Immune competency of a hairless mouse strain for improved preclinical studies in genetically engineered mice

Exploring the Role of Spatial Confinement in Immune Cell Recruitment and Regeneration of Skin Wounds

Microporous annealed particle (MAP) scaffolds are injectable granular materials comprised of micron sized hydrogel particles (microgels). The diameter of these microgels directly determines the size of the interconnected void space between particles where infiltrating or encapsulated cells reside. This tunable porosity allows the authors to use MAP scaffolds to study the impact of spatial confinement (SC) on both cellular behaviors and the host response to biomaterials. Despite previous studies showing that pore size and SC influence cellular phenotypes, including mitigating macrophage inflammatory response, there is still a gap in knowledge regarding how SC within a biomaterial modulates immune cell recruitment in vivo in wounds and implants. Thus, the immune cell profile within confined and unconfined biomaterials is studied using small (40 µm), medium (70 µm), and large (130 µm) diameter spherical microgels, respectively. This work uncovered that MAP scaffolds impart regenerative wound healing with an IgG1-biased Th2 response. MAP scaffolds made with large microgels promote a balanced pro-regenerative macrophage response, resulting in enhanced wound healing with mature collagen regeneration and reduced inflammation levels.

Recuperative herbal formula Jing Si maintains vasculature permeability balance, regulates inflammation and assuages concomitants of "Long-Covid"

Coronavirus disease 2019 (COVID-19) is a worldwide health threat that has long-term effects on the patients and there is currently no efficient cure prescribed for the treatment and the prolonging effects. Traditional Chinese medicines (TCMs) have been reported to exert therapeutic effect against COVID-19. In this study, the therapeutic effects of Jing Si herbal tea (JSHT) against COVID-19 infection and associated long-term effects were evaluated in different in vitro and in vivo models. The anti-inflammatory effects of JSHT were studied in lipopolysaccharide (LPS)-stimulated RAW 264.7 cells and in Omicron pseudotyped virus-induced acute lung injury model. The effect of JSHT on cellular stress was determined in HK-2 proximal tubular cells and H9c2 cardiomyoblasts. The therapeutic benefits of JSHT on anhedonia and depression symptoms associated with long COVID were evaluated in mice models for unpredictable chronic mild stress (UCMS). JSHT inhibited the NF-ƙB activities, and significantly reduced LPS-induced expression of TNFα, COX-2, NLRP3 inflammasome, and HMGB1. JSHT was also found to significantly suppress the production of NO by reducing iNOS expression in LPS-stimulated RAW 264.7 cells. Further, the protective effects of JSHT on lung tissue were confirmed based on mitigation of lung injury, repression in TMRRSS2 and HMGB-1 expression and reduction of cytokine storm in the Omicron pseudotyped virus-induced acute lung injury model. JSHT treatment in UCMS models also relieved chronic stress and combated depression symptoms. The results therefore show that JSHT attenuates the cytokine storm by repressing NF-κB cascades and provides the protective functions against symptoms associated with long COVID-19 infection.

Using bioluminescence to image gene expression and spontaneous behavior in freely moving mice

Bioluminescence imaging (BLI) of gene expression in live animals is a powerful method for monitoring development, tumor growth, infections, healing, and other progressive, long-term biological processes. BLI remains an effective approach for reducing the number of animals needed to monitor dynamic changes in gene activity because images can be captured repeatedly from the same animals. When examining these ongoing changes, it is sometimes necessary to remove rhythmic effects on the bioluminescence signal caused by the circadian clock's daily modulation of gene expression. Furthermore, BLI using freely moving animals remains limited because the standard procedures can alter normal behaviors. Another obstacle with conventional BLI of animals is that luciferin, the firefly luciferase substrate, is usually injected into mice that are then imaged while anesthetized. Unfortunately, the luciferase signal declines rapidly during imaging as luciferin is cleared from the body. Alternatively, mice are imaged after they are surgically implanted with a pump or connected to a tether to deliver luciferin, but stressors such as this surgery and anesthesia can alter physiology, behavior, and the actual gene expression being imaged. Consequently, we developed a strategy that minimizes animal exposure to stressors before and during sustained BLI of freely moving unanesthetized mice. This technique was effective when monitoring expression of the Per1 gene that serves in the circadian clock timing mechanism and was previously shown to produce circadian bioluminescence rhythms in live mice. We used hairless albino mice expressing luciferase that were allowed to drink luciferin and engage in normal behaviors during imaging with cooled electron-multiplying-CCD cameras. Computer-aided image selection was developed to measure signal intensity of individual mice each time they were in the same posture, thereby providing comparable measurements over long intervals. This imaging procedure, performed primarily during the animal's night, is compatible with entrainment of the mouse circadian timing system to the light cycle while allowing sampling at multi-day intervals to monitor long-term changes. When the circadian expression of a gene is known, this approach provides an effective alternative to imaging immobile anesthetized animals and can removing noise caused by circadian oscillations and body movements that can degrade data collected during long-term imaging studies.

Particle Engineering of Innovative Nanoemulsion Designs to Modify the Accumulation in Female Sex Organs by Particle Size and Surface Charge

Particle engineering of nanosized drug delivery systems (DDS) can be used as a strategic tool to influence their pharmacokinetics after intravenous (i.v.) application by the targeted adaptation of their particle properties according to the needs at their site of action. This study aimed to investigate particle properties depending on patterns in the biodistribution profile to modify the accumulation in the female sex organs using tailor-made nanoemulsion designs and thereby to either increase therapeutic efficiency for ovarian dysfunctions and diseases or to decrease the side effects caused by unintended accumulation. Through the incorporation of the anionic phospholipid phosphatidylglycerol (PG) into the stabilizing macrogol 15 hydroxystearate (MHS) layer of the nanoemulsions droplets, it was possible to produce tailor-made nanoparticles with tunable particle size between 25 to 150 nm in diameter as well as tunable surface charges between −2 to nearly −30 mV zeta potential using a phase inversion-based process. Three chosen negatively surface-charged nanoemulsions of 50, 100, and 150 nm in diameter showed very low cellular toxicities on 3T3 and NHDF fibroblasts and merely interacted with the blood cells, but instead stayed inert in the plasma. In vivo and ex vivo fluorescence imaging of adult female mice i.v. injected with the negatively surface-charged nanoemulsions revealed a high accumulation depending on their particle size in the reticuloendothelial system (RES), being found in the liver and spleen with a mean portion of the average radiant efficiency (PARE) between 42–52%, or 8–10%, respectively. With increasing particle size, an accumulation in the heart was detected with a mean PARE up to 8%. These three negatively surface-charged nanoemulsions overcame the particle size-dependent accumulation in the female sex organs and accumulated equally with a small mean PARE of 5%, suitable to reduce the side effects caused by unintended accumulation while maintaining different biodistribution profiles. In contrast, previously investigated neutral surface-charged nanoemulsions accumulated with a mean PARE up to 10%, strongly dependent on their particle sizes, which is useful to improve the therapeutic efficacy for ovarian dysfunctions and diseases.

