Expression of chemokine receptor CXCR3 by lymphocytes and plasmacytoid dendritic cells in human psoriatic lesions

In psoriasis, leukocytes that infiltrate skin lesions have been shown to be involved in the pathogenesis of this disease. Previous investigations reporting the presence of CXCR3(+) T lymphocytes in psoriatic lesional skin have suggested a role of this receptor in the recruitment of T cells into the lesion. The purpose of this study was to quantify the mRNA levels of CXCR3 and to perform a systematic analysis of the cell populations that express CXCR3 in human lesional and non-lesional psoriatic biopsies. We showed by real-time reverse transcriptase-polymerase chain reaction that the mRNA levels of CXCR3 and its ligands, CXCL9-11, were significantly elevated in psoriatic lesions, as compared to non-lesional samples. Serial cryostat sections of psoriasis skin biopsies were evaluated by immunohistochemistry. The number of CXCR3(+) cells was low in non-lesional tissues. Quantitative image analysis demonstrated significant increases in the number of both epidermal and dermal CXCR3(+) cells in lesional compared with non-lesional biopsies. The majority of CXCR3(+) cells were located in the dermis of the lesional skin and 74% were demonstrated to be CD3(+) T lymphocytes. A small number of CXCR3(+) cells were CD68(+) myeloid cells. In addition, we found that nearly all BDCA-2(+) plasmacytoid dendritic cells in the psoriatic biopsies were CXCR3(+). These findings support and extend prior reports suggesting the potential role for CXCR3 in the pathophysiology of plaque psoriasis, by mediating the recruitment of plasmacytoid dendritic cells and T cells into the developing lesions.