Mast Cell-Mediated Reactions In Vivo.

Mast cells are involved in many physiological reactions in which their functions can be very diverse. Models of allergic skin inflammation and systemic anaphylactic reactions in mice are validated methods in which the role of mast cells is well established. In this chapter, we will therefore present protocols for passive cutaneous anaphylaxis and contact hypersensitivity, i.e., models which can be used to identify and characterize the role of mast cells as well as mast cell mediators and receptors in allergic IgE-dependent and IgE-independent skin inflammation, and for passive systemic anaphylaxis, a model ideally suited to characterize the systemic effects of mast cell-derived mediators and mast cell receptors.

Niche- and Gender-Dependent Immune Reactions in Relation to the Microbiota Profile in Pediatric Patients with Otitis Media with Effusion.

Otitis media with effusion (OME) is a common inflammatory disease that primarily affects children. OME is defined as a chronic low-grade inflammation of the middle ear (ME), without any signs of infection and with effusion persisting in the ME for more than 3 months. The precise pathogenesis is, however, not fully understood. Here, we comprehensively characterized and compared the host immune responses (inflammatory cells and mediators) and the overall microbial community composition (microbiota) present in matched middle ear effusion (MEE) samples, external ear canal (EEC) lavages, and nasopharynx (NPH) samples from children with OME. Female patients had significantly increased percentages of T lymphocytes and higher levels of a wide array of inflammatory mediators in their MEE compared to that of male patients, which were unrelated to microbiota composition. The relative abundances of identified microorganisms were strongly associated with their niche of origin. Furthermore, specific inflammatory mediators were highly correlated with certain bacterial species. Interestingly, some organisms displayed a niche-driven inflammation pattern in which presence of Haemophilus spp. and Corynebacterium propinquum in MEE was accompanied by proinflammatory mediators, whereas their presence in NPH was accompanied by anti-inflammatory mediators. For Turicella and Alloiococcus, we found exactly the opposite results, i.e., an anti-inflammatory profile when present in MEE, whereas their presence in the the NPH was accompanied by a proinflammatory profile. Together, our results indicate that immune responses in children with OME are highly niche- and microbiota-driven, but gender-based differences were also observed, providing novel insight into potential pathogenic mechanisms behind OME.

Exacerbated and prolonged inflammation impairs wound healing and increases scarring.

Altered inflammation in the early stage has long been assumed to affect subsequent steps of the repair process that could influence proper wound healing and remodeling. However, the lack of explicit experimental data makes the connection between dysregulated wound inflammation and poor wound healing elusive. To bridge this gap, we used the established rabbit ear hypertrophic scar model for studying the causal effect of dysregulated inflammation. We induced an exacerbated and prolonged inflammatory state in these wounds with the combination of trauma-related stimulators of pathogen-associated molecular patterns from heat-killed Pseudomonas aeruginosa and damage-associated molecular patterns from a dermal homogenate. In stimulated wounds, a heightened and lengthened inflammation was observed based on quantitative measurements of IL-6 expression, tissue polymorphonuclear leukocytes infiltration, and tissue myeloperoxidase activity. Along with the high level of inflammation, wound healing parameters (epithelial gap and others) at postoperative day 7 and 16 were significantly altered in stimulated wounds compared to unstimulated controls. By postoperative day 35, scar elevation of stimulated wounds was higher than that of control wounds (scar elevation index: 1.90 vs. 1.39, p < 0.01). Moreover, treatment of these inflamed wounds with Indomethacin (at concentrations of 0.01, 0.1, and 0.4%) reduced scar elevation but with adverse effects of delayed wound closure and increased cartilage hypertrophy. In summary, successful establishment of this inflamed wound model provides a platform to understand these detrimental aspects of unchecked inflammation and to further test agents that can modulate local inflammation to improve wound outcomes.

A Listeria monocytogenes-based vaccine that secretes sand fly salivary protein LJM11 confers long-term protection against vector-transmitted Leishmania major.

