Functional changes in Hofbauer cell glycobiology during human pregnancy

• Little glycogen could be demonstrated in the cells.
• Glycogen synthase was barely detectable but glycogen phosphorylase was abundant.
• GLUT-3 but not GLUT-1 was present in the cells.
• These results show glucose is a more important fuel than glycogen in these cells.
• Lectin histochemistry showed that Hofbauer cells were heavily glycosylated.

IntroductionThis study examines the glucose metabolism and glycosylation of villous macrophages (Hofbauer cells) over the course of pregnancy.Materials and methodsSections of placentae from 6 weeks to term were stained with antibodies to α-amylase, glycogen synthase, glycogen phosphorylase and glucose transporters 1 and 3 (GLUT-1 and GLUT-3) while a panel of 24 lectins was applied to resin sections from 4 weeks onwards. Hofbauer cells were identified by the binding of anti-CD 163 antibody.ResultsLittle stored glycogen could be demonstrated by Bandeiraea simplicifolia-II agglutinin binding and, by immunocytochemistry, low levels of glycogen synthase were located within the cells, though glycogen phosphorylase expression, an enzyme releasing glucose from glycogen chains, was intense. Glucose transporter-3 but not −1 was present in the cells as has been found in other types of macrophage. Lectin histochemistry showed that many classes of glycan were present in the cells, both N and O-linked, though simple fucose residues could not be demonstrated. Glycan profiles were obtained for Hofbauer cell plasma membranes, cytosol, lysosomes and small granules. With some lectins, the intensity of binding diminished after the second trimester. Morphological changes also occurred over the course of pregnancy.DiscussionHofbauer cells have properties commensurate with their phagocytic activity with numerous lysosomal vacuoles and heavily glycosylated plasma membranes and granules, most evident in the first half of pregnancy. Their carbohydrate metabolism appears to rely on glucose mobilisation rather than storage as glycogen, reflecting their peripatetic mode of existence.

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