Assessment of preferential Th1 or Th2 induction by low-molecular-weight compounds using a reverse transcription-polymerase chain reaction method: comparison of two mouse strains, C57BL/6 and BALB/c

Immunomodulatory effects of nanoparticles on dendritic cells in a model of allergic contact dermatitis: importance of PD-L2 expression

Nanoparticle (NP) skin exposure is linked to an increased prevalence of allergic contact dermatitis. In our prior studies using the mouse contact hypersensitivity (CHS) model, we reported that silica 20 nm (SiO2) NPs suppressed the allergic response and titanium dioxide NPs doped with manganese (mTiO2) exacerbated it. In this work, we conducted in vitro experiments using bone marrow-derived dendritic cells (BMDCs) to study the combinatorial effect of the potent 2,4-dinitrofluorobenzene (DNFB) hapten sensitizer with SiO2 and mTiO2 NPs on BMDC cytotoxicity, cytokine secretion and phenotype using the B7 family ligands. Results show that DNFB and mTiO2 behave similarly and exhibit proinflammatory characteristics while SiO2 promotes a naive phenotype. We observe that the B7-H3 (CD276) ligand is only expressed on CD80 + (B7-1) BMDCs. Results from adoptive transfer CHS studies, combined with BMDC phenotype analysis, point to the importance of PD-L2 expression in modulating the adaptive immune response. This work identifies metrics that can be used to predict the effects of NPs on contact allergy and to guide efforts to engineer cell-based therapies to induce hapten specific immune tolerance.

The Monocytic Cell Line THP-1 as a Validated and Robust Surrogate Model for Human Dendritic Cells

We have implemented an improved, cost-effective, and highly reproducible protocol for a simple and rapid differentiation of the human leukemia monocytic cell line THP-1 into surrogates for immature dendritic cells (iDCs) or mature dendritic cells (mDCs). The successful differentiation of THP-1 cells into iDCs was determined by high numbers of cells expressing the DC activation markers CD54 (88%) and CD86 (61%), and the absence of the maturation marker CD83. The THP-1-derived mDCs are characterized by high numbers of cells expressing CD54 (99%), CD86 (73%), and the phagocytosis marker CD11b (49%) and, in contrast to THP-1-derived iDCs, CD83 (35%) and the migration marker CXCR4 (70%). Treatment of iDCs with sensitizers, such as NiSO4 and DNCB, led to high expression of CD54 (97%/98%; GMFI, 3.0/3.2-fold induction) and CD86 (64%/96%; GMFI, 4.3/3.2-fold induction) compared to undifferentiated sensitizer-treated THP-1 (CD54, 98%/98%; CD86, 55%/96%). Thus, our iDCs are highly suitable for toxicological studies identifying potential sensitizing or inflammatory compounds. Furthermore, the expression of CD11b, CD83, and CXCR4 on our iDC and mDC surrogates could allow studies investigating the molecular mechanisms of dendritic cell maturation, phagocytosis, migration, and their use as therapeutic targets in various disorders, such as sensitization, inflammation, and cancer.

Transcriptome profiling reveals Th2 bias and identifies endogenous itch mediators in poison ivy contact dermatitis

In the United States, poison ivy is the most common naturally occurring allergen that causes allergic contact dermatitis (ACD). The immune and pruritic mechanisms associated with poison ivy ACD remain largely unexplored. Here, we compared skin whole transcriptomes and itch mediator levels in mouse ACD models induced by the poison ivy allergen, urushiol, and the synthetic allergen, oxazolone. The urushiol model produced a Th2-biased immune response and scratching behavior, resembling findings in poison ivy ACD patients. Urushiol-challenged skin contained elevated levels of the cytokine thymic stromal lymphopoietin (TSLP), a T cell regulator and itch mediator, and pruritogenic serotonin (5-HT) and endothelin (ET-1) but not substance P (SP) or histamine. The oxazolone model generated a mixed Th1/Th2 response associated with increased levels of SP, 5-HT, and ET-1 but not TSLP or histamine. Injections of a TSLP monoclonal neutralizing antibody or serotonergic or endothelin inhibitors, but not SP inhibitors or antihistamines, reduced scratching behaviors in urushiol-challenged mice. Our findings suggest that the mouse urushiol model may serve as a translational model of human poison ivy ACD. Inhibiting signaling by TSLP and other cytokines may represent alternatives to the standard steroid/antihistamine regimen for steroid-resistant or -intolerant patients and in exaggerated systemic responses to poison ivy.

Characterization of the immune and pruritic pathways in a mouse model of poison ivy-induced allergic contact dermatitis.

Immune-modulation via IgD B-cell receptor suppresses allergic skin inflammation in experimental contact hypersensitivity models despite of a Th2-favoured humoral response

Atopic dermatitis (AD) and allergic contact dermatitis (ACD) are common skin inflammatory conditions. B and T cells are strongly implicated in allergic contact hypersensitivity (CHS) conditions. Activation of IgD B-cell receptor (BCR) by anti-IgD stimulation depletes mature B cells and modulates T-helper cell type 1/2 (Th1/2) responses in vivo. It is not known whether these effects by anti-IgD exacerbates or ameliorates chronic skin inflammations. This study investigated the effects of anti-IgD and B-cell depleting anti-CD20 antibody on skin inflammation in CHS murine models. Chronic CHS were induced by challenges with allergens trimellitic anhydride (TMA) or 2,4 dinitrochlorobenzene (DNCB). Mice were treated with an anti-IgD or anti-CD20 at various time-points following allergen challenges. This study revealed that early therapeutic treatments with anti-IgD at 4 h after allergen challenge significantly reduced skin inflammation in both TMA- and DNCB-induced CHS models (P < 0.05). In contrast, anti-CD20 treatment exacerbated skin inflammation in DNCB-induced CHS despite of an extensive B cell depletion (P < 0.05). Anti-IgD treatment depleted mature CD19⁺IgD⁺ B cells but enhanced allergen-specific IgM and total IgE productions, suggesting a Th2-favoured humoral response. Anti-IgD reduced neutrophilic infiltrations but increases accumulation of mast cells in dermal tissues. The anti-inflammatory effects of anti-IgD were supported by evidence of an increase in the percentage of regulatory B cells and T cells. Collectively, this study demonstrates that immune-modulation by anti-IgD treatment suppresses Th2-mediated allergic skin inflammation in murine models despite a skew toward a Th2-favvoured humoral response and therefore may present a novel treatment for chronic human AD and ACD.

