Implication of Perifollicular Clusters and Folliculotropic Distribution of Dendritic Cells in the Pathogenesis of Seborrhoeic Dermatitis

The pathogenesis of seborrhoeic dermatitis is controversial and remains unclear. Malassezia is considered to be a commensal fungi and is found not only in the stratum corneum but also in hair follicles. It is an important pathogenic factor in seborrhoeic dermatitis. The aim of this study was to clarify the pathogenesis of seborrhoeic dermatitis, morphologically, through comparison with psoriasis vulgaris. Fifteen cases of seborrhoeic dermatitis, 7 of psoriasis, and 6 of normal skin were examined using routine histopathology, immunohistochemistry, and electron microscopy. Macrophages were found to be diffusely distributed in the upper dermis of seborrhoeic dermatitis and psoriasis. In contrast, a significant increase in the number of dendritic cells in the follicular epithelium and dendritic cell clusters in the perifollicular dermis were found only in seborrhoeic dermatitis. Ultrastructural examination of the clusters demonstrated that dendritic cells interacted with lymphocytes, macrophages, and other dendritic cells. In conclusion, folliculotropic distribution of dendritic cells as well as dendritic cell-immune cell clusters play an important role in the pathogenesis of seborrhoeic dermatitis.