Background/Purpose: S100A11 protein, a member of S100 family, has been associated with several autoimmune inflammatory conditions such as rheumatoid arthritis (RA). Moreover, its pro-inflammatory effect on mononuclear cells has been reported (1). Although the pathogenesis of autoimmune diseases is not fully understood, the formation of NETs seem to play a certain role. Recent data indicate that some DAMPs including S100A8/A9 are released via NETosis and can further augment inflammatory responses.

Methods: To assess the expression of S100A11 by neutrophils of RA synovial tissue (n=5), immunofluorescence staining of S100A11 and myeloperoxidase (MPO) was performed. The levels of S100A11 and MPO in RA synovial fluid (n=24) and serum (n=36) were measured by ELISAs (RayBiotech and Abcam). For in vitro experiments, NETosis was induced by adding phorbol 12-myristate 13-acetate (PMA) to the neutrophils purified from peripheral blood of RA patients (n=7). Release of NETs was visualised by immunocytochemistry (n=4-7) and the presence of S100A11 in supernatants was analysed by ELISA (RayBiotech). Neutrophils purified from healthy donors were stimulated by S100A11 and the release of cytokines TNFα, IL-6 was measured by ELISA (RayBiotech).

Results: S100A11 was expressed by synovial tissue neutrophils of the RA patients (n=5). The levels of S100A11 in the serum and in the synovial fluid of patients with RA were significantly associated with the levels of neutrophil MPO (r=0.463, p=0.005 and r=0.500, p=0.013). We demonstrated that the neutrophils treated by LPS (n=7) did not up-regulate the secretion of S100A11 compared to unstimulated controls (0.28±0.07 vs. 0.25±0.06; p=ns). However, the release of S100A11 was significantly up-regulated in PMA stimulated neutrophils undergoing NETosis compared to untreated controls (0.30±0.08 vs. 1.14±0.22; p=0.006). Moreover, our results showed that DPI treatment abolished PMA-induced S100A11 secretion. By immunofluorescence staining we demonstrated that the neutrophils activated by PMA release NETs containing S100A11 protein whereas cells stimulated by DPI+PMA were not able to form NETs. In addition, extracellular S100A11 did not modulate the secretion of pro-inflammatory cytokines TNFα and IL-6 by human neutrophils (n=5).

Conclusion: Here we show for the first time that the release of S100A11 by neutrophils could be dependent on NETosis. Moreover, extracellular S100A11 does not further augment the inflammatory response of neutrophils in RA.

Acknowledgement: Supported by MHCR 023728 and SVV – 260373
References: (1) Andrés Cerezo et al., Arthritis Research & Therapy (2017) 19:79, DOI 10.1186/s13075-017-1288-y

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/s100a11-calgizzarin-is-released-during-neutrophil-extracellular-traps-nets-formation-in-rheumatoid-arthritis-ra/