Figure 2.

Maintenance of homeostasis in the lung by surfactant protein D (SP-D). Shown is an overview of the roles of SP-D in the lung. Indicated is the role SP-D plays in neutralizing, agglutinating and clearing viruses as well as reducing the inflammatory response upon infection with influenza A virus, respiratory syncytial virus (RSV), and human immunodeficiency virus (HIV). The role of SP-D in enhancing phagocytosis by dendritic cells (DCs) while simultaneously reducing antigen presentation and activation of co-stimulatory markers is indicated. Also shown is the role of SP-D in keeping T cells in a hyporesponsive state to increase CTLA4 expression, reduce T cell proliferation, reduce allergen induced Th2 cytokine production and modulate apoptosis. The role of SP-D in clearing and agglutinating noxious particles, pollen and pathogens is indicated. Similarly, the role of SP-D in enhancing macrophage-mediated pathogen killing, modulating inflammatory cytokine production by macrophages and macrophage chemotaxis and reducing antigen presentation is displayed. Also shown is the role of SP-D in clearing apoptotic and necrotic cells in the lung as well as its interaction with neutrophils in binding to neutrophil NETS, and eosinophil extracellular traps, preventing degranulation and modulating cytokine production. Finally, the role of SP-D and rfhSP-D in correcting the phenotype of the SP-D knockout mouse is indicated, specifically their role in decreasing emphysema, excessive phospholipid production, decreasing inflammatory cell and apoptotic and necrotic cell numbers, decreasing the level of reactive oxygen species (ROS), decreasing inflammatory cytokines including IL-6 and IL-12 and decreasing the susceptibility of SP-D knockout mice to pathology as a result of challenge with pathogens, allergens and noxious particles. Adapted from “Alveolar Epithelium (Comparison)”, by BioRender.com (2020). Retrieved from https://app.biorender.com/biorender-templates.