The mouse homolog of the mutant WASp responsible for human X-linked neutropenia renders granulopoiesis ineffective.

Severe congenital neutropenia (SCN) is characterized by severe neutropenia and recurrent critical infections. X-linked neutropenia (XLN) is caused by a gain-of-function mutation in the Wiskott-Aldrich syndrome gene (WAS), the product of which (WASp) is expressed only in blood cells, especially during neutrophil maturation. To investigate the mechanism of neutropenia, we established a novel knock-in mouse line expressing WASp-I292T. WASp-I292T neutrophils exhibited activated (dysregulated) actin polymerization. Although WASp-I292T mice did not recapitulate neutropenia, neutrophil levels were increased in the bone marrow, and extramedullary hematopoiesis was observed. Bone marrow neutrophils from WASp-I292T mice exhibited attenuated transmigration. These abnormalities were associated with downregulation of NFκB and TP53 and faulty activation of their downstream pathways.