Induction of scratching behaviour and dermatitis in various strains of mice cohabiting with NC/Nga mice with chronic dermatitis

Subcutaneous Injection and Brush Application of Ovalbumin-Aluminum Salt Solution Induces Dermatitis-like Changes in Mice

Background: Intraperitoneal sensitization combined with topical and/or epicutaneous treatment using an ovalbumin (OVA)-aluminum salt solution (OVA-AL) represents a model for inducing atopic dermatitis (AD). However, the combination of sensitization with subcutaneous treatment and cutaneous application of OVA-AL via a brush has not been explored as a method for inducing AD. Methods: Adult mice were subcutaneously injected with OVA-AL following sensitization on days 0, 7, and 14 and were treated with OVA-AL via brush application to the dorsal skin fortnightly until days 35 and 49. Concomitant alloknesis and skin changes were assessed. Mice of the Balb/c and ICR-CD1 strains were treated with OVA-AL until day 35, with only the ICR-CD1 strain continuing treatment until day 49. Control animals received saline. At 35 and 49 days, dorsal skin was harvested and processed for histological analysis. Results: Mice treated with OVA-AL developed dry skin, with no scratching or alloknesis. Histological examination of dorsal skin revealed an increase in mast cells and collagen deposition. Conclusions: Dermatitis-like symptoms were observed in mice treated with OVA-AL using this administration method.

Experimental Study: Interleukin-31 Augments Morphine-Induced Antinociceptive Activity and Suppress Tolerance Development in Mice

Morphine-induced antinociception is partially reduced in interleukin-31 (IL-31) receptor A (IL-31RA)-deficient mice, indicating that IL-31RA is crucial for morphine-induced peripheral antinociception. Herein, we examined the combined effects of IL-31 and morphine on the antinociceptive activity and itch-associated scratching behavior (LLS) in mice and elucidated the regulatory mechanisms. A hot-plate test was used to assess antinociception. LLS was automatically detected and recorded via a computer. IL-31RA mRNA expression was assessed using real-time polymerase chain reaction. Repeated pre-treatment with IL-31 resulted in significant antinociceptive activity. Repeated administration of morphine decreased the morphine-induced antinociceptive activity, LLS counts, and regular dose and inhibited IL-31-induced LLS. These results suggested that the repeated administration of morphine depleted inter-neuronal IL-31RA levels, preventing morphine-induced antinociception. Therefore, IL-31 may be helpful as an adjunct analgesic to morphine. To explore the benefits of IL-31, its influence on morphine-induced antinociceptive tolerance in mice was examined. An IL-31 and morphine combination increased the analgesic action, which increased the expression of DRG neuronal IL-31RA, elucidating the site of peripheral antinociception of morphine. This site may induce exocytosis of IL-31RA in the sensory nervous system. Collectively, the suppressive effect of IL-31 on morphine-induced antinociceptive tolerance may result from IL-31RA supplementation in sensory nerves.

Interleukin-31 Receptor A Expression in the Dorsal Root Ganglion of Mice with Atopic Dermatitis

Atopic dermatitis (AD) is a common skin disease caused by genetic and environmental factors. However, the mechanisms underlying AD development remain unclear. In this study, we examined the genetic factors contributing to the onset of itch-associated scratching in different strains of mice. Interleukin-31 (IL-31) induces severe scratching and dermatitis in mice. However, the site of action of IL-31 remains unclear. Cutaneous IL-31 and IL-31 receptor A (IL-31RA) mRNAs in the dorsal root ganglion (DRG) are expressed exclusively in the AD model, i.e., NC/Nga mice. Here we evaluated the effects of repeated administration of IL-31 on the scratching behavior in NC/Nga, BALB/c, and C57BL/6 mice. The results showed that repeated administration of IL-31 significantly increased itch-associated scratching (LLS) behavior in the three strains of mice. One hour after an intravenous IL-31 injection, BALB/c mice showed alloknesis-like behavior. Mite infestation and IL-31 administration triggered itchy skin, increased LLS counts and DRG neuronal IL-31RA expression, and eventually caused dermatitis. The dermatitis severity and LLS counts induced by mite infestation and IL-31 administration were in the order NC/Nga > BALB/c > C57BL/6. In conclusion, neuronal IL-31RA expression in the DRG was the most important genetic factor affecting the severity of LLS and dermatitis in mice.

