The lung collectins, SP-A and SP-D, modulate pulmonary innate immunity.
Pulmonary surfactant, which covers the peripheral airway, is a mixture of lipids and proteins. The hydrophilic surfactant proteins A (SP-A) and D (SP-D) play important roles in host defense mechanisms of the lung. These proteins belong to a collectin subgroup in which lectin domains are associated with collagenous structures. Collectins involve mannose-binding lectin, and are considered to function in innate immune systems. SP-A and SP-D interact with various microorganisms and pathogen-derived components. They act as opsonins by binding and agglutinating pathogens. The lung collectins also possess direct inhibitory effects on bacterial growth. SP-A and SP-D associate with immune cells, and activate various cellular functions. The direct interactions of SP-A and SP-D with macrophages result in modulation of phagocytosis or the production of reactive oxygen species. Moreover, by associating with cell surface pattern-recognition receptors, SP-A and SP-D regulate inflammatory cellular responses such as the release of lipopolysaccharides-induced proinflammatory cytokines. Animal models of SP-A- or SP-D-deficiency reveal significant defect in host defense. Significant susceptibility to bacterial and viral infections, delayed microbial clearance, and overexpression of proinflammatory cytokines are observed in SP-A or SP-D knockout mice. A more complete understanding of the mechanisms is required, but the biological relevance of SP-A and SP-D against various respiratory infections has been increasingly recognized.
Sano
Hitomi
H
Department of Biochemistry, Sapporo Medical University School of Medicine, South-1, West-17, Chuo-ku, Sapporo 060-8556, Japan. sanohito@sapmed.ac.jp
Kuroki
Yoshio
Y
D000818:Animals; D007113:Immunity, Innate; D007239:Infections / Q000276:immunology / Q000382:microbiology; D007249:Inflammation / Q000276:immunology / Q000628:therapy; D008168:Lung / Q000276:immunology*; D010587:Phagocytosis / Q000276:immunology*; D037662:Pulmonary Surfactant-Associated Protein A / Q000235:genetics / Q000502:physiology* / Q000627:therapeutic use; D037663:Pulmonary Surfactant-Associated Protein D / Q000235:genetics / Q000502:physiology* / Q000627:therapeutic use; D017382:Reactive Oxygen Species / Q000494:pharmacology
D037662:Pulmonary Surfactant-Associated Protein A; D037663:Pulmonary Surfactant-Associated Protein D; D017382:Reactive Oxygen Species