system
Given the following post, respond as if you're commenting on Reddit:
human
How are antibodies transferred by breastfeeding? 

According to quite reputable sources, antibodies can be passed on from mother to infant by breastfeeding. The problem I'm having is that it seems to contradict my knowledge of digestion and absorption.

Antibodies are proteins. Proteins are large molecules that are too big to move through cell membranes on their own (i.e. without a vesicle). So, proteins are broken down into amino acids in the stomach by proteases, which can then be absorbed into the bloodstream.

Considering this, how is it that antibodies are able to move through the infant's digestive system without destruction, and then pass through into the blood, thus transferring immunity? Does the infant's digestive system operate differently? Is there something in the colostrum that aids this?
gpt
The antibodies that are secreted in milk have special modifications which cause them to resist proteolytic activity and low pH.  Once they get through the stomach, they are reabsorbed by special receptors in the intestinal epithelium.  Because they are recognized by receptors, they enter the cell though endocytosis and travel through the cell by transcytosis - thereby avoiding degradation in the absorbing cell.  After that, they are trafficked to the bloodstream.

Edit:  Duh low pH, not high pH.