Background: The distribution of adverse pregnancy, birth and subsequent child developmental and health outcomes in the U.S. is characterized by pronounced racial (particularly Black-white) disparities. In this context, chronic stress exposure represents a variable of considerable importance, and the immune/inflammatory system represents a leading candidate biological pathway of interest. Previous pregnancy studies examining racial disparities in immune processes have largely utilized circulating cytokine levels, and have yielded null or mixed results. Circulating cytokines primarily represent basal secretion and do not necessarily represent functional features of immune responsivity and regulation. Thus, in order to conduct a more in-depth characterization of racial differences in functional immune properties during pregnancy, we utilized an ex vivo stimulation assay, a dynamic measure of immune function at the cellular level, to investigate Black-white racial differences in in mid- and late-gestation in i) pro-inflammatory (IL-6) responsivity of leukocytes to antigen [lipopolysaccharide (LPS)] challenge, and ii) regulation (dampening) of this pro-inflammatory response by glucocorticoids.
Method: 177 women (N = 42 Black (24%), n = 135 white (76%)) with a singleton, intrauterine pregnancy provided 20 mL venous blood in mid- (16.6 ± 2.4 wks) and late (33.3 ± 1.1 wks) pregnancy. Maternal pro-inflammatory responsivity of leukocytes was quantified by assessing the release of the pro-inflammatory cytokine IL-6 in response to LPS stimulation, and regulation of the pro-inflammatory response was quantified by assessing the suppression of the stimulated IL-6 response after co-incubation with progressively increasing levels of dexamethasone [10-7, 10-6, 10-5 M] (i.e., glucocorticoid receptor resistance (GRR)). A priori model covariates included maternal age, parity, SES (socioeconomic status), and pre-pregnancy BMI.
Results: Maternal pro-inflammatory responsivity (LPS-stimulated IL-6) and GRR increased significantly across mid- and late gestation (adjusted β = 0.157, p = 0.007; β = 0.627, p < 0.001, respectively). Across both time points in pregnancy Black women exhibited significantly higher LPS-stimulated IL-6 release and reduced glucocorticoid regulation of the IL-6 response (i.e., higher GRR) relative to white women, before and after adjusting for covariates (β = 0.381, p = 0.0030; β = 0.391, p = 0.0075, respectively). There was no racial difference in the concentrations of circulating IL-6 (p = 0.9199).
Conclusion: Our findings support the hypothesis postulating significant racial (Black-white) differences in key functional properties of the maternal immune system in pregnancy, which were not apparent using circulating cytokine measures. These data elucidate a potentially important physiological mechanism underlying the transduction of environmental conditions into racial disparities in reproductive and subsequent child health outcomes, and the use of these ex vivo measures should be considered in future studies.
Keywords: African American; Black; Glucocorticoid receptor resistance; Inflammation; Interleukin-6; Racial disparities.
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