This is the first study to find ubiquitinated proteins in NETs, and evidence for adaptive immune responses directed towards ubiquitinated NET proteins in SLE. The distinct differences in ubiquitin species profile in NETs compared with healthy controls may contribute to dampened anti-inflammatory responses observed in SLE. These results also support a role for extracellular ubiquitin in inflammation in SLE.

Formation of autoantibodies to carbamylated proteins (anti-CarP) is considered detrimental in the prognosis of erosive rheumatoid arthritis (RA). The source of carbamylated antigens and the mechanisms by which anti-CarP antibodies promote bone erosion in RA remain unknown. Here, we find that neutrophil extracellular traps (NETs) externalize carbamylated proteins and that RA subjects develop autoantibodies against carbamylated NET (cNET) antigens that, in turn, correlate with levels of anti-CarP. Transgenic mice expressing the human RA shared epitope (HLADRB1* 04:01) immunized with cNETs develop antibodies to citrullinated and carbamylated proteins. Furthermore, anti–carbamylated histone antibodies correlate with radiographic bone erosion in RA subjects. Moreover, anti–carbamylated histone–immunoglobulin G immune complexes promote osteoclast differentiation and potentiate osteoclast-mediated matrix resorption. These results demonstrate that carbamylated proteins present in NETs enhance pathogenic immune responses and bone destruction, which may explain the association between anti-CarP and erosive arthritis in RA.

Infection is a frequent finding in patients with DAH and SLE; we found similar mortality between adult SLE and juvenile SLE. Factors that we describe associated with infections may influence the therapeutic selection for these patients.

This is the largest reported series of patients with SLE and PRES. We were able to corroborate the known risk factors for of PRES, and found two previously undescribed factors (lymphopenia and dyslipidemia), which suggests that endothelial dysfunction is a key element in PRES pathogenesis in lupus patients.

Our data suggest that lymphopenia, PDN treatment and low levels of C3 are independent risk factors for the development of severe infections in SLE patients, including diverse microorganisms, not only opportunistic infections.