PO:01:005 Phenotypic, functional and metabolic assessment of myeloid derived supressor cells in systemic lupus erythematosus

and 15 healthy controls from Karolinska University Hospital.LN samples were collected before immunosuppressive therapy (T0) and after one year (T1).Complement proteins Ba, Bb, C3a, C4a, C5a, sC5b-9, factor H, and factor I were assessed using Quidel MicroVue Multiplex Complement Array.Serum levels were normalised to the median HC concentration.Urine concentrations were normalized to urinary creatinine (ng protein/mg creatinine).The Mann-Whitney U test was used to compare protein levels between groups.Results Serum C4a and sC5b-9 were significantly higher in LN patients versus SLE without LN or HC (p<0.001 and p<0.0001; p<0.05 and p<0.01, respectively), while serum C3a, factor I, and factor H were higher in SLE without LN (p<0.05,p<0.001, p<0.01).After one year of immunosuppressive therapy, LN patients showed significantly reduced serum Ba (p<0.001),Bb (p<0.01),sC5b-9 (p<0.001),factor I (p<0.01),factor H (p<0.05), and C5a (p<0.05).Urine analysis revealed significantly elevated complement proteins in LN patients versus SLE without LN and HC (p<0.0001).Urine Ba and C5a decreased significantly after one year of therapy (p<0.05).Complement activation did not differ between active and remission SLE.Conclusions Elevated urine levels of complement activation and regulatory markers are characteristic of SLE patients with LN.Serum levels of Ba, Bb, sC5b-9, factor I, factor H, C5a, and urine levels of Ba and C5a were significantly reduced follow-ing therapy, suggesting their potential as biomarkers of renal activity.