Perinatal conditions and SP-D

Surfactant protein D (SP-D) is a member of the collectin family, a class of proteins which play an important role in the innate immune system and immunomodulation. In particular, SP-D is mainly produced in the epithelial cells of the lung, but can also be found in epithelial cells and secretory glands in the gastrointestinal tract and in other tissues. This protein has important immunomodulatory properties, by binding to specific carbohydrate and lipid structures on the surface of microorganisms. This binding mediates mechanisms like aggregation, chemotaxis, mediation of phagocytosis, and permeabilization. However, the precise role of SP-D in the metabolism of surfactant is still quite unclear.
Studies of amniotic fluid and lung tissue demonstrate increasing levels of SP-D with increasing gestational age. Levels of SP-A and D in amniotic fluid have therefore been suggested as markers of lung maturation. The levels of SP-A in umbilical cord blood also depend on gestational age and perinatal condition. However, the influence of gestational age and perinatal factors on SP-D levels has not been investigated previously.
A recent study conducted in Denmark aimed to go deeper into the knowledge of SP-D, by establishing normal values of SP-D in the umbilical cord blood and capillary blood of mature newborn infants and assessing the influence of perinatal conditions on these levels.
A total of 458 infants, of gestational age ≥ 36 weeks and with a median birth weight of 3600 g, were enrolled in this study. Umbilical cord blood was drawn immediately after birth and capillary blood at age 4 to 10 days and then the concentrations of SP-D were measured by enzyme-linked immunosorbent assay.
The median concentration of SP-D in umbilical cord blood was 392.1 ng/mL and was found negatively correlated with maternal smoking and length of labor. In particular, the SP-D levels in umbilical cord blood of infants of smoking mothers was significantly lower than other infants. For what concerns mother's age, the SP-D level in umbilical cord blood was lowest in children of the youngest mothers. In the capillary blood, the median concentration of SP-D was 777.5 ng/mL and was found to be influenced by birth weight and the mode of delivery, the highest levels being observed in infants born by cesarean section.
From these findings, it is possible to conclude that SP-D concentrations in umbilical cord blood and capillary blood are highly variable. This is consistent of what has been previously determined in healthy adults. In particular, SP-D concentrations depend on several perinatal conditions, both in positive and in negative relationship. However, further studies are needed to elucidate the effect of respiratory distress and infection on SP-D concentrations, considering also preterm infants, with their even more vulnerable innate as well as adaptive immune systems. In this class of infants, the effects of perinatal variations in SP-D levels may be shown even more clearly than in normal-term infants, as well as the influcence of SP-D concentration on immunomodulation.

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