An 80-kDa syncytiotrophoblast alloantigen bound to maternal alloantibody in term placenta.

The research investigates an 80-kDa protein antigen found in the placenta at term, theorizing that the development of antibodies to this antigen may be crucial for a successful pregnancy. The researchers further discovered that this antigen is resistant to certain digestive enzymes and noted its presence in different blood cells.

Methodology

• The researchers isolated microvesicles from term human placenta, and purposely adjusted the surrounding environment’s pH to a value of 3 to elute the IgG antibodies present.
• These acid-eluted IgG antibodies were then reacted with acid-treated vesicles from other placentas.

Results

• The alloantibody continually attached itself to the preparation it was originally obtained from, but reacted with only approximately 10% of the other placenta preparations treated with acid. This indicates a degree of specificity in the interaction between these antibodies and their original antigen sources.
• They found a similar protein associated with IgG antibodies in term horse placentae, indicating potential similarities across species.
• Despite these similarities, no cross-reactivity between the antibodies of different species was observed, indicating that the antibodies remain species-specific.
• By using labeled antibodies and techniques such as complement dependent cytotoxicity and FACS two-color analysis, the researchers identified the presence of the human polymorphic antigen on peripheral blood monocytes and B-lymphocytes.
• They found that the R80k antigen, present on intact microvesicles, was resistant to the digestion enzyme trypsin. However, after acid elution of IgG, trypsin was able to break down a soluble 50 kDa fragment, which still reacted with the acid-eluted IgG antibody. This suggests a level of protection the antigen offers to these antibodies.

Conclusions

• The team concluded that the presence of antibodies to the R80K antigen in all the term placentae studied, including those from first pregnancies, implies that the development of this alloantibody may be a normal, and potentially essential, process for a successful pregnancy.