Exposure to the immunomodulatory chemical triclosan differentially impacts immune cell populations in the skin of haired (BALB/c) and hairless (SKH1) mice

Workers across every occupational sector have the potential to be exposed to a wide variety of chemicals, and the skin is a primary route of exposure. Furthermore, exposure to certain chemicals has been linked to inflammatory and allergic diseases. Thus, understanding the immune responses to chemical exposures on the skin and the potential for inflammation and sensitization is needed to improve worker safety and health. Responses in the skin microenvironment impact the potential for sensitization; these responses may include proinflammatory cytokines, inflammasome activation, barrier integrity, skin microbiota, and the presence of immune cells. Selection of specific mouse strains to evaluate skin effects, such as haired (BALB/c) or hairless (SKH1) mice, varies dependent on experimental design and needs of a study. However, dermal chemical exposure may impact reactions in the skin differently depending on the strain of mouse. Additionally, there is a need for established methods to evaluate immune responses in the skin. In this study, exposure to the immunomodulatory chemical triclosan was evaluated in two mouse models using immunophenotyping by flow cytometry and gene expression analysis. BALB/c mice exposed to triclosan (2%) had a higher number and frequency of neutrophils and lower number and frequency of dendritic cells in the skin compared to controls. Although these changes were not observed in SKH1 mice, SKH1 mice exposed to triclosan had a higher number and frequency of type 2 innate lymphoid cells in the skin. Taken together, these results demonstrate that exposure to an immunomodulatory chemical, triclosan, differentially impacts immune cell populations in the skin of haired and hairless mice. Additionally, the flow cytometry panel reported in this manuscript, in combination with gene expression analysis, may be useful in future studies to better evaluate the effect of chemical exposures on the skin immune response. These findings may be important to consider during strain selection, experimental design, and result interpretation of chemical exposures on the skin.

Transposon-triggered innate immune response confers cancer resistance to the blind mole rat

Blind mole rats (BMRs) are small rodents, characterized by exceptionally long lifespan (> 21 years) and resistance to both spontaneous and induced tumorigenesis. Here we report that cancer resistance in the BMR is mediated by retrotransposable elements (RTEs). BMR cells and tissues express very low levels of DNA methyltransferase 1 (DNMT1). Upon cell hyperplasia, the BMR genome DNA loses methylation, resulting in activation of RTEs. Up-regulated RTEs form cytoplasmic RNA/DNA hybrids, which activate cGAS-STING pathway to induce cell death. Although this mechanism is enhanced in the BMR, we show that it functions in mice and human. We propose that RTEs were coopted to serve as tumor suppressors that monitor cell proliferation and are activated in premalignant cells to trigger cell death via activation of innate immune response. RTEs activation is a double-edged sword, serving as a tumor suppressor but in late life contributing to aging via induction of sterile inflammation.

Coxiella burnetii Whole Cell Vaccine Produces a Th1 Delayed-Type Hypersensitivity Response in a Novel Sensitized Mouse Model

Q-VAX®, a whole cell, formalin-inactivated vaccine, is the only vaccine licensed for human use to protect against Coxiella burnetii, the cause of Q fever. Although this vaccine provides long-term protection, local and systemic reactogenic responses are common in previously sensitized individuals which prevents its use outside of Australia. Despite the importance of preventing these adverse reactions to develop widely accepted, novel vaccines against C. burnetii, little is understood about the underlying cellular mechanisms. This is mostly attributed to the use of a guinea pig reactogenicity model where complex cellular analysis is limited. To address this, we compared three different mouse strains develop a model of C. burnetii whole cell vaccine reactogenic responses. SKH1 and C57Bl/6, but not BALBc mice, develop local granulomatous reactions after either infection- or vaccine-induced sensitization. We evaluated local and systemic responses by measuring T cell populations from the vaccination site and spleen during elicitation using flow cytometry. Local reaction sites showed influx of IFNγ+ and IL17a+ CD4 T cells in sensitized mice compared with controls and a reduction in IL4+ CD4 T cells. Additionally, sensitized mice showed a systemic response to elicitation by an increase in IFNγ+ and IL17a+ CD4 T cells in the spleen. These results indicate that local and systemic C. burnetii reactogenic responses are consistent with a Th1 delayed-type hypersensitivity. Our experiments provide insights into the pathophysiology of C. burnetii whole cell vaccine reactogenicity and demonstrate that C57Bl/6 and SKH1 mice can provide a valuable model for evaluating the reactogenicity of novel C. burnetii vaccine candidates.

Characterization of Permeability Barrier Dysfunction in a Murine Model of Cutaneous Field Cancerization Following Chronic UV-B Irradiation: Implications for the Pathogenesis of Skin Cancer

Simple Summary

In the present work, we developed an experimental preclinical model of skin with cutaneous field cancerization after chronic UV-B light exposure in an immunologically intact mouse model (SKH1 aged mice). We observed impairments in the transepidermal water loss, stratum corneum hydration, and surface pH. We also detected a marked hyperkeratotic hyperplasia of the epidermis, induction of keratinocyte hyperproliferation, incidental actinic keratosis, and in situ squamous cell carcinomas in the UV-B light-irradiated groups. In this context, the association between the permeability barrier impairment and keratinocyte hyperproliferation might be considered a new target in the management of skin with cutaneous field cancerization. As current therapeutic approaches to actinic keratosis and cutaneous field cancerization only focus on the direct antineoplastic, immunomodulatory, or photodynamic effects of approved topical drugs, this mouse model of skin with cutaneous field cancerization might be helpful for both the identification and screening of potentially new preventive strategies or treatments (e.g., skin barrier therapies).

