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Description
Immune complex vasculitis is a vascular inflammation that mainly affects small blood vessels. Initial steps are formation of immune complexes in the vessel, followed by neutrophil and IC interaction, accumulation, deposition, activation and ensuing destruction of vessel wall. It is unknown how and which cytotoxic components cause the vessel damage. Stimulated neutrophils produce extracellular structures called neutrophil extracellular traps. NETs are filaments of decondensed chromatin associated with proteins like histones, elastase and myeloperoxidases which can have a cytotoxic effect to the endothelium. NETosis is stimulated by several molecules, like ICs, but the relevance in importance in skin-limited IgA ICV is unknown. The objective was to investigate the impact of NETs from human neutrophils on vessel damage during skin-limited IgA ICV in vivo, in vitro and ex vivo.
We were able to show together with deposited neutrophils a presence of cytotoxic NET structures (H3Cit, MPO and Ela) in lesion skin. We confirmed that neutrophils of skin-limited IgA ICV patients are able to release high amounts of NET after stimulation with IgA ICs or PMA in comparison to healthy donor neutrophils. That’s why we assumed, that neutrophils of skin-limited IgA ICV patients are primed and examined serum samples from the patients. We found and elevated level of IL-6, IL-18 and S100A8/S100A9 and were able to show an enhanced reaction potential of healthy donor neutrophils to release NET after pre stimulating the cells with IL-6 or S100A8/S100A9. IL-18 showed no effect on the NETosis rate. In vitro we were able to evaluate the highly cytotoxic effect of NET released from skin-limited IgA ICV patients. To reconstruct the in vivo conditions we used a shear-flow system and showed an aggregation of neutrophils after addition of IgA ICs followed by deposition of these aggregates to the activated endothelium under low-flow. Accompanying the released NET was highly cytotoxic to the endothelium under flow if the DNA structure was not destroyed by DNase. In our mouse model a degradation of DNA after inducing vasculitis, by passive reverse Arthus reaction, resulted in an improved disease outcome. These findings indicate the importance of neutrophils and NET during the evolvement of vessel damage in skin-limited IgA ICV.
