Photodynamische Therapie und Pathomechanismen des Lichen planus

Lichen planus (LP) is a common chronic inflammatory autoimmune dermatosis, which affects the skin and/or the mucous membranes. Thereby oral Lichen planus (OLP) is a particularly common form. So far treatment has been limited to symptomatic therapies, which have been associated with a variety of side effects. New treatments with fewer side effects, such as the photodynamic therapy (PDT), might offer promising alternatives. Latest research proposes a T cell-mediated autoimmune pathogenesis, yet neither the aetiopathogenesis of LP nor the existence of an (auto-)antigen have been fully discovered. Autoreactive CD8+ cytotoxic T cells have been demonstrated to induce apoptosis of basal keratinocytes and thereby causing a disintegration of the epithelium, consequently leading to the characteristic clinical picture. The impact of other T cells is largely unknown, however there are strong indications for the involvement of CD4+ T cells with a TH1 dominance. This work studies both the general pathological mechanisms in LP, as well as the effects of PDT on immunological parameters and is therefore organized into two parts (A and B). Part A aims to contribute to the identification of a possible LP antigen through an analysis of antigen-specific T cells in peripheral blood of LP patients. Furthermore it should contribute to a more profound understanding of the role of different T cell subpopulations in the pathogenesis of LP. By the use of enzyme-linked immunosorbent assay (ELISA), chemokine and cytokine plasma levels were analyzed. Compared to healthy control plasma levels of the inflammatory TH1-cytokine CCL5 were significantly elevated, confirming the assumed TH1 bias and suggesting that CCL5 may play an important role in the pathogenesis of LP. For the detection of antigen-specific T cells via enzyme-linked immunospot assay (ELISpot assay), peripheral blood mononuclear cells, which were isolated from CPDA blood, were stimulated by desmoglein 1 (Dsg1), desmoglein 3 (Dsg3) and bullous pemphigoid antigen 180 (BP180) and analyzed for the secretion of interferon gamma (IFNγ), interleukin-5 (IL-5) and interleukin-17a (IL-17a). Stimulation with BP180-NH2 showed significantly increased numbers of IFNγ-secreting T cells, which strongly indicates the presence of BP180-NH2-specific T cells in LP and further confirms the TH1 bias. Therefore BP180-NH2 constitutes a potential autoantigen of LP, which might lead to an increased secretion of inflammatory mediators, such as CCL5 and IFNγ. Part B focuses on the immunological effects of PDT in OLP. Here, pre- and post-therapeutically obtained peripheral blood samples and oral mucosal biopsies were used to analyze the effects of PDT on different T cell subpopulations. Furthermore, it was examined whether PDT led to a measurable decrease of inflammatory parameters. Based on the clinical results, which showed a decrease in size of the lesions, PDT was rated as a success and specific immunological changes were interpreted as an approach to physiological values. The analysis of different T cell subsets in peripheral blood via flow cytometry showed significantly elevated percentages of γ/δ-TCR+-lymphocytes in the lymphocyte subpopulation after PDT. The post-therapeutic increase indicates that PDT has a specific effect on this T cell subset. In part B, the analysis of peripheral chemokine- and cytokine levels by ELISA was performed for plasma and for saliva. Here, plasmatic levels of the chemokine CXCL10, which presents a chemotactic stimulus for activated T cells, were decreased significantly after therapy. This reduction seems to be associated with a concomitant decrease of T cells in the lesional tissue, which could reveal CXCL10 as an important factor for T cell migration in the pathogenesis of (O)LP. No significant post-therapeutic changes were observed regarding the chemokine- and cytokinelevels in saliva. By ELISpot assay, peripheral T cells were stimulated by phytohaemagglutinin (PHA), Dsg3 and BP180-NH2, but no significant posttherapeutic change was noticed in this experimental approach. The specific immunological effects of PDT also became apparent in the immunohistologic analysis of the lesional inflammatory infiltrate. Here, a significant post-therapeutic decrease of CD4+ cells in the entire infiltrate was detected, indicating the involvement of this T cell subset in the pathogenesis. Nonetheless, due to the relatively constant total cell numbers of the infiltrate after PDT, it requires further examination. In summary, it has been shown here, that PDT has a specific immunomodulatory effect on peripheral and lesional T cells in OLP and can reduce particular inflammatory parameters.