Nati Harnik / AP

A new study published Wednesday may help scientists develop preventative measures against gestational diabetes, recurrent spontaneous miscarriage, and other pregnancy complications.

What they found: The human immune system matures in utero as early as the second trimester but has a tweak — a greater amount of protein arginase-2 — which may allow for greater immune tolerance, according to the scientists behind the semi-controversial study.

Why the findings matter: The knowledge could help guide the timing of intra-uterine stem cell transplants or other gene therapies that could save the life of a fetus or help prevent immune-related issues like gestational diabetes and miscarriages, per an article in Nature. The knowledge could also be applied to helping remedy some adult afflictions, like avoiding the rejection of organ transplants.

Study author Florent Ginhoux told Axios the study was the first to have "clearly mapped the system of this network of cells in human tissue." He said little is known about the initial stages of development for cells central to the immune system in the womb due to ethical concerns surrounding the use of fetal tissue in experiments.

Study details: Ginhoux teamed up with Singapore clinician Jerry Chan, who conducts experimental gene and cell therapies to treat fetal diseases. They studied tissues from 96 fetuses (from clinically indicated pregnancy terminations) from the second trimester of pregnancy and sorted out the immune cells, which they found in the skin, spleen, thymus, and lungs. They exposed the cells to toxic antigens and to non-related adult cells to see if they would trigger an immune response.

Similar to adult cells: They found there were immunologically active cells, called dendritic cells, which showed the capacity to both sense pathogens and stimulate T cells in the second trimester of gestation. The fetal dendritic cells responded to regular antigens in a similar manner as adult dendritic cells react.

Different from adult cells: However, when exposed to adult cells as the antigen, the fetal dendritic cells did not respond with an immune response as adult cells would (think of the immune problems with kidney transplants) but dampened the immune response. The team said the cause of this may be greater amounts of the protein arginase-2, which is found in abundance in fetal dendritic cells but not adult ones.

Immune tolerance and going forward: Arginase-2 is the likely explanation of "immune tolerance" between mother and fetus, where neither immune system attacks the other, Ginhoux said. He said this is important because further studies could see if this tolerance can be applied to adults. While this study discovered one pathway of immunosuppression, Ginhoux said more research is needed to discover other pathways of immunosuppression and to completely map whole system of cell development in fetuses.

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