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. Author manuscript; available in PMC: 2015 Dec 1.
Published in final edited form as: Immunol Lett. 2014 May 27;162(0):10–21. doi: 10.1016/j.imlet.2014.05.008

Fig. 3.

Fig. 3

Sources of SIgA in the intestine. Polymeric IgA is synthesized by local plasma cells in the lamina propria of lactating mammary glands, and transported across alveolar epithelial cells into milk by pIgR. The pIgR-derived SC moiety protects SIgA from degradation during transit through the GI tract of the suckling infant. Newborn mammals do not produce endogenous SIgA in the intestine, and are reliant on breast milk-derived SIgA for antibody-mediated protection in the intestinal lumen. As the intestinal immune system develops after birth, SIgA can also be supplied by pIgR-mediated epithelial transcytosis of endogenously synthesized polymeric IgA. In mice, intestinal SIgA is derived exclusively from breast milk during the suckling period, and by endogenous transport after weaning. The pace of development of endogenous SIgA production is highly variable in human infants, and make take several years to achieve adult levels.