Abstract

Chronic ultraviolet B (UV-B) irradiation is known to be one of the most important hazards acting on the skin and poses a risk of developing photoaging, skin with cutaneous field cancerization (CFC), actinic keratosis (AKs), and squamous cell carcinomas (SCCs). Most of the UV-B light is absorbed in the epidermis, affecting the outermost cell layers, the stratum corneum, and the stratum granulosum, which protects against this radiation and tries to maintain the permeability barrier. In the present work, we show an impairment in the transepidermal water loss, stratum corneum hydration, and surface pH after chronic UV-B light exposure in an immunologically intact mouse model (SKH1 aged mice) of skin with CFC. Macroscopic lesions of AKs and SCCs may develop synchronically or over time on the same cutaneous surface due to both the presence of subclinical AKs and in situ SCC, but also the accumulation of different mutations in keratinocytes. Focusing on skin with CFC, yet without the pathological criteria of AKs or SCC, the presence of p53 immunopositive patches (PIPs) within the epidermis is associated with these UV-B-induced mutations. Reactive epidermis to chronic UV-B exposure correlated with a marked hyperkeratotic hyperplasia, hypergranulosis, and induction of keratinocyte hyperproliferation, while expressing an upregulation of filaggrin, loricrin, and involucrin immunostaining. However, incidental AKs and in situ SCC might show neither hypergranulosis nor upregulation of differentiation markers in the upper epidermis. Despite the overexpression of filaggrin, loricrin, involucrin, lipid enzymes, and ATP-binding cassette subfamily A member 12 (ABCA12) after chronic UV-B irradiation, the permeability barrier, stratum corneum hydration, and surface pH were severely compromised in the skin with CFC. We interpret these results as an attempt to restore the permeability barrier homeostasis by the reactive epidermis, which fails due to ultrastructural losses in stratum corneum integrity, higher pH on skin surface, abundant mast cells in the dermis, and the common presence of incidental AKs and in situ SCC. As far as we know, this is the first time that the permeability barrier has been studied in the skin with CFC in a murine model of SCC induced after chronic UV-B irradiation at high doses. The impairment in the permeability barrier and the consequent keratinocyte hyperproliferation in the skin of CFC might play a role in the physiopathology of AKs and SCCs.

Control of Breast Cancer Pathogenesis by Histone Methylation and the Hairless Histone Demethylase

Breast cancer is a highly heterogeneous disease, encompassing many subtypes that have distinct origins, behaviors, and prognoses. Although traditionally seen as a genetic disease, breast cancer is now also known to involve epigenetic abnormalities. Epigenetic regulators, such as DNA methyltransferases and histone-modifying enzymes, play essential roles in gene regulation and cancer development. Dysregulation of epigenetic regulator activity has been causally linked with breast cancer pathogenesis. Hairless (HR) encodes a 130-kDa transcription factor that is essential for development and tissue homeostasis. Its role in transcription regulation is partly mediated by its interaction with multiple nuclear receptors, including thyroid hormone receptor, retinoic acid receptor-related orphan receptors, and vitamin D receptor. HR has been studied primarily in epidermal development and homeostasis. Hr-mutant mice are highly susceptible to ultraviolet- or carcinogen-induced skin tumors. Besides its putative tumor suppressor function in skin, loss of HR function has also been implicated in increased leukemia susceptibility and promotes the growth of melanoma and brain cancer cells. HR has also been demonstrated to function as a histone H3 lysine 9 demethylase. Recent genomics studies have identified HR mutations in a variety of human cancers, including breast cancer. The anticancer function and mechanism of action by HR in mammary tissue remains to be investigated. Here, we review the emerging role of HR, its histone demethylase activity and histone methylation in breast cancer development, and potential for epigenetic therapy.

Ovarian Accumulation of Nanoemulsions: Impact of Mice Age and Particle Size

Nanotechnology in the field of drug delivery comes with great benefits due to the unique physicochemical properties of newly developed nanocarriers. However, they may come as well with severe toxicological side effects because of unwanted accumulation in organs outside of their targeted site of actions. Several studies showed an unintended accumulation of various nanocarriers in female sex organs, especially in the ovaries. Some led to inflammation, fibrosis, or decreasing follicle numbers. However, none of these studies investigated ovarian accumulation in context to both reproductive aging and particle size. Besides the influences of particle size, the biodistribution profile may be altered as well by reproductive aging because of reduced capacities of the reticuloendothelial system (RES), changes in sex steroid hormone levels as well as altering ovarian stromal blood flow. This systematic investigation of the biodistribution of intravenously (i.v) injected nanoemulsions revealed significant dependencies on the two parameters particle size and age starting from juvenile prepubescent to senescent mice. Using fluorescent in vivo and ex vivo imaging, prepubescent mice showed nearly no accumulation of nanoemulsion in their uteri and ovaries, but high accumulations in the organs of the RES liver and spleen independently of the particle size. In fertile adult mice, the accumulation increased significantly in the ovaries with an increased particle size of the nanoemulsions by nearly doubling the portion of the average radiant efficiency (PARE) to ~10% of the total measured signal of all excised organs. With reproductive aging and hence loss of fertility in senescent mice, the accumulation decreased again to moderate levels, again independently of the particle size. In conclusion, the ovarian accumulation of these nanocarriers depended on both the age plus the particle size during maturity.

Reevaluation of the efficacy of favipiravir against rabies virus using in vivo imaging analysis

Rabies virus (RABV) is a highly neurotropic virus and the causative agent of rabies, an encephalitis with an almost 100% case-fatality rate that remains incurable after the onset of symptoms. Favipiravir (T-705), a broad-spectrum antiviral drug against RNA viruses, has been shown to be effective against RABV in vitro but ineffective in vivo. We hypothesized that favipiravir is effective in infected mice when RABV replicates in the peripheral tissues/nerves but not after virus neuroinvasion. We attempted to clarify this point in this study using in vivo bioluminescence imaging. We generated a recombinant RABV from the field isolate 1088, which expressed red firefly luciferase (1088/RFLuc). This allowed semiquantitative detection and monitoring of primary replication at the inoculation site and viral spread in the central nervous system (CNS) in the same mice. Bioluminescence imaging revealed that favipiravir (300 mg/kg/day) treatment commencing 1 h after intramuscular inoculation of RABV efficiently suppressed viral replication at the inoculation site and the subsequent replication in the CNS. However, virus replication in the CNS was not inhibited when the treatment began 2 days after inoculation. We also found that higher doses (600 or 900 mg/kg/day) of favipiravir could suppress viral replication in the CNS even when administration started 2 days after inoculation. These results support our hypothesis and suggest that a highly effective drug-delivery system into the CNS and/or the enhancement of favipiravir conversion to its active form are required to improve favipiravir treatment of rabies. Furthermore, the bioluminescence imaging system established in this study will facilitate the development of treatment for symptomatic rabies.

