Background The factors underlying the transition of psoriasis (PsO) to psoriatic arthritis (PsA) are poorly understood. The lymphatic system may control the homing of disease-associated T-cells to skin and extra-cutaneous sites like synovial joints and entheses.
Objectives To study the capacity of lymphatic endothelial cells (LEC) to regulate T-cell homing capabilities in PsA.
Methods Human dermal LEC (0.5x104), and fibroblast-like synoviocytes of a patient with PsA (PsA-FLS; 1.0x104) were pre-incubated for 3 days with PsA synovial fluid (PsA-SF; 0/10/20% v/v) and co-cultured with 2.5x104 allogeneic CD4+CD45RO+CD25- T-cells that were sorted from peripheral blood mononuclear cells of 3 donors (with or without stimulation with αCD3/αCD28). After 72 h, T-cells were analyzed by flow cytometry. The CCR6+ T-helper (Th) subsets Th17.1 (CCR4-/CXCR3+), Th17/Th22 (CCR4+/CXCR3-), Th17 (CCR4+/CXCR3-/CCR10-) and Th22 (CCR4+/CXCR3-/CCR10+), and CCR6- subsets Th1 (CCR4-/CXCR3+), and Th2 (CCR4+/CXCR3-) were identified. We also looked at cutaneous lymphocyte- associated antigen (CLA). IL-17A, IL-22, and TNF protein levels were determined by ELISA. Statistical analysis included unpaired t-test (two-sided) for two-group comparison or one-way ANOVA with the Tukey-Kramer post hoc test for multi-group comparisons.
Results Stimulation of CD4+CD45RO+ T-cells in co-culture with PsA-FLS skewed towards the CCR6+ subset Th17/Th22, which were predominantly Th17 cells. Th17 differentiation upon stimulation was suppressed in co-culture with LEC, even when LEC were pre-incubated with PsA-SF. T-cell stimulation in co-culture with LEC, as compared to PsA-FLS, promoted the generation of the Th22 subset. Upon co-culture with untreated LEC, stimulated T-cells showed higher expression of the skin homing receptor CLA than those that were co-cultured with PsA-FLS. The proportional reduction in CLA expression on T-cells in the co-cultures with LEC pre-incubated with PsA-SF 20% was comparable to PsA-FLS, however LEC conserved CLA expression on CD4+CD45RO T-cells at a higher level than PsA-FLS; this phenomenon particularly affected the CCR6+ T-cells. In line, a trend towards lower IL-17A and higher IL-22 levels were observed in the co-cultures with LEC that were pretreated with PsA-SF 20%, as compared to the co-culture with PsA-FLS. No differences were seen for TNF protein levels.
Conclusions LECs are directly involved in T-cell differentiation and homing capabilities, as shown by suppression of Th17 differentiation upon stimulation, as compared to PsA-FLS. Also, LEC promoted Th22 generation, and conserved CLA expression in CCR6+ T-cells, even when LEC were preincubated with PsA-SF. Studies are underway to confirm that LECs from relevant biological tissues (e.g. synovium and lymph nodes) are critical for tissue-restricted T-cell migration to skin and synovial membranes in PsA.
Disclosure of Interest None declared