Investigation of the Relationship between Invasion of Fungi and Alteration of Cell Kinetics in Hair Apparatus in Experimental Dermatophytosis, Especially in Comparison with Human Hair Fungal Infection

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It is well known that the experimental Trichophyton (T) dermatophytosis produced in hairy animals shows natural healing within a few weeks, but human dermatophytosis caused by T is usually apt to be uncurable without therapy. In the present study, in order to elucidate the process of the natural healing of the experimental dermatophytosis, a strain of T mentagrophytes was inoculated in the guinea pig back skin by a wet disc method and the skin lesions were successively biopsied and examined. Histologically, inflammatory changes in the epidermis and upper dermis reached the maximal state on day 14. Most of the hair apparatus began to retract their hair bulbs on day 16. It was shown by periodic acid-Schiff staining that the infected fungi intruded down into the keratinizing zone of the hair cortex, although few inflammatory cells infiltrated around the lower part of the hair apparatus. By BrdU staining, BrdU-labeling indices (LI) in the hair bulbs as well as in the basal layrs of the epi … More dermis and follicular epithelia significantly increased on day 14. Subsequently, the BrdU-LI became lower and lower with retraction of hair bulbs. From these observations, although hyperproliferation of the epidermis is a factor for the natural healing of the experimental dermatophytosis, it is strongly suggested that fungal infection may first evoke proliferative changes in the hair bulbs as well as in the epidermis, and, then, induce retraction of the hair bulbs and falling away of hairs, resulting in complete elimination of the infectinf fungi. The infecting fungi appear to directly affect the cell kinetics in hair bulbs. On the other hand, in human dermatophytosis caused by various kinds of T,especially when the hair apparatus is affected, the fungi invade and intrude into the keratinizing zone of the hair cortex ; however, the hair apparatus seldom shows retraction of the hair bulb, although the produced hair becomes atrophic (Arch Dermatol Res 283 : 233,1991). If it is assuming that the ability of tissue injury by T is the same both in animal and human skin tissues, the contradictious findings of animal and human hair apparatus infected by T may be due to structural differences, such as difference in size of hair bulb, differences in cell kinetics in hair bulbs, including hair cycle, and/or difference in tolerance of hair bulbar cells to the poison from the fungi, between animals and human beeings. Less