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Neutrophil extracellular traps (NETs) play important roles in sepsis and deep-seated infections, but whether NET formation correlates with clinical outcomes of patients with streptococcal bloodstream infections (BSIs) is unclear.We analyzed serum levels of complexes of myeloperoxidase and DNA (MPO-DNA) in patients with streptococcal-BSIs. In vitro assay of NET induction by serum from BSI patients was performed.MPO-DNA values for the Streptococci-BSI group (n = 59) were significantly higher than those for healthy controls (p 0.00001) and matched control groups (n = 59, p = 0.004). The rate of higher MPO-DNA levels (1.87 μg/mL) were higher in abscess-prone streptococcal groups (streptococcus milleri group) (72.2% vs. 52.5%, p = 0.02). For patients with BSIs due to highly infective endocarditis (IE)-prone pathogens, the values of serum MPO-DNA were also higher in patients diagnosed of IE compared to their counterparts (p = 0.009). Notably, serum from patients with leukopenia could induce higher amounts of in vitro NET formation, despite having low MPO-DNA levels, suggesting that NET formation could be influenced by WBC counts. Therefore, we combined WBC counts with MPO-DNA to predict all-cause 30-day mortality in patients with commensal streptococcal-BSIs. The mortality risk was lowest among patients who had neither high MPO-DNA levels nor abnormal WBC counts (p = 0.058). Furthermore, this group of patients also had a favorable composite outcome consisting of major adverse cardiovascular events (MACE) and all-cause mortality (p = 0.026).Together, these study data suggested that serum MPO-DNA can be a biomarker for predicting a composite outcome consisting of MACE and all-cause mortality in patients with commensal streptococcal-BSIs.

The inhibitory Fc receptors function to regulate the antigen-driven activation and expansion of lymphocytes. In B cells, the Fc gammaRIIB1 is a potent inhibitor of B cell antigen receptor (BCR) signaling when coligated to the BCR by engagement of antigen-containing immune complexes. Inhibition is mediated by the recruitment of the inositol phosphatase, SHIP, to the Fc gammaRIIB1 phosphorylated tyrosine-based inhibitory motif (ITIM). Here we show that BCR-independent aggregation of the Fc gammaRIIB1 transduces an ITIM- and SHIP-independent proapoptotic signal that is dependent on members of the c-Abl tyrosine kinase family. These results define a novel Abl family kinase-dependent Fc gammaRIIB1 signaling pathway that functions independently of the BCR in controlling antigen-driven B cell responses.