THE ROLE OF CURLI/eDNA COMPLEXES IN HUMAN SYSTEMIC LUPUS ERYTHEMATOSUS

Abstract

Infections are a major cause of morbidity and mortality in the autoimmune disease systemic lupus erythematosus(SLE). We have previously demonstrated that bacterial amyloid curli, produced by Escherichia coli, can accelerate disease in mouse models of lupus. Uropathogenic Escherichia. coli (UPEC) is responsible for the majority of urinary tract infections in SLE. Based on our previous results in mice, we hypothesize that exposure to UPECs containing curli/eDNA complexes can activate the immune system in humans. To establish significance in human SLE we tested if humans have antibodies against curli/eDNA complexes. We investigated 96 SLE patients who met at least 4 SLICC criteria. (Systemic Lupus international collaborating clinics). We tested the presence of anti-curli/eDNA complex antibodies for both IgG and IgA subclasses. Results were compared to 54 age, sex, and race matched healthy controls. We then correlated the levels of anti-curli/eDNA antibodies with clinical parameters, lupus disease status, and frequency of bacteriuria. We found anti-curli/eDNA antibodies in SLE and controls plasma. In SLE plasma the levels correlated with asymptomatic persistent bacteriuria and disease flares in lupus patients. Persistent bacteriuria was associated with an inflammatory phenotype and UPECs from lupus patients produced biofilms containing curli/eDNA complexes. Finally, curli/eDNA complexes cross-reacted with lupus autoantigens such as dsDNA in binding autoantibodies. Neutrophil extracellular traps (NETs) are part of the innate immune system and are pathogenic in SLE. Therefore, we investigated 56 lupus patients who met at least 4 SLICC criteria. Results were compared to 20 age, sex, and race matched healthy controls. We found that curli/eDNA induced more NETs in SLE PMNs (polymorphonuclear leukocytes) compared to healthy controls. In SLE, patients who were high inducers of NETs by curli/eDNA complexes also made a high amount of NETs when stimulated with LPS or PMA. Interestingly, patients who were anti-dsDNA positive made more NETs in response to curli/eDNA complexes. Moreover, we found anti-dsDNA positive patients who strongly responded to curli/eDNA complexes also responded strongly to LPS. Conversely, patients who were anti-dsDNA negative did not have a strong response to both LPS and curli/eDNA complexes. Our results suggest that lupus PMNs are in a chronic inflammatory state. Similarly, to LPS and PMA, we found SLE PMNs use NADPH oxidase to induce NETosis in response to curli/eDNA complexes. We found SLE PMNs use PAD4 to induce NETosis in response to curli/eDNA complexes. PAD4 inhibition did not significantly reduce NET production upon PMA or LPS stimulation, potentially showing a different mechanism on how curli/eDNA complexes induce NETosis compared to PMA and LPS. Remarkably, we found SLE patients responded more to curli/eDNA complexes if they had current bacteriuria or were anti-dsDNA AB positive. We conclude curli/eDNA complexes can activate the innate immune system and exposure to UPECs could be a mechanism to trigger, sustain, or activate lupus disease.