Mouse Model of Hydroquinone Hypersensitivity via Innate and Acquired Immunity and its Promotion by Combined Reagents

We established a mouse model of contact hypersensitivity (CHS) to hydroquinone (HQ), a widespread chemical in our environment. HQ was painted onto flanks; then, HQ was challenged by painting onto ear pinnas on days 7 and 14. The CHS after the second challenge was markedly greater than that after the first challenge. Both challenges increased thymic stromal lymphopoietin and T helper type 2 cytokines in ear pinnas, whereas IFN-γ (typical T helper type 1 cytokine) was decreased, despite an increase in IL-18 (typical IFN-γ inducer). In nude mice (T cell-reduced), although a first challenge induced CHS, a second challenge did not augment it. In severe combined immunodeficient, severe combined immunodeficient-beige, and IL-1-deficient mice, CHS was not induced. However, CHS was inducible in severe combined immunodeficient-beige mice after transfer of natural killer cells from HQ-sensitized normal mice. Tretinoin (used for enhancing the skin-whitening effect of HQ) and resin monomers (used to prevent polymerization of HQ) lowered the HQ concentration needed to establish sensitization to HQ. The augmented CHS after a second challenge was reduced by JNJ7777120, dexamethasone, suplatast tosilate (T helper type 2-cytokine inhibitor), and anti-thymic stromal lymphopoietin antibody. These results suggest that (i) thymic stromal lymphopoietin, IL-1, and T and/or natural killer cells are important in establishing and augmenting CHS to HQ and (ii) inflammatory chemicals may promote CHS to HQ as adjuvants.

Duality at the gate: Skin dendritic cells as mediators of vaccine immunity and tolerance

Since Edward Jenner's discovery that intentional exposure to cowpox could provide lifelong protection from smallpox, vaccinations have been a major focus of medical research. However, while the protective benefits of many vaccines have been successfully translated into the clinic, the cellular and molecular mechanisms that differentiate effective vaccines from sub-optimal ones are not well understood. Dendritic cells (DCs) are the gatekeepers of the immune system, and are ultimately responsible for the generation of adaptive immunity and lifelong protective memory through interactions with T cells. In addition to lymph node and spleen resident DCs, a number of tissue resident DC populations have been identified at barrier tissues, such as the skin, which migrate to the local lymph node (migDC). These populations have unique characteristics, and play a key role in the function of cutaneous vaccinations by shuttling antigen from the vaccination site to the draining lymph node, rapidly capturing freely draining antigens in the lymph node, and providing key stimuli to T cells. However, while migDCs are responsible for the generation of immunity following exposure to certain pathogens and vaccines, recent work has identified a tolerogenic role for migDCs in the steady state as well as during protein immunization. Here, we examine the roles and functions of skin DC populations in the generation of protective immunity, as well as their role as regulators of the immune system.

A Novel Prime and Boost Regimen of HIV Virus-Like Particles with TLR4 Adjuvant MPLA Induces Th1 Oriented Immune Responses against HIV

HIV virus-like particles (VLPs) present the HIV envelope protein in its native conformation, providing an ideal vaccine antigen. To enhance the immunogenicity of the VLP vaccine, we sought to improve upon two components; the route of administration and the additional adjuvant. Using HIV VLPs, we evaluated sub-cheek as a novel route of vaccine administration when combined with other conventional routes of immunization. Of five combinations of distinct prime and boost sequences, which included sub-cheek, intranasal, and intradermal routes of administration, intranasal prime and sub-cheek boost (IN+SC) resulted in the highest HIV-specific IgG titers among the groups tested. Using the IN+SC regimen we tested the adjuvant VesiVax Conjugatable Adjuvant Lipid Vesicles (CALV) + monophosphoryl lipid A (MPLA) at MPLA concentrations of 0, 7.5, 12.5, and 25 μg/dose in combination with our VLPs. Mice that received 12.5 or 25 μg/dose MPLA had the highest concentrations of Env-specific IgG2c (20.7 and 18.4 μg/ml respectively), which represents a Th1 type of immune response in C57BL/6 mice. This was in sharp contrast to mice which received 0 or 7.5 μg MPLA adjuvant (6.05 and 5.68 μg/ml of IgG2c respectively). In contrast to IgG2c, MPLA had minor effects on Env-specific IgG1; therefore, 12.5 and 25 μg/dose of MPLA induced the optimal IgG1/IgG2c ratio of 1.3. Additionally, the percentage of germinal center B cells increased significantly from 15.4% in the control group to 31.9% in the CALV + 25 μg MPLA group. These mice also had significantly more IL-2 and less IL-4 Env-specific CD8⁺ T cells than controls, correlating with an increased percentage of Env-specific central memory CD4⁺ and CD8⁺ T cells. Our study shows the strong potential of IN+SC as an efficacious route of administration and the effectiveness of VLPs combined with MPLA adjuvant to induce Env specific Th1-oriented HIV-specific immune responses.

NKG2D-dependent activation of dendritic epidermal T cells in contact hypersensitivity

The interaction between keratinocytes (KCs) and skin-resident immune cells has an important role in induction of contact hypersensitivity. A specific subset of γδ T cells termed dendritic epidermal T cells (DETCs) are located in mouse epidermis, and we have recently shown that DETCs become activated and produce IL-17 in an IL-1β-dependent manner during contact hypersensitivity. Various receptors on DETCs, including NKG2D, are involved in DETC responses against tumors and during wound healing. The ligands for NKG2D (NKG2DL) are stress-induced proteins such as mouse UL16-binding protein-like transcript 1 (Mult-1), histocompatibility 60 (H60), and retinoic acid early inducible-1 (Rae-1) in mice and major histocompatibility complex (MHC) class I-chain-related A (MICA), MHC class I-chain-related B, and UL16-binding protein in humans. Here, we show that allergens upregulate expression of the NKG2DL Mult-1, H60, and Rae-1 in cultured mouse KCs and of MICA in primary human KCs. We demonstrate that Mult-1 is expressed in mouse skin exposed to allergen. Furthermore, we find that the vast majority of DETCs in murine epidermis and skin-homing cutaneous lymphocyte-associated antigen positive γδ T cells in humans express NKG2D. Finally, we demonstrate that blocking of NKG2D partially inhibits allergen-induced DETC activation. These findings demonstrate that NKG2D and NKG2DL are involved in allergen-induced activation of DETCs and indicate that the NKG2D/NKG2DL pathway might be a potential target for treatment of contact hypersensitivity.

Utilization of the Ex Vivo LLNA

Dermal exposure to chemicals may result in allergic or irritant contact dermatitis. In this study, we performed ex vivo local lymph node assay: bromodeoxyuridine-enzyme-linked immunosorbent assay (LLNA: BrdU-ELISA) to compare the differences between irritation and sensitization potency of some chemicals in terms of the 3 end points: lymphocyte proliferation, cytokine profiles (interleukin 2 [IL-2], interferon-γ (IFN-γ), IL-4, IL-5, IL-1, and tumor necrosis factor α [TNF-α]), and ear swelling. Different concentrations of the following well-known sensitizers and irritant chemicals were applied to mice: dinitrochlorobenzene, eugenol, isoeugenol, sodium lauryl sulfate (SLS), and croton oil. According to the lymph node results; the auricular lymph node weights and lymph node cell counts increased after application of both sensitizers and irritants in high concentrations. On the other hand, according to lymph node cell proliferation results, there was a 3-fold increase in proliferation of lymph node cells (stimulation index) for sensitizer chemicals and SLS in the applied concentrations; however, there was not a 3-fold increase for croton oil and negative control. The SLS gave a false-positive response. Cytokine analysis demonstrated that 4 cytokines including IL-2, IFN-γ, IL-4, and IL-5 were released in lymph node cell cultures, with a clear dose trend for sensitizers whereas only TNF-α was released in response to irritants. Taken together, our results suggest that the ex vivo LLNA: BrdU-ELISA method can be useful for discriminating irritants and allergens.

