The NPM1 gene is frequently a target of genetic alteration in hematological tumors, particularly of the myeloid lineage. Complete inactivation of Npm1 in the mouse disrupts primitive hematopoiesis and results in embryonic lethality. Npm1 heterozygosity produces features similar to those of MDS that progress to overt leukemia, and specific point mutations of Npm1 lead to bone marrow failure due to loss of hematopoietic stem cells. However, little is known about NPM1s role in mature, differentiated cells. Here we generated a conditional mouse mutant to inactivate Npm1 across the myelomonocytic lineage, and investigated its ability to influence macrophage maturation and function. We found that Npm1 is not required to maintain macrophage viability, while its loss in mature macrophages reduces production of reactive oxygen species, chemotactic properties and phagocytic capacity. Taking advantage of our recently established Npm1D180del mouse model of ribosome dysfunction and hematological disease, we identify cellular translation and rRNA 2-O-methlyation as a crucial element in controlling macrophage function. These analyses demonstrate a role for Npm1 in adult immune cells, and reveal the importance of translation regulation in macrophage function.### Competing Interest StatementThe authors have declared no competing interest.

Macrophage Function is Regulated by NPM1-Mediated 2′-O-Methylation