By Deborah Borfitz
February 15, 2022 | Researchers in Norway, led by professor and molecular scientist Ann-Charlotte Iversen, have used cytokine profiling to create a baseline for what the immune system looks like in normal pregnancies as a starting point for discerning when something is going wrong—preeclampsia, for example, one of the most common complications of pregnancy and a leading cause of premature births. As it turns out, immune activity predictably modulates throughout uneventful pregnancies, according to Anders Hagen Jarmund, research program student at the Norwegian University of Science and Technology's Centre for Molecular Inflammation Research (CEMIR).
The pattern begins with elevated immune activation in the first three months, followed by a calmer phase during the second trimester, and then higher activity in the final stretch and most especially when childbirth is imminent, he says. But this “immune clock of pregnancy” has a few important caveats.
Immune activation in the initial three months is higher in women who have given birth previously, for example, but lower than first-time mothers as labor approaches. Going over term also appears to robustly raise cytokine levels.
Results of this first-ever survey of women’s immune responses over the course of pregnancy published last fall in Frontiers in Immunology (DOI: 10.3389/fimmu.2021.752660). In a companion study from the same research group more recently published in the Journal of Clinical Endocrinology & Metabolism (JCEM; DOI: 10.1210/clinem/dgab684), disruption of the usual pattern and overall higher immune activation was associated specifically with polycystic ovary syndrome (PCOS).
The studies, Jarmund says, were possible due to close collaboration between supervisors from different disciplines—Iversen, professor and obstetrician Eszter Vanky, and associate professor and statistician Guro F. Giskeødegård.
The diagnostic possibilities are intriguing here, particularly if cytokine profiles can be identified for the dozens of complications unique to pregnancy, Jarmund says. Over the longer term, improved understanding of these obstetric conditions could provide clues about how to better treat them as well as reduce the risk of their occurrence by modulating the implicated cytokines and the corresponding immune activation.
Meaningfully reducing pregnancy complications requires expanding knowledge of the underlying causes, including immunological processes, he says. No one knows why some babies are born too early, and the etiology of preeclampsia remains unknown, although the placenta is thought to play a key role. It may in fact be a mixture of conditions rather than a single disease.
Also unknown is the exact origin of PCOS, which affects about 17% of women of childbearing age and puts them at heightened risk of a multitude of pregnancy-related complications, according to the Centers for Disease Control and Prevention. These include early pregnancy loss and gestational diabetes.
Previous studies have looked at changing cytokine levels during pregnancy, but this is the first one attempting to map the staged and often complex immunological adaptions that occur, Jarmund says about the Frontiers in Immunology article. The analysis was based on the serum levels of 22 cytokines and C-reactive protein (CRP) of 707 women with normal singleton pregnancies.
Cytokine profiling revealed diverse but characteristic trimester-specific trajectories, he says. It is difficult to sort out when spikes in immune activation were due to inflammation alone or an assortment of other factors such as maternal body mass index (BMI), smoking, number of times a woman had given birth, fetal sex, and birth weight.
Getting a better read on the immune clock of pregnancy required a fair amount of technological innovation, Jarmund points out, since high-throughput immunoassays lack standardized methods for batch and plate adjustment. The research team addressed those variations for each of the 22 cytokines to avoid effects possibly leading to incorrect conclusions.
In the second study in JCEM, led by Live Marie T. Stokkeland (a Ph.D. candidate at CEMIR), the research team again used the multi-cytokine approach to profile 358 women with PCOS relative to a control group without the condition. The results indicate women with PCOS have marked immunological changes in serum cytokines throughout pregnancy as well as higher levels of 17 cytokines and CRP at week 10 of pregnancy.
The immunological dynamics in women with PCOS were also significantly affected by maternal BMI, smoking, and fetal sex, as reported in the article. Importantly, the researchers point out, the overall cytokine pattern was independent of pregnancy complications although connections could be made with some specific serum cytokines.
Interestingly, male fetuses were associated with higher serum levels of five cytokines, which would help explain previous reports of a heightened risk of preterm birth based on the baby’s sex. In this sense, the immune system may also be an indicator of “whether it’s a boy or a girl,” says Jarmund.
While it is not yet known if complications of pregnancy generate a unique fingerprint in terms of immune response, Jarmund and his colleagues intend to find out. Women whose pregnancy is favorable for preeclampsia, for example, might therefore be more closely monitored by their obstetrician. Although preeclampsia can sometimes be short-term managed with medications to give the baby more time to mature in the womb, the most effective treatment is still delivery—at least for now, he adds.
On the diagnostic front, development of a marketable cytokine profiling test for preeclampsia could take another few years, Jarmund says. Over time the methodology might expand to cover other pregnancy-related complications. “Right now, we are more doing the basic research.”
Cytokine profiling has been a niche area within the broader field of reproductive immunology, says Jarmund. Another group working in this arena just published a small study in Cytokine (DOI: 10.1016/j.cyto.2021.155758) where they observed patterns for inflammatory and immune markers from pregnancy to a year postpartum—and the patterns were associated with number of births, pre-pregnancy BMI, and child sex.
How the mother and fetus are interacting will be an important area of investigation moving forward, Jarmund says. At CEMIR, research is now underway to better elucidate the crosstalk between mother, baby, and the placenta providing a bridge between them.