Innate Mucosal Immune System Response of BALB/c vs C57BL/6 Mice to Injury in the Setting of Enteral and Parenteral Feeding

BACKGROUND

Outbred mice exhibit increased airway and intestinal immunoglobulin A (IgA) following injury when fed normal chow, consistent with humans. Parenteral nutrition (PN) eliminates IgA increases at both sites. Inbred mice are needed for detailed immunological studies; however, specific strains have not been evaluated for this purpose. BALB/c and C57BL/6 are common inbred mouse strains but demonstrate divergent immune responses to analogous stress. This study addressed which inbred mouse strain best replicates the outbred mouse and human immune response to injury.

METHODS

Intravenously cannulated mice received chow or PN for 5 days and then underwent sacrifice at 0 or 8 hours following controlled surgical injury (BALB/c: n = 16-21/group; C57BL/6: n = 12-15/group). Bronchoalveolar lavage (BAL) was analyzed by enzyme-linked immunosorbent assay for IgA, tumor necrosis factor-α (TNF-α), interleukin (IL)-1β, and IL-6, while small intestinal wash fluid (SIWF) was analyzed for IgA.

RESULTS

No significant increase in BAL IgA occurred following injury in chow- or PN-fed BALB/c mice (chow: P = .1; PN: P = .7) despite significant increases in BAL TNF-α and SIWF IgA (chow: 264 ± 28 vs 548 ± 37, P < .0001; PN: 150 ± 12 vs 301 ± 17, P < .0001). Injury significantly increased mucosal IgA in chow-fed C57BL/6 mice (BAL: 149 ± 33 vs 342 ± 87, P = .01; SIWF: 236 ± 28 vs 335 ± 32, P = .006) and BAL cytokines. After injury, PN-fed C57BL/6 mice exhibited no difference in BAL IgA (P = .9), BAL cytokines, or SIWF IgA (P = .1).

CONCLUSIONS

C57BL/6 mice exhibit similar airway responses to injury as outbred mice and humans, providing an appropriate model for studying mucosal responses to injury. The BALB/c mucosal immune system responds differently to injury and does not replicate the human injury response.

Effect of simultaneous exposure to mixture of two skin sensitizers on skin sensitization response in guinea pigs and mice

Skin sensitization resulting in allergic contact dermatitis is a common occupational health issue. In this study, the effect of mixing two skin sensitizers on the skin sensitization response was investigated. Skin sensitizers are generally classified into T helper type 1 (Th1) or T helper type 2 (Th2), depending on the induced cytokine profile. Dinitrochlorobenzene (DNCB) and oxazolone (Oxa) are Th1 skin sensitizers and phthalic anhydride (PA) and toluene diisocyanate (TDI) are Th2 skin sensitizers. We investigated the effect on skin sensitization response to mixtures of three pairs of these sensitizers: DNCB and Oxa, DNCB and PA, and PA and TDI, using guinea pig maximization test and mouse ear swelling test. In guinea pigs sensitized with the mixture of DNCB and Oxa or PA and TDI, there were changes of skin sensitization response to DNCB and Oxa, and that to PA. On the other hand, there was no mixture effect in guinea pigs sensitized with the mixture of DNCB and PA. The skin sensitization responses were decreased in mice sensitized with the mixtures of DNCB and Oxa or PA and TDI, whereas the mixture effect was not observed in mice sensitized with the mixture of DNCB and PA. The present findings revealed that mixture effect on the skin sensitization response was observed after simultaneous exposure to two skin sensitizers, and the effect was determined by combinations of mixed skin sensitizers.

[Regulatory mechanisms of calcitonin gene-related peptide (CGRP) in skin inflammation]

Skin inflammation is one of several allergic symptoms that are regulated by several mediator molecules. One of these molecules, calcitonin gene-related peptide (CGRP) affects several immune cells including T cells, B cells, dendiritic cells and mast cells. CGRP binds to CGRP receptors composed of receptor activity-modifying protein 1 (RAMP1) and calcitonin receptor-like receptor (CLR) to modulate various functions such as pain transmission and vasodilation. Studies showing that CGRP physiologically regulates skin inflammation using a CGRP antagonist, capsaicin-induced depletion model, RAMP1-deficient mice and mouse contact hypersensitivity (CHS) model have been reported. Interestingly, while CGRP has inhibitory effects on Th1-mediated CHS, it was demonstrated that CGRP enhances Th2-mediated CHS response. Moreover, these skin inflammations were affected by elevated CGRP concentrations through an abnormal condition of the nervous system induced by exposure to psychological stress or neonatal chemical stimulation. In this review, we present the importance of CGRP in the regulation of skin inflammation under the several nervous conditions and provide a new insight into understanding various types of skin inflammation and skin diseases.

Quantitative evaluation of therapeutic effect of Liriope platyphylla on phthalic anhydride-induced atopic dermatitis in IL-4/Luc/CNS-1 Tg mice

ETHNOPHARMACOLOGICAL RELEVANCE

A variety of previous pharmacological studies have suggested that Liriope platyphylla may exert beneficial biological effects on inflammation, diabetes, neurodegenerative disorder, obesity, and atopic dermatitis (AD).

AIM OF THE STUDY

The therapeutic effect of aqueous extract of Liriope platyphylla (AEtLP) on AD was quantified using the luciferase report system in IL-4/Luc/CNS-1 transgenic (Tg) mice.

MATERIALS AND METHODS

Alteration of the luciferase signal was quantified in IL-4/Luc/CNS-1 Tg mice co-treated with phthalic anhydride (PA) and AEtLP for 2 weeks using the IVIS imaging system. Phenotypes of AD were assessed by ear thickness analysis, measurement of immune-related organ weights, ELISA, and histological and pathological analysis in Tg mice.

RESULTS

A strong luciferase signal was detected in the abdominal region of IL-4/Luc/CNS-1 Tg mice treated with only PA. However, this signal was significantly reduced in IL-4/Luc/CNS-1 Tg mice co-treated with PA+AEtLP in an AEtLP concentration-dependent manner. Especially, three organs, the thymus, pancreas, and submandibular lymph node (SL), showed a high signal response to PA treatment. Furthermore, to verify whether or not alteration of the luciferase signal is associated with AD, these disease response phenotypes were measured in the same group of mice. Common allergenic responses including increases in ear thickness, lymph node weight, IgE concentration, and infiltrated mast cells were detected in IL-4/Luc/CNS-1 Tg mice treated with PA. However, these responses were dramatically decreased by AEtLP treatment for 2 weeks.

CONCLUSION

These results indicate that the luciferase signal may successfully reflect the therapeutic effects of AEtLP in IL-4/Luc/CNS-1 Tg mice. Further, we suggest additional evidence that Liriope platyphylla may be considered as an effective therapeutic drug for the treatment of AD.

