Immunohistochemical evaluation of psoriatic plaques following selective photothermolysis of the superficial capillaries

Background Elongated and tortuous capillary loops are distinctive features of psoriasis. The significance of these microvascular changes in the pathog enesis of plaques, however, remains unclear. Objectives To determine what part the expanded superficial capillary bed pl ays in the pathogenesis of clinical lesions by selectively thermolysing pso riatic capillaries with a pulsed dye laser (PDL). Methods Cutaneous lesions were biopsied before and after treatment and sect ions assessed by standard immunohistochemical techniques for changes in kno wn indicators of angiogenesis, including endothelial surface area, endothel ial cell proliferation and endothelial cell expression of adhesion molecule s. We also measured lymphocytic infiltration and epidermal thickness, and q uantified the presence of a marker of keratinocyte proliferation before and after treatment. Results The effect of the PDL was limited to the superficial capillary bed, with no changes in the microvessels (including venules and arterioles) of the upper reticular dermis. Although there was significant clinical improve ment in plaques after treatment (P = 0.02), complete clearance of lesions w as not achieved. Thermolysis of psoriatic capillaries caused a reduction in both endothelial surface area (P < 0.01) and endothelial cell proliferatio n in the superficial dermis (P = 0.04). Endothelial expression of surface a dhesion molecules (integrins and E-selectin) important in angiogenesis was not, however, altered by treatment. The CD4+ and CD8+ T-cell infiltrate was significantly reduced in the superficial papillary dermis (P = 0.02 and P = 0.04, respectively), but not in the epidermis or upper reticular dermis. Laser treatment significantly reduced epidermal thickness (P = 0.001), but did not alter epidermal keratinocyte proliferation (P = 0.2). Conclusions The results demonstrate that dermal capillary changes alone are unlikely to be causal in psoriasis. They indicate that the expanded psoria tic capillaries may be important in facilitating the access of activated T cells to the skin and in maintaining the psoriatic plaque. These results do not refute the consensus view that plaque formation may be mediated by the release of growth factors/cytokines from activated epidermal T cells/kerat inocytes.