The Hierarchy Of Pro-Inflammatory Cytokines In Ocular Inflammation

Purpose: The concept of tissue-dependent cytokine hierarchy has been demonstrated in a number of diseases, but it has not been investigated in ophthalmic diseases. Here, we evaluated the functional hierarchy of interleukin-1 (IL-1), IL-6, IL-17A, and tumor necrosis factor (TNF) in the induction of ocular inflammation.Materials and Methods: We delivered adeno-associated virus (AAV) vectors expressing IL-1, IL-6, IL-17A, or TNF intravitreally in naive C57/BL6 mice and compared and contrasted the inflammatory effects in the eye 5weeks after AAV-mediated gene transfer. We also used an in vitro human system to test the effect of cytokines on barrier function.Results: We found that IL-1 had the highest ability to initiate ocular inflammation. The continuous overexpression of IL-1 resulted in a significant upregulation of additional proinflammatory mediators in the eye. Using scanning laser ophthalmoscope and optical coherence tomography imaging techniques, we showed that a low dose of AAVIL-1 was sufficient and was as pathogenic as a high dose of TNF in inducing vascular leakage, retinal degeneration, and cellular infiltration. Furthermore, only a marginal increase in IL-1 was enough to cause cellular infiltration, thus confirming the highly pathogenic nature of IL-1 in the eye. Contrary to our expectation, IL-6 or IL-17A had minimal or no effect in the eye. To examine the clinical relevance of our findings, we used an impedance assay to show that IL-1 alone or TNF alone was able to cause primary human retinal endothelial cell barrier dysfunction in vitro. Again, IL-6 alone or IL-17A alone had no effect on barrier function; however, in the presence of IL-1 or TNF, IL-17A but not IL-6 may provide additive proinflammatory effects.Conclusions: Our studies demonstrate the existence of a functional hierarchy of proinflammatory cytokines in the eye, and we show that IL-1 is the most pathogenic when it is continuously expressed in the eye.