Three‐Dimensional Immunofluorescence Analysis of Psoriatic Plaques Before and After Pulsed Dye Laser Treatment: Reduced T‐Cell Content Without Changes in Nerve Fiber or Blood Vessel Density

Objectives Pulsed dye laser (PDL) treatment for psoriasis has demonstrated its potential for treatment‐free remission periods exceeding 1 year. The mechanism leading to remission is not fully understood, but PDL is known to heat the vasculature in the skin. We hypothesized that heat diffuses from the vasculature to the surrounding environment, including perivascular nerves and T‐cells, leading to an interruption of the neurogenic inflammatory cycle that drives psoriasis. Methods We compared histological features of the vasculature, nerves, and leukocyte infiltrate in 120 biopsy sections (80 µm thick) from 20 patients, collected before and after two PDL treatments. The alterations in vasculature were categorized into three distinct classifications: papillary vasculature, reticular vasculature, and total vasculature. Nerve fibers were divided into free epidermal nerve fibers, perivascular nerve fibers around capillaries, and reticular nerves. The densities of these structures, as well as the volume of the epidermal and dermal leukocyte infiltrate, were calculated from the three‐dimensional (3D) fluorescence microscopy images. Results Two sessions of PDL treatment significantly reduced CD3 + leukocyte infiltrate in the skin. Furthermore, pruritus and epidermal thickness were also significantly reduced. Vascular and nerve fiber density did not significantly differ before and after two treatments. Conclusions Using 3D immunofluorescence microscopy to quantify T‐cells, vasculature and nerve fibers, we found that two PDL treatments were associated with a significant reduction in CD3 + T‐cells, even in patients whose clinical severity did not improve, while vascular and nerve fiber density remained unchanged. Perivascular heat diffusion and potential alterations in vascular integrity may contribute to this reduction, but this hypothesis requires confirmation in future studies.