An in vitro model of dermatophyte invasion of the human hair follicle.

A novel in vitro model for the study of hair invasion by Trichophyton mentagrophytes was developed. Hair was obtained by microdissection and plucking. Following inoculation of the hair follicle with arthroconidia growth of the fungus was seen on the hair and within the follicle. Growth was observed to begin at the shaft end and to extend along the hair shaft towards the bulb area. In follicles maintained in organ culture the inner root sheath in particular was invaded by T. mentagrophytes and provided a good substrate for fungal growth. Initially, the cuticle formed a barrier to fungal penetration of the hair. After incubation for 4 days, germlings of T. mentagrophytes were seen to penetrate under the cuticle and in between the layers of cuticular cells to invade the cortex. There was no evidence of intracellular growth; fungal elements were seen intercellularly. There were similarities between the findings in this study of the process of hair invasion by dermatophyte fungi and that in the natural disease.