Human Allergic Contact Dermatitis Research Articles

Expression of COUP‐TF‐interacting protein 2 (CTIP2) in human atopic dermatitis and allergic contact dermatitis skin

Chicken ovalbumin upstream promoter-transcription factor-interacting protein 2 (CTIP2) is a transcriptional regulator that is highly expressed in skin during mouse development, as well as in proliferating cells of adult mouse skin. We investigated expression of CTIP2 along with proliferation marker Ki-67 in normal human skin, and in skin from atopic dermatitis (AD), and in allergic contact dermatitis (ACD) samples by immunohistochemistry (IHC). We discovered for the first time that CTIP2 was expressed in proliferating basal and suprabasal layer in normal human epidermis. CTIP2 expression was dramatically increased in the epidermis from the AD and ACD samples compared with normal samples, and was labelled in both proliferating basal and suprabasal layers. Altogether our results suggest that CTIP2 expression could be linked to disease progression and/or maintenance in AD and ACD patients.

Th17/Tc17 infiltration and associated cytokine gene expression in elicitation phase of allergic contact dermatitis

Allergic contact dermatitis (ACD) is a typical delayed-type hypersensitivity to sensitizing haptens mediated by T cells. Th1/Tc1 cells are currently considered to be the primary effectors in ACD. There is little information concerning the role played in ACD in humans by Th17/Tc17 cells, a recently defined subpopulation of effector T cells. In the present report we attempted to characterize Th17/Tc17 cells in the infiltrates of the skin in the elicitation phase of ACD. Th17 as well as Th1/Th2 cytokine gene expression was examined by semiquantitative real-time polymerase chain reaction in paired samples of positive patch test biopsies and normal skin from 11 patients allergic to nine different allergens. The in situ characterization of interleukin (IL)-17-producing cells was carried out using anti-RORC and anti-T-cell subset antibodies by double immunofluorescence. Compared with normal paired skin samples, gene expression of transcription factor for human Th17 cells, RORC, and Th17-related cytokines IL-17A, IL-17F and IL-23 was significantly increased in positive patch test biopsies. The mRNA for interferon-gamma and IL-4 was also increased. In the dermal infiltrates, about 20% of the infiltrating cells were IL-17-producing cells as they expressed RORC, and such RORC-expressing cells were detected in both CD4+ (approximately 30%) and CD8+ (approximately 20%) subsets. This is the first demonstration of Th17/Tc17 cells in the elicitation phase of human ACD, showing that they are a regular participant in the immunopathology of this common allergic reaction regardless of the nature of the triggering allergen.

Investigation of the Dermal Sensitizing Potential of Traditional Medical Extracts in Local Lymph Node Assays

Traditional medical extracts are commonly used as complex mixtures, which may contain naturally occurring contact sensitizers. In this investigation, the mice local lymph node assay (LLNA) was performed to evaluate the dermal sensitization potential of Myrrh, Borneolum, Olibanum, Moschus and Cassia Bark, which are widely used in topical traditional medication. In the radioactive LLNA, the stimulation index (SI) values were calculated for each medical extract. Myrrh, Borneolum, Olibanum and Moschus induced dose-dependent cell proliferation and SI was more than 3. Cassia Bark showed no positive response over the range of test concentrations. In the flow cytometry analysis, the total number of CD3(+), CD4(+), and CD8(+) cells in local lymph nodes was increased in Moschus-, Olibanum-, Myrrh- and Borneolum-treated mice. The ratio of the B220(+)/CD3(+) (B/T cell ratio) and the percentage of I-A(k+) cells that was also positive for the CD69 marker (I-A(k+)/ CD69(+)) were increased in the Moschus-, Olibanum- and Myrrh-treated mice. However, no ofbvious change was observed in Borneolum-treated mice. Cassia Bark did not induce changes in the lymphocyte subpopulations. These results indicate that Moschus, Olibanum and Myrrh can be regarded as sensitizers, and Borneolum regarded as an irritant. Cassia Bark is neither a sensitizer nor an irritant. The combination of radioactive and flow cytometric LLNA can be used for the prediction of sensitizing potential of medical extracts which lead to allergic contact dermatitis in humans.