Therapeutic effects of fermented soycrud on phenotypes of atopic dermatitis induced by phthalic anhydride

Atopic dermatitis (AD), which is known as the most common pruritic skin disease, is caused by epidermal barrier dysfunction, allergies, microwave radiation, histamine intolerance, and genetic defects. To investigate the therapeutic effects of fermented soycrud (FSC) on AD pathology, alteration of AD phenotypes induced by phthalic anhydride (PA) treatment was assessed by ear thickness analysis, measurement of immune-related organ weights, ELISA, and histological and pathological analyses of ICR mice after FSC treatment for 2 weeks. Except for water content, the concentrations of most major components were lower in FSC compared to common tofu (CMT). Thymus and lymph node weights were significantly reduced in ICR mice treated with PA+CMT or PA+FSC, whereas spleen and body weights were maintained. Elevation of ear thickness induced by PA treatment was rapidly diminished in the CMT- and FSC-treated groups, although there was no significant difference between the two groups. Furthermore, significant reduction of epidermal thickness was detected in both the PA+CMT- and PA+FSC-treated groups. However, IgE concentration and dermal thickness were reduced only by PA+FSC treatment, whereas PA+CMT treatment maintained levels comparable to PA+vehicle treatment. The number of infiltrated mast cells was higher in the PA+vehicle-treated group compared to the untreated control. Following CMT or FSC treatment, mast cell infiltration was slightly reduced, although the CMT-treated group showed greater cell numbers. These results indicate that FSC may significantly relieve the phenotypes of AD induced by PA treatment and should be considered as a potential candidate for AD therapy.

Lack of transient receptor potential melastatin 8 activation by phthalate esters that enhance contact hypersensitivity in mice

We studied the involvement of sensory neurons in skin sensitization to allergens using a mouse model in which the T-helper type 2 response is essential. Skin sensitization to fluorescein isothiocyanate (FITC) has been shown to be enhanced by several phthalate esters, including dibutyl phthalate (DBP). For different types of phthalate esters, we found a correlation between the ability of transient receptor potential (TRP) A1 activation and that of enhancing skin sensitization. A TRPA1-specific antagonist, HC-030031, was shown to suppress skin sensitization in the presence of DBP. However, since phthalate esters also activate TRPV1, phthalate esters could activate other types of TRP channels non-selectively. Furthermore, sensitization to FITC is also enhanced by menthol, which activates TRPA1 and TRPM8. Here we established an in vitro system for measuring TRPM8 activation. The selectivity for TRPM8 was established by the fact that two TRPM8 agonists (menthol and icilin) induced calcium mobilization, whereas agonists of TRPA1 and TRPV1 did not. We demonstrated that phthalate esters do not activate TRPM8. TRPA1-antagonist HC-030031 did not inhibit TRPM8 activation induced by menthol or icilin. These results show that phthalate esters activate TRPA1 and TRPV1 with selectivity. TRPM8 activation is not likely to be involved in the sensitization to FITC.

Pathogenesis and disease mechanisms of occupational asthma

Occupational asthma (OA) is one of the most common forms of work-related lung disease in all industrialized nations. The clinical management of patients with OA depends on an understanding of the multifactorial pathogenetic mechanisms that can contribute to this disease. This article discusses the various immunologic and nonimmunologic mechanisms and genetic susceptibility factors that drive the inflammatory processes of OA.

Lack of IL-2 in PPAR-α-deficient mice triggers allergic contact dermatitis by affecting regulatory T cells

The aim of the present work was to decipher the cellular basis of the immunoregulatory role of peroxisome proliferator-activated receptor (PPAR)-α in cutaneous hypersensitivity reactions. After challenge with a contact allergen, we observed augmented hypersensitivity reactions with increased numbers of activated T lymphocytes in the skin of PPAR-α-/- mice. Furthermore, following antigen challenge, the percentages of Tregs in the blood, draining lymph nodes and skin were decreased in these mice. PPAR-α deficiency impaired the production of IL-2 in lymph nodes, whereas TGF-β levels remained unchanged. Injection of IL-2 into PPAR-α-/- mice restored the Treg population in the skin-draining lymph nodes of allergen-challenged mice. In vivo induction of Tregs from WT CD4+ CD25- T cells was impaired when adoptively transferred into PPAR-α-/- mice as compared with transfer into WT mice, and reversed by injection of IL-2 into PPAR-α-/- mice. Furthermore, the suppressive capacity of PPAR-α-/- Tregs was impaired when compared to WT Tregs in vitro and in co-adoptive transfer experiments. Finally, injection of IL-2 to PPAR-α-/- mice decreased skin inflammation to a level similar to WT mice. In conclusion, the pro-inflammatory skin phenotype of PPAR-α-/- mice is due to lack of IL-2-mediated Treg induction in these mice.

Calcitonin gene-related peptide is an important regulator of cutaneous immunity: effect on dendritic cell and T cell functions

Some cutaneous inflammations are induced by percutaneous exposure to foreign Ags, and many chemical mediators regulate this inflammation process. One of these mediators, calcitonin gene-related peptide (CGRP), is a neuropeptide released from nerve endings in the skin. CGRP binds to its receptors composed of receptor activity-modifying protein 1 and calcitonin receptor-like receptor to modulate immune cell function. We show that CGRP regulates skin inflammation under physiological conditions, using contact hypersensitivity (CHS) models of receptor activity-modifying protein 1-deficient mice. CGRP has different functions in CHS responses mediated by Th1 or Th2 cells; it inhibits Th1-type CHS, such as 2,4,6-trinitrochlorobenzene-induced CHS, but promotes Th2-type CHS, such as FITC-induced CHS. CGRP inhibits the migration of Langerin(+) dermal dendritic cells to the lymph nodes in 2,4,6-trinitrochlorobenzene-induced CHS, and upregulates IL-4 production of T cells in the draining lymph nodes in FITC-CHS. These findings suggest that CGRP regulates several types of CHS reactions under physiological conditions and plays an important role in cutaneous immunity.

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.

Methyl methacrylate and respiratory sensitization: a critical review

Methyl methacrylate (MMA) is a respiratory irritant and dermal sensitizer that has been associated with occupational asthma in a small number of case reports. Those reports have raised concern that it might be a respiratory sensitizer. To better understand that possibility, we reviewed the in silico, in chemico, in vitro, and in vivo toxicology literature, and also epidemiologic and occupational medicine reports related to the respiratory effects of MMA. Numerous in silico and in chemico studies indicate that MMA is unlikely to be a respiratory sensitizer. The few in vitro studies suggest that MMA has generally weak effects. In vivo studies have documented contact skin sensitization, nonspecific cytotoxicity, and weakly positive responses on local lymph node assay; guinea pig and mouse inhalation sensitization tests have not been performed. Cohort and cross-sectional worker studies reported irritation of eyes, nose, and upper respiratory tract associated with short-term peaks exposures, but little evidence for respiratory sensitization or asthma. Nineteen case reports described asthma, laryngitis, or hypersensitivity pneumonitis in MMA-exposed workers; however, exposures were either not well described or involved mixtures containing more reactive respiratory sensitizers and irritants. The weight of evidence, both experimental and observational, argues that MMA is not a respiratory sensitizer.

