Date of Award
Doctor of Philosophy (PhD)
Psoriasis is a skin disease originally thought to be a primary keratinocyte differentiation and maturation disease. Several T cell targeted theraputics were found to reverse disease, and thus subsequent research has focussed on the adaptive immune system, particularly effector CD8+ T cells infiltrating the epidermis. Recent studies, however, show that inhibitors of tumor necrosis factor (TNF) are also effective therapeutics. Activated dendritic cells (DCs) produce large ammounts of TNF which acts in an autocrine loop to increase DC maturation. Thus, TNF inhibitors may inhibit DC maturation and downstream T cell activation. This thesis elucidates DC subsets present in normal human skin and psoriasis lesional skin, and the mechanisms by which psoriatic inflammatory DCs activate Th17 T cells and downstream mediators to maintainan psoriatic cutanous inflammation. In normal blood, ther exists 3 non-overlapping subsets of myeloid dendritic all of which are Lin-CD11c+HLA-DR+ and either BDCA-1+ (24 ± 2%), CD16+ (70 ± 4%), or BDCA-3+ (5 ± 1%), in order of immunostimulatory capacity. Only two myloid dendritic cell populations exist in normal human dermis: Lin-CD11c+HLA-DR+CD16+ and either BDCA-1+ ( 90%) or BDCA-3+ ( 10%). In situ double-label immunofluorescence showed that approximately 10-15% of CD11c+ dermal cells cluster together in lymphoidlike structures and are BDCA-1+CD205+DC-LAMP+. Upon emigration from the dermis, 90-95% of BDCA-1+ cells expressed these mature antigens, stimulated allogeneic T cells, and increased immunostimulatory capacity after the addition of TNF, PGE2, IL-1, and IL-6. Functional studies were not performed on BDCA-3+ cells because of limited cell numbers. In normal dermis there also exists a large population of FXIIIA+CD163+ macrophages that are not immunostimulatory and phagocytose large particles. As in normal blood, psoriasis patient blood contained 3 non-overlapping subsets of myeloid DCs (BDCA-1+, CD16+, or BDCA-3+). In psoriatic skin the frequency and distribution of BDCA-1+ and BDCA-3+ cells is similar to normal, however, there was a 30-fold increase in “inflammatory“ CD11c+ cells that did not express either marker. Most BDCA-1+ cells expressed maturation markers CD205 and DC-LAMP, while most BDCA-1- inflammatory cells expressed CD209 immature DC/ macrophage marker. Some myeloid cells expressed TNF and inducible nitric oxide synthase (iNOS). Treatment of psoriasis patients with the TNF neutralizing antibody etanercept not only inhibited dendritic cells as expected, but also had inhibitory effects on a newly appreciated type of T cell – Th17 cells. Etanercept reduced inflammatory DC products that drive Th17 cell proliferation (IL-23) as well as Th17 products and downstream effector mollecules (IL-17, IL-22, CCL20, and DEFB4). In contrast, Th1 cellular products and effector molecules (IFN, LTA-1, and MX-1) were reduced late in disease resolution. Using affymetrix gene array we characterized a global set of 4 gene clusters modulated temporally over the course of etanercept treatment. TNF and IL-17 pathway genes were downmodulated with a similar velocity, while IFN pathway genes were downmodulated later.
Zaba, Lisa C., "Dendritic Cells in Normal and Inflamed Human Skin" (2008). Student Theses and Dissertations. 207.