A light-emitting mouse to image skin inflammation.

Background: The mouse ear swelling test is a well-accepted method for quantitating the inflammatory response to contact irritants and sensitizing agents. However, this assay measures edema rather than the cellular component of skin inflammation.

Objective: To develop a quantitative and noninvasive assay of inflammatory cell infiltration in contact dermatitis.

Methods: We bred a transgenic bioluminescent mouse that emits light proportional to cutaneous infiltration of inflammatory cells. We characterized this model by correlating luminescence with edema and histologic analysis of affected skin. A mouse strain expressing cyclization recombinase enzyme (cre) recombinase exclusively in myeloid cells was crossed with a reporter strain containing an inactivated form of the luciferase gene. In progeny mice, cre-mediated recombination repaired the luciferase gene, causing light emission from myeloid cells. Light emission and swelling from the inflamed ear was quantitated and compared to the contralateral ear.

Results: Light intensity correlated with the inflammatory cell infiltration in the dermis. In sensitized mice challenged with squaric acid, luminescence increased about 2.2-fold while swelling increased about 1.5-fold.

Conclusion: Our model may serve as a useful screening assay for topical antiinflammatory molecules. Moreover, this approach allows real-time imaging of skin infiltration by specific inflammatory cell lineages in living animals.