Signalling lymphocyte activation molecule family member 9 is found on select subsets of antigen‐presenting cells and promotes resistance to Salmonella infection

Summary Signalling lymphocyte activation molecule family member 9 (SLAMF9) is an orphan receptor of the CD2/SLAM family of leucocyte surface proteins. Examination of SLAMF9 expression and function indicates that SLAMF9 promotes inflammation by specialized subsets of antigen‐presenting cells. Within healthy liver and circulating mouse peripheral blood mononuclear cells, SLAMF9 is expressed on CD11b + , Ly6C − , CD11c low , F4/80 low , MHC‐II + , CX 3 CR1 + mononuclear phagocytes as well as plasmacytoid dendritic cells. In addition, SLAMF9 can be found on peritoneal B1 cells and small (F4/80 low ), but not large (F4/80 high ), peritoneal macrophages. Upon systemic challenge with Salmonella enterica Typhimurium, Slamf9 −/− mice were impaired in their ability to clear the infection from the liver. In humans, SLAMF9 is up‐regulated upon differentiation of monocytes into macrophages, and lipopolysaccharide stimulation of PMA‐differentiated, SLAMF9 knockdown THP‐1 cells showed an essential role of SLAMF9 in production of granulocyte–macrophage colony‐stimulating factor, tumour necrosis factor‐ α , and interleukin‐1 β . Taken together, these data implicate SLAMF9 in the initiation of inflammation and clearance of bacterial infection. Signalling lymphocyte activation molecule family member 9 (SLAMF9) is a cell surface receptor found on specialized subsets of mononuclear phagocytes. Deficiencies in SLAMF9 expression lead to altered pro‐inflammatory cytokine production in human cells and reduced capacity to clear Salmonella infection in mice.