Surfactant protein A is an
innate immune system
The innate immune system or nonspecific immune system is one of the two main immunity strategies in vertebrates (the other being the adaptive immune system). The innate immune system is an alternate defense strategy and is the dominant immune s ...
collectin. It is water-soluble and has collagen-like domains similar to
SP-D. It is part of the innate immune system and is used to opsonize bacterial cells in the
alveoli marking them for
phagocytosis
Phagocytosis () is the process by which a cell (biology), cell uses its plasma membrane to engulf a large particle (≥ 0.5 μm), giving rise to an internal compartment called the phagosome. It is one type of endocytosis. A cell that performs ph ...
by alveolar
macrophages
Macrophages (; abbreviated MPhi, φ, MΦ or MP) are a type of white blood cell of the innate immune system that engulf and digest pathogens, such as cancer cells, microbes, cellular debris and foreign substances, which do not have proteins that ...
. SP-A may also play a role in negative feedback limiting the secretion of pulmonary surfactant. SP-A is not required for
pulmonary surfactant
Pulmonary surfactant is a surface-active complex of phospholipids and proteins formed by Type II cells, type II alveolar cells. The proteins and lipids that make up the surfactant have both hydrophilic and hydrophobic regions. By adsorption, adso ...
to function but does confer immune effects to the organism.
During parturition
The role of surfactant protein A (SP-A) in childbirth is indicated in studies with mice.
Mice which gestate for 19 days typically show signs of SP-A in amniotic fluid at around 16 days. If SP-A is injected into the uterus at 15 days, mice typically deliver early. Inversely, an SP-A inhibitor injection causes notable delays in birth.
The presence of surfactant protein A seemed to trigger an inflammatory response in the uterus of the mice, but later studies found an anti-inflammatory response in humans.
In fact, the level of SP-A in a human uterus typically decreases during labor.
Immune functions
Research on SP-A has been done mainly in rodents including mice and rats. This research has shown that mice deficient in SP-A are more susceptible to infections from group B streptoccoal organisms, ''Pseudomonas aeruginosa'', and likely other organisms. The immune functions of SP-A are time-, temperature-, and concentration-dependent.
Location
SP-A is found in the pulmonary surfactant in lungs. SP-A and SP-D are also present in extrapulmonary tissues.
See also
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pulmonary surfactant
Pulmonary surfactant is a surface-active complex of phospholipids and proteins formed by Type II cells, type II alveolar cells. The proteins and lipids that make up the surfactant have both hydrophilic and hydrophobic regions. By adsorption, adso ...
*
SFTPA1
*
SFTPA2
External links
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References
Collectins
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