Surfactant protein A (SP-A)and SP-D are members of a family of immune proteins known as collectins, or collagen-like lectins.
SP-A and SP-D interact with various pathogens through their lectin domains and enhance pathogen uptake by phagocytes.
SP-A and SP-D regulate functions of a variety of immune cells, including dendritic cells, T cells, neutrophils and macrophages.
SP-A- and SP-D-null mice have an increased susceptibility to infection and inflammation.
Recent studies indicate that SP-A and SP-D might function at sites in addition to the lung, where they were first discovered and are most abundant.
SP-A has been shown to initiate an inflammatory response in the uterus and to induce labour.
Because the lungs function as the body's gas-exchange organ, they are inevitably exposed to air that is contaminated with pathogens, allergens and pollutants. Host-defence mechanisms within the lungs must facilitate clearance of inhaled pathogens and particles while minimizing an inflammatory response that could damage the thin, delicate gas-exchanging epithelium. Pulmonary surfactant is a complex of lipids and proteins that enhances pathogen clearance and regulates adaptive and innate immune-cell functions. In this article, I review the structure and functions of the surfactant proteins SP-A and SP-D in regulating host immune defence and in modulating inflammatory responses.
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My sincere thanks to S. L. Young and to Wright Lab members, M. Bolger, K. Evans, S. Giles, R. Lovingood, D. Malherbe, J. Malloy and M. Reidy, for their critical review of the manuscript. I extend my sincere apologies to those colleagues whose original work could not be cited due to space limitations. My laboratory is supported by grants from the National Institutes of Health (United States).
The author declares no competing financial interests.
- RESPIRATORY-DISTRESS SYNDROME
A disease that affects premature newborns, resulting in increased difficulty in breathing. The disease is caused by a lack of surfactant, which helps to keep the lungs from collapsing.
- CHRONIC OBSTRUCTIVE PULMONARY DISEASE
(COPD). A group of lung diseases in which air-flow is limited and there is airway inflammation and destruction of lung tissue.
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