IL-23 and T H17-mediated inflammation in human allergic contact dermatitis

IL-17-producing T(H) (T(H)17) cells are key mediators of chronic inflammation in mice. Recent studies have implicated T(H)17-mediated inflammation in the pathogenesis of human autoimmune diseases; however, the involvement of T(H)17 cells in allergic disorders remains largely elusive. To investigate T(H)17-mediated inflammation in human beings with allergic contact dermatitis; in particular, the innate response of keratinocytes to contact allergen, the induction of allergen-specific T(H)17 cells, and the presence of T(H)17-related effector cells in inflamed skin. Human keratinocytes were stimulated with nickel in vitro followed by measurements of IL-23 and IL-12 production by quantitative PCR and ELISA. Allergen-specific memory T cells from the blood of individuals with nickel allergy and healthy controls were identified and characterized by using a short-term ex vivo assay. Nickel patch test lesions and normal skin were analyzed for the expression of T(H)17-related cells and molecules by using immunohistochemistry. Keratinocytes were found to produce IL-23, but no detectable IL-12, in a response to nickel stimulation. Memory T cells isolated from peripheral blood of individuals with nickel allergy, but not healthy controls, contained T(H)17 and T(H)1 cells proliferating in response to nickel-pulsed DCs. Inflamed skin of nickel-challenged allergic individuals contained infiltrating neutrophils and cells expressing IL-17, IL-22, CCR6, and IL-22R. Our results demonstrate the involvement of T(H)17-mediated immunopathology in human allergic contact dermatitis, including both innate and adaptive immune responses to contact allergens.

Human Natural Killer T Cells Infiltrate into the Skin at Elicitation Sites of Allergic Contact Dermatitis

The purpose of this study is to identify invariant natural killer T cells (NKT cells) in cellular infiltrate of human allergic contact dermatitis (ACD) skin challenge sites. Skin biopsy specimens were taken from positive patch test reactions from 10 different patients (9 different allergens) and studied by immunochemistry, real-time PCR, nested PCR, and in situ hybridization to identify NKT cells and the cytokines associated with this cell type. Invariant NKT cells were identified in all the 10 skin biopsy specimens studied, ranging from 1.72 to 33% of the cellular infiltrate. These NKT cells were activated in all cases, as they expressed cytokine transcripts for IFN-gamma and IL-4. Invariant NKT cells are present in ACD, regardless of the allergen that triggers the reaction, and are in an activated state. We conclude that innate immunity plays a role in late phases of type IV hypersensitivity reactions and may be responding to self-lipids released during allergic inflammation. These data complement the previous work by other investigators that suggest that NKT cells are important in the early cellular response during primary immune responses to allergens. Herein, it is demonstrated that NKT cells are constantly present during the late elicitation phase of human type IV hypersensitivity reactions.

Quantitative relationships between patch test reactivity and use test reactivity: an overview

Use tests such as the provocative use test (PUT) or repeated open application test (ROAT) have been created to better understand the clinical significance of patch test results. It has been suggested that since these tests typically utilize only one substance at a time and avoid occlusion, they minimize the occurrence of irritation and false positives and, thus, are more reflective of real-life exposure to an allergen. In this analysis, we compare and analyze different studies comparing patch test and use test reactivity. With regard to colophony, cinnamic aldehyde, methyldibromo glutaronitrile, 5-chloro-2-methyl-4-isothiazolin-3-one and 2-methyl-4-isothiazolin-3-one, and isoeugenol, increased patch test sensitivity resulted in increased use test sensitivity. However, this was not true for formaldehyde or chromium. The reason for the latter allergens’ divergence from the trend is not yet understood. Additionally, we note the presence of an increasing slope in the relationship between use test reactivity and minimum eliciting concentration on patch testing for methyldibromo glutaronitrile. Expansion of databases relating serial dilution patch test reactivity and use test data should aid dermatologic management, public health policy, and an understanding of the complexity of allergic contact dermatitis in humans.