Cutaneous leishmaniasis is a sand fly-transmitted disease characterized by skin ulcers that carry significant scarring and social stigmatization. Over the past years, there has been cumulative evidence that immunity to specific sand fly salivary proteins confers a significant level of protection against leishmaniasis. In this study, we used an attenuated strain of Listeria monocytogenes as a vaccine expression system for LJM11, a sand fly salivary protein identified as a good vaccine candidate. We observed that mice were best protected against an intradermal needle challenge with Leishmania major and sand fly saliva when vaccinated intravenously. However, this protection was short-lived. Importantly, groups of vaccinated mice were protected long term when challenged with infected sand flies. Protection correlated with smaller lesion size, fewer scars, and better parasite control between 2 and 6 weeks postchallenge compared to the control group of mice vaccinated with the parent L. monocytogenes strain not expressing LJM11. Moreover, protection correlated with high numbers of CD4(+), gamma interferon-positive (IFN-γ(+)), tumor necrosis factor alpha-positive/negative (TNF-α(+/-)), interleukin-10-negative (IL-10(-)) cells and low numbers of CD4(+) IFN-γ(+/-) TNF-α(-) IL-10(+) T cells at 2 weeks postchallenge. Overall, our data indicate that delivery of LJM11 by Listeria is a promising vaccination strategy against cutaneous leishmaniasis inducing long-term protection against ulcer formation following a natural challenge with infected sand flies.

Nonallergenic urushiol derivatives inhibit the oxidation of unilamellar vesicles and of rat plasma induced by various radical generators.

Urushiols consist of an o-dihydroxybenzene (catechol) structure and an alkyl chain of 15 or 17 carbons in the 3-position of a benzene ring and are allergens found in the family Anacardiaceae. We synthesized various veratrole (1,2-dimethoxybenzene)-type and catechol-type urushiol derivatives that contained alkyl chains of various carbon atom lengths, including -H, -C1H3, -C5H11, -C10H21, -C15H31, and -C20H41, and investigated their contact hypersensitivities and antioxidative activities. 3-Decylcatechol and 3-pentadecylcatechol displayed contact hypersensitivity, but the other compounds did not induce an allergic reaction, when the ears of rats were sensitized by treatment with the compounds every day for 20 days. Catechol-type urushiol derivatives (CTUDs) exerted very high radical-scavenging activity on the 1,1-diphenyl-2-picrylhydrazyl radical and inhibited lipid peroxidation in a methyl linoleate solution induced by 2,2'-azobis(2,4-dimethylvaleronitrile) (AMVN). However, veratrole-type urushiol derivatives did not scavenge or inhibit lipid peroxidation. CTUDs also acted as effective inhibitors of lipid peroxidation of the egg yolk phosphatidylcholine large unilamellar vesicle (PC LUV) liposome system induced by various radical generators such as AMVN, 2,2'-azobis(2-amidino-propane) dihydrochloride, and copper ions, although their efficiencies differed slightly. In addition, CTUDs suppressed formation of cholesteryl ester hydroperoxides in rat blood plasma induced with copper ions. CTUDs containing more than five carbon atoms in the alkyl chain showed excellent lipophilicity in a n-octanol/water partition experiment. These compounds also exhibited high affinities to the liposome membrane using the ultrafiltration method of the PC LUV liposome system. Therefore, CTUDs seem to act as efficient antioxidative compounds against membranous lipid peroxidation owing to their localization in the phospholipid bilayer. These results suggest that nonallergenic CTUDs act as antioxidants to protect against oxidative damage of cellular and subcellular membranes.

Human papillomavirus e7 oncoprotein transgenic skin develops an enhanced inflammatory response to 2,4-dinitrochlorobenzene by an arginase-1-dependent mechanism.

