Conditional disruption of Hematopoietic protein-1 in mice reveals an essential role for Hem-1 in myeloid cell functions

Abstract Hematopoietic protein1 (Hem-1) is a hematopoietic cell-specific subunit of WAVE (WASP-family verprolin homologous protein) complex, which acts downstream immune receptors (including BCR, TCR, TLR, and cytokine receptors) to stimulate filamentous actin (F-actin) polymerization. Inactivating mutations in NCKAP1L, the gene encoding Hem-1, have been recently associated with Primary Immunodeficiency Disease in humans (unpublished), and high NCKAP1L expression has been associated with a poor prognosis in Chronic Lymphocytic Leukemia. Using constitutive Hem-1 null mice, we previously published that Hem-1 is critical for normal lymphopoiesis and innate immunity. However, the cell autonomous functions of Hem-1 in individual immune cell types remain an enigma. The objective of this study was to define the cell autonomous roles of Hem-1 in myeloid cells. We created conditional Nckap1l   fl/fl mice, which were bred to LyzMCre mice to delete Hem-1 specifically in myeloid cells. We found that neutrophils from myeloid cell specific Hem-1 null mice exhibited defective F-actin polymerization and impaired migration in response to the chemoattractant fMLP. Hem-1 deficient macrophages were unable to efficiently phagocytose live bacteria. Myeloid specific Hem-1 null mice were much more susceptible to influenza virus (H1N1/PR8) infection based on significantly increased body weight loss, increased peribronchial inflammation, reduced alveolar macrophage number, and increased pro-inflammatory cytokines in bronchiolar lavage fluid. Collectively, our results reveal previously uncharacterized cell autonomous roles for Hem-1 in primary myeloid cells, and suggest that Hem-1 is critically important for effective anti-viral immunity.