Predatory bacteria can protect SKH-1 mice from a lethal plague challenge

With the rise of antimicrobial resistance, novel ways to treat bacterial infections are required and the use of predatory bacteria may be one such approach. Bdellovibrio species have been shown in vitro to predate on a wide range of other Gram-negative bacteria, including CDC category A/B pathogens such as Yersinia pestis. The data reported here show that treatment of SKH-1 mice with Bdellovibrio bacteriovorus HD100 provided significant protection from a lethal challenge of Yersinia pestis CO92. This is the first report of protection conferred by predation in vivo against a systemic pathogen challenge. However, this protective effect was not observed in a preliminary study with Balb/c mice. Therefore the effects of the predatory bacteria are complex and may be dependent on immune status/genetics of the host. Overall, predatory bacteria may have utility as a therapeutic modality but further work is required to understand the predator-host interaction.

Liver fibrosis affects the targeting properties of drug delivery systems to macrophage subsets in vivo

Myeloid immune cells promote inflammation and fibrosis in chronic liver diseases. Drug delivery systems, such as polymers, liposomes and microbubbles, efficiently target myeloid cells in healthy liver, but their targeting properties in hepatic fibrosis remain elusive. We therefore studied the biodistribution of three intravenously injected carrier material, i.e. 10 nm poly(N-(2-hydroxypropyl)methacrylamide) polymers, 100 nm PEGylated liposomes and 2000 nm poly(butyl cyanoacrylate) microbubbles, in two fibrosis models in immunocompetent mice. While whole-body imaging confirmed preferential hepatic uptake even after induction of liver fibrosis, flow cytometry and immunofluorescence analysis revealed markedly decreased carrier uptake by liver macrophage subsets in fibrosis, particularly for microbubbles and polymers. Importantly, carrier uptake co-localized with immune infiltrates in fibrotic livers, corroborating the intrinsic ability of the carriers to target myeloid cells in areas of inflammation. Of the tested carrier systems liposomes had the highest uptake efficiency among hepatic myeloid cells, but the lowest specificity for cellular subsets. Hepatic fibrosis affected carrier uptake in liver and partially in spleen, but not in other tissues (blood, bone marrow, lung, kidney). In conclusion, while drug carrier systems target distinct myeloid cell populations in diseased and healthy livers, hepatic fibrosis profoundly affects their targeting efficiency, supporting the need to adapt nanomedicine-based approaches in chronic liver disease.

3D-printed Wash Station with Integrated Anesthesia Delivery Manifold for High-throughput Depilation of Laboratory Mice

Depilation (that is, hair removal) is a necessary prerequisite for many small animal surgeries and optical imaging experiments. Over-the-counter depilatory creams are widely used, owing to their efficacy, safety, and low rates of skin irritation and infection. However, the use of these creams is generally messy and time-consuming and generates considerable waste. Furthermore, the process itself varies markedly among laboratories. Here we present a 3D-printed device that simplifies the depilation procedure by integrating 3 key elements: 1) a multiple-port, self-scavenging anesthesia manifold, 2) curved animal holders with flow-through slats, and 3) a removable waste collection tray. Reflecting insights gained from an international survey about depilatory lab procedures that highlighted the lack of standardized protocols, this apparatus is designed to improve the neatness, throughput, and safety of mouse depilation, resulting in efficient and repeatable processes that bolster the welfare of both researchers and subjects.

Repeat application of microneedles does not alter skin appearance or barrier function and causes no measurable disturbance of serum biomarkers of infection, inflammation or immunity in mice in vivo

We address, for the first time, the impact of skin insertion on multiple occasions of polymeric microneedle arrays in an animal model in vivo. Dissolving microneedle arrays prepared from aqueous blends of 20% w/w Gantrez® S-97 BF and 40% w/w poly(vinyl pyrrolidone) 58kDa and hydrogel-forming microneedle arrays prepared from aqueous blends of and poly(ethyleneglycol) 10kDa were repeatedly applied to the skin of hairless mice in vivo. Skin appearance and skin barrier function, as illustrated by measurement of transepidermal water loss, were not measurably altered during the entire study period. Biomarkers of infection, immunity and inflammation/irritation were also statistically unchanged, regardless of the microneedle formulation, needle density or number of applications. Mice remained healthy throughout and continued to gain weight during the study. For example, transepidermal water loss values were typically in the range 10-15gm-2h-1 immediately prior to microneedle insertion and 15-25gm-2h-1 immediately following microneedle removal, regardless of when they were measured during the study periods. Serum biomarker levels, measured immediately post-mortem were always in the range 10-20µgml-1 for C-reactive protein, 0.5-1.5mgml-1 for Immunoglobulin G and 1000-2500pgml-1 for interleukin 1-β and were never statistically different from untreated controls. No measurable levels of tumour necrosis factor-α were found in any animals. These findings are encouraging for the formulations investigated, suggesting that their repeated use by patients will not cause undesirable side-effects. By beginning to address potential regulatory questions at an early stage, the microneedles field will be ideally-placed to take advantage of the potential market. This work illustrates a potential pre-clinical strategy for development of regulatory dossiers on microneedle technologies.