We have shown that the expression of human papillomavirus type 16 E7 (HPV16.E7) protein within epithelial cells results in local immune suppression and a weak and ineffective immune response to E7 similar to that occuring in HPV-associated premalignancy and cancers. However, a robust acute inflammatory stimulus can overcome this to enable immune elimination of HPV16.E7-transformed epithelial cells. 2,4-Dinitrochlorobenzene (DNCB) can elicit acute inflammation and it has been shown to initiate the regression of HPV-associated genital warts. Although the clinical use of DNCB is discouraged owing to its mutagenic potential, understanding how DNCB-induced acute inflammation alters local HPV16.E7-mediated immune suppression might lead to better treatments. Here, we show that topical DNCB application to skin expressing HPV16.E7 as a transgene induces a hyperinflammatory response, which is not seen in nontransgenic control animals. The E7-associated inflammatory response is characterized by enhanced expression of Th2 cytokines and increased infiltration of CD11b(+)Gr1(int)F4/80(+)Ly6C(hi)Ly6G(low) myeloid cells, producing arginase-1. Inhibition of arginase with an arginase-specific inhibitor, N(omega)-hydroxy-nor-L-arginine, ameliorates the DNCB-induced inflammatory response. Our results demonstrate that HPV16.E7 protein enhances DNCB-associated production of arginase-1 by myeloid cells and consequent inflammatory cellular infiltration of skin.

Systemic immunogenicity of para-Phenylenediamine and Diphenylcyclopropenone: two potent contact allergy-inducing haptens.

p-Phenylenediamine (PPD) and Diphenylcyclopropenone (DPCP) are two potent haptens. Both haptens are known to cause delayed-type hypersensitivity, involving a cytokine response and local infiltration of T-cell subpopulations, resulting in contact dermatitis. We investigated the systemic immune effects of PPD and DPCP, two relatively unexplored skin allergens. The dorsal sides of the ears of BALB/c mice were exposed to PPD or DPCP (0.1% w/v or 0.01% w/v), or vehicle alone. Mice were treated once daily for 3 days (induction period) and subsequently twice per week for 8 weeks. Local and systemic immune responses in the auricular and pancreatic lymph nodes, spleen, liver, serum, and ears were analyzed with cytokine profiling MSD, flow cytometry, and qPCR. Ear swelling increased significantly in mice treated with 1% PPD, 0.01% DPCP or 0.1% DPCP, compared with vehicle treatment, indicating that the mice were sensitized and that there was a local inflammation. Auricular lymph nodes, pancreatic lymph nodes, spleen, and liver showed changes in regulatory T-cell, B-cell, and NKT-cell frequencies, and increased activation of CD8(+) T cells and B cells. Intracellular cytokine profiling revealed an increase in the IFN-γ- and IL-4-positive NKT cells present in the liver following treatment with both haptens. Moreover, we saw a tendency toward a systemic increase in IL-17A. We observed systemic immunological effects of PPD and DPCP. Furthermore, concentrations too low to increase ear thickness and cause clinical symptoms may still prime the immune system. These systemic immunological effects may potentially predispose individuals to certain diseases.

Complementary methods for contact hypersensitivity (CHS) evaluation in mice.

Contact hypersensitivity (CHS) is an experimental model of allergic contact dermatitis (ACD) that can be studied in mice. For CHS responses, mice are immunized by painting with a reactive hapten, such as 1-fluoro-4,6-dinitrobenzene (DNFB), on the shaved abdominal and chest skin. Subsequently, the ears are challenged with diluted hapten, eliciting 'hypersensitive' ear-swelling reactions, which can be measured with a micrometer. In this manuscript we present complementary methods that can be used to evaluate CHS in mice that include: ear weight, vascular permeability, myeloperoxidase (MPO) activity, IFN-γ concentration in ear extracts and also IFN-γ production by auricular lymph node cells (ELNC). The biochemical evaluation of CHS can be also supported by proliferation assay, measurement of IFN-γ production by skin-draining lymph node cells employing ELISA test and by evaluation of IFN-γ(+) TCRαß CD8 cells with the use of flow cytometry.

