Comparisons of mouse models for hair follicle reconstitution.

Three methods are currently available to reconstitute hair follicles in mice. Direct comparisons have yet to be made to determine which method is most efficient. In this study, mouse epithelial cells (MECs) and mouse dermal cells (MDCs) were grafted onto the dorsal skin of nude mice using the chamber, flap or patch assays. Comparisons were made based on gross, scanning electron microscopic and histological observations. MDCs alone induced hair follicle reconstitution with the production of hairs yielding false-positive results caused by contamination by hair follicle remnants. Neither primary MECs nor cultured MDCs alone formed hair follicles but did result in hair follicle formation when mixed together. Frozen MECs or MDCs resulted in decreased hair follicle-inductive activity but could still regenerate hairs. The hair patch assay was the quickest model (20±3 days) to determine whether cell mixtures would reconstitute hair follicles that produce hairs; however, the hair follicles were randomly orientated and often associated with foreign body granulomas. The flap assay took the longest time (29±2 days) to produce follicles and hairs to develop with a clinically natural appearance, but an epidermal sheet was needed. The chamber assay was the most labour-intensive and cell number-dependent procedure but follicles developed in a dense, clinically normal manner.