Nerve growth factor modulates toll-like receptor (TLR) 4 and 9 expression in cultured primary VKC conjunctival epithelial cells

PURPOSE: To investigate if nerve growth factor (NGF) might modulate toll-like receptor (TLR) 4 and 9 expression in primary cultures of vernal keratoconjunctivitis (VKC)-derived conjunctival epithelial cells (VKC-ECs). METHODS: Primary cultures of ECs were established from VKC (n=7) and healthy-control (n=5) conjunctival specimens. Primary untouched and short-term NGF-exposed VKC-ECs were analyzed for molecular (relative real-time PCR) and biochemical (confocal and fluorescence-activated cell sorting analysis of TLR4 and TLR9 expression. Data were compared to their untreated as well as stimulated healthy-control counterparts. Conditioned media were analyzed for interferon (IFN)-γ, interleukin (IL)-4, IL-10, and IL-12 p40 secretion. RESULTS: Primary untouched VKC-ECs showed TLR4 increase and TLR9 decrease compared to their healthy-control counterparts. NGF exposure resulted in a strong upregulation of TLR4 and a moderate upregulation of TLR9 in few passages VKC-ECs. Both TLR4 and TLR9 upregulation occurred in a dose-dependent fashion and were supported by biochemical analysis. NGF triggered a dose-response release of IL-10 in VKC-ECs conditioned media, an effect not detected for IL-4, IL-12 p40, and IFN-γ. CONCLUSIONS: Our data indicate that NGF is able to induce TLR4/TLR9 overexpression in VKC-ECs. These cells exhibited poor IL-4, IL-12 p40, and IFN-γ responses to NGF, while a significant IL-10 decreased secretion was detected. The different NGF-induced TLR response between VKC and healthy-control conjunctival ECs as well as the different cytokine response might reflect a different pattern of cell activation according to the state of VKC.