Trifuhalol A Suppresses Allergic Inflammation through Dual Inhibition of TAK1 and MK2 Mediated by IgE and IL-33

The activation and degranulation of immune cells play a pivotal role in allergic inflammation, a pathological condition that includes anaphylaxis, pruritus, and allergic march-related diseases. In this study, trifuhalol A, a phlorotannin isolated from Agarum cribrosum, inhibited the degranulation of immune cells and the biosynthesis of IL-33 and IgE in differentiated B cells and keratinocytes, respectively. Additionally, trifuhalol A suppressed the IL-33 and IgE-mediated activation of RBL-2H3 cells through the regulation of the TAK1 and MK2 pathways. Hence, the effect of trifuhalol A on allergic inflammation was evaluated using a Compound 48/80-induced systemic anaphylaxis mouse model and a house dust mite (HDM)-induced atopic dermatitis (AD) mouse model. Trifuhalol A alleviated anaphylactic death and pruritus, which appeared as an early-phase reaction to allergic inflammation in the Compound 48/80-induced systemic anaphylaxis model. In addition, trifuhalol A improved symptoms such as itching, edema, erythema, and hyperkeratinization in HDM-induced AD mice as a late-phase reaction. Moreover, the expression of IL-33 and thymic stromal lymphopoietin, inflammatory cytokines secreted from activated keratinocytes, was significantly reduced by trifuhalol A administration, resulting in the reduced infiltration of immune cells into the skin and a reduction in the blood levels of IgE and IL-4. In summarizing the above results, these results confirm that trifuhalol A is a potential therapeutic candidate for the regulation of allergic inflammation.

Social Environment Ameliorates Behavioral and Immune Impairments in Tyrosine Hydroxylase Haploinsufficient Female Mice

The social environment can influence the functional capacity of nervous and immune systems, and consequently the state of health, especially in aged individuals. Adult female tyrosine hydroxylase haploinsufficient (TH-HZ) mice exhibit behavioral impairments, premature immunosenescence and oxidative- inflammatory stress. All these deteriorations are associated with a lower lifespan than wild type (WT) counterparts. The aim was to analyze whether the cohabitation with WT animals could revert or at least ameliorate the deterioration in the nervous and immune systems that female TH-HZ mice show at adult age. Female TH-HZ and WT mice at age of 3-4 weeks were divided into following groups: control TH-HZ (5 TH-HZ mice in the cage; TH-HZ100%), control WT (5 WT mice in the cage; WT100%), TH-HZ > 50% and WT < 50% (5 TH-HZ with 2 WT mice in each cage) as well as TH-HZ < 50% and WT > 50% (2 TH-HZ and 5 WT mice in each cage). At the age of 37-38 weeks, all mice were submitted to a battery of behavioral tests, evaluating sensorimotor abilities, exploratory capacities and anxiety-like behaviors. Subsequently, peritoneal leukocytes were extracted and several immune functions as well as oxidative and inflammatory stress parameters were analyzed. The results showed that the TH-HZ < 50% group had improved behavioral responses, especially anxiety-like behaviors, and the immunosenescence and oxidative stress of their peritoneal leukocytes were ameliorated. However, WT mice that cohabited with TH-HZ mice presented higher anxiety-like behaviors and deterioration in immune functions and in their inflammatory stress parameters. Thus, this social environment is capable of ameliorating the impairments associated with a haploinsufficiency of the th gene. Graphical Abstract.

