Purpose: To explore the crucial role of the human corneal epithelium-derived proallergic cytokine thymic stromal lymphopoietin (TSLP) in initiation and regulation of immune responses.
Methods: Primary corneal epithelial cells, established from donor limbal explants, were treated with 11 microbial ligands and proinflammatory and Th2 cytokines, alone or in combination. TSLP mRNA and protein were determined by real-time PCR and ELISA, respectively. NF-kappaB activation was detected by immunostaining and Western blot.
Results: TSLP was found to be expressed by human corneal epithelium and its cultures. TSLP in corneal epithelial cells were largely induced in a concentration-dependent fashion by polyI:C, flagellin, and FSL-1, the ligands for toll-like receptor (TLR)-3, -5, and -6, respectively. Compared with the control, TSLP mRNA was increased by 60-, 12- and 8-fold and TSLP protein increased by 67-, 19- and 7-fold by these three ligands, respectively. The proinflammatory (TNF-alpha and IL-1beta) and Th2 (IL-4 and IL-13) cytokines moderately induced TSLP expression and production. IL-4 and -13 strongly synergized with PolyI:C, flagellin, and TNF-alpha to promote TSLP production in ex vivo tissues and in vitro cultures of corneal epithelium. PolyI:C, flagellin, or TNF-alpha also induced NF-kappaB p65 protein nuclear translocation. The NF-kappaB inhibitor quinazoline blocked p65 nuclear translocation and further suppressed TSLP expression and production induced by these stimuli.
Conclusions: These findings provide the first evidence of TSLP induction in the human eye and suggest the novel phenomenon that human corneal epithelium-derived TSLP may serve as a link between the innate and adaptive immune responses. TSLP may become a novel therapeutic target for allergic and inflammatory ocular surface diseases.