All of the following are accurate statements about neonatal immunity EXCEPT:
A)Transfer of maternal IgG across the placenta is mediated by an Fc receptor structurally similar to class I MHC.
B)IgA is absorbed in the gut from breast milk and re-secreted by the infant into the bronchial mucosa.
C)IgA secretion into breast milk involves transport through breast epithelial cells,and is dependent on the poly-Ig receptor.
D)Transport of IgG across the neonatal intestinal epithelium is mediated by an Fc receptor structurally similar to class I MHC.
E)Loss of maternal antibodies is partly responsible for increased frequency of infections in infants at about 6 months of agE.

Question

Quizplus · Accepted Answer

IgA is secreted into breast milk via poly-Ig receptor-mediated transcellular transport,but it is not reabsorbed in the infant's gut.Rather,IgA remains in the lumen of the alimentary canal as a defense against intestinal microbes.IgG from breast milk is reabsorbed into the circulation from the gut lumen by the class I MHC-like neonatal Fc receptor (FcRN).This same receptor also mediates transplacental transport of IgG.Passive immunity mediated by maternal antibodies wanes with time;at about 6 months,infants have a nadir of circulating antibodies because maternal antibodies are depleted and antibodies produced by the infant have not reached maximal levels.This nadir corresponds to a period of increased susceptibility to infections,which is even more exaggerated in children with immunodeficiency diseases.

All of the Following Are Accurate Statements About Neonatal Immunity