Detection of allergenic compounds using an IL-4/luciferase/CNS-1 transgenic mice model

The interleukin-4 (IL-4) signaling cascade has been identified as a potentially important pathway in the development of allergies. The principal objective of this study was to produce novel transgenic (Tg) mice harboring the luciferase gene under the control of the human IL-4 promoter and the enhancer of IL-4 (CNS-1), in an effort to evaluate three types of allergens including a respiratory sensitizer, vaccine additives, and crude extracts of natural allergens in vivo. A new lineage of Tg mice was generated by the microinjection of pIL-4/Luc/CNS-1 constructs into a fertilized mice egg. The luciferase activity was successfully regulated by the IL-4 promoter in splenocytes cultured from IL-4/Luc/CNS-1 Tg mice. From the first five founder lines, one (#57) evidencing a profound response to ovalbumin was selected for use in evaluating the allergens. Additionally, the lungs, thymus, and lymph nodes of IL-4/Luc/CNS-1 Tg mice evidenced high luciferase activity in response to allergens such as phthalic anhydride (PA), trimellitic anhydride, ovalbumin, gelatin, Dermatophagoides pteronyssinus extracts, and Japanese cedar pollen, whereas key allergy-related indicators including ear thickness, Immunoglobulin E concentration, and the infiltration of inflammatory leukocytes in response to PA were unaltered in the Tg mice relative to the non-Tg mice. Furthermore, the expression levels of endogenous type 2 helper T cells cytokines and proinflammatory cytokines were similarly increased in these organs of IL-4/Luc/CNS-1 Tg mice in response to allergens. These results indicate that IL-4/Luc/CNS-1 Tg mice may be used as an animal model for the evaluation and prediction of the human body response to a variety of allergens originating from the environment and from certain industrial products.

Chemical allergy: translating biology into hazard characterization

The induction by chemicals of allergic sensitization and allergic disease is an important and challenging branch of toxicology. Skin sensitization resulting in allergic contact dermatitis represents the most common manifestation of immunotoxicity in humans, and many hundreds of chemicals have been implicated as skin sensitizers. There are far fewer chemicals that have been shown to cause sensitization of the respiratory tract and asthma, but the issue is no less important because hazard identification remains a significant challenge, and occupational asthma can be fatal. In all areas of chemical allergy, there have been, and remain still, intriguing challenges where progress has required a close and productive alignment between immunology, toxicology, and clinical medicine. What the authors have sought to do here is to exemplify, within the framework of chemical allergy, how an investment in fundamental research and an improved understanding of relevant biological and biochemical mechanisms can pay important dividends in driving new innovations in hazard identification, hazard characterization, and risk assessment. Here we will consider in turn three specific areas of research in chemical allergy: (1) the role of epidermal Langerhans cells in the development of skin sensitization, (2) T lymphocytes and skin sensitization, and (3) sensitization of the respiratory tract. In each area, the aim is to identify what has been achieved and how that progress has impacted on the development of new approaches to toxicological evaluation. Success has been patchy, and there is still much to be achieved, but the journey has been fascinating and there have been some very important developments. The conclusion drawn is that continued investment in research, if coupled with an appetite for translating the fruits of that research into imaginative new tools for toxicology, should continue to better equip us for tackling the important challenges that remain to be addressed.

Langerhans cells are critical in the development of atopic dermatitis-like inflammation and symptoms in mice

Genetic or vitamin D3-induced overexpression of thymic stromal lymphopoietin (TSLP) by keratinocytes results in an atopic dermatitis (AD)-like inflammatory phenotype in mice echoing the discovery of high TSLP expression in epidermis from AD patients. Although skin dendritic cells (DC) are suspected to be involved in AD, direct evidence of a pathogenetic role for skin DC in TSLP-induced skin inflammation has not yet been demonstrated. In a mouse model of AD, i.e. mice treated with the low-calcemic vitamin D3 analogue, MC903, we show that epidermal Langerhans cells (LC)-depleted mice treated with MC903 do neither develop AD-like inflammation nor increased serum IgE as compared to vitamin D3 analogue-treated control mice. Accordingly, we show that, in mice treated with MC903 or in K14-TSLP transgenic mice, expression of maturation markers by LC is increased whereas maturation of dermal DC is not altered. Moreover, only LC are responsible for the polarization of naïve CD4(+) T cells to a Th2 phenotype, i.e. decrease in interferon-gamma and increase in interleukin (IL)-13 production by CD4(+) T cells. This effect of LC on T-lymphocytes does not require OX40-L/CD134 and is mediated by a concomitant down-regulation of IL-12 and CD70. Although it was previously stated that TSLP up-regulates the production of thymus and activation-regulated chemokine (TARC)/chemokine (C-C motif) ligand 17 (CCL17) and macrophage-derived chemokine (MDC)/CCL22 by human LC in vitro, our work shows that production of these Th2- cell attracting chemokines is increased only in keratinocytes in response to TSLP overexpression. These results demonstrate that LC are required for the development of AD in mouse models of AD involving epidermal TSLP overexpression.

Chronic mouse model of TMA-induced contact hypersensitivity

Due to the steadily increasing incidence of atopic dermatitis (AD), especially in children, there is a high medical need for new therapies and improved animal models. In mice, trimellitic anhydride (TMA) is routinely used to trigger T-cell-dependent contact hypersensitivity (CHS) reactions. In this study, we compared the standard acute TMA-induced CHS in Balb/c mice with subacute and chronic models of TMA-induced ear inflammation. Compared to the acute model, the chronic CHS model more closely reflects characteristics of AD, such as typical morphological changes of the inflamed skin, strong infiltration with T cells, major histocompatibility complex II-positive cells, eosinophils, and mast cells, a T-helper cell-type (Th) 2 cytokine profile and a strong increase of serum IgE levels. Moreover, a strong lymph node involvement with T-helper cell dominance and a mixed Th1/Th2 T-cell differentiation and activation pattern was demonstrated. Importantly, as demonstrated by successful therapy with prednisolone, the chronic TMA-induced CHS model, in contrast to acute and subacute models, made prolonged therapeutic treatment of a pre-established skin inflammation possible. Altogether, we present an improved model of mouse T-cell-dependent skin inflammation for AD. We hope this model will enhance the predictive value of animal models for therapeutic treatment of atopic eczema.

Cell types involved in allergic asthma and their use in in vitro models to assess respiratory sensitization

This review first describes the mechanism and cell types involved in allergic asthma, which is a complex clinical disease characterized by airway obstruction, airway inflammation and airway hyperresponsiveness to a variety of stimuli. The development of allergic asthma exists of three phases, namely the induction phase, the early-phase asthmatic reaction (EAR) and the late-phase asthmatic reaction (LAR). In the induction phase, antigen-presenting cells play a major role. Most important cells in the EAR are mast cells, and during the LAR, various cell types, such as eosinophils, neutrophils, T cells, macrophages, dendritic cells (DCs), and cells that endow structure are involved. In occupational asthma, this immunological mechanism is involved in 90% of the cases. The second part of this review gives an overview of in vitro models to assess the hazardous potential of high- and low-molecular weight chemicals on the respiratory system. In order to develop a good in vitro model for respiratory allergy, the choice of appropriate cell types is important. Epithelial cells, macrophages and DCs are currently the most used models in this field of research.

