Table 1.

Innate leukocytes recruited to the lungs during murine influenza A virus (IAV) infection and their roles in immunoprotection and immunopathology. Leukocytes with crucial roles in IAV infection are listed, along with the timepoints of maximal accumulation in the lung. Roles in immunoprotection and immunopathology to the host in IAV infection are listed. IFN; interferon, NETosis; neutrophil extracellular trap(osis), CTL; CD8⁺ cytotoxic T lymphocyte, ROS; reactive oxygen species.

Leukocyte	Peak Accumulation in the Lung Following IAV Infection	Immunoprotection Roles	Immunopathology Roles
Monocyte	5 days [36]	Pro-inflammatory cytokine production [37], differentiation into dendritic cells [9]	Excessive pulmonary inflammation and tissue damage leading to mortality [38]
Alveolar macrophage	2 days [39]	Phagocytosis of infected cells [39], prevention of epithelial cell infection [40]	Excessive pulmonary inflammation and tissue damage leading to mortality [41]
Dendritic cell	10 days [36]	Type I IFN production [42], activation and recruitment of antigen-specific T cells [36]	Excessive pulmonary inflammation and tissue damage leading to mortality [43]
Neutrophil	3–5 days [44]	Pro-inflammatory cytokine production [44], phagocytosis of infected cells [39], anti-bacterial granule release and NETosis to limit viral replication [45], recruitment of CD8+ T cells [46]	Excessive pulmonary inflammation, ROS production [47] and tissue damage leading to mortality [48]
Natural killer cell	2–4 days [49], 6 days [50]	Pro-inflammatory cytokine production [51], cytotoxicity of IAV infected cells [49], recruitment of dendritic cells and T cells to mediastinal lymph node [52], enhancement of CTL responses [53]	Excessive lung inflammation, increased phagocyte and neutrophil recruitment [54]