The ratio of prematurely aging to non-prematurely aging mice cohabiting, conditions their behavior, immunity and lifespan

Adult prematurely aging mice (PAM) show behavioral deterioration, premature immunosenescence and increased oxidative stress, impairments that are associated with their shorter lifespan, compared to the corresponding exceptional non-prematurely aging mice (ENPAM). When PAM live in a predominantly ENPAM environment (2/5, respectively) they exhibit an improvement of immunity and redox state in their spleen and thymus leukocytes, and an increased lifespan. Nevertheless, it is unknown if other PAM/ENPAM ratios could affect behavioral and peritoneal leukocyte functions of PAM and change their lifespan. ENPAM and PAM were divided into the following groups: C-ENPAM (8 ENPAM in the cage); C-PAM (8 PAM in the cage); ENPAM>50% and PAM<50% (5 ENPAM/2 PAM in each cage); ENPAM = 50% and PAM = 50% (4 ENPAM/4 PAM in each cage), and PAM>50% and ENPAM<50% (5 PAM/2 ENPAM in each cage). After two months, mice were submitted to a battery of behavioral tests. Several functions and oxidative stress parameters were then assessed in their peritoneal leukocytes. Animals were maintained in these conditions to analyze their lifespan. The results showed that PAM>50%, PAM = 50% and PAM<50% exhibited better behavioral responses, immunity and redox states in their peritoneal leukocytes than C-PAM. This improvement was higher when the number of ENPAM in the cage was increased, with most of the parameters in PAM<50% reaching similar values to those in C-ENPAM, and an increased lifespan. However, ENPAM that cohabited with PAM showed, in general, an impairment of parameters studied. In conclusion, the PAM/ENPAM cohabitation ratio is relevant to behavior and immunity.

Anti-Inflammatory Effects of Alnus Sibirica Extract on In Vitro and In Vivo Models

Alnus sibirica extracts (ASex) have long been used in Oriental medicine to treat various conditions. To provide a scientific basis for this application and the underlying mechanism, we investigated the anti-inflammatory effects of ASex in vitro and in vivo. The in vitro model was established using human dermal fibroblasts (HDFs) treated with inflammatory stimulants (lipopolysaccharide, tumor necrosis factor-alpha, interferon-gamma). Lactate dehydrogenase and reverse transcription-polymerase chain reaction showed that ASex inhibited the increased expression of acute-phase inflammatory cytokines. The in vivo model was established by inducing skin inflammation in NC/Nga mice via the repeated application of house dust mite (HDM) ointment to the ears and back of the mice for eight weeks. HDM application increased the severity of skin lesions, eosinophil/mast cell infiltration, and serum immunoglobulin E levels, which were all significantly decreased by ASex treatment, demonstrating the same degree of protection as hydrocortisone. Overall, ASex showed excellent anti-inflammatory effects both in vitro and in vivo, suggesting its potential as an excellent candidate drug to reduce skin inflammation.

Quail egg homogenate alleviates food allergy induced eosinophilic esophagitis like disease through modulating PAR-2 transduction pathway in peanut sensitized mice

The present pharmacotherapy for eosinophilic esophagitis (EoE) fundamentally depend on inhaled corticosteroids. Despite the fact that oral intake of topical steroids can be successful in restricting EoE-related inflammation, there are concerns with respect to the long term utilization of steroids, especially in kids. In the current research, we assess the effect of quail egg, which is reportedly a known serine protease inhibitor, on symptomatology and immune responses in a peanut-sensitized mouse model of food allergy induced EoE. Daily oral treatment with quail egg attenuated mice symptomatology and immune response. Treatment with quail egg inhibited antigen-prompted increments in mouse tryptase and eosinophil cationic protein (ECP) in serum and eosinophil in inflamed tissues like oesophagus, lung, and digestive system. Quail egg treatment resulted in decreased antibody specific IgE and IgG1 and a variety of inflammatory genes that were abnormally expressed in EoE. Other effects included increased IL-10, decreased PAR-2 activation and NF-kB p65 in inflamed tissues. Our results suggest that quail egg treatment may have therapeutic potential in attenuating the symptoms of food allergy induced EoE like disease through regulating PAR-2 downstream pathway by blocking the activation of the transcription factor NF-kB p65 activity.

