Maternal plasma cytokines in early- and mid-gestation of normal human pregnancy and their association with maternal factors
Introduction
Cytokines secreted from both immune and non-immune (e.g. decidual, chorionic) cells are thought to be involved in several aspects of reproduction, including ovarian follicle development, implantation, growth and development of trophoblasts, and parturition (Bowen et al., 2002, Saito, 2000). Interleukin (IL)-6 may have a pivotal role in angiogenesis and initiation of labor, while granulocyte-macrophage colony-stimulating factor (GM-CSF) appears to promote preimplantation embryo development (Motro et al., 1990, Sjoblom et al., 2002, Greig et al., 1997). Wegmann et al.'s (1993) Th1/Th2 paradigm originally characterized successful pregnancy by increased production of Th2 cytokines (e.g. IL-6) and decreased production of Th1 cytokines (e.g. IL-2, tumor necrosis factor (TNF)-α, interferon (IFN)-γ), although it now appears that categorization of cytokines into either Th1 or Th2 oversimplifies their roles within the inflammatory network. An increasing amount of evidence suggests TNF-α and IFN-γ are critical for early human pregnancy maintenance (Ashkar et al., 2000, Parr et al., 1995).
Knowledge of systemic cytokine patterns during normal pregnancy is incomplete. Although a number of studies have reported elevations in cytokines in conjunction with normal labor onset (reviewed by Bowen et al., 2002), few have described levels of circulating cytokines over the course of pregnancy (Vassiliadis et al., 1998, Austgulen et al., 1994, Opsjon et al., 1993, Makhseed et al., 2000), and results have been inconclusive. Most studies are cross-sectional in design, and virtually all have very small sample sizes (i.e. 15–30 subjects per trimester). Furthermore, while the influence of direct infectious or immune stimuli on cytokine levels has been documented, it is unknown whether and to what extent pregnancy cytokine levels vary by other maternal factors.
This study has measured plasma cytokine levels in a large longitudinal cohort of women who subsequently delivered at or after 37 weeks’ gestation. Our objectives were to: (1) determine concentrations of and relationships between IL-2, IL-6, IL-12, TNF-α, IFN-γ and GM-CSF in early- and mid-pregnancy; (2) describe changes in concentration from early- to mid-pregnancy; and (3) evaluate associations between cytokine levels and pre-pregnancy body mass index (BMI), maternal age, gravidity and prior preterm delivery.
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Subject selection and study details
The Danish National Birth Cohort (DNBC) is an ongoing longitudinal study of 101,042 women recruited during pregnancy between 1996 and 2002. Women were eligible if they intended on carrying their pregnancy to term and spoke Danish. It was estimated that approximately 35% of all women in Denmark who were pregnant during the recruitment period participated in the study. Methods of the DNBC study are described in detail elsewhere (Olsen et al., 2001).
DNBC personnel administered detailed telephone
Descriptives
Of the 1274 subjects analyzed, 1079 (85%) provided a blood sample in early-pregnancy (median [IQR]: 8.5 weeks [7.1, 10.0]) and 908 (71%) in mid-pregnancy (25.0 weeks [24.1, 26.1]). Fifty-five percent of women (n = 707) provided blood samples at both time points. Subjects delivered singleton infants at a median of 282 days. Most women were less than 35 years of age, without a prior preterm delivery, of high socioeconomic status, had normal pre-pregnancy BMI and had a spouse or partner (Table 1).
Correlations between cytokine concentrations in early- and mid-pregnancy
We
Discussion
We have used a large longitudinal design to establish patterns of circulating early- and mid-pregnancy cytokines in women delivering singleton infants >37 weeks in order to better understand the dynamics of the human inflammatory network during gestation. Our results indicate that cytokines are detectable in circulation and interrelated both in early- and mid-gestation of normal pregnancy. Concentrations modulate as pregnancy progresses, implying continuous immune regulation associated with the
Acknowledgements
We would like to acknowledge Rebecca Buus for her contribution to the study design, and Jørn Olsen and Mads Melbye for their work on the Danish National Birth Cohort. This research was supported by the March of Dimes Birth Defects Foundation (grant no. 20-FY03-28), a cooperative agreement (grant no. UR3/CCU018305-03) from the Centers for Disease Control and Prevention, and an American Women in Science award.
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