Serotonin Activates Human Monocytes and Prevents Apoptosis

Monocytes play a critical role in chronic atopic dermatitis (AD) and are the primary leukocytes that interact with activated platelets. Although activated platelets release a variety of mediators, the role of platelets in cutaneous allergic inflammation remains unclear. Serotonin (5-hydroxytryptamine, 5-HT) is one of the prototypic mediators produced by activated platelets. We examined the effect of 5-HT on the function and lifespan of human monocytes. Normal human monocytes treated with 5-HT exhibited upregulated expression of costimulatory molecules, enhanced capacity to produce cytokines following lipopolysaccharide treatment, and to stimulate allogeneic CD4+ T cells. 5-HT also attenuated the apoptosis in normal human monocytes in a dose-dependent manner. The plasma levels of 5-HT were increased in patients with AD compared with controls and correlated with the SCORAD index. 5-HT also inhibited monocyte apoptosis in these patients. 5-HT upregulated Bcl-2 and Mcl-1, and inhibited the activation of caspase-3. The effects of 5-HT on monocyte apoptosis were mediated by the 5-HT1 and/or 5-HT7 receptors. 5-HT and a 5-HT(1/6/7)-receptor agonist induced phosphorylation of extracellular signal-regulated kinase1/2 and activation of nuclear transcription factor-kappaB. These findings support that 5-HT activates monocytes and inhibits apoptosis, allowing them to remain in the tissue and contribute to chronic inflammation.

"Serotonergic Mechanisms in Human Allergic Contact Dermatitis

Expression of serotonin (5-hydroxytryptamine; 5-HT), 5-HT receptors 1A (5-HT1AR) and 2A, and serotonin transporter protein (SERT) was studied in positive epicutaneous reactions to nickel sulphate in nickel-allergic patients, at 72 h post-challenge with the antigen. In addition, the effects of 5-HT2AR agonist 2,5-dimethoxy-4-iodoamphetamine (DOI), and the selective serotonin reuptake inhibitors (SSRIs) citalopram and fluoxetine, were tested on nickel-stimulated peripheral blood mononuclear cells from nickel-allergic patients, regarding their proliferation and interleukin (IL)-2 production, as well as the effect of these SSRIs on a murine Langerhans' cell-like line (XS52), regarding its IL-1beta production. Serotonin-positive platelets were increased in the inflamed skin compared with control skin. A decrease (p <0.01) in 5-HT1AR-positive mononuclear cells was evident in the eczematous skin compared with control skin, whereas 5-HT2AR- and SERT-positive cells were increased (p <0.001 for both) in the eczematous skin. Treatment of nickel-stimulated peripheral blood mononuclear cells with 5x10(-5) mol/l of DOI inhibited (p <0.01) the proliferation of nickel-stimulated peripheral blood mononuclear cells, while no effect was found regarding IL-2 production. Citalopram at 10(-6) mol/l tended to inhibit the production of IL-1beta by the XS52 cell line. These results indicate the implication of the serotonergic system in the contact allergic reaction.

Vasoactive intestinal polypeptide inhibits the established allergic contact dermatitis in humans.