[Premature immunosenescence in catecholamines syntesis deficient mice. Effect of social environment]

INTRODUCTION

Healthy state depends on the appropriate function of the homeostatic systems (nervous, endocrine and immune systems) and the correct communication between them. The functional and redox state of the immune system is an excellent marker of health, and animals with premature immunosenescence show a shorter lifespan. Since catecholamines modulate the function of immune cells, the alteration in their synthesis could provoke immunosenescence. The social environment could be a strategy for modulating this immunosenescence.

AIM

To determine if an haploinsufficiency of tyrosine hydroxylase (TH), the limiting enzyme of synthesis of catecholamines, may produce a premature immunosenescence and if this immunosenescence could be modulated by the social environment.

MATERIALS AND METHODS

Adult (9±1 months) male ICR-CD1 mice with deletion of a single allele (hemi-zygotic: HZ) of the tyrosine hydroxylase enzyme (TH-HZ) and wild-type (WT) mice were used. Animals were housed in four subgroups: WT>50% (in the cage, the proportion of WT mice was higher than 50% in relation to TH-HZ), WT<50%, TH-HZ<50% and TH-HZ>50%. Peritoneal leukocytes were collected and phagocytosis, chemotaxis and proliferation of lymphocytes in the presence of lipopolysaccharide were analyzed. Glutathione reductase and glutathione peroxidase activities as well as oxidized/reduced glutathione ratio were studied.

RESULTS

TH-HZ>50% mice showed a deteriorated function and redox state in leukocytes respect to WT>50% and similar to old mice. However, TH-HZ<50% animals had similar values to those found in WT<50% mice.

CONCLUSION

The haploinsufficiency of TH generates premature immunosenescence, which appears to be compensated by living together with an appropriate number of WT animals.

Repeated administration of IL-31 upregulates IL-31 receptor A (IL-31RA) in dorsal root ganglia and causes severe itch-associated scratching behaviour in mice

We investigated the effects of repeated administration of interleukin-31 (IL-31) on itch-associated scratching counts (long-lasting scratching, LLS) and IL-31-related receptor mRNA expression in mice. Intra-dermal (i.d.) injection of IL-31 (100 and 300 ng/site) every 12 h for 3 days significantly increased LLS. Repeated administration of IL-31 also increased the expression of IL-31 receptor A (IL-31RA) and oncostatin M receptor beta (OSMRβ) in dorsal root ganglia (DRG). After the repeated administration of IL-31 was discontinued, IL-31RA expression decreased and reached the baseline level 2 days after the last dose of IL-31. LLS changed along with DRG IL-31RA expression. Moreover, IL-31-induced IL-31RA protein expression was confirmed by Western blotting analysis. These data suggest that IL-31 upregulates IL-31RA expression in DRG neuron cell bodies, and cutaneous-injected IL-31-induced itching is enhanced by DRG IL-31RA expression in mice.

A single dose of interleukin-31 (IL-31) causes continuous itch-associated scratching behaviour in mice

We investigated the effects of a single dose of mouse interleukin-31 (IL-31) on scratching behaviour in comparison with spontaneous skin-lesion- or serotonin (5-HT)- induced scratching behaviour in NC/Nga and BALB/c mice. Intradermal (i.d.) injection of IL-31 caused a gradual increase in long-lasting scratching (LLS, over 1.5 s) about 3 h after administration followed by a gradual decrease for over 24 h after administration. I.d. injection of IL-31 significantly increased the total LLS counts/24 h but not short-lasting scratching (SLS, 0.3-1.5 s). In skin-lesioned NC/Nga mice, the LLS but not SLS counts were significantly higher than those in non-skin-lesioned NC/Nga mice. We also investigated 5-HT-induced scratching in BALB/c mice, SLS but not LLS increased immediately after the injection and then decreased to baseline after at 20 min. These results suggest that IL-31 may participate in the sensation of itching and promote scratching behaviour in skin-lesioned NC/Nga mice, an animal model of atopic dermatitis (AD).