Spontaneous and Vaccine-Induced Clearance of Mus Musculus Papillomavirus 1 Infection

Mus musculus papillomavirus 1 (MmuPV1/MusPV1) induces persistent papillomas in immunodeficient mice but not in common laboratory strains. To facilitate the study of immune control, we sought an outbred and immunocompetent laboratory mouse strain in which persistent papillomas could be established. We found that challenge of SKH1 mice (Crl:SKH1-Hrhr) with MmuPV1 by scarification on their tail resulted in three clinical outcomes: (i) persistent (>2-month) papillomas (∼20%); (ii) transient papillomas that spontaneously regress, typically within 2 months (∼15%); and (iii) no visible papillomas and viral clearance (∼65%). SKH1 mice with persistent papillomas were treated by using a candidate preventive/therapeutic naked-DNA vaccine that expresses human calreticulin (hCRT) fused in frame to MmuPV1 E6 (mE6) and mE7 early proteins and residues 11 to 200 of the late protein L2 (hCRTmE6/mE7/mL2). Three intramuscular DNA vaccinations were delivered biweekly via in vivo electroporation, and both humoral and CD8 T cell responses were mapped and measured. Previously persistent papillomas disappeared within 2 months after the final vaccination. Coincident virologic clearance was confirmed by in situ hybridization and a failure of disease to recur after CD3 T cell depletion. Vaccination induced strong mE6 and mE7 CD8⁺ T cell responses in all mice, although they were significantly weaker in mice that initially presented with persistent warts than in those that spontaneously cleared their infection. A human papillomavirus 16 (HPV16)-targeted version of the DNA vaccine also induced L2 antibodies and protected mice from vaginal challenge with an HPV16 pseudovirus. Thus, MmuPV1 challenge of SKH1 mice is a promising model of spontaneous and immunotherapy-directed clearances of HPV-related disease.IMPORTANCE High-risk-type human papillomaviruses (hrHPVs) cause 5% of all cancer cases worldwide, notably cervical, anogenital, and oropharyngeal cancers. Since preventative HPV vaccines have not been widely used in many countries and do not impact existing infections, there is considerable interest in the development of therapeutic vaccines to address existing disease and infections. The strict tropism of HPV requires the use of animal papillomavirus models for therapeutic vaccine development. However, MmuPV1 failed to grow in common laboratory strains of mice with an intact immune system. We show that MmuPV1 challenge of the outbred immunocompetent SKH1 strain produces both transient and persistent papillomas and that vaccination of the mice with a DNA expressing an MmuPV1 E6E7L2 fusion with calreticulin can rapidly clear persistent papillomas. Furthermore, an HPV16-targeted version of the DNA can protect against vaginal challenge with HPV16, suggesting the promise of this approach to both prevent and treat papillomavirus-related disease.

Actinic keratosis modelling in mice: A translational study

Background

Actinic keratoses (AK) are pre-malignant cutaneous lesions caused by prolonged exposure to ultraviolet radiation. As AKs lesions are generally accepted to be the initial lesions in a disease continuum that progresses to squamous cell carcinoma (SCC), AK lesions have to be treated. They are also the second most common reason for visits to the dermatologist. Several treatments are available but their efficacy still needs to be improved. The UV-B-induced KA lesion mouse model is used in preclinical studies to assess the efficacy of novel molecules, even though it is often more representative of advanced AK or SCC.

Objectives

Here we report on a translational study, comparing the various stages of AK development in humans and in the UV-B irradiated mouse model, as well as the optimization of photograph acquisition of AK lesions on mouse skin.

Methods

Human and mouse skin lesions were analysed by histology and immunohistochemistry. Mouse lesions were also assessed using a digital dermatoscope.

Results

An histological and phenotypic analysis, including p53, Ki67 and CD3 expression detection, performed on human and mouse AK lesions, shows that overall AK modelling in mice is relevant in the clinical situation. Some differences are observed, such as disorganization of keratinocytes of the basal layer and a number of atypical nuclei which are more numerous in human AK, whereas much more pronounced acanthosis is observed in skin lesion in mice. Thanks to this translational study, we are able to select appropriate experimental conditions for establishing either early or advanced stage AK or an SCC model. Furthermore, we optimized photograph acquisition of AK lesions on mouse skin by using a digital dermatoscope which is also used in clinics and allows reproducible photograph acquisition for further reliable assessment of mouse lesions. Use of this camera is illustrated through a pharmacological study assessing the activity of CARAC^®.

Conclusion

These data demonstrate that this mouse model of UV-B-induced skin lesions is predictive for the identification of novel therapeutic treatments for both early and advanced stages of the disease.

Comparison of the acute ultraviolet photoresponse in congenic albino hairless C57BL/6J mice relative to outbred SKH1 hairless mice

Hairless albino Crl:SKH1-Hr(hr) mice are commonly utilized for studies in which hair or pigmentation would introduce an impediment to observational studies. Being an outbred strain, the SKH1 model suffers from key limitations that are not seen with congenic mouse strains. Inbred and congenic C57BL/6J mice are commonly utilized for modified genetic mouse models. We compare the acute UV-induced photoresponse between outbred SKH1 mice and an immune competent, hairless, albino C57BL/6J congenic mouse line [B6.Cg-Tyr(c-2J) Hr(hr) /J]. Histologically, B6.Cg-Tyr(c-2J) Hr(hr) /J skin is indistinguishable from that of SKH1 mice. The skin of both SKH1 and B6.Cg-Tyr(c-2J) Hr(hr) /J mice exhibited a reduction in hypodermal adipose tissue, the presence of utricles and dermal cystic structures, the presence of dermal granulomas and epidermal thickening. In response to a single 1500 J/m(2) ultraviolet B dose, the oedema and apoptotic responses were equivalent in both mouse strains. However, B6.Cg-Tyr(c-2J) Hr(hr) /J mice exhibited a more robust delayed sunburn reaction, with an increase in epidermal erosion, scab formation and myeloperoxidase activity relative to SKH1 mice. Compared with SKH1 mice, B6.Cg-Tyr(c-2J) Hr(hr) /J also exhibited an aberrant proliferative response to this single UV exposure. Epidermal Ki67 immunopositivity was significantly suppressed in B6.Cg-Tyr(c-2J) Hr(hr) /J mice at 24 h post-UV. A smaller non-significant reduction in Ki67 labelling was observed in SKH1 mice. Finally, at 72 h post-UV, SKH1 mice, but not B6.Cg-Tyr(c-2J) Hr(hr) /J mice, exhibited a significant increase in Ki67 immunolabelling relative to non-irradiated controls. Thus, B6.Cg-Tyr(c-2J) Hr(hr) /J mice are suitable for photobiology experiments.