The endogenous cytokine profile and nerve fibre density in mouse ear Leishmania major-induced lesions related to nociceptive thresholds.

Several reports have shown that cutaneous leishmaniasis lesions are painless, suggesting that Leishmania infection interferes with pain perception. Comparisons of inflammation-induced hyperalgesia between BALB/c and C57BL/6 mice have been little explored in the literature, and comparative data regarding nociception in leishmaniasis are non-existent. In susceptible BALB/c mice and resistant C57BL/6 mice that were intradermally inoculated with a low dose of Leishmania major in the ear, we investigated the variation in nociception over a 12-wk period post-infection and this variation's association with the structure of nerve fibres and the presence of endogenous cytokines that are classically considered hyper- or hypo-nociceptive. Infected BALB/c mice presented susceptibility and severe lesions. Infected C57BL/6 mice exhibited resistance and healing lesions. The immune response involved pro- and anti-inflammatory cytokine secretion, respectively. The infection-induced hypoalgesia in BALB/c mice after wks 9 was accompanied by decreased levels of IL-6 and IL-10 in ear tissue with intact nerves. C57BL/6 mice showed short-lived hyperalgesia in wks 2, which was related to increased local levels of IL-6, KC/CXCL-1, TNF-α and IL-10 and a decrease in nerve density. The increase in pro-inflammatory cytokine IL-6, KC/CXCL-1 and TNF-α levels during hyperalgesia suggested a role for these mediators in afferent nerve sensitisation, which was secondary to the inflammatory damage of nerve fibres stained by PGP 9.5. In contrast, the mechanisms of hypoalgesia may include the downregulation of cytokines, the preservation of the structure of nerve endings, and as yet uninvestigated unidentified differences in neurotransmitter release or a direct role of the parasites in the context of the progressive and permissive inflammatory response of BALB/c mice.

Construction and phenotypic analysis of mice carrying a duplication of the major histocompatibility class I (MHC-I) locus.

Copy number variation (CNV) has been associated increasingly with altered susceptibility to human disease. Large CNVs are likely to incur disease risk or resilience via predictable changes in gene dosage that are relatively straightforward to model using chromosomal engineering in mice. The classical class I major histocompatibility locus (MHC-I) contains a dense set of genes essential for innate immune system function in vertebrates. MHC-I genes are highly polymorphic and genetic variation in the region is associated with altered susceptibility to a wide variety of common diseases. Here we investigated the role of gene dosage within MHC-I on susceptibility to disease by engineering a mouse line carrying a 1.9-Mb duplication of this region [called Dp(MHC-I)]. Extensive phenotypic analysis of heterozygous (3N) Dp(MHC-I) animals did not reveal altered blood and stem cell parameters, susceptibility to high-fat diet, death by cancer, or contact dermatitis. However, several measures of disease severity in a model of atherosclerosis were improved, suggesting dosage-sensitive modulators of cardiovascular disease. Homozygous Dp(MHC-I)/Dp(MHC-I) mice demonstrated embryonic lethality. These mice serve as a model for studying the consequences of targeted gene dosage alteration in MHC-I with functional and evolutionary implications.

Immunity to sand fly salivary protein LJM11 modulates host response to vector-transmitted leishmania conferring ulcer-free protection.

Leishmania vaccines that protect against needle challenge fail against the potency of a Leishmania-infected sand fly transmission. Here, we demonstrate that intradermal immunization of mice with 500 ng of the sand fly salivary recombinant protein LJM11 (rLJM11) from Lutzomyia longipalpis, in the absence of adjuvant, induces long-lasting immunity that results in ulcer-free protection against Leishmania major delivered by vector bites. This protection is antibody independent and abrogated by depletion of CD4(+) T cells. Two weeks after challenge, early induction of IFN-γ specifically to rLJM11 correlates to diminished parasite replication in protected animals. At this time point, Leishmania-specific induction of IFN-γ in these mice is low in comparison with its high level in non-protected controls. We hypothesize that early control of parasites in a T-cell helper type 1 environment induced by immunity to LJM11 permits the slow development of Leishmania-specific immunity in the absence of open ulcers. Leishmania-specific immunity observed 5 weeks after infection in rLJM11-immunized mice shows a twofold increase over controls in the percentage of IFN-γ-producing CD4(+) T cells. We propose LJM11 as an immunomodulator that drives an efficient and controlled protective immune response to a sand fly-transmitted Leishmania somewhat mimicking "leishmanization"-induced protective immunity but without its associated lesions.