Intracellular expression of cytokines and granzyme B in auricular lymph nodes draining skin exposed to irritants and sensitizers

The murine local lymph node assay (LLNA) has been extensively utilized to evaluate sensitizing chemicals. However, there have been some concerns that its use to discriminate between classes of chemicals is minimal. It is thus desirable to identify better or alternative immune endpoints with in LLNA itself. Here, we evaluated the protein and/or mRNA levels of cytokines and granzyme B (GzmB), a cytotoxic lymphocyte product, to discriminate between sensitizers and irritants and to characterize the chemical sensitizers when used as supplemental indicators in LLNA endpoints. For this, CBA/N mice were topically treated daily with a well-known chemical sensitizer such as a strong contact sensitizer 1-chloro-2,4-dinitrobenzene (DNCB), a skin contact sensitizer 2-phenyl-4-ethoxymethylene-5-oxazolone (OXA), and a skin or respiratory sensitizer toluene 2,4-diisocyanate (TDI), and the non-sensitizing irritants, croton oil (CRO) and nonanoic acid (NA), for 3 consecutive days. The protein and/or mRNA levels in auricular lymph nodes draining the ear skin were then analyzed by real-time RT-PCR and immunoassay. The sensitizers, but not the irritants, evoked pronounced interleukin (IL)-2, IL-3 and IL-4 or interferon (IFN)-gamma. Significantly, different sensitizers evoked different cytokine patterns of IL-4 and IFN-gamma, as DNCB strongly up-regulated both IFN-gamma and IL-4, OXA up-regulated IFN-gamma strongly but IL-4 weakly, and TDI up-regulated IL-4 strongly but IFN-gamma weakly. The sensitizers also strongly up-regulated GzmB mRNA, while the irritants had a much weaker effect. Thus, these cytokines and GzmB mRNA may be useful as additional endpoints for discriminating between irritants and sensitizers or contact and respiratory sensitizers in the LLNA.

Controlled delivery of T-box21 small interfering RNA ameliorates autoimmune alopecia (Alopecia Areata) in a C3H/HeJ mouse model

Autoimmune alopecia (alopecia areata) is considered to be triggered by a collapse of immune privilege in hair follicles. Here we confirmed that infiltrating CD4 T lymphocytes around hair follicles of patients with alopecia areata were primarily CCR5-positive with few CCR4-positive cells, suggesting a dominant role of Th1 cells in the alopecic lesion. Given this finding, we sought to elucidate the effect of cytokine therapy in C3H/HeJ mice, a mouse model of alopecia areata, by applying recombinant interleukin-4 and neutralizing anti-interferon-gamma antibody. We found that local injections of both interleukin-4 and neutralizing anti-interferon-gamma antibody effectively treated alopecia in C3H/HeJ mice. Results from immunohistochemistry and semiquantitative reverse transcription-polymerase chain reaction demonstrated that intralesional injection of interleukin-4 suppressed CD8 T cell infiltrates around the hair follicles and repressed enhanced interferon-gamma mRNA expression in the affected alopecic skin. Furthermore, Th1 transcription factor T-box21 small interfering RNAs conjugated to cationized gelatin showed mitigating effects on alopecia in C3H/HeJ mice, resulting in the restoration of hair shaft elongation. Taken together, the use of gelatin-small interfering RNA conjugates promises to be a novel, efficient, and safe tool as an alternative gene therapy for the treatment of various human diseases. To our knowledge, this is the first report of effective controlled delivery of small interfering RNA using biodegradable cationized gelatin microspheres in an animal model of disease.

Th2 Cytokines in Skin Draining Lymph Nodes and Serum IgE Do Not Predict Airway Hypersensitivity to Intranasal Isocyanate Exposure in Mice

Isocyanate exposure in the workplace has been linked to asthma and allergic rhinitis. Recently, investigators have proposed that Th2 cytokine responses in lymph nodes draining the site of dermal application of chemicals including isocyanates may be used to identify sensitizers that cause asthma-like responses. The purpose of this study was to determine if the cytokine profile induced after dermal sensitization with isocyanates and serum IgE predict immediate (IHS) and methacholine-induced late (LHS) respiratory hypersensitivity responses after intranasal challenge. Dermal application of hexylmethane diisocyanate (HMDI), toluene diisocyanate (TDI), or methylene diisocyanate (MDI) significantly increased interleukin-4 (IL-4), IL-5, and IL-13 secretion in parotid lymph node cells. Isophorone diisocyanate (IPDI) increased IL-4 and IL-13, but not IL-5. Tolyl(mono)isocyanate (TMI), tetramethylene xylene diisocyanate (TMXDI), or the contact sensitizer dinitrochlorobenzene (DNCB), only induced minor increases in some of the Th2 cytokines. HMDI, TDI, MDI, and IPDI elicited greater increases in total serum IgE than DNCB, TMI, and TMXDI. All chemicals except TMXDI caused IHS after intranasal challenge of sensitized female BALB/c mice. Only HMDI-, TMI-, or TMXDI-sensitized and challenged mice had increases in LHS. All chemicals elicited epithelial cytotoxicity indicative of nasal airway irritation. The discordance between dermal cytokine profiles and respiratory responses suggests that dermal responses do not necessarily predict respiratory responses. Serum IgE also was not predictive of the respiratory responses to the isocyanates, suggesting that other unknown mechanisms may be involved.

Airway inflammation and bronchial remodelling in toluene diisocyanate-exposed BALB/c mouse model

Toluene diisocyanate (TDI), a highly reactive industrial chemical, is one of the leading causes of occupation-related asthma in industrialized countries. The pathogenesis of TDI-induced asthma, however, remains not fully understood, in part due to lack of appropriate animal models. Twenty five female BALB/c mice (age: 8 weeks) were randomly divided into 5 groups: Ovabumin (OVA); OVA peptide amino acid residues No. 323-339 (Pep); TDI; alum and physiological saline. Mice were intraperitoneally injected with 25 microg OVA or pep absorbed on 300 microg alum, 300 microg alum or saline on days 0, 7 and 14. For the TDI group, mice were sensitized subcutaneously with 20 microl neat TDI on day 0; 20 microl of TDI in olive oil (1:10) on days 7 and 14; on days 21-23. Then each group was challenged intranasally with 20 microl of 1% OVA, 1% Pep, 1% TDI, 10% alum and saline respectively. On day 28, mice were killed under pentothal anesthesia. The results demonstrated that neutrophil-dominant inflammation with a few eosinophil infiltration occurred in the peri-bronchial and peri-vascular regions of the lungs. This was accompanied by hyperplasia/hypertrophy of cells lining the airways and mucus production as shown by HE staining. Positive immunohistochemical MBP staining in parenchyma was also shown. Th2 cytokine IL-4 and IgE production were significant increased 5 days after last challenge while IFN-gamma level was below the detection limit.

CONCLUSION

the clear elevation of IL-4 and IgE could allow to conclude a possible Th2-like dominated allergic response in TDI-exposed BALB/c mouse model.

What makes a chemical a respiratory sensitizer?

PURPOSE OF REVIEW

In this article we consider the characteristics that are associated with chemical respiratory allergens, and that may be essential for effective sensitization of the respiratory tract.

RECENT FINDINGS

Chemical respiratory allergens share some characteristics with other chemical allergens, specifically chemical allergens that cause skin sensitization and allergic contact dermatitis. The unique and defining characteristic of chemical respiratory allergens, which in most instances distinguishes them from contact allergens, is the ability to provoke the preferential development of T helper 2-type immune responses. There are, in addition, other characteristics, such as the ability to increase matrix metalloproteinase expression or to cause perturbation of redox homeostasis, that may in some instances facilitate the induction or expression of respiratory allergy, but it is not yet clear if these attributes are common or essential properties of all chemical respiratory sensitizers.