Topical application of PPARα (but not β/δ or γ) suppresses atopic dermatitis in NC/Nga mice

BACKGROUND

Peroxisome proliferator-activated receptors (PPARs) are nuclear receptors, which regulate not only adipogenesis and proliferation/differentiation but also the immune response of cells. Because topical application of the activators of some PPAR isoforms improved clinical symptoms in patients with atopic dermatitis (AD), we investigated the role of PPAR activators using a murine AD model in NC/Nga mice; to the best of our knowledge, this has not been previously reported.

METHODS

Activators of three PPAR isoforms (α, β/δ, γ) were topically applied on inflamed skin in a murine AD model that was developed by repeated topical application of mite antigen in NC/Nga mice. The efficacy of each topical PPAR activator was evaluated immunologically and serologically.

RESULTS

Topical application of the PPARα activator, but not of the activators of PPARβ/δ or PPARγ, improved clinical dermatitis, reduced inflammatory cell infiltration in the dermis, and alleviated the elevation of serum IgE levels. In addition, PPARα expression was downregulated in the epidermis in our murine AD model, as is seen in patients with AD.

CONCLUSIONS

Topical application of PPARα activator could be a potent therapeutic agent for patients with AD and could take the place of topical steroid treatments.

T cell-specific overexpression of interleukin-27 receptor α subunit (WSX-1) prevents spontaneous skin inflammation in MRL/lpr mice

BACKGROUND

Interleukin (IL)-27 and WSX-1, the receptor α-specific subunit, have been shown to play important roles in initiating Th1 responses and in inducing immune modulation, and the immunosuppressive effect of IL-27 appears to be exerted via suppression of IL-10 and IL-17, which may participate in the pathogenesis of human systemic lupus erythematosus (SLE).

OBJECTIVES

To examine the significance of IL-27/WSX-1 signalling in spontaneous skin inflammation of MRL/lpr mice, a model for SLE.

METHODS

The severity and development of skin lesions, dermal inflammatory cells and epidermal-dermal depositions in the skin lesions of MRL/lpr mice with CD2-promoted WSX-1 overexpression (WSX-1 Tg mice) and those with globally disrupted WSX-1 (WSX-1 KO mice) were examined and compared with those of MRL/lpr mice.

RESULTS

By 4 months of age, both WSX-1 KO mice and control MRL/lpr mice developed predominantly similar skin inflammation, while WSX-1 Tg mice hardly did so, demonstrating that intensifying IL-27/WSX-1 signalling on T cells prevents the spontaneous skin inflammation. WSX-1 KO mice showed Th2-type skin inflammation as evidenced by the Th2-prone dermal infiltrating cells and an absence of cutaneous Th1-type IgG deposition. Interestingly, there were significant IL-17+ dermal infiltrating cells in both WSX-1 KO and control MRL/lpr mice, which might potentially contribute to the formation of skin inflammation in these mice.

CONCLUSIONS

These data indicate that IL-27/WSX-1 signalling may play a protective role in the development of SLE-like skin inflammation, and modulating IL-27/WSX-1 signalling might be an interesting therapeutic strategy in the treatment of SLE.