Tracking of Inhaled Near-Infrared Fluorescent Nanoparticles in Lungs of SKH-1 Mice with Allergic Airway Inflammation

Molecular imaging of inflammatory lung diseases, such as asthma, has been limited to date. The recruitment of innate immune cells to the airways is central to the inflammation process. This study exploits these cells for imaging purposes within the lung, using inhaled polystyrene nanoparticles loaded with the near-infrared fluorescence dye Itrybe (Itrybe-NPs). By means of in vivo and ex vivo fluorescence reflectance imaging of an ovalbumin-based allergic airway inflammation (AAI) model in hairless SKH-1 mice, we show that subsequent to intranasal application of Itrybe-NPs, AAI lungs display fluorescence intensities significantly higher than those in lungs of control mice for at least 24 h. Ex vivo immunofluorescence analysis of lung tissue demonstrates the uptake of Itrybe-NPs predominantly by CD68(+)CD11c(+)ECF-L(+)MHCII(low) cells, identifying them as alveolar M2 macrophages in the peribronchial and alveolar areas. The in vivo results were validated by confocal microscopy, overlapping tile analysis, and flow cytometry, showing an amount of Itrybe-NP-containing macrophages in lungs of AAI mice significantly larger than that in controls. A small percentage of NP-containing cells were identified as dendritic cells. Flow cytometry of tracheobronchial lymph nodes showed that Itrybe-NPs were negligible in lung draining lymph nodes 24 h after inhalation. This imaging approach may advance preclinical monitoring of AAI in vivo over time and aid the investigation of the role that macrophages play during lung inflammation. Furthermore, it allows for tracking of inhaled nanoparticles and can hence be utilized for studies of the fate of potential new nanotherapeutics.

Hairless mice as an experimental model of infection with Leishmania (Leishmania) amazonensis

HRS/J Hairless mice have been investigated as an experimental model in cutaneous leishmaniasis induced by Leishmania (Leishmania) amazonensis. The animals were inoculated with 10(6) promastigotes into the right hind footpad and the course of infection was followed up for 30, 60 and 90 days. BALB/c mice were infected and used as control. Hairless mice were susceptible to L. (L.) amazonensis infection and a progressive increase in number of parasites and footpad thickness was detected over time. Signals of dissemination and visceralization were confirmed by the presence of parasite in the draining lymph node of lesion and spleen, at different times post infection. IL-10 gene expression evaluated by RT-PCR was significantly higher in Hairless mice at 60 days post infection, corroborating the pattern of susceptibility. These results point this inbred strain as a promising susceptible model for the study of experimental infection induced by L. (L.) amazonensis. This model would allow the use of other infection sites that minimize secondary interference and best monitoring the skin lesion, as in the case of in vivo assays of potential drugs for LT.

HR-1 Mice: A New Inflammatory Acne Mouse Model

Background

There is no appropriate in vivo animal model that reflects the inflammatory response of human acne.

Objective

This study investigated the effect of Propionibacterium acnes on the development of inflammatory acne-like lesions in four mouse strains with different degrees of immune response for the development of an optimal mouse model of inflammatory acne.

Methods

Human P. acnes suspensions (10⁸ and 10⁹ colony forming unit [CFU]/µl) were injected into the backs of HR-1, BALB/c, vitamin D receptor-knockout (VDR k/o), and severe combined immunodeficiency disease mice. Inflammation levels were evaluated two weeks after injection of P. acnes suspensions. In addition, histopathological examination and immunohistochemical staining of the expressions of inflammatory biomarkers (i.e., CD4+/CD8+ T lymphocytes, neutrophils, myeloperoxidase, interleukin-1β, matrix metalloprotease (MMP)-2, MMP-3, MMP-9, toll-like receptor (TLR)-2, LL-37, and integrin α6) were performed on tissue specimens.

Results

The HR-1 mouse strain exhibited the most remarkable inflammatory reaction with epithelial proliferation and microcomedone-like cyst formation. HR-1 mice also demonstrated aberrant integrin expression in the epidermis around both inflamed lesions and newly formed microcomedones. These findings were more prominent in the group receiving 10⁹ CFU/µl P. acnes than 10⁸ CFU/µl. MMP-9 expression in HR-1 mice was also upregulated around the microcomedone-like cysts. Finally, expression levels of TLR-2 and LL-37 were higher in HR-1 and BALB/c mice than the VDR k/o and SCID mice strains.

Conclusion

P. acnes induces acneiform inflammation with small microcomedones in HR-1 mice. Therefore, the HR-1 mouse strain represents a good candidate for the development of a new inflammatory acne mouse model.

Development of a novel adjuvanted nasal vaccine: C48/80 associated with chitosan nanoparticles as a path to enhance mucosal immunity

In a time in which mucosal vaccines development has been delayed by the lack of safe and effective mucosal adjuvants, the combination of adjuvants has started to be explored as a strategy to obtain potent vaccine formulations. This study describes a novel adjuvant combination as an effective approach for a nasal vaccine - the association of the mast cell activator compound 48/80 with chitosan based nanoparticles. It was hypothesized that mucoadhesive nanoparticles would promote the cellular uptake and prolong the antigen residence time on nasal cavity. Simultaneously, mast cell activation would promote a local microenvironment favorable to the development of an immune response. To test this hypothesis, two different C48/80 loaded nanoparticles (NPs) were prepared: Chitosan-C48/80 NP (Chi-C48/80 NP) and Chitosan/Alginate-C48/80 NP (Chi/Alg-C48/80 NP). The potential as a vaccine adjuvant of the two delivery systems was evaluated and directly compared. Both formulations had a mean size near 500nm and a positive charge; however, Chi-C48/80 NP was a more effective adjuvant delivery system when compared with Chi/Alg-C48/80 NP or C48/80 alone. Chi-C48/80 NP activated mast cells at a greater extent, were better internalized by antigen presenting cells than Chi/Alg-C48/80 NP and successfully enhanced the nasal residence time of a model antigen. Superiority of Chi-C48/80 NP as adjuvant was also observed in vivo. Therefore, nasal immunization of mice with Bacillus anthracis protective antigen (PA) adsorbed on Chi-C48/80 NP elicited high levels of serum anti-PA neutralizing antibodies and a more balanced Th1/Th2 profile than C48/80 in solution or Chi/Alg-C48/80 NP. The incorporation of C48/80 within Chi NP also promoted a mucosal immunity greater than all the other adjuvanted groups tested, showing that the combination of a mast cell activator and chitosan NP could be a promising strategy for nasal immunization.

Imaging preclinical tumour models: improving translational power

Recent developments and improvements of multimodal imaging methods for use in animal research have substantially strengthened the options of in vivo visualization of cancer-related processes over time. Moreover, technological developments in probe synthesis and labelling have resulted in imaging probes with the potential for basic research, as well as for translational and clinical applications. In addition, more sophisticated cancer models are available to address cancer-related research questions. This Review gives an overview of developments in these three fields, with a focus on imaging approaches in animal cancer models and how these can help the translation of new therapies into the clinic.