SUMMARY

Predicting which chemical allergens may selectively induce respiratory sensitization is an important objective, but remains a significant challenge because our understanding of the relevant physicochemical characteristics and biological properties that confer on chemicals respiratory allergenic potential is incomplete.

Early up-regulation of Th2 cytokines and late surge of Th1 cytokines in an atopic dermatitis model

We investigated cytokine profiles in interleukin (IL)-4 transgenic (Tg) mice with a skin inflammatory disease resembling human atopic dermatitis. cDNA microarray revealed that the mRNAs encoding IL-1beta, IL-2, IL-3, IL-4, IL-5, IL-6, IL-10, IL-12p40, IL-13, tumour necrosis factor (TNF)-alpha, TNF-beta and interferon (IFN)-gamma were up-regulated in the skin of late lesion Tg mice and to a lesser degree in non-lesion Tg mice when compared to those of non-Tg mice. Real time reverse transcription-polymerase chain reaction (RT-PCR) analyses indicated that the cDNA copy numbers of IL-1beta, IL-4, IL-6, IL-10, TNF-alpha and IFN-gamma from the skin of late, early and non-lesions increased significantly compared to non-Tg mice. IL-2 and IL-12p40 cDNA copy numbers were increased significantly in early, but not late, lesions. Interestingly, IL-1beta, IL-3, IL-4, IL-5, IL-6, IL-10, IL-13, TNF-alpha, and IFN-gamma cDNAs were increased significantly the skin of before-onset and/or non-lesion mice. Flow cytometry analyses demonstrated an increased percentage of keratinocytes producing IL-4 as the disease progressed. The percentage of IL-2, IL-4, IL-10 and IFN-gamma-producing T cells and IL-12-producing antigen-presenting cells in skin-draining lymph nodes and inflammatory skin also increased, particularly in mice with late lesion. These results suggest that disease induction is primarily triggered by Th2 cytokines and that Th1, Th2 and non-Th proinflammatory cytokines are all involved in the disease process.

Cytokine mRNA profiles for isocyanates with known and unknown potential to induce respiratory sensitization

Isocyanates are low-molecular-weight chemicals implicated in allergic asthmatic-type reactions. Identification of chemicals likely to cause asthma is difficult due to the lack of a validated test method. One hypothesis is that differential cytokine induction (Th1 versus Th2 profiles) in the draining lymph node following dermal application can be used to identify asthmagens and distinguish them from contact allergens. In this study, we compared the cytokine mRNA profiles of six chemicals: toluene diisocyanate (TDI), diphenylmethane-4,4'-diisocyanate (MDI), dicyclohexylmethane-4,4'-diisocyanate (HMDI), isophorone diisocyanate (IPDI), p-tolyl(mono)isocyanate (TMI), and meta-tetramethylene xylene diisocyanate (TMXDI). Whereas TDI and MDI are well-known respiratory sensitizers, documentation for HMDI, IPDI, TMI, and TMXDI is limited, but suggests that HMDI and IPDI may have respiratory sensitization potential in humans and TMI and TMXDI do not. Following dermal exposure of BALB/c mice, all six isocyanates induced cytokines characteristic of a Th2 response. Although LLNAs suggested that the doses chosen for the RPA were immunologically equivalent, the isocyanates tested differentiated into two groups, high responders and low responders. However, two of the low responders (TMI and TMXDI) were further tested and induced higher levels of Th2 cytokine message than dinitrochlorobenzene (not an asthmagen). Further study of these chemicals is needed to determine whether the Th2 cytokine responses observed for these low responders is predictive of asthmagenic potential or represents an insufficient signal.

TARC and RANTES, but not CTACK, are induced in two models of allergic contact dermatitis. Effects of cilomilast and diflorasone diacetate on T-cell-attracting chemokines

BACKGROUND

Skin-infiltrating T cells play a predominant role in allergic and inflammatory skin diseases such as atopic dermatitis and allergic contact dermatitis. These T cells are attracted by chemotactic factors, e.g. RANTES (regulation on activation, normal T cell expressed and secreted; CCL5), TARC (thymus and activation regulated chemokine; CCL17) and CTACK (cutaneous T-cell attracting chemokine; CCL27).

OBJECTIVES

To investigate which T-cell-attracting chemokines are involved in allergic contact dermatitis in mice.

METHODS

Allergic contact dermatitis was induced by application of dinitrochlorobenzene (DNCB) or toluene-2,4-diisocyanate (TDI), and chemokine concentrations were determined by enzyme-linked immunosorbent assay. The effects on chemokine concentrations of the highly selective phosphodiesterase 4 inhibitor cilomilast and the glucocorticoid diflorasone diacetate were studied in mouse ears.

RESULTS

RANTES and TARC were elevated in both models of allergic contact dermatitis 24 h after challenge, whereas CTACK remained unchanged. The increase in RANTES was diminished in mouse ears pretreated with cilomilast or diflorasone diacetate. TARC was reduced by diflorasone diacetate in the DNCB model but was highly induced in the TDI model; in contrast, TARC was not influenced by cilomilast.

CONCLUSIONS

TARC and RANTES, but not CTACK, are involved in these two models of allergic contact dermatitis.

Identifying airway sensitizers: cytokine mRNA profiles induced by various anhydrides

Exposure to low molecular weight (LMW) chemicals in the workplace has been linked to a variety of respiratory effects. Within the LMW chemicals, one of the major classes involved in these effects are the acid anhydrides. The immunological basis of respiratory hypersensitivity involves CD4+ cells. By virtue of their induction of cytokines typical of CD4+ T-helper type 2 (Th2) cells-interleukin (IL)-4, 10, and 13-respiratory sensitizers may be identified and differentiated from contact sensitizers which induce Th1 cytokines (IL-2 and IFN-gamma). Our previous work suggested that the ribonuclease protection assay (RPA) was useful in identifying the respiratory sensitizer, trimellitic anhydride (TMA), based on quantitative differences in Th2 cytokine mRNA as compared to the contact sensitizer dinitrochlorobenzene (DNCB). Therefore, the purpose of the studies described in this report was to expand the chemicals tested in the RPA. To this end, four acid anhydrides with known respiratory sensitization potential, TMA, maleic anhydride (MA), phthalic anhydride (PA) and hexahydrophthalic anhydride (HHPA), were tested. Although previously determined to induce immunologically equivalent responses in a local lymph node assay (LLNA), the initial dose chosen (2.5%) failed to induce Th2 cytokine mRNA expression. To determine if the lack of cytokine expression was related to dose, LLNAs were conducted at higher doses for each of the anhydrides. The highest doses evaluated (four- to six-fold higher than those used in the initial RPA) gave equivalent proliferative responses for the various anhydrides and were used for subsequent RPA testing. At these higher doses, significant increases in Th2 versus Th1 cytokine mRNA were observed for all anhydrides tested. These results suggest that the RPA has the potential to serve as a screen for the detection of LMW airway sensitizing chemicals. However, the basis for selecting immunologically equivalent doses may require some modification.