There is increasing evidence indicating that the nervous system influences the immune response. In the present study the potential immunomodulatory role of vasoactive intestinal polypeptide (VIP) in established allergic contact dermatitis in humans was investigated. Positive patch-test reactions were elicited by application of nickel sulphate for 48 h. VIP was applied under patch-test conditions after another 24-h period. The test areas were measured before and 24 h after application of VIP and biopsy specimens were taken for immunohistochemistry. After application of VIP at 10(-5) mol/L, there was a significant reduction in the diameter of the test reaction. In addition, there was a reduction in the number of Leu 3a+ cells. The influence of VIP on the proliferative response of peripheral blood mononuclear cells from nickel-allergic subjects to nickel sulphate was also tested. The cells were cultured for 6 days and VIP was added after 3 days. There was no effect on the proliferative response. However, when VIP was added at 10(-6) and 10(-5) mol/L, a higher level of interferon gamma was found in the nickel-treated cell cultures compared to the controls. In conclusion, VIP may have an inhibitory effect on established allergic contact dermatitis. This inhibitory effect is possibly mediated through an increased production of interferon gamma by peripheral blood mononuclear cells.

CD8+ T Cells Are Effector Cells of Contact Dermatitis to Common Skin Allergens in Mice

Allergic contact dermatitis (ACD) to strong experimental haptens is mediated by specific CD8+ T cells. Here, we show that similar mechanisms occur for weak haptens, which comprise the vast majority of chemicals responsible for human ACD. We used a model of ACD, that is, the contact hypersensitivity reaction, to test for the allergenicity of three weak haptens involved in fragrance allergy. ACD to weak haptens could not be induced in normal mice. In contrast, mice acutely depleted in CD4+ T cells developed a typical ACD reaction to the three weak fragrance allergens that peaked 24 hours after challenge. Priming of CD8+ T cells was observed in draining lymph nodes 5 days after sensitization and development of ACD was associated with the infiltration of activated CD8+ T cells in the challenged skin. CD8+ T cells were effectors of the ACD reaction as in vivo treatment with depleting anti-CD8 mAbs abrogated the ACD responses and as purified CD8+ T cells could adoptively transfer ACD to naive recipients. In conclusion, our data demonstrate a dominant role of CD8+ T cells as initiators of ACD to weak haptens, and suggest that CD8+ T cells may represent potential targets for preventing or treating ACD.

Pyrethrum Allergic Contact Dermatitis in Humans—Real?, Common?, or Not Documented?: An Evidence-Based Approach

Pyrethrum has been reported to produce allergic contact dermatitis in humans. Moreover, it has been speculated that cross reactions occur in ragweed-sensitized people. This review presents the botany, contemporary chemistry, and case reports of alleged allergic contact dermatitis. Our interpretation suggests that the evidence presented in literature does not show that allergic contact dermatitis results from exposure to pyrethrum. Similarly, the data do not suggest cross reactions in ragweed-sensitized people. Changes in the chemical composition of the refined pyrethrins suggest the putative sensitizer is present at a lower level in today's refined extracts than in ground pyrethrum flowers or the extracts used earlier.

Upregulation of the Axonal Growth and the Expression of Substance P and its NK1 Receptor in Human Allergic Contact Dermatitis

Nerve fibers and sensory neuropeptides substance P and calcitonin gene-related peptide (CGRP) have been reported to be involved in allergic contact dermatitis (ACD). In the present study, we investigated the general innervation (using antibody against protein gene product 9.5, PGP 9.5), axonal growth (using antibody against growth associated protein, GAP-43), CGRP, and substance P with its receptor neurokinin 1 (NK1), in positive epicutaneous reactions to nickel sulphate from nickel-allergic patients, at the peak of inflammation, 72 hr after challenge with the antigen. There was an increased (p < 0.01) number of GAP-43 positive fibers in the eczematous compared with control skin, indicating an increased axonal growth already at 72 hr postchallenge. Double staining revealed a coexpression of CGRP and GAP-43 on dermal nerve fibers. There was no difference in the number of substance P and CGRP positive nerve fibers between eczematous and control skin. However, semiquantification analyses showed an increased expression of substance P positive inflammatory cells, being CD3, CD4, or CD8 positive, and NK1R positive inflammatory cells, being tryptase or CD3 positive. These results indicate a contribution of regenerating nerve fibers and substance P to the contact allergic reaction.

