TSLP-activated dendritic cells induce T helper type 2 inflammation in Aspergillus fumigatus keratitis.

Thymic stromal lymphopoietin (TSLP) is an IL-7-like cytokine, which is secreted by epithelial cells under the stimulation of Toll-like receptor (TLR) ligands. Dendritic cells (DCs) which express the thymic stromal lymphopoietin receptor (TSLPR) can be activated by TSLP. Mature DCs can express the OX40 ligand, which has the ability to combine with OX40 on the surface of T cells to stimulate T cell proliferation. TSLP secreted by corneal epithelial cells can engage in the process of T helper type 2 (Th2) inflammation in Aspergillus fumigatus keratitis, but the mechanism remains unclear. We demonstrated that in A. fumigatus-infected corneas, DCs aggregated, matured, and gradually migrated not only from the basement membrane to the corneal epithelium, but also from the corneal limbus to the central cornea. Mature DCs secreted Th2-attracting chemokines, the thymus and activation-regulated chemokine (TARC), and the macrophage-derived chemokine (MDC), encouraging the secretion of TNF-α and Th2 cytokine Interleukin (IL) -4, IL-5, and IL-13. The above processes were all restricted with subconjunctivally injection of TSLP siRNA, while they were strengthened with the injection of rTSLP. We demonstrated that in A. fumigatus keratitis, TSLP, through combination with TSLPR on the surface of DCs, induced DC aggregation, maturation, and migration, and then the mature DCs secreted Th2-attracting chemokines, promoting the secretion of proinflammatory cytokine TNF-α and Th2 cytokines, which finally induced Th2 inflammation.