TNFRSF17 and systemic lupus erythematosus: While one study reported increased BCMA expression on almost all B cell subsets and a positive correlation of BCMA expression on total B cells with disease activity [26], another study described decreased BCMA expression on almost all B cell subsets in a small cohort of SLE patients compared to healthy controls and a negative correlation between BCMA-expressing B cells and disease activity [39].