Zygosity determination in hairless mice by PCR based on Hr(hr) gene analysis

We analyzed the Hr gene of a hairless mouse strain of unknown origin (HR strain, http://animal.nibio.go.jp/e_hr.html) to determine whether the strain shares a mutation with other hairless strains, such as HRS/J and Skh:HR-1, both of which have an Hr^hr allele. Using PCR with multiple pairs of primers designed to amplify multiple overlapping regions covering the entire Hr gene, we found an insertion mutation in intron 6 of mutant Hr genes in HR mice. The DNA sequence flanking the mutation indicated that the mutation in HR mice was the same as that of Hr^hr in the HRS/J strain. Based on the sequence, we developed a genotyping method using PCR to determine zygosities. Three primers were designed: S776 (GGTCTCGCTGGTCCTTGA), S607 (TCTGGAACCAGAGTGACAGACAGCTA), and R850 (TGGGCCACCATGGCCAGATTTAACACA). The S776 and R850 primers detected the Hr^hr allele (275-bp amplicon), and S607 and R850 identified the wild-type Hr allele (244-bp amplicon). Applying PCR using these three primers, we confirmed that it is possible to differentiate among homozygous Hr^hr (longer amplicons only), homozygous wild-type Hr(shorter amplicons only), and heterozygous (both amplicons) in HR and Hos:HR-1 mice. Our genomic analysis indicated that the HR, HRS/J, and Hos:HR-1 strains, and possibly Skh:HR-1 (an ancestor of Hos:HR-1) strain share the same Hr^hr gene mutation. Our genotyping method will facilitate further research using hairless mice, and especially immature mice, because pups can be genotyped before their phenotype (hair coat loss) appears at about 2 weeks of age.

Quantum dots for imaging neural cells in vitro and in vivo

Quantum dots (QDs) have been used for optical imaging of neural cells in vitro and in vivo. This chapter lists the basic materials, instrumentation and step-by-step procedures to image live microglia cells and to show the functional and biochemical changes in microglia exposed to QDs. Details are also provided for the real-time imaging of cerebral ischemic lesions in animals and for the assessment of lesion reduction after therapeutic interventions. Microglia are brain cells which detect, internalize, and eliminate particulate matter, thereby maintaining homeostasis in the central nervous system. Although the protocols for imaging microglia shown here are developed for QDs without specific ligands or antibodies, the principles are the same for imaging other QDs.

Skin perfusion and oxygenation changes in radiation fibrosis

BACKGROUND

Ionizing radiation is known to have deleterious chronic effects on skin, including fibrosis and poor wound healing, hypothesized as mediated by ischemia and hypoxia. Past studies have been unable to simultaneously investigate changes in perfusion and oxygenation as separate parameters. Hyperspectral imaging has emerged as a tool with which to concurrently measure skin perfusion and oxygenation. The authors investigated the use of hyperspectral imaging in a novel murine model of chronic radiation injury.

METHODS

Areas of flank skin (n = 20) on hairless mice were exposed to a 50-Gy dose of beta-radiation. Hyperspectral imaging acquisition was performed at select points through 8 weeks. Immunohistochemical staining and gene expression analysis were performed to evaluate cutaneous vascular density, epidermal cell hypoxia, and angiogenic factors.

RESULTS

All irradiated areas developed a chronic-phase wound by day 28. Hyperspectral imaging demonstrated a 21 percent decline in perfusion on day 56 (p < 0.001), whereas oxygenation levels were unchanged. A 1.7-fold reduction in blood vessel density was measured in irradiated skin compared with control tissue (p < 0.001), but no difference in epidermal cell hypoxia was observed. Vascular endothelial growth factor and related receptor expression were significantly lower in irradiated tissue.

CONCLUSIONS

The authors' analysis does not support the presence of hypoxia in chronic-phase irradiated skin but suggests that hypoperfusion may be a predominant characteristic. The concurrent states of hypoperfusion and normoxia may be explained by the lower metabolic demands of fibrosed tissue.

Proof-of-concept rare cancers in drug development: the case for rhabdomyosarcoma

Rare diseases typically affect fewer than 200,000 patients annually, yet because thousands of rare diseases exist, the cumulative impact is millions of patients worldwide. Every form of childhood cancer qualifies as a rare disease-including the childhood muscle cancer, rhabdomyosarcoma (RMS). The next few years promise to be an exceptionally good era of opportunity for public-private collaboration for rare and childhood cancers. Not only do certain governmental regulation advantages exist, but these advantages are being made permanent with special incentives for pediatric orphan drug-product development. Coupled with a growing understanding of sarcoma tumor biology, synergy with pharmaceutical muscle disease drug-development programs, and emerging publically available preclinical and clinical tools, the outlook for academic-community-industry partnerships in RMS drug development looks promising.

Characterization of human osteoarthritic cartilage using optical and magnetic resonance imaging

Purpose

Osteoarthritis (OA) is a degenerative disease starting with key molecular events that ultimately lead to the breakdown of the cartilage. The purpose of this study is to use two imaging methods that are sensitive to molecular and macromolecular changes in OA to better characterize the disease process in human osteoarthritic cartilage.

Procedures

Human femoral condyles were collected from patients diagnosed with severe OA during total knee replacement surgeries. T_1ρ and T₂ magnetic resonance measurements were obtained using a 3-Tesla whole body scanner to assess macromolecular changes in the damaged cartilage matrix. Optical imaging was performed on specimens treated with MMPSense 680 to assess the matrix metalloproteinase (MMP) activity. A linear regression model was used to assess the correlation of MMP optical data with T_1ρ magnetic resonance (MR) measurements. Slices from a representative specimen were removed from regions with high and low optical signals for subsequent histological analysis.

Results

All specimens exhibit high T_1ρ and T₂ measurements in the range of 48–75 ms and 36–69 ms, respectively. They also show intense photon signals (0.376 to 7.89 × 10⁻⁴ cm²) from the activated MMPSense 680 probe, indicative of high MMP activity. The analysis of variance test of the regression model indicates a positive correlation between the MMP optical signal and T_1ρ measurements (R² = 0.8936, P = 0.0044). Histological data also confirmed that regions with high MMP optical signal and intense T_1ρ relaxation exhibit severe clefting, abnormal tidemarks, and irregular cellularity.

