In psoriatic lesions, T cells and keratinocytes are in an activated state. Ligation of CD40 expressed on activated keratinocytes with CD154 expressed on activated T cells is thought to be involved in the pathogenesis of psoriasis. However, the presence of CD40+ and CD154+ cells in psoriatic skin has not been thoroughly studied. The present study has therefore examined their presence by immunohistochemistry in the lesional and non-lesional skin of ten patients. The influence of CD154-CD40 ligation on the release of chemokines (IL-8, RANTES, and MCP-1) and complement components (C3 and factor B) from keratinocytes was also investigated in vitro. Studies using single and double staining showed that clusters of CD40+ keratinocytes were present in both lesional and non-lesional skin; CD40+CD1a+ Langerhans cells in lesional, non-lesional, and normal skin; and numerous CD40+CD83+ cells in lesional skin. CD1a+ and CD83+ cells always expressed CD40 strongly. Numerous T cells were seen in lesional skin. A small number of T cells expressed CD154. CD154+ T cells were seen in the lesional epidermis of seven of ten patients - in six, in juxtaposition to CD40+ cells including keratinocytes. In non-lesional epidermis, CD154+ T cells were seen in two patients - in one, in juxtaposition to CD40+ keratinocytes. In vitro studies showed that IFN-γ-treated keratinocytes released small amounts of IL-8, RANTES, and MCP-1; ligation of these cells with CD154-transfected J558 cells or soluble CD154 greatly enhanced the release. This ligation did not enhance the release of C3 and factor B. These results warrant further studies on the role of CD40 ligation in the pathogenesis of psoriasis. Copyright

CD40-CD154 ligation, IL-8, Keratinocytes, MCP-1, Psoriasis, RANTES,
Journal of Pathology

van Pasch, L.D, Timár, L, van Meurs, M, Heydendael, V.M.R, Bos, J.D, Laman, J.D, & Asghar, S.S. (2004). In situ demonstration of CD40- and CD154-positive cells in psoriatic lesions and keratinocyte production of chemokines by CD40 ligation in vitro. Journal of Pathology, 203(3), 839–848. doi:10.1002/path.1581