Oxazolone Atopic Dermatitis Model
The oxazolone atopic dermatitis model is a chronic, Th2-skewed hapten dermatitis in the mouse. Mice are sensitised, then challenged ten times with oxazolone over 28 days. Lesions develop on two sites, the back skin and the ear, and are read out by clinical scoring, caliper measurements and terminal histology. Corticosteroid and JAK-inhibitor reference data are available in house.
Why the oxazolone atopic dermatitis model
- Repeated oxazolone challenges produce a chronic Th2-like hypersensitivity reaction with multiple features of human atopic dermatitis (Man et al., J Invest Dermatol 2008).
- Repeated challenge reproduces the erythema, scaling, excoriation and skin thickening of lesional atopic skin, with epidermal hyperplasia.
- The two lesion sites are independent. The back skin carries the barrier and scratch-driven pathology, while the ear gives a clean local oedema signal.
- The design uses about 50 animals and non-invasive readouts, which makes it suitable for dose ranking before a larger-animal study.
- The model uses immunocompetent mice (BALB/c strain). SKH1 hairless mice are used when OCT imaging is the primary endpoint.
Oxazolone atopic dermatitis model protocol (28-day format)
- Sensitisation on D1: oxazolone 2 %, 100 µL applied topically on the back.
- Challenges from D8 to D26: ten applications of oxazolone 1 %, 80 µL on the back plus 20 µL on the right ear.
- Treatment is preventive. It starts with the first challenge (D8) and continues to D27, by topical or systemic route. A topical corticosteroid reference can start later in the series.
- Sampling on D28: blood, skin, ear, spleen and lymph nodes. Terminal sampling can be scheduled earlier when histology, biomarkers or imaging are the main endpoints (see below).
- A typical design has vehicle, reference (corticosteroid and/or JAK inhibitor) and test-item groups at n = 8, plus a small non-induced sham group.
Endpoints of the oxazolone atopic dermatitis model
- Clinical scoring (equivalent to SCORAD) covers erythema, scaling and excoriations, each scored 0 to 4 (total 0 to 12). Scores are taken at D1 and every two days from D8 to D28, before the challenge.
- Back skin and right ear thickness are measured by caliper on the same days.
- Calibrated photography is taken at D8, D14, D21 and D28. Spleen and body weight are recorded at sampling.
- Histology (HES) measures epidermis and dermis thickness, dermal infiltrate (nuclei count) and a squamo-crust score. Toluidine blue gives mast cell number and degranulation state.
- Plasma and skin biomarkers include IgE, IL-6, MMP-9 and Th1 and Th2 cytokine panels, with skin transcripts by qPCR.
- Flow cytometry panels cover Th1, Th2, eosinophils and mast cells in back skin, lymph nodes and spleen.
- Scratching-bout counting by video is available as an add-on for itch. Excoriation scoring measures skin damage, not pruritus.
- Ethical endpoints are body weight, feeding and drinking behaviour, general behaviour and a maximal scoring threshold.
- Clinical scores (cumulative score and AUC) and histomorphometry are analysed statistically. Induction with other haptens (calcipotriol, DNCB) is also available.
Model characterisation at Imavita
- Flow cytometry in back skin, lymph nodes and spleen, 24 h after the 2nd and the 10th challenge, shows CD4 Th1 cells (T-bet) predominating at D11 and CD4 Th2 cells (GATA3) at D27. Repeated challenge therefore turns a delayed-type hypersensitivity reaction into a Th2-skewed lesion.
- IL-4 and IL-5 are raised in back skin extracts against sham, plasma IgE is increased about 200-fold, and mast cells are present in the dermis.
- A Th1 component persists, so the model is mixed Th1/Th2 rather than purely Th2.
- Cytokine content in skin extracts depends on mast-cell degranulation state. Skin cytokines are therefore best read as transcripts or released mediators, not as total tissue content.