Fisiopatologia da dermatite de contato alérgica: papel das células T CD8 efetoras e das células T CD4 regulatórias

A dermatite de contato alérgica (DCA), também conhecida como hipersensibilidade de contato (HSC) é uma das dermatoses inflamatórias mais freqüentes, sendo caracterizada por eritema, pápulas e vesículas, seguidas de ressecamento e descamação. A DCA é induzida pelo contato da pele com substâncias químicas não protéicas denominadas haptenos, e corresponde a uma reação de hipersensibilidade cutânea do tipo tardio, mediada por células T hapteno-específicas. Durante a fase de sensibilização, tanto os precursores de células T CD4+ quanto os de CD8+ são ativados nos linfonodos de drenagem através da apresentação de peptídeos conjugados a haptenos pelas células dendríticas (CD) da pele. A subseqüente exposição de pele ao hapteno em um local a distância induz o recrutamento e ativação de células T específicas no local de provocação, levando à apoptose dos queratinócitos, recrutamento de células inflamatórias e desenvolvimento de sintomas clínicos. Estudos experimentais dos últimos 10 anos demonstraram que, em respostas normais de HSC a haptenos fortes, as células T CD8+ do tipo 1 são efetoras da HSC através de citotoxicidade e produção de IFNgama, enquanto que as células T CD4+ são dotadas de funções de regulação negativa. Estas últimas podem corresponder à população de células T regulatórias CD4+ CD25+ recentemente descritas. Entretanto, em algumas situações, especialmente naquelas em que há um pool deficiente de células T CD8, as células T CD4+ podem ser efetoras da HSC. Estudos em andamento deverão confirmar que a fisiopatologia da DCA em humanos é semelhante à HSC em camundongos, e que a resposta de HSC a haptenos fracos comuns, mais freqüentemente envolvidos na DCA em humanos, é semelhante à descrita para haptenos fortes.

Contribution of CD4+ and CD8+ T-cells in contact hypersensitivity and allergic contact dermatitis

Allergic contact dermatitis, also referred to as contact hypersensitivity, is one the most frequent inflammatory skin diseases, and is characterized by redness, papule and vesicles, followed by scaling and dryness. Allergic contact dermatitis is elicited upon skin contact with nonprotein chemicals, haptens, and corresponds to a cutaneous delayed type hypersensitivity reaction, mediated by hapten-specific T-cells. During the sensitization phase, both CD4+ and CD8+ T-cell precursors are activated in the draining lymph nodes by presentation of haptenated peptides by skin dendritic cells. Subsequent hapten painting on a remote skin site induces the recruitment and activation of specific T-cells at the site of challenge. This leads to apoptosis of keratinocytes, recruitment of inflammatory cells and development of clinical symptoms. Experimental studies from the last 10 years have demonstrated that, in normal contact hypersensitivity responses to strong haptens, CD8+ type 1 T-cells are effector cells of contact hypersensitivity through cytotoxicity and interferon-γ production, while CD4+ T-cells are endowed with downregulatory functions. The latter may correspond to the recently described CD4+CD25+ regulatory T-cell population. However, in some instances, especially when there is a deficient CD8+ T-cell pool, CD4+ T-cells can be effector cells of contact hypersensitivity. Ongoing studies will have to confirm that the pathophysiology of human allergic contact dermatitis is similar to the mouse contact hypersensitivity and that the contact hypersensitivity response to common weak haptens, most frequently involved in human allergic contact dermatitis, is similar to that reported for strong haptens.

Immunopathologic features of allergic contact dermatitis in humans: participation of plasmacytoid dendritic cells in the pathogenesis of the disease?

