Signalling lymphocytic activation molecule (SLAM, CD150), originally identified as a lymphocyte activation molecule, is now known to be expressed also on mature dendritic cells and on activated monocytes. Importantly, SLAM is distinct from other monocyte activation markers because its expression on monocytes is readily induced in vitro by bacteria derived ligands of Toll-like receptors (TLRs), and not by single stimulation with inflammatory cytokines.¹

This study analysed SLAM expression on monocytes and macrophages in two distinct chronic inflammatory pathologies. In Crohn’s disease, the chronic inflammation in the gut is thought to result from inappropriate and ongoing activation of the mucosal immune system driven by the presence of normal luminal flora. The bacterial product flagellin has been suggested to be a dominant antigen in Crohn’s disease.² Flagellin is the ligand for TLR5 and induces SLAM on monocytes.¹ In contrast to Crohn’s disease, in multiple sclerosis (MS), the chronic inflammation in the central nervous system is commonly assumed not to …