Conditional Disruption of Hem-1 Results in Impaired Development of Alveolar Macrophages, Pulmonary Alveolar Proteinosis, and Increased Susceptibility to Influenza Virus Infection

Abstract

Hematopoietic protein-1 is a hematopoietic cell specific member of the actin-regulatory WAVE (Wiskott-Aldrich syndrome verprolin-homologous protein) complex 2, which acts downstream of many immune receptors and activated Rac to stimulate F-actin nucleation. Mutations in the gene encoding Hem-1 (NCKAP1L) have recently been found to result in Primary Immunodeficiency Disease, characterized by recurrent bacterial and viral respiratory infections, skin infections, otitis, and bacteremia. However, the cell-type specific functions of Hem-1 in immune cells are not known. In this study, we generated constitutive and myeloid cell specific Hem1 knockout mice using the Cre-LoxP system to dissect the importance of Hem-1 in the development and functions of myeloid cells. We found that mice with constitutive or myeloid cell specific disruption of Hem-1 develop pulmonary alveolar proteinosis (PAP), due in part to impaired development of alveolar macrophages (AMs) at the pre-AMs to mature AMs stage. Bronchoalveolar lavage fluid (BALF) from myeloid cell specific Hem1 null mice contained greatly increased cellular debris, protein, proinflammatory cytokines and chemokines. Hem1 null neutrophils and monocytes failed to migrate normally in vitro and in vivo to lung tissue in response to LPS or CCL2 stimulation. Myeloid-specific Hem1 null mice exhibited greatly increased sensitivity to influenza virus infection. These results collectively suggest that Hem-1 is essential for the normal development of alveolar macrophages, and for normal myeloid cell migration, providing essential new information regarding the mechanisms of how mutations in NCKAP1L results in recurring respiratory infections in PID patients.