Conclusions

The high T_1ρ and T₂ measurements suggest that there is a severe loss of proteoglycans with high water mobility in the damaged cartilage. The intense optical signals found in these specimens indicate the presence of active MMPs, and the positive correlation with T_1ρ measurements implicates MMP’s involvement in OA progression, characterized by a severe loss of proteoglycans in the cartilage matrix. The bimodal approach using optical and MR imaging may provide key molecular and macromolecular information of the disease pathway, offering insights toward the development of new tools for the early detection, treatment, and/or prevention of OA.

Loss of hairless confers susceptibility to UVB-induced tumorigenesis via disruption of NF-kappaB signaling

In order to model squamous cell carcinoma development in vivo, researchers have long preferred hairless mouse models such as SKH-1 mice that have traditionally been classified as ‘wild-type’ mice irrespective of the genetic factors underlying their hairless phenotype. The work presented here shows that mutations in the Hairless (Hr) gene not only result in the hairless phenotype of the SKH-1 and Hr^−/− mouse lines but also cause aberrant activation of NFκB and its downstream effectors. We show that in the epidermis, Hr is an early UVB response gene that regulates NFκB activation and thereby controls cellular responses to irradiation. Therefore, when Hr expression is decreased in Hr mutant animals there is a corresponding increase in NFκB activity that is augmented by UVB irradiation. This constitutive activation of NFκB in the Hr mutant epidermis leads to the stimulation a large variety of downstream effectors including the cell cycle regulators cyclin D1 and cyclin E, the anti-apoptosis protein Bcl-2, and the pro-inflammatory protein Cox-2. Therefore, Hr loss results in a state of uncontrolled epidermal proliferation that promotes tumor development, and Hr mutant mice should no longer be considered merely hairless 'wild-type' mice. Instead, Hr is a crucial UVB response gene and its loss creates a permissive environment that potentiates increased tumorigenesis.

Dual Roles of METCAM in the Progression of Different Cancers

METCAM, an integral membrane cell adhesion molecule (CAM) in the Ig-like gene superfamily, is capable of performing typical functions of CAMs, such as mediating cell-cell and cell-extracellular interactions, crosstalk with intracellular signaling pathways, and modulating social behaviors of cells. METCAM is expressed in about nine normal cells/tissues. Aberrant expression of METCAM has been associated with the progression of several epithelial tumors. Further in vitro and in vivo studies show that METCAM plays a dual role in the progression of different tumors. It can promote the malignant progression of several tumors. On the other hand, it can suppress the malignant progression of other tumors. We suggest that the role of METCAM in the progression of different cancer types may be modulated by different intrinsic factors present in different cancer cells and also in different stromal microenvironment. Many possible mechanisms mediated by this CAM during early tumor development and metastasis are suggested.

Hyperspectral imaging for early detection of oxygenation and perfusion changes in irradiated skin

Studies examining acute oxygenation and perfusion changes in irradiated skin are limited. Hyperspectral imaging (HSI), a method of wide-field, diffuse reflectance spectroscopy, provides noninvasive, quantified measurements of cutaneous oxygenation and perfusion. This study examines whether HSI can assess acute changes in oxygenation and perfusion following irradiation. Skin on both flanks of nude mice (n=20) was exposed to 50 Gy of beta radiation from a strontium-90 source. Hyperspectral images were obtained before irradiation and on selected days for three weeks. Skin reaction assessment was performed concurrently with HSI. Desquamative injury formed in all irradiated areas. Skin reactions were first seen on day 7, with peak formation on day 14, and resolution beginning by day 21. HSI demonstrated increased tissue oxygenation on day 1 before cutaneous changes were observed (p<0.001). Further increases over baseline were seen on day 14, but returned to baseline levels by day 21. For perfusion, similar increases were seen on days 1 and 14. Unlike tissue oxygenation, perfusion was decreased below baseline on day 21 (p<0.002). HSI allows for complete visualization and quantification of tissue oxygenation and perfusion changes in irradiated skin, and may also allow prediction of acute skin reactions based on early changes seen after irradiation.

Bioluminescent diagnostic imaging to characterize altered respiratory tract colonization by the burkholderia pseudomallei capsule mutant

Pneumonia is a common manifestation of the potentially fatal disease melioidosis, caused by the select agent bacteria Burkholderia pseudomallei. In this study we describe a new model system to investigate pulmonary melioidosis in vivo using bioluminescent-engineered bacteria in a murine respiratory disease model. Studies were performed to validate that the stable, light producing B. pseudomallei strain JW280 constitutively produced light in biologically relevant host-pathogen interactions. Hairless outbred SKH1 mice were used to enhance the ability to monitor B. pseudomallei respiratory disease, and were found to be similarly susceptible to respiratory melioidosis as BALB/c mice. This represents the first demonstration of in vivo diagnostic imaging of pulmonary melioidosis permitting the detection of B. pseudomallei less than 24 h post-infection. Diagnostic imaging of pulmonary melioidosis revealed distinct temporal patterns of bacterial colonization unique to both BALB/c and SKH1 mice. Validation of these model systems included the use of the previously characterized capsule mutant, which was found to colonize the upper respiratory tract at significantly higher levels than the wild type strain. These model systems allow for high resolution detection of bacterial pulmonary disease which will facilitate studies of therapeutics and basic science evaluation of melioidosis.

SpyA, a C3-like ADP-ribosyltransferase, contributes to virulence in a mouse subcutaneous model of Streptococcus pyogenes infection

Streptococcus pyogenes is an important human pathogen with an expansive repertoire of verified and putative virulence factors. Here we demonstrate that a mutant deficient in the production of the streptococcal ADP-ribosyltransferase SpyA generates lesions of reduced size in a subcutaneous mouse infection model. At early stages of infection, when the difference in lesion size is first established, inflamed tissue isolated from lesions of mice infected with spyA mutant bacteria has higher levels of mRNA encoding the chemokines CXCL1 and CCL2 than does tissue isolated from mice infected with wild-type bacteria. In addition, at these early times, the mRNA levels for the gene encoding the intermediate filament vimentin are higher in the mutant-infected tissue. As wound resolution progresses, mRNA levels of the gene encoding matrix metallopeptidase 2 are lower in mutant-infected tissue. Furthermore, we demonstrate that the spyA mutant is internalized more efficiently than wild-type bacteria by HeLa cells. We conclude that SpyA contributes to streptococcal pathogenesis in the mouse subcutaneous infection model. Our observations suggest that the presence of SpyA delays wound healing in this model.