Survival and digestibility of orally-administered immunoglobulin preparations containing IgG through the gastrointestinal tract in humans

Oral immunoglobulin (Ig) preparations are prime examples of medicinal nutrition from natural sources. Plasma products containing Ig have been used for decades in animal feed for intestinal disorders to mitigate the damaging effects of early weaning. These preparations reduce overall mortality and increase feed utilization in various animal species leading to improved growth. Oral administration of Ig preparations from human serum as well as bovine colostrum and serum have been tested and proven to be safe as well as effective in human clinical trials for a variety of enteric microbial infections and other conditions which cause diarrhea. In infants, children, and adults, the amount of intact IgG recovered in stool ranges from trace amounts up to 25% of the original amount ingested. It is generally understood that IgG can only bind to antigens within the GI tract if the Fab structure is intact and has not been completely denatured through acidic pH or digestive proteolytic enzymes. This is a comprehensive review of human studies regarding the survivability of orally-administered Ig preparations, with a focus on IgG. This review also highlights various biochemical studies on IgG which potentially explain which structural elements are responsible for increased stability against digestion.