ETAF/interleukin-1 and epidermal lymphocyte chemotactic factor in epidermis overlying an irritant patch test

Redox-modulated pathways in inflammatory skin diseases

Inflammatory skin diseases account for a large proportion of all skin disorders and constitute a major health problem worldwide. Contact dermatitis, atopic dermatitis, and psoriasis represent the most prevalent inflammatory skin disorders and share a common efferent T-lymphocyte mediated response. Oxidative stress and inflammation have recently been linked to cutaneous damage in T-lymphocyte mediated skin diseases, particularly in contact dermatitis. Insights into the pathophysiology responsible for contact dermatitis can be used to better understand the mechanism of other T-lymphocyte mediated inflammatory skin diseases, and may help to develop novel therapeutic approaches. This review focuses on redox sensitive events in the inflammatory scenario of contact dermatitis, which comprise for example, several kinases, transcription factors, cytokines, adhesion molecules, dendritic cell surface markers, the T-lymphocyte receptor, and the cutaneous lymphocyte-associated antigen (CLA). In vitro and animal studies clearly point to a central role of several distinct but interconnected redox-sensitive pathways in the pathogenesis of contact dermatitis. However, clinical evidence that modulation of the skin's redox state can be used therapeutically to modulate the inflammatory response in contact dermatitis is presently not convincing. The rational for this discrepancy seems to be multi-faceted and complex and will be discussed.

A study of skin responses to follow-up, rechallenge and combined effects of irritants using non-invasive measurements

Irritant contact dermatitis is a common clinical problem. Primary irritation can be easily recognized, but cumulative irritation by daily exposure is hard to be diagnosed and the condition may fail to be clear even away from work. The mechanism of irritant dermatitis produced by repeated or combined exposure to clinical or subclinical doses of irritants is still poorly understood. In order to find out whether the subclinical doses of irritants affect each other by repeated or combined exposure according to their concentrations, non-invasive measurements, transepidermal water loss and laser Doppler flowmetry were used. Sodium lauryl sulfate, sodium hydroxide and benzalkonium chloride were serially diluted and patch-tested with large Finn chambers on Scanpor tape on the back of normal human volunteers and responses were followed up for 7 days. Twice repeated exposure with subclinical doses of irritants at 1 day intervals were also performed. Repeated daily applications for 5 days with subclinical doses of single or premixed irritants were performed to know the combined irritating effect. The irritant response was well correlated to the concentration of the irritants. However, increased response was not observed when subclinical doses were rechallenged on the previously patch tested sites. Twice-repeated exposure of subclinical doses of irritants increased skin irritancy when measured by transepidermal water loss and laser Doppler flowmetry. Some correlation and some discrepancies were observed between different evaluation methods in combined and repeated application tests with irritants of subclinical doses. Responses of skin irritancy induced by subclinical doses showed somewhat different pattern from that given strong irritants.(ABSTRACT TRUNCATED AT 250 WORDS)

The modulation of skin irritation

Irritant contact dermatitis (ICD) is a multifactorial disease, the onset and modulation of which depend on both endogenous and exogenous factors. Among the former, age, race, site, sex and history of dermatitis may all be important. Such variables can now readily be quantified by objective noninvasive techniques, such as measurement of transepidermal water loss (TEWL). Moreover, effects of irritants on the epidermis are related to the particular chemical properties of each molecule, contributing further to clinical heterogeneity. Release of cytokines and mediators may be initiated by a number of cells, including living keratinocytes and those of the stratum corneum, thus modulating inflammation and repair. Furthermore, differences in mechanisms of inflammation between acute and chronic ICD may exist, the former being characterized predominantly by inflammation, the latter by hyperproliferation and transient hyperkeratosis. These findings may explain the complexity and difficulty of investigating ICD. Better understanding and quantification of these mechanisms may lead to identification of high-risk individuals and more effective prevention and treatment.

Differential patterns of epidermal leukocyte infiltration in patch test reactions to structurally unrelated chemical irritants

