S100A8 and systemic lupus erythematosus: This aim of this study, as part of the MRC MASTERPLANS Consortium, was to determine the serum and urine concentrations of S100 proteins S100A8/A9 and S100A12 in SLE to test associations with active renal disease (LN) and investigate their applicability as predictors of treatment response to B cell depletion with RTX.