The collectins family encompasses several collagenous Ca2+-dependent defense lectins that are described as pathogen recognition molecules. They play an important role in both adaptive and innate immunity. Surfactant proteins A and D are two of these proteins which were initially discovered in association with surfactant in the pulmonary system. The structure, immune and inflammatory functions, and genetic variations have been well described in relation to their roles, function and pathophysiology in the pulmonary system. Subsequently, these proteins have been discovered in a wide range of other organs and organ systems. The role of these proteins outside the pulmonary system is currently an active area of research. This review intends to provide a current overview of the genetics, structure and extra-pulmonary functions of the surfactant collectin proteins.

Necrotizing enterocolitis (NEC) is a significant cause of morbidity and mortality in the neonatal population. Formula feeding is among the many risk factors for developing the condition, a practice often required in the cohort most often afflicted with NEC, preterm infants. While the virtues of many bioactive components of breast milk have been extolled, the ability to digest and assimilate the nutritional components of breast milk is often overlooked. The structure of formula differs from that of breast milk, both in lipid composition and chemical configuration. In addition, formula lacks a critical digestive enzyme produced by the mammary gland, bile salt-stimulated lipase (BSSL). The gastrointestinal system of premature infants is often incapable of secreting sufficient pancreatic enzymes for fat digestion, and pasteurization of donor milk (DM) has been shown to inactivate BSSL, among other important compounds. Incompletely digested lipids may oxidize and accumulate in the distal gut. These lipid fragments are thought to induce intestinal inflammation in the neonate, potentially hastening the development of diseases such as NEC. In this review, differences in breast milk, pasteurized DM, and formula lipids are highlighted, with a focus on the ability of those lipids to be digested and subsequently absorbed by neonates, especially those born prematurely and at risk for NEC.

Surfactant Protein D (SP-D), an essential protein related to innate immunity, is expressed in multiple tissue types throughout the body. A closely-related protein, Surfactant Protein A (SP-A), is present in the mouse retina and is associated with neovascularization (NV) in the Oxygen-Induced Retinopathy (OIR) mouse model, mimicking retinopathy of prematurity (ROP). We hypothesized that SP-D would be present in the retina and is also associated with OIR and ROP, which is one of the leading causes of pediatric blindness due to increasing survival rates of extremely preterm newborns. In our study, we did not detect SP-D in the mouse retina through proteomic and genomic investigation at baseline and in pathways known to up-regulate SP-D in other mammal tissues. It is therefore unlikely that SP-D participates in neovascularization in the mouse retina.