In previous studies, we showed that a number of aspects of the histopathology of irritant contact dermatitis are profoundly influenced by the chemical nature of the irritant applied. We report here that this phenomenon also extends to the infiltration of leukocytes into the epidermis. Healthy volunteers were patch tested with the following irritants and their appropriate controls: benzalkonium chloride, sodium lauryl sulphate, croton oil, dithranol, nonanoic acid, and propylene glycol. After visually grading the intensity of the resulting inflammation, biopsies were removed and the major phenotypic classes of leukocytes identified immunocytochemically. Dermal and epidermal cell densities were determined, and the expression of several activation/proliferation antigens studied. We found a similar pattern of cellular infiltration in the dermis of all irritant groups; the densities of most of the cell types rising in line with the intensity of inflammation. Within the epidermis, however, there were marked differences in the patterns of cellular infiltration between the irritant groups, leading to poorer correlations between leukocyte density and visual grading. The greatest disparity occurred between croton oil and nonanoic acid biopsies, the former being characterized by the influx of large numbers of leukocytes, the latter showing remarkably little exocytosis. Infiltration of neutrophils occurred to varying degrees with all irritants, but a disproportionately large number were present in sodium lauryl sulphate biopsies. All control groups showed a rise in CD4+ cells, with distilled water also producing increases in CD11c+ cells and neutrophils. A selective influx of CD25+ cells occurred in the epidermis of both irritant and control groups. Our observations further highlight the heterogeneous nature of irritant contact dermatitis, and confirm previous findings that visually negative control patch tests show marked cellular reactivity.

Phenotypic determination of T-lymphocytes responding to chemotactic stimulation from fMLP, IL-8, human IL-10, and epidermal lymphocyte chemotactic factor

Human T lymphocytes were collected after they had migrated towards N-formyl-methionyl-leukylphenylalanine (fMLP), rIL-8, human IL-10 (hIL-10), and epidermal lymphocyte chemotactic factor (ELCF). They were stained for determination of their phenotype by FACS analysis using anti-CD4, -CD8, -CD18, -CD45R0 and OPD4 antibodies. Human IL-10 increased the percentage of CD8+ T lymphocytes in the migrating cell population by 152% compared with cells migrating towards the medium and decreased the number of CD4+ T lymphocytes by 79%. ELCF increased the number of CD4+ T lymphocytes by 18%, and the number of CD45R0+ T lymphocytes by 52%, while the number of CD8+ T lymphocytes was decreased by 20%. rIL-8 increased the number of CD4+ T lymphocytes and decreased the CD8+ T lymphocytes. The distribution of the different subpopulations of T lymphocytes was not changed significantly by fMLP. The observed changes in the phenotypes did not occur when incubating T lymphocytes with the chemotaxins. Our observations demonstrate that individual chemotactic factors will attract specific subsets of T lymphocytes. They may help to explain the predominance of memory T lymphocytes (CD4R0+, CD4+) in allergic contact dermatitis and certain other skin diseases. They also confirm the results of a recent study, that showed hIL-10 to be selectively chemotactic for CD8+ T lymphocytes.

Differential effects of structurally unrelated chemical irritants on the density of proliferating keratinocytes in 48 h patch test reactions

Alterations in the proliferative capacity of human epidermis following topical exposure to structurally unrelated chemical irritants were investigated, with the aim of improving our understanding of the cellular changes that take place during the development of irritant contact dermatitis (ICD). Healthy volunteers were patch tested for 48 h with the following six irritants and their appropriate vehicle and occlusion controls: 5% sodium lauryl sulphate (SLS), 0.5% benzalkonium chloride, 80% nonanoic acid (NAA), 0.02% dithranol, 0.8% croton oil, and 100% propylene glycol (PG). After the degree of inflammation induced was visually graded, biopsy samples were removed and the dividing keratinocytes were identified immunocytochemically by using the monoclonal antibody Ki-67, with quantification being performed on the basis of the number of positive cells/100 basal keratinocytes. Statistically significant increases in the density of proliferating cells occurred in the reactions to SLS, NAA, and PG, whereas, in contrast, dithranol caused a marked decrease in the number of dividing keratinocytes. Overall, the density of proliferating keratinocytes did not show a linear relationship with the visually assessed intensity of inflammation, indicating that the changes observed were related to the chemical nature of the individual irritants and their specific biochemical interactions with the keratinocytes, rather than being the consequence of a generalized inflammatory response. Differential release of epidermal cytokines and mediators by the six irritants may account for these varying states of keratinocyte proliferation. Application of the Spearman rank coefficient of correlation revealed that the changes in mitotic activity of keratinocytes were unrelated either to the total density of leukocytes infiltrating the epidermis and dermis, or to the individual densities of the major phenotypic classes of inflammatory cells present. This makes it unlikely that the localized release of cytokines by infiltrating leukocytes is, by itself, the primary factor in the alteration in epidermal cell kinetics seen in ICD. Our results provide a further demonstration of the diverse actions of different chemical irritants on human skin and emphasize the need to regard ICD as a heterogeneous disorder.

The immunology of contact dermatitis. A review with special reference to the pathophysiology of eczema

This review summarizes current knowledge of the pathophysiological events which lie behind the development of contact dermatitis. The clinical distinction between allergic and irritant eczema is discussed. New observations are evaluated on our understanding of how allergic and irritant eczema may in many respects be similar, evolving through common physiological pathways of immune inflammation.