Assay window and variability
Vehicle versus non-induced sham, from an Imavita 28-day study (vehicle n = 8; sham n = 2, so sham values are indicative). Mean ± SD.
| Endpoint | Sham | Vehicle | Window | CV |
|---|---|---|---|---|
| Composite clinical score, AUC D1 to D28 | 0 | 77.4 ± 15.9 | full 0 to 12 range | 21 % |
| Back skin thickness, AUC | 22.3 | 48.2 ± 5.4 | 2.2-fold | 11 % |
| Right ear thickness, AUC | 5.2 | 10.2 ± 0.7 | 2.0-fold | 7 % |
| Spleen weight at D28 (mg) | 103.2 | 132.1 ± 17.0 | 1.3-fold | 13 % |
Endpoint hierarchy and group size
Endpoints are ranked on measured variance. Two-sided α = 0.05, 80 % power, effect expressed on the sham-corrected disease window (AUC D1 to D28).
| Endpoint | CV | Detectable effect with n = 8 | n for a 25 % effect | Use |
|---|---|---|---|---|
| Scaling score | 11 % | 17 % | 5 | Primary |
| Right ear thickness | 7 % | 20 % | 6 | Primary |
| Composite clinical score | 21 % | 31 % | 12 | Primary |
| Back skin thickness | 11 % | 32 % | 13 | Secondary |
| Erythema score | 34 % | 52 % | 31 | Supporting |
| Excoriations | 55 % | 83 % | 77 | Not powered |
| Spleen weight | 13 % | 89 % | 88 | Descriptor |
- n = 8 is adequate for scaling, ear thickness and composite score. Use n = 10 to 12 if the composite score stays primary and doses closer than two-fold must be separated.
- Scores oscillate with the 48 h challenge cycle, so the cumulative score and AUC are the endpoints of record.
- Excoriation scoring is too variable to rank compounds. Add a pruritus endpoint instead of increasing group size.
Reference pharmacology
Betamethasone and oclacitinib were qualified in the same run as the vehicle and sham groups (n = 8 per group; AUC D1 to D28; one-way ANOVA with Dunnett’s test versus vehicle).
| Reference | Regimen | Composite score AUC | Scaling AUC | Ear thickness (induced window) |
|---|---|---|---|---|
| Betamethasone 0.05 % (topical) | about 2.5 mg/kg, q.2d., D15 to D27 | −33 %, p < 0.0001 | −40 %, p < 0.0001 | −53 % |
| Oclacitinib (JAK1 inhibitor, oral) | 30 mg/kg, b.i.d., D8 to D27 | −43 %, p < 0.0001 | −41 %, p < 0.0001 | −14 % |
- Back skin thickening returns to sham level under betamethasone from D22 and is only weakly affected by oclacitinib.
- Betamethasone has a systemic corticosteroid signal (spleen weight −75 %, body weight −7 %). Oclacitinib returns spleen weight to sham level.
- The topical arm starts one week later and on a different schedule than the oral arms, so it sets the ceiling of the model and is not a like-for-like comparator.
Sampling window
At D28, 48 h after the tenth challenge, the lesion is already resolving, and single-day group comparisons under-read treatment effects that are clear on cumulative and AUC data. Terminal sampling for histology, biomarkers or imaging should be scheduled earlier, while the lesion is at plateau.
Strengths and limitations
- The model is reproducible and fully characterised, with a stable plateau, a zero-background sham, two lesion sites and reference pharmacology qualified in the same run.
- Itch is inferred, not measured, unless a behavioural endpoint is added.
- Oxazolone contact hypersensitivity has a Th1/Th17 component alongside the Th2 shift, so part of the lesion does not depend on Th2 signalling.
- Clinical scoring does not read out target engagement. For mechanism-specific compounds, add skin transcripts, circulating biomarkers and exposure sampling.
- Ordinal 0 to 4 scores saturate and depend on the observer. Instrumented erythema and imaging can complement them.
- Efficacy data are research data and are not GLP-compliant.
Shorter format
An 18-day version with five challenges and sampling at D18 is also available. It is ear-driven and one third shorter, and it suits screening and ranking with OCT imaging and ear histology. The 28-day format remains the choice for a wide back-skin window and cumulative scores.
Imavita handles the APAFIS regulatory submission, ethical review and reporting, and agrees study design and statistical sizing with you before the first animal. Please inquire for more details on the oxazolone-induced atopic dermatitis model.