CFTR-deficiency renders mice highly susceptible to cutaneous symptoms during mite infestation

Pruritus, also known as itch, is a sensation that causes a desire to scratch. Prolonged scratching exacerbates skin lesions in several skin diseases such as atopic dermatitis. Here, we identify the cystic fibrosis transmembrane conductance regulator (CFTR/Cftr), an integral membrane protein that mediates transepithelial chloride transport, as a determinant factor in mice for the susceptibility to several cutaneous symptoms during mite infestation. Mice that endogenously express dysfunctional Cftr (Cftr(ΔF508/ΔF508)) show significant increase of scratching behavior and skin fibrosis after mite exposure. These phenotypes were due to the increased expression of nerve growth factor (NGF) that augments the sensitization of peripheral nerve fibers. Moreover, protein gene product 9.5 (PGP9.5)-positive neurites were abundant in the epidermis of mite-infested Cftr(ΔF508/ΔF508) mice. Furthermore, mite-infested Cftr(+/+) mice orally administered with a chloride channel inhibitor glibenclamide had higher scratching count and increased level of NGF than vehicle-treated mice. Consistently, mite extract-exposed primary and transformed human keratinocytes, treated with CFTR inhibitor, had significantly higher level of NGF mRNA compared with vehicle-treated, mite extract-exposed cells. These results reveal that CFTR in keratinocytes plays a critical role for the regulation of peripheral nerve function and pruritus sensation, and suggest that Cftr(ΔF508/ΔF508) mice may serve as a novel mouse model that represents NGF-dependent generation of pruritus.

Role of scratch-induced cutaneous prostaglandin D2production on atopic-like scratching behaviour in mice

NC/Nga mice are known to develop scratching dermatitis akin to atopic dermatitis, under conventional (Conv), but not under the specific-pathogen-free (SPF) condition. In this study, we examined the effects of mechanical-scratching on the spontaneous scratching counts (sign of itching), in relation to the cutaneous prostaglandin D2 (PGD2) levels in NC/Nga or BALB/c mice. Mechanical-scratching increased the cutaneous barrier damage and PGD2 levels in both strain mice under the SPF condition. By 4 weeks of cohabitation with the skin-lesioned NC/Nga mice, both the increase in the spontaneous scratching and development of dermatitis score were higher in the Conv-NC/Nga than in the Conv-BALB/c mice. At this time-point, the cutaneous PGD2 level induced by mechanical-scratching was significantly lower in the Conv-NC/Nga when compared with that in the SPF-NC/Nga mice, and that in the Conv-BALB/c was almost equal to that in the SPF-BALB/c mice. With mechanical scratches, the cohabitation-induced scratching was suppressed in the Conv-BALB/c, but not in the Conv-NC/Nga mice. These results suggest that the scratch-induced cutaneous PGD2 inhibits scratching and the subsequent development of dermatitis in BALB/c, while the impaired scratch-induced cutaneous PGD2 production in the NC/Nga mice resulted in no suppression of scratching, and aggravated the dermatitis.

A hypothetical mechanism of intraepidermal neurite formation in NC/Nga mice with atopic dermatitis

BACKGROUND

Pruritus is a symptom in atopic dermatitis (AD). Previous studies have reported that increased intraepidermal neurites are observed in AD, suggesting that the neuritogenesis is related to itching in the skin.

OBJECTIVE

This study was conducted to reveal the mechanism of intraepidermal neurite formation in AD.

METHODS

In this study, we used conventional (Conv) NC/Nga mice with AD. NC/Nga mice maintained in specific pathogen-free (SPF) condition were used as a control with no AD. Distribution of intraepidermal neurites and expression patterns of growth factors (NGF and amphiregulin (AR)) and cell-cell junctional molecules (E-cadherin, zona occludens 1 (ZO-1) and desmoglein 3 (Dsg3)) were examined in the skins by immunohistochemistry or quantitative RT-PCR. Furthermore, detection of gelatinase activity was performed with in situ zymography. The same experiments were conducted in ICR mice for comparison with NC/Nga mice.

RESULTS

Neurite density and expression levels of growth factors and gelatinase were remarkably increased in the epidermis of Conv-NC/Nga mice compared with those of SPF-NC/Nga mice. Decreased expression of E-cadherin and ZO-1 and misexpression of Dsg3 were also observed in the atopic skins. In comparison with ICR mice, increases of neurite density and gelatinase activity were found in the skins of SPF-NC/Nga mice but expression levels of growth factors and cell-cell junctional molecules were unchanged.