Contrary to our abundant knowledge about the sensitization phase of human contact hypersensitivity, little is known about the cell types orchestrating the effector phase. In order to address this issue, we phenotypically analyzed biopsies from 72 h epicutaneous patch test reactions (n=10) and normal human skin (n=5) for the presence of various leukocyte differentiation antigens. The inflammatory infiltrate was dominated by CD3+/CD4+ T cells with approximately 30% of the cells coexpressing CD25 and CTLA-4, a phenotype consistent with either activated effector or regulatory T cells. In our search for professional antigen-presenting cells, we were surprised to find not only sizeable numbers of CD1a+ dendritic cells and CD1c+ dendritic cells, but also of CD123+, CD45RA+, BDCA-2+, CLA+, and CD62L+ plasmacytoid dendritic cells. Although virtually absent in normal human skin, these cells were detectable already 6 h after hapten challenge and were often found in close proximity to CD56+ natural killer cells, indicative of a functional interaction between these cell types. The detailed knowledge of the cellular composition of the inflammatory infiltrate in allergic contact dermatitis and its kinetics should form the basis for the investigation of the immunologic and molecular events operative in the perpetuation and resolution of the eczematous response.

Topical pimecrolimus in the treatment of human allergic contact dermatitis

Contact dermatitis is a common clinical problem, with prevalent sensitizers being cosmetics, metals, medicines, and plants. Plants of the Toxicodendron species cause allergic contact dermatitis (ACD) in 50% to 70% of the population. Pimecrolimus is an ascomycin macrolactam developed for the treatment of inflammatory skin diseases and approved by the US Food and Drug Administration for atopic dermatitis. There are studies supporting the effectiveness of macrolactams when administered before antigen challenge, but there are no studies describing the effectiveness of these drugs in the treatment of established human ACD. To investigate the effect of topical pimecrolimus in the treatment of Toxicodendron-induced ACD once rash is evident. Poison ivy tincture was applied to the bilateral anterior forearms of 12 subjects with Finn Chambers (Allerderm Diagnostic Products, Petaluma, CA). After dermatitis was evident, volunteers treated each arm twice daily with either 1% topical pimecrolimus cream or placebo in a blinded fashion. Outcomes measured were a dermatitis grading score and time to rash and itch resolution. The median +/- SEM time for rash resolution was 16.55 +/- 1.59 days in the treatment group and 16.27 +/- 1.82 days in the placebo group (P = 0.601). The median time for itch resolution was 4.73 +/- 1.56 days in the treatment group and 4.91 +/- 1.59 days in the placebo group (P = 0.167). The average dermatitis score was 2.26 +/- 0.17 in the treatment group and 2.32 +/- 0.15 in the placebo group (P = 0.62). The application of topical pimecrolimus is ineffective in the treatment of ongoing Toxicodendron-induced ACD.

Environmental persistence of chemicals and their carcinogenic risks to humans

A “chemical population”-based investigation of xenobiotics (i.e. a sample of 10,000 chemicals representative of agents in commerce, industry, and the environment, both synthetic and natural) that have the potential for ecotoxicity because of their persistence in the environment and their potential association with carcinogenic risks to humans was undertaken. The analyses revealed a statistically significant association between resistance to environmental biodegradation and the prevalence of chemical with the potential to induce systemic toxicity and cancer. On the other hand, there was no association between biopersistence and the potential for inducing toxicities unrelated to carcinogenesis, e.g. allergic contact dermatitis in humans and sensory irritation in mice.

SAR modeling: effect of experimental ambiguity.

The applicability of SAR (structure-activity relationship) techniques to data obtained using high throughput screening (HTS) and toxicogenomic techniques is explored. The reason for this study derives from the fact that for economical and time considerations HTS bioassays may consist of single determinations, i.e. lack of duplication. This introduces an element of uncertainty. Using two different data bases of fairly complex biological phenomena (allergic contact dermatitis in humans and the induction of mutations in Salmonella), it is demonstrated that the resulting SAR models can tolerate up to 20% ambiguity in the experimental data.

