The Developmental Expression of Surfactant Protein-A (SP-A) in the Murine Intestinal Tract

Abstract

Surfactant protein-A (SP-A) plays a critical role in the innate immune system and has well characterized effects in the lung where it attenuates inflammatory responses and controls invasion of bacteria. Extra-pulmonary sources of SP-A have also been indentified: SP-A mRNA and protein have been detected in the adult gastrointestinal (GI) tract, while significant levels of SP-A protein have been detected in amniotic fluid. To date it is not clear if newborn intestinal exposure to SP-A comes from ingested amniotic fluid or from production in the newborn intestinal tract. RNA in situ hybridization with a digoxigenin-labeled anti-sense SP-A probe was used to detect cells with the SP-A mRNA message in the intestinal tract of post-natal day (PND) 3 and PND 6 mice. Immunohistochemistry in PND 7 mice was used to determine intestinal SP-A protein expression. We report positive staining for SP-A protein in cells of the lamina propria of the intestinal tract, although results were mixed as some SP-A null intestinal tissue also stained positively. RNA in situ hybridization with a digoxigenin-labeled anti-sense SP-A probe hybridized to SP-A mRNA in the lamina propria and muscularis externa of the intestinal tract, the same cells that stained positively for SP-A protein. These results indicate that SP-A is likely produced in the intestinal tract in newborn mice.