Mouse MRP8 and MRP14, two intracellular calcium-binding proteins associated with the development of the myeloid lineage

MRP8 and MRP14 are two S100-like calcium-binding proteins of unknown function, associated with numbers of human inflammatory disorders. Both molecules have been described as L1 complex, cystic fibrosis antigen, or p8 and p14. We report here the cloning of mouse MRP8 and MRP14 and their pattern of expression during hematopoiesis. Mouse MRP8 and MRP14 proteins share 59% identity with their human counterparts, but they are more divergent than the other members of the S100 protein family. Mouse MRP proteins are coexpressed in fetal myeloid progenitors, where they are detected as early as day 11 of gestation. In fetal liver and yolk sac, MRP+ cell populations increased in number, in association with the development of the myeloid lineage. In adult mouse, we identified MRP8 and MRP14 proteins in immature myeloid cells of the bone marrow, myeloid cells in the splenic red pulp and marginal zone, in addition to monocytes and blood neutrophils. However, MRP expression is lost as cells terminally differentiate into tissue macrophages. In addition, using thioglycollate-induced peritoneal inflammatory exudates, we showed that MRP8 and MRP14 proteins are highly expressed in recruited neutrophils and monocytes.