AWD 12-281, a highly selective phosphodiesterase 4 inhibitor, is effective in the prevention and treatment of inflammatory reactions in a model of allergic dermatitis

AWD 12-281 (N-(3,5-dichloro-4-pyridinyl)-2-[1-(4-fluorobenzyl)-5-hydroxy-1H-indol-3-yl]-2-oxoacetamide), a phosphodiesterase 4 inhibitor, which is optimized for topical administration, was tested in a model of allergic dermatitis in mice. To obtain an allergic dermatitis, BALB/c mice were sensitized to toluene-2,4-diisocyanate (TDI). The allergic reaction was challenged by topical administration of TDI onto the mice ears. AWD 12-281 was tested for its anti-inflammatory potential by oral, intraperitoneal and topical administration. The phosphodiesterase 4 inhibitor, cilomilast (SB 207499), and/or the corticosteroid, diflorasone diacetate, were used as reference compounds. Given orally and intraperitoneally 2 h before as well as 5 and 24 h after TDI challenge, AWD 12-281 showed no, or only a transient inhibition of the allergen-induced ear swelling, whereas cilomilast significantly inhibited this ear swelling. Applied topically onto the ears before TDI challenge, AWD 12-281, cilomilast and diflorasone diacetate caused total inhibition of ear swelling 24 h after challenge, confirmed by a decrease of the pro-inflammatory cytokines interleukin-4, interleukin-6 and macrophage inhibitory protein-2. Administered topically after TDI challenge as therapeutic intervention, AWD 12-281 and diflorasone diacetate caused significant inhibition of ear swelling; cilomilast failed to do so. These results indicate that topically administered AWD 12-281 may be potent in the prevention and treatment of allergic/inflammatory skin diseases.

Methods for the identification of chemical respiratory allergens in rodents: comparisons of cytokine profiling with induced changes in serum IgE

No validated or widely recognized test methods are currently available for the prospective identification of chemicals with the potential to cause respiratory allergy. The cellular and molecular mechanisms that result in the induction of chemical sensitization of the respiratory tract are unclear, although there is evidence for the selective development of T helper 2 (Th2)-type responses and, in some cases, the production of IgE antibody. We have therefore examined the utility of cytokine profiling using BALB/c mice, together with the measurement of induced increases in the total serum concentration of IgE in the Brown Norway (BN) rat, as markers for the prospective identification of chemical respiratory allergens. Responses provoked by the reference respiratory allergen trimellitic anhydride (TMA) have been compared with those stimulated by the respiratory sensitizing diisocyanates toluene diisocyanate (TDI) and hexamethylene diisocyanate (HDI) and by the acid anhydride hexahydrophthalic anhydride (HHPA). Topical exposure of BN rats to TMA, TDI and HHPA each provoked marked immune activation (increases in lymph node cellularity and proliferation). However, only treatment with TMA stimulated vigorous increases in the total serum concentration of IgE. In contrast, exposure to HHPA, TDI or HDI failed to provoke significant changes in serum IgE concentration or induced only transient and relatively weak increases in serum IgE levels. In parallel experiments using BALB/c strain mice, however, topical application of all four chemical respiratory allergens provoked a marked Th2-type cytokine secretion profile in draining lymph node cells. These data suggest that the measurement of induced changes in serum IgE is not sufficiently sensitive for the robust identification of chemical respiratory allergens. Furthermore, irrespective of the reasons for variations in TMA-induced IgE production among BN rats, doubts remain regarding the utility of these animals for the characterization of immune responses to chemical allergens. Cytokine profiling using the BALB/c strain mouse apparently provides a more robust method for the hazard assessment of chemical respiratory allergens.

Impact of exposure duration by low molecular weight compounds on interferon-gamma and interleukin-4 mRNA expression and production in the draining lymph nodes of mice

The local lymph node assay (LLNA) is used to identify allergens by means of dermal exposure. For hazard identification, besides identification also the distinction between contact and respiratory allergens is of importance. We have previously shown that a modified LLNA can be used to identify respiratory allergens, on the basis of Con A induced IL-4 production. Here we show a good qualitative correlation between mRNA expression and production of IFN-gamma and IL-4. This suggests that distinction between contact and respiratory allergens may also be studied at the mRNA expression level. Secondly, another assay, similar to the modified LLNA but differing in the duration and the number of allergen applications as well as in the ex vivo culture conditions, here denoted as 'longer' assay, has been reported to be able to identify contact allergens, on the basis of (spontaneous) IFN-gamma production. In the present study we have compared these assays. Similar to our previous findings, in the modified LLNA exposure to the respiratory allergen trimellitic anhydride (TMA) resulted in a approximately 10-fold higher Con A induced IL-4 production compared with the contact allergen dinitrochlorobenzene (DNCB), while exposure to both allergens resulted in a similar Con A induced IFN-gamma production. In the 'longer' assay, TMA exposure resulted in Con A induced IL-4 production whereas DNCB exposure did not. Importantly, only a 2-fold higher spontaneous IFN-gamma production was induced by DNCB compared with TMA, the difference being not statistically significant. Thus, although the 'longer' assay indeed showed a somewhat higher IFN-gamma induction by DNCB compared with TMA, the magnitude and robustness of this effect question its applicability. These results favor the modified LLNA since it is shorter, and combines identification of allergens (by cell proliferation) with identification of respiratory allergens (by IL-4 production). Compounds that induce cell proliferation with a low concomitant IL-4 production may thus be identified as contact allergens, although the need to positively identity such allergens remain.

Cytokine fingerprinting of chemical allergens: species comparisons and statistical analyses

The cellular and molecular mechanisms that result in the induction of chemical respiratory sensitization are unclear, although there is evidence for the development of T helper (Th) 2 type responses and, in some cases, the production of IgE. We have compared cytokine secretion patterns stimulated by topical exposure of BALB/c strain mice or Brown Norway (BN) strain rats to the reference respiratory allergen trimellitic anhydride (TMA), or to the reference contact allergen 2,4-dinitrochlorobenzene (DNCB). Under conditions where TMA and DNCB provoke similar levels of immune activation [increases in lymph node cell (LNC) cellularity and proliferation] divergent cytokine expression patterns are elicited. TMA-activated LNC isolated from BALB/c mice or BN rats elaborated high levels of the Th2-type cytokines interleukin (IL)-10 and IL-13, but relatively little of the Th1-type cytokines IL-12 or interferon gamma. For LNC derived from both species there was a requirement for restimulation in vitro with the mitogen concanavalin A for IL-4 production. Generally, DNCB-stimulated LNC displayed the converse type 1 cytokine phenotype. The cytokine secretion profiles of LNC isolated from BN rats were considerably more variable than those observed for LNC from BALB/c mice. Statistically significant differences (P<0.01) between DNCB- and TMA-activated LNC were recorded for all cytokines in BALB/c strain mice. For the BN rat, differences reached statistical significance (P<0.01) only for the expression of IL-4 and IL-13. These data demonstrate that the intrinsic ability of DNCB and TMA to promote preferential Th1- and Th2-type responses, respectively, is species-independent and provide further evidence that chemical respiratory allergens are associated with polarized Th2-type responses. For the prospective assessment of chemical respiratory allergens as a function of induced cytokine secretion profiles, however, these data suggest that the use of the BALB/c strain mouse will provide the more robust method.