A Comparative Study of the Expression of Cytotoxic Proteins in Allergic Contact Dermatitis and Psoriasis: Spongiotic Skin Lesions in Allergic Contact Dermatitis Are Highly Infiltrated by T Cells Expressing Perforin and Granzyme B

Recent reports indicate that cytotoxic T cells are critically involved in contact hypersensitivity reactions in animals. In this study we sought to investigate the in vivo expression of cytotoxic granule proteins in the elicitation phase of allergic contact dermatitis in humans. Skin biopsy specimens were obtained from patients with allergic contact dermatitis (n = 8) and psoriasis (n = 6) and from controls with normal skin (n = 6). Expression of perforin and granzyme B was investigated by in situ hybridization and immunohistochemistry. In contrast to normal skin and psoriasis, a significant enhancement of perforin and granzyme B gene expression and immunoreactivity was observed in the mononuclear cell infiltrate of allergic contact dermatitis. Immunoreactivity for perforin and granzyme B was mainly found in the cytoplasm of lymphocytic cells, which were located in the dense perivascular infiltrate as well as at sites of marked spongiosis in the epidermis. Double immunostaining revealed that both CD4+ and CD8+ T cells are capable of expressing perforin and granzyme B. In conclusion, our data suggest that T-cell-mediated mechanisms involving cytotoxic granule proteins may elicit epidermal cell injury in vivo and thereby strongly contribute to the development of allergic contact dermatitis in humans.

Morphologic and immunohistochemical features of experimentally induced allergic contact dermatitis in Göttingen minipigs.

Many preclinical studies in investigative dermatology are performed preferably in pigs because pig skin is more similar to human skin than is rodent skin. A frequently used model is allergic contact dermatitis (ACD); however, this T-cell-mediated skin condition so far is not well characterized in pigs. The present study is aimed at the evaluation of morphologic and immunohistochemical features of experimentally induced acute ACD in Göttingen minipigs using 2,4-dinitrofluorobenzene (DNFB) as a hapten. Eight minipigs were sensitized with 10% DNFB and challenged 2 weeks later at different sites with 1% DNFB. In addition to clinical examinations, cutaneous blood flow was quantified by laser Doppler velocimetry (Periflux PF3). These examinations were performed before challenge and 8, 24, 48, and 72 hours after challenge. Skin biopsies were taken at the same time points, fixed, sectioned, and stained with Giemsa for histologic evaluation, or with mouse anti-swine monoclonal antibodies (CD1, CD2, CD4, CD5, CD8, CD25, CD45, MHCII) and with one mouse anti-human monoclonal antibody (CD62E) cross-reacting with swine for immunohistochemical evaluation. Positively stained cells were counted per square millimeter of epidermis and dermis by using a video image analyzing system (Videoplan Kontron). Erythema and cutaneous blood flow peaked at 24 hours. The major epidermal changes most pronounced at 48 hours were acanthosis, spongiosis, intracellular edema, exocytosis, and abscesses mainly containing neutrophils and mononuclear cells (MNC). Perivascular infiltrates of MNC as well as neutrophils and eosinophils were the most significant dermal changes, with peak levels at 24-48 hours. In biopsies taken before challenge, CD1+ dendritic cells were found in similar numbers and locations as MHCII+ cells in the epidermis. In the epidermis the maximum CD1+ cell decrease occurred at 24 hours whereas in the dermis the maximum increase in CD1+ stained cells was seen at 72 hours. The dermal infiltrate (CD2+, CD5+, CD25+, and CD45+) was most dense at 48 hours. Between 8 and 48 hours more CD4+ were present than CD8+, cells, whereas at 72 hours CD4+ and CD8+ cells were similar in numbers. These findings closely resemble changes in human ACD. Therefore, DNFB-induced ACD in Göttingen minipigs is considered to be an appropriate animal model to study immunopathologic mechanisms and pharmacologic intervention.