Researchers at the Hadassah Medical Organization in Israel have identified “natural killer cells” as a key component in answering the perplexing question as to why first pregnancies are harder than subsequent ones, according to Ellen Hershkin, president of Hadassah The Women’s Zionist Organization in America. The study, published in the medical journal Immunity, is the product of six years of research led by Dr. Simcha Yagel, head of OB/GYN at HMO.
“Once again, HMO researchers are in the vanguard of providing life-saving, state-of-the-art medical research that is critical to the care, safety and wellbeing of women not only in Israel but around the world,” Hershkin says. “This new study furthers Hadassah’s mission to protect and empower women at one of the most critical and defining moments of their life.”
Natural killer cells are part of the body’s immune system. Their name is derived from their ability to wipe out tumors and pathogen-infected cells. These cells are abundant in the decidua, the uterine lining that forms part of the placenta. Yagel’s research team discovered a population of natural killer cells found in repeated pregnancies that have a unique transcription and epigenetic signature. They named them “Pregnancy Trained Decidual Natural Killer Cells” (PTdNK).
Natural killer cells protect the embryo and ensure its development, although they can also cause problems. Yagel explains: “A fetus is essentially a parasite or a tumor. It invades the mother’s tissue and now receives oxygen and nutrient from the mother. 70% of cells in the fetal-maternal interface are natural killer cells. That’s too much for just immune protection so we delved further and discovered that rather than ‘kill,’ the natural killer cells actually improve the chances of a healthy child … The biggest surprise was that these natural killer cells have memory — they fight diseases, such as the CMV virus. These cells also improve ‘placentation,’ the formation or arrangement of the placenta.”
Yagel and his team note that this is why preeclampsia, a condition caused by inadequate placentation, drops in subsequent pregnancies. “Our findings may provide an explanation as to why complications of pregnancy, especially the ‘great obstetrical syndromes’ (intrauterine growth and small birth size) are less frequent in repeated pregnancies,” Yagel says.
His goal is to develop a test to screen risk factors. “By understanding how natural killer cells work, we can ask what’s missing in the first pregnancies and eventually develop a treatment.”