Re: Are antibodies from mother to fetus treated as 'non-self'/ foreign ?

Fortunately, these antibodies do not trigger an immune response.

One of the wonderful things about mothers is their ability to transfer antibodies to the fetus or baby, giving the baby a certain level of passive immunity. Antibodies of the IgG class are transferred to the developing fetus from around the 30th week of gestation through delivery. After delivery, antibodies may continue to be transferred to the newborn through breast milk. The "colostrum", a protein-rich fluid secreted by mom's breast in the first few days is especially rich in antibodies of the secretory IgA class. As a pediatrician, I do everything I can to get moms to breastfeed, at least for the first 6 months when the baby's immune system is still immature.

As you know, antibodies are proteins, and proteins make the best antigens. Nevertheless, human antibodies, when transferred to another human, are just not recognized by the recipient's system as non-self, and do not stimulate an immune response. They just go floating about the bloodstream, doing their job until they are either destroyed while fighting infection, or destroyed by the liver - it's very sad when you think about it. Human antibodies are so useful that infusions of IVIG (intravenous immune globulin) are used to treat a variety of diseases in medicine. Also, many passive immunizations used AFTER exposure to an infectious agent may include human antibodies, such as VZIG (varicella- zoster immune globulin) and HBIG (hepatitis-B immune globulin).

Now, although antibodies may not be recognized by the RECIPIENT as non- self, the antibodies may see things differently. When ANTIBODIES see the recipient as non-self, then you're in a heap of trouble. This can happen even with the mom and baby situation. If mom has antibodies to the baby's blood type, for example, these will cross the placenta, recognize the fetus' cells as foreign and may actually cause lysis of fetus' red blood cells. And until those antibodies are used up or destroyed, these problems will continue.

Things are also a little different when animals other than humans are involved. Animals make antibodies similar to ours, but they are different enough to be recognized as foreign and may set off a hypersensitivity reaction. "Serum sickness" is something you may have heard about. This is a hypersensitivity response which occurs when a person is given a large amount of foreign protein, such as immunoglobulins from a horse to fight snake venom. This is a little different from your original question, but you should understand the other side of things.

I hope this info helps. For more information, try these websites:
Mount Sinai Journal of Medicine
Neonatology on the Webz

Chris Bassett, MD
Pediatrician