Influenza-Induced Interferon Lambda Response Is Associated With Longer Time to Delivery Among Pregnant Kenyan Women

Abstract

Specific causes of preterm birth remain unclear. Several recent studies have suggested that immune changes during pregnancy are associated with the timing of delivery, yet few studies have been performed in low-income country settings where the rates of preterm birth are the highest. We conducted a retrospective nested case-control evaluation within a longitudinal study among HIV-uninfected pregnant Kenyan women. To characterize immune function in these women, we evaluated unstimulated and stimulated peripheral blood mononuclear cells in vitro with the A/California/2009 strain of influenza to understand the influenza-induced immune response. We then evaluated transcript expression profiles using the Affymetrix Human GeneChip Transcriptome Array 2.0. Transcriptional profiles of sufficient quality for analysis were obtained from 54