CONCLUSIONS

Increases of growth factors and gelatinase activity may be related to neurite outgrowth in the epidermis of atopic NC/Nga mice. Additionally, abnormal expressions of cell-cell junctional molecules in the epidermis may provide intercellular spaces for the neurite formation.

The anti-pruritic efficacy of TS-022, a prostanoid DP1 receptor agonist, is dependent on the endogenous prostaglandin D2 level in the skin of NC/Nga mice

TS-022 is a prostanoid DP(1) receptor agonist, originally developed as a novel anti-pruritic drug for atopic dermatitis. The drug has been shown to suppress scratching and improve the skin inflammation in the NC/Nga (NC) mouse, a model of atopic dermatitis. Corticosteroids are commonly used as effective agents for the treatment of atopic dermatitis. We examined the anti-pruritic efficacy of TS-022 in NC mice cohabited with skin-lesioned NC mice, which showed spontaneous scratching without skin lesions in the early phase and chronic itching with severe dermatitis in the late phase, in comparison with that of dexamethasone. We have previously reported that prostaglandin D(2) might have a physiological role in the inhibition of pruritus. While after 2 weeks of cohabitation with skin-lesioned NC mice (early phase of dermatitis, characterized by the appearance of spontaneous scratching), topically applied TS-022 exhibited a weak anti-pruritic effect in the NC mice, after 6 weeks of cohabitation (late phase, characterized by both chronic scratching and dermatitis), the drug exerted potent anti-pruritic activity. In contrast, dexamethasone exerted potent anti-pruritic effect in both the early and late phases. Indomethacin aggravated the scratching in the early phase, but had no effect in the late phase. The skin prostaglandin D(2) level was significantly increased in the early phase, to subsequently declined and return to the basal level in the late phase. The cutaneous ability for prostaglandin D(2) production following topical application of arachidonic acid or mechanical scratching was decreased in the late phase. Moreover, the expression level of the prostanoid DP(1) receptor in the skin was increased in the late phase. These findings suggest that the potent anti-pruritic activity of TS-022 in the late phase might be attributable to the decrease of endogenous prostaglandin D(2) production and increase of prostanoid DP(1) receptor expression.

Involvement of IL-31 on scratching behavior in NC/Nga mice with atopic-like dermatitis

Pruritus is an important symptom in atopic dermatitis (AD), but the major pruritogen has not been identified. NC/Nga mice, spontaneously develop an eczematous AD-like skin lesion when kept under conventional conditions, but not under specific pathogen-free (SPF) conditions, have been thought to be an animal model for AD. In this study, to determine whether newly identified cytokine, IL-31, may be involved in pruritus of AD, we examined the IL-31 expression in spontaneous dermatitis model which showed itch-associated long-lasting (over 1.5 s duration) scratching behavior and compared with that of hapten-induced contact dermatitis model without itch-associated long-lasting scratching behavior, using NC/Nga mice. In NC/Nga mice cohabited with NC/Nga mice which developed severe dermatitis for 2 weeks (conventional NC/Nga mice), the numbers of long-lasting scratching counts were significantly increased. Yet in 2,4,6-trinitrochlorobenzene (TNCB)-sensitized and challenged mice (TNCB-applied NC/Nga mice), no significant increase in long-lasting scratching counts was observed. In conventional NC/Nga mice with long-lasting scratching behavior, expression of IL-31 mRNA was increased, while in TNCB-applied NC/Nga mice without long-lasting scratching behavior, the expression of IL-31 mRNA were unchanged. There was a good correlation between the scratching counts and expression of IL-31 mRNA in conventional NC/Nga mice, but not so in TNCB-applied NC/Nga mice. These results suggest that IL-31 causes the itch-associated scratching behavior in conventional NC/Nga mice, an experimental animal model for AD.