Dermal dendritic cells (DCs) are involved in the pathogenesis of psoriasis, although the quantity of these cells does not appear to account for the preferential involvement of extensor skin, according to research published in the January issue of the Journal of the American Academy of Dermatology.
Loren E. Clarke, M.D., of the Penn State Hershey Medical Center, and colleagues tested their hypothesis that psoriasis may preferentially involve extensor skin, such as the knees and elbows, because of differences in the number or type of dermal DCs between flexural and extensor skin. The investigators stained cells with 11 distinct dendritic cell immunohistochemical markers (CD11a, CD11c, CD1a, CD34, CD68, FXIIIa, S100A4, S100A6, CD303 [BDCA-2], CD123, CD207 [Langerin]) to compare the number, distribution, and type of Langerhans cells, myeloid DCs, and plasmacytoid DCs in 26 healthy flexural and extensor skin biopsy samples, 10 psoriatic lesions, and 10 age- and site-matched nummular dermatitis lesions.
According to the researchers, compared with normal-appearing flexural skin, extensor skin contained fewer CDE11a+ and CD11c+ cells, although this difference did not reach statistical significance. Psoriatic and nummular dermatitis lesions expressed increased numbers of dermal DCs, including both myeloid and plasmacytoid subtypes, but this finding was not site-specific. Additionally, CD11a, CD11c, CD123, CD303, and CD207 expression was increased in psoriatic and nummular dermatitis lesions, with the only significant difference between the two types of lesions being a reduction in the number of S100A6+ cells in psoriasis.
"The data did not support the hypothesis that psoriasis favors extensor skin because of differences in dendritic cell localization. However, dermal dendritic cells were significantly increased in psoriasis by comparison with normal-appearing skin, supporting existing evidence that they are involved in the overall pathogenesis of psoriasis," the authors write.
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