The role of neutrophil extracellular trap formation in equine recurrent uveitis (ERU)

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The equine recurrent uveitis (ERU) is the main reason for blindness in horses, and 10% of the european horses are affected. Significantly, ERU is an important available model for human autoimmune uveitis as the clinical and immune-pathological characteristics are similar. As a cause for ERU, various hypotheses are described in the literature. On the one hand, infections with Leptospira interrogans are discussed as well as other bacterial, parasitic or viral infections. Independent of the initiating cause, there are numerous indications that ERU is an immune-mediated disease. In the body after the control of the primary infection, an overreaction of the immune system occurs in response to activated immune cells. In addition to lymphocytes, these immune cells can also be neutrophil granulocytes. Among various antimicrobial functions, neutrophils have been shown to release neutrophil extracellular traps (NETs). NETs are extracellular DNA fibers with associated proteases and antimicrobial peptides which are released by activated cells. NETs mediate entrap of invading pathogens, but when massively released may contribute to detrimental autoimmune reactions of the host. The research project presented here is intended to provide essential insights for the involvement of NETs in the pathogenesis of ERU. In the first phase of our study, our findings indicate an involvement of NETs in the pathogenesis of ERU with detrimental effects. In short, NETs correlate to disease severity, seem to damage the blood retinal cells, and induce autoantibodies against NET proteins. We hypothesize, that those autoantibodies might shield the NETs from degradation by DNases, resulting in their persistence and potentially in new disease episodes. Thus, in the current project we aim to characterize if and how the phase of disease (non-active quiescent phase versus acute inflammatory phase) influences cellular involvement and extracellular DNA release. Based on our previous data, we further hypothesize that different cell types besides neutrophils play a role in extracellular DNA release during the progression of ERU, which enables crosstalk between various immune cells. Therefore, we will study the release of ETs by other immune cells besides neutrophils and its interplay with adaptive immune cells. Finally, since the use of gentamicin in the treatment of ERU patients is established, the aim is to determine the influence of gentamicin in varying concentrations and along with distinct stimuli on equine immune cells, focusing on ET release.