SIGLEC1 and rheumatoid arthritis: However, the recent report of Xiong et al. 43, showing a positive correlation for Siglec-1 protein expression on PBMCs with disease activity in established RA, and the parallel decrease in SIGLEC1 expression with DAS28 after DMARD treatment, suggests that SIGLEC1 and the more RA-restricted MS4A4A identified are both potential biomarkers of disease activity in persistent arthritis.