Periostin promotes chronic allergic inflammation in response to Th2 cytokines.

Allergic inflammation triggered by exposure of an allergen frequently leads to the onset of chronic inflammatory diseases such as atopic dermatitis (AD) and bronchial asthma. The mechanisms underlying chronicity in allergic inflammation remain unresolved. Periostin, a recently characterized matricellular protein, interacts with several cell surface integrin molecules, providing signals for tissue development and remodeling. Here we show that periostin is a critical mediator for the amplification and persistence of allergic inflammation using a mouse model of skin inflammation. Th2 cytokines IL-4 and IL-13 stimulated fibroblasts to produce periostin, which interacted with αv integrin, a functional periostin receptor on keratinocytes, inducing production of proinflammatory cytokines, which consequently accelerated Th2-type immune responses. Accordingly, inhibition of periostin or αv integrin prevented the development or progression of allergen-induced skin inflammation. Thus, periostin sets up a vicious circle that links Th2-type immune responses to keratinocyte activation and plays a critical role in the amplification and chronicity of allergic skin inflammation.

Cantharidin-induced inflammation in mouse ear model for translational research of novel anti-inflammatories.

The murine model of cantharidin-induced ear inflammation was profiled in detail for its alignment with the human model and to explore the mechanism of anti-inflammatory activity of the macrolide antibiotics, clarithromycin and azithromycin. Ear swelling in CD1 mice persisted for 7 days, with peak intensity at 16 h after inflammation induction. As in humans, cantharidin (12.5 µg/ear) generated macrophage-inflammatory protein (MIP)-2, monocyte chemoattractant protein (MCP)-1, keratinocyte-derived chemokine (KC), interleukin (IL)-6, IL-1ß, and myeloperoxidase (MPO) production, as well as neutrophil accumulation in mouse ear tissue. The tested macrolides, clarithromycin and azithromycin, administered orally (2 × 150 mg/kg) 0.5 h before and 5 h after cantharidin challenge, reduced MIP-2, MCP-1, KC, and MPO concentrations and thereby decreased ear swelling. Our results suggest that cantharidin-induced acute inflammation represents an excellent model for translational research of novel anti-inflammatories.

ONZIN deficiency attenuates contact hypersensitivity responses in mice.

ONZIN is abundantly expressed in immune cells of both the myeloid and lymphoid lineage. Expression by lymphoid cells has been reported to further increase after cutaneous exposure of mice to antigens and haptens capable of inducing contact hypersensitivity (CHS), suggesting that ONZIN has a critical role in this response. Here, we report that indeed ONZIN-deficient mice develop attenuated CHS to a number of different haptens. Dampened CHS responses correlated with a significant reduction in pro-inflammatory IL-6 at the challenge site in ONZIN-deficient animals, compared with wild-type controls. Together the study of these animals indicates that loss of ONZIN impacts the effector phase of the CHS response through the regulation of pro-inflammatory factors.

Prevention of type 1 diabetes by inducing subclinical dermatitis on a small area.

OBJECTIVE: We have previously epidemiologically shown that type 1 diabetes is inversely associated with contact allergy. This finding is intriguing as type 1 diabetes and contact allergy are two completely different diseases, although T cells are involved in both diseases. The objective of this study was therefore to experimentally study the effect of contact allergens on the development of diabetes in non-obese diabetic mice. METHODS: Non-obese diabetic mice 4 weeks of age were separated into seven groups. One group was exposed to tapped water every 14th day, whereas the remaining six groups were split into sensitizations groups or elicitation groups (exposure every 14th day). These groups were then treated with one of the selected contact allergens (PPD or DNCB) or vehicle (AOO). All groups received the sensitizing treatment regime, and hereafter only the elicitation groups were further treated. If the blood glucose reached 14 mM, the mice were considered diabetic and euthanized. Cardiac heart blood was drawn at euthanization, and a Luminex analysis was done on the serum. RESULTS: We showed that repeated application of a low dose of PPD reduced the incidence of diabetes compared to application with water (47% versus 93%, p=0.004). The rest of the groups developed diabetes with a cumulative incidence rate above 80%. The Luminex cytokine analysis revealed no differences between the groups, and no elevated cytokine level suggested a systemic response. Dermatitis was not noticeable by visual inspection, a histological examination, however, revealed a slight infiltration in the ears in the elicitation groups exposed to contact allergens. CONCLUSION: This study showed that repeated topical application on the ears with a contact allergen could prevent the development of diabetes in non-obese diabetic mice. The contact allergens gave a non-visible, subclinical dermatitis on the application site. Activation of NKT cells to the ear lymph nodes seems to be involved.

Tissue inflammation modulates gene expression of lymphatic endothelial cells and dendritic cell migration in a stimulus-dependent manner.

Chemokines and adhesion molecules up-regulated in lymphatic endothelial cells (LECs) during tissue inflammation are thought to enhance dendritic cell (DC) migration to draining lymph nodes, but the in vivo control of this process is not well understood. We performed a transcriptional profiling analysis of LECs isolated from murine skin and found that inflammation induced by a contact hypersensitivity (CHS) response up-regulated the adhesion molecules ICAM-1 and VCAM-1 and inflammatory chemokines. Importantly, the lymphatic markers Prox-1, VEGFR3, and LYVE-1 were significantly down-regulated during CHS. By contrast, skin inflammation induced by complete Freund adjuvant induced a different pattern of chemokine and lymphatic marker gene expression and almost no ICAM-1 up-regulation in LECs. Fluorescein isothiocyanate painting experiments revealed that DC migration to draining lymph nodes was more strongly increased in complete Freund adjuvant-induced than in CHS-induced inflammation. Surprisingly, DC migration did not correlate with the induction of CCL21 and ICAM-1 protein in LECs. Although the requirement for CCR7 signaling became further pronounced during inflammation, CCR7-independent signals had an additional, albeit moderate, impact on enhancing DC migration. Collectively, these findings indicate that DC migration in response to inflammation is stimulus-specific, mainly CCR7-dependent, and overall only moderately enhanced by LEC-induced genes other than CCL21.

Th1/Th2 balance in mouse delayed-type hypersensitivity model with mercuric chloride via skin and oral mucosa.

In order to compare delayed-type hypersensitivity (DTH) among different exposure sites, we evaluated the sensitization potency of mercuric chloride (HgCl(2)) via exposure to the skin, or oral or esophageal mucosa using the mouse ear swelling test. Furthermore, we investigated in vitro splenocyte proliferation reaction and cytokine profile in HgCl(2)-exposed and control mice. Sensitization with HgCl(2) was established via the skin and oral mucosa but not via the esophageal mucosa. The splenocyte proliferation reaction was significantly enhanced to a similar degree in skin and oral mucosa-sensitized mice compared with in the control mice. IL-10 levels from cultured splenocytes were significantly increased in skin and oral mucosa-sensitized mice compared with those in control mice, whilst IFN-γ significantly increased only in splenocytes from skin-sensitized mice. These results suggest that exposure of the skin or oral mucosa to HgCl(2) can induce DTH, but that Th1/Th2 balance differs according to the site of antigen exposure.

In vitro and in vivo analysis of pro- and anti-inflammatory effects of weak and strong contact allergens.

Inflammation is a crucial step in the development of allergic contact dermatitis. The primary contact with chemical allergens, called sensitization, and the secondary contact, called elicitation, result in an inflammatory response in the skin. The ability of contact allergens to induce allergic contact dermatitis correlates to a great extent with their inflammatory potential. Therefore, the analysis of the sensitizing potential of a putative contact allergen should include the examination of its ability and potency to cause an inflammation. In this study, we examined the inflammatory potential of different weak contact allergens and of the strong sensitizer 2,4,6-trinitrochlorobenzene (TNCB) in vitro and in vivo using the contact hypersensitivity model, the mouse model for allergic contact dermatitis. Cytokine induction was analysed by PCR and ELISA to determine mRNA and protein levels, respectively. Inflammation-dependent recruitment of skin-homing effector T cells was measured in correlation with the other methods. We show that the sensitizing potential of a contact allergen correlates with the strength of the inflammatory response. The different methods used gave similar results. Quantitative cytokine profiling may be used to determine the sensitizing potential of chemicals for hazard identification and risk assessment.

Repeated exposure to hair dye induces regulatory T cells in mice.

BACKGROUND: We have recently shown that commercial p-phenylenediamine (PPD)-containing hair dyes are potent immune activators that lead to severe contact hypersensitivity in an animal model. However, only a minority of people exposed to permanent hair dyes develops symptomatic contact hypersensitivity. This suggests that the majority of people exposed to hair dyes does not become sensitized or develop immunological tolerance. OBJECTIVES: To study the immune response in mice repeatedly exposed to PPD-containing hair dye in a consumer-like manner. METHODS: A commercial hair dye containing PPD was tested in C57BL/6 mice. The local immune response was measured by ear swelling and by histological examinations. The immune response in the draining lymph nodes was analysed by flow cytometry. RESULTS: The hair dye induced local inflammation as seen by swelling and cell infiltration of the treated ears. In addition, exposure to hair dye caused T-cell activation as seen by T-cell proliferation and production of interferon-γ and interleukin (IL)-17 within the draining lymph nodes. The inflammatory response peaked at the fourth exposure to hair dye. From this point on, an upregulation of regulatory T cells and IL-10-producing cells was seen. CONCLUSIONS: This study shows that PPD-containing hair dyes strongly affect the immune system. In addition to being potent skin sensitizers that activate inflammatory T cells, hair dyes also induce anti-inflammatory mechanisms. This might explain why many consumers can use hair dyes repeatedly without developing noticeable allergies, but it also raises the question whether the immune modulatory effects of hair dyes might influence the development of autoimmune diseases and cancers.

Nickel sensitisation in mice: a critical appraisal.

BACKGROUND: The market release of new domestic and industrial chemical and metal products requires certain safety certification, including testing for skin sensitisation. Although various official guidelines have described how such testing is to be done, the validity of the available test models are in part dubious, for which reason regulatory agencies and research aim to further improve and generalise the models for testing of skin sensitisation. OBJECTIVE: We applied a recently published murine model of nickel allergy as to test its applicability in a regulatory setting and to study and better understand the events leading to type-IV hypersensitivity. Nickel was chosen as model hapten since it induces allergic contact dermatitis with high incidence in the general population. METHOD: Typically, C57BL/6 mice were sensitised and challenged by intradermal applications of nickel, and cutaneous inflammation was analysed by the mouse ear-swelling test, by histology, and by lymphocyte reactivity in vitro. RESULT: Surprisingly, the study suggested that the skin reactions observed were results of irritant reactions rather than of adaptive immune responses. Non-sensitised mice responded with cutaneous inflammation and in vitro lymphocyte reactivity which were comparable with nickel-sensitised mice. Furthermore, histological examinations as well as experiments in T-cell deficient mice demonstrated that lymphocytes were not involved and that nickel caused an irritant contact dermatitis rather a true allergic type-IV contact dermatitis. CONCLUSION: The authors question the validity of the described murine model of nickel allergy.