IL-10-Producing Potential Treg Precursor in Placenta

The maternal immune system needs to be tolerant of allogeneic fetal tissue for reproductive success. The regulatory immune cell network plays an essential role in maintaining maternal tolerance to the fetus. We herein demonstrate in a green fluorescent protein (GFP)/IL-10 reporter mouse system that unique IL-10-expressing cells exist presumably in chorionic villi within the placenta. Flow cytometric analysis revealed that these IL-10- expressing cells exhibit a unique CD19 negative, CD3 negative, and B220 positive phenotype. Interestingly, these cells were enriched during in vitro culture, but well-known stimuli for T cells and B cells failed to enhance their growth, suggesting that the CD19^- CD3^- B220⁺ cells were self renewing. Unexpectedly, in an adoptive cell trans fer experiment, IL-10 production was detected in Sca-1⁺ CD4⁺ CD25⁺ regulatory T cells (Treg). To our knowledge, this is the first report to identify IL-10-producing CD19^- CD3^- B220⁺ cells in the fetus. These cells may rep resent a potential progenitor of Sca-1⁺ Treg or pluripotent precursor cells for immune tolerance.