CD38 and systemic lupus erythematosus: While SIGLEC-1 expression in monocytes from SLE patients was significantly increased in both SLE cohorts, and SIGLEC-1+ monocytes robustly expressed CD38 (Supplementary Figure S2B), there was no correlation with average CD38 expression on total monocytes or intermediate monocytes across the patients, indicating that a stimulus independent from IFN-I may have induced the increased CD38 expression in SLE intermediate monocytes.