Description and characterization of a unique human immunoglobulin G1 kappa idiotype found in placental tissue

- Placenta is transporting a unique IgG1k subpopulation.
- A special dodecapeptide sequence is found in the 3rd framework region of the H chain.
- This region binds to TLR2>TLR4 and induces cytokine production.

Does maternal IgG found in placental tissue provide the fetus with more than just humoral immunity? To address this question, the IgGs from twelve placentas were studied and four of these samples were examined using mass spectrometry which revealed an IgG1k idiotype. A special dodecapeptide portion of the 3rd framework region of the VH chain sequence was identified as an idiotypic determinant in these placental- IgG1k (p-IgG1k) and referred to as peptideX2 and found to have biological activity. Antiserum to peptideX2 was made and then used with Western Immunoblotting to show that this unique H chain (containing peptideX2) appears to be present in all p-IgG tested and in all subjects tested. It appears that the placenta contains not only conventional polyclonal maternal IgGs but also an idiotypic population of maternal IgG1k which binds to TLR2>TLR4 via the epitope “peptideX2″ and promotes IL-6, TNFα, and IL-10 production and may play a role in maternal-fetal tolerance.