor Vbeta stimulatory properties predicted for SAg-induced skin reactions. By 6 hours after patch testing with SAg's, TNF-alpha mRNA had increased in the epidermis (but not the dermis) in biopsies from psoriatics, compared with controls. Immunohistochemical studies revealed significantly higher HLA-DR expression in keratinocytes from psoriatics than from controls. However, a mutant TSST-1 protein that fails to bind HLA-DR did not elicit an inflammatory skin reaction. These results indicate that keratinocyte expression of HLA-DR enhances inflammatory skin responses to SAg's. They may also account for previous studies failing to demonstrate selective expansion of T-cell receptor Vbetas in psoriatics colonized with SAg-producing Staphylococcus aureus, and they identify a novel T cell-independent mechanism by which SAg's contribute to the pathogenesis of inflammatory skin diseases.

Interferon-gamma promotes exaggerated cytokine production in keratinocytes cultured from patients with atopic dermatitis

Recent studies suggest that skin keratinocytes from patients with atopic dermatitis (AD) and nonatopic subjects differ in their intrinsic ability to respond to proinflammatory stimuli. In this study keratinocyte cultures established from the normal-looking skin of six adult patients with AD and six healthy, nonatopic control subjects were compared in their response to interferon (IFN)-gamma, a potent proinflammatory lymphokine whose expression is increased in chronic AD lesions. Basal expression of IFN-gamma receptor as well as IFN-gamma-induced membrane expression of HLA-DR and intercellular adhesion molecule (ICAM)-1 were evaluated by flow cytometry. Keratinocyte release of IL-1alpha, IL-1 receptor antagonist (IL-1ra), granulocyte-macrophage colony stimulating factor (GM-CSF), and tumor necrosis factor (TNF)-alpha were measured by ELISA on culture supernatants after treatment with IFN-gamma or medium alone. Expression of membrane IFN-gamma receptor was similar in keratinocytes cultured from nonatopic subjects and subjects with AD. IFN-gamma (10 to 500 U/ml) induced comparable levels of membrane HLA-DR and ICAM-1 in both groups of keratinocytes. In contrast, spontaneous release of IL-1alpha, IL-1ra, GM-CSF, and TNF-alpha was increased in the supernatants of unstimulated keratinocytes from patients with AD compared with keratinocytes from control subjects, with IL-1ra and GM-CSF reaching statistically significant difference. Moreover, IFN-gamma-induced release of all the cytokines tested was much higher for keratinocytes from patients with AD, but the IL-1ra/IL-1alpha ratio for the two groups of keratinocytes was not substantially different, either basally or after IFN-gamma stimulation. The results indicate that keratinocytes from patients with AD are hyperresponsive to IFN-gamma in terms of cytokine release.

Characterization of the cutaneous inflammatory infiltrate in canine atopic dermatitis

Sections from lesional atopic, clinically normal atopic, and normal canine skin were investigated by light microscopy and an immunoperoxidase method using monoclonal antibodies specific for canine leukocyte antigens. We confirmed that skin-infiltrating cells of canine atopic dermatitis are constituted of mast cells, dendritic antigen-presenting cells, memory helper T-lymphocytes, low numbers of eosinophils and neutrophils, and rare B-lymphocytes. The presence of epidermal eosinophil microaggregates and clustered Langerhans' cells supports the hypothesis of epidermal allergen contact. The hyperplasia of epidermal T-cells expressing the gamma/delta T-cell receptor appears specific to canine atopic dermatitis compared with its human counterpart. This finding could be explained by an interspecies difference in skin immune systems or, alternatively, by an active participation of these epitheliotropic gamma/delta T-cells in the cutaneous allergic immune response in dogs. The paucity of dermal neutrophils in spontaneous lesions of canine atopic dermatitis is notably different from the neutrophil-rich late-phase reactions provoked by intradermal allergen injections in allergic dogs. This difference in the cellular infiltrate probably results from variations in the immune reaction between single and repeated allergen exposure as well as epidermal versus dermal antigen contact.

Differential in situ cytokine gene expression in acute versus chronic atopic dermatitis

The mechanisms involved in the initiation and maintenance of skin inflammation in atopic dermatitis (AD) are poorly understood. Recent data suggest that the pattern of cytokines expressed locally plays a critical role in modulating the nature of tissue inflammation. In this study, we used in situ hybridization to investigate the expression of interleukin 4 (IL-4), IL-5, and interferon-gamma (IFN-gamma) messenger RNA (mRNA) in skin biopsies from acute and chronic skin lesions of patients with AD. As compared with normal control skin or uninvolved skin of patients with AD, acute and chronic skin lesions had significantly greater numbers of cells that were positive for mRNA, IL-4 (P < 0.01), and IL-5 (P < 0.01), but not for IFN-gamma mRNA expressing cells. However, as compared with acute AD skin lesions, chronic AD skin lesions had significantly fewer IL-4 mRNA-expressing cells (P < 0.01), but significantly greater IL-5 mRNA (P < 0.01). T cells constituted the majority of IL-5-expressing cells in acute and chronic AD lesions. Chronic lesions also expressed significantly greater numbers of activated EG2+ eosinophils than acute lesions (P < 0.01). These data indicate that although acute and chronic AD lesions are associated with increased activation of IL-4 and IL-5 genes, initiation of acute skin inflammation in AD is associated with a predominance of IL-4 expression whereas maintenance of chronic inflammation is predominantly associated with increased IL-5 expression and eosinophil infiltration.

Predominantly indurated reactions to sensitizers may not cause keratinocytes to express HLA-DR

Dermal reactions to primary intradermal or appendageal sensitization are compared to predominantly dermal reactions to standard patch tests and to intradermal antigen tests. In contrast to epicutaneous spongiotic contact dermatitis, HLA-DR was only seen on skin appendages and nearby basal keratinocytes in indurated tissue reactions with the exception of the reactions with focal basal cell layer disruption and an indurated patch test performed one week post angry back syndrome. Other intradermal skin tests showed only minimal epidermal HLA-DR expression despite spongiotic epidermal changes. Predominantly dermal hypersensitivity reactions can be induced by intradermal or epicutaneous routes. They can evoke hypersensitivity responses which do not cause most epidermal keratinocytes to express HLA-DR.

Keratinocyte expression of OKM5 antigen in inflammatory cutaneous disease

Keratinocyte expression of the monocyte/macrophage surface antigens defined by OKM1 and OKM5 antibodies (Ortho Diagnostics) was examined using the peroxidase anti-peroxidase immunohistochemical technique. A range of inflammatory cutaneous disorders were investigated, including lichen planus, psoriasis and atopic dermatitis. Positive suprabasal keratinocyte expression of OKM5 antigen was observed in all disorders, while keratinocyte staining with OKMI antibody was consistently negative. These results provide further evidence that keratinocytes may play an important role in cutaneous immune responses. Furthermore, they are consistent with the recent observation that HLA-DR positive keratinocytes may modulate cutaneous immunological reactions by inducing T-cell unresponsiveness.

Characterization of intercellular adhesion molecule-1 and HLA-DR expression in normal and inflamed skin: modulation by recombinant gamma interferon and tumor necrosis factor

Lymphocytes bind to cultured keratinocytes that are treated with interferon gamma (IFN-gamma) and tumor necrosis factor (TNF). When the lymphocytes are preincubated with antibody to lymphocyte function associated antigen-1 (LFA-1), this adherence is inhibited. Because intercellular adhesion molecule-1 (ICAM-1) is a ligand for LFA-1, we studied the cellular expression of ICAM-1, as well as two other IFN-gamma-inducible antigens, (HLA) human lymphocyte antigens DR and DQ, in both normal and diseased skin. The modulation of these cell surface antigens by IFN-gamma and TNF with the use of short-term organ cultures of skin was compared with isolated keratinocytes grown in a conventional tissue culture system. While in normal skin, keratinocytes did not express HLA-DR, DQ, or ICAM-1, when organ cultures were supplemented with IFN-gamma, rapid induction of keratinocyte ICAM-1 expression occurred after 24 hours; HLA-DR but not DQ expression occurred after 48 hours. TNF also induced keratinocyte ICAM-1 expression (although to a lesser degree than IFN-gamma) but did not induce either keratinocyte HLA-DR or DQ expression. There was good correlation of keratinocyte expression of ICAM-1 and HLA-DR by IFN-gamma and TNF when the epidermis of the organ culture system was compared with the isolated keratinocytes grown in tissue culture. The presence of intraepidermal lymphocytes correlated extremely well with keratinocyte ICAM-1 expression but not with keratinocyte HLA-DR expression in psoriasis, atopic dermatitis, lichen planus, and mycosis fungoides. The intensity of endothelial cell expression of ICAM-1 correlated with the degree of dermal inflammation. We conclude that IFN-gamma, once produced by activated T lymphocytes in the dermis, may be of importance in lymphocyte trafficking in the epidermis by the induction of keratinocyte ICAM-1 expression. The use of the short-term organ culture system, in which there is inducible ICAM-1 expression, provides an experimental bridge between purely in vitro and in vivo investigations to further our understanding of the molecular basis for lymphocyte apposition to keratinocytes in the skin.

Gamma-interferon induced human keratinocyte HLA-DR synthesis: the role of dermal activated T lymphocytes

Experiments were performed to examine the hypothesis that the surface expression of HLA-DR by keratinocytes in certain disease states is conferred by the activity of gamma-interferon, derived from dermal activated T lymphocytes. In vivo studies revealed a spatial relationship between keratinocyte HLA-DR expression and activated T lymphocytes within the dermal inflammatory infiltrate. In vitro studies confirmed that gamma-interferon can induce keratinocyte synthesis of HLA-DR. These results suggest that, in vivo, gamma-interferon produced by activated T lymphocytes induces keratinocyte HLA-DR synthesis and expression.

Products of class II major histocompatibility complex gene subregions are differentially expressed on keratinocytes in cutaneous diseases

Aberrant expression of class II major histocompatibility complex (MHC) subregion antigens by keratinocytes was examined immunohistochemically in a range of cutaneous disorders. Although cell surface expression of human lymphocyte antigen (HLA)-DR was observed, HLA-DQ and HLA-DP were not expressed in any disorder investigated except for allergic contact dermatitis. Epidermal Langerhans cells expressed antigens of all three subregions on the cell surface. Differential expression of class II MHC subregion antigens may be related to tissue levels of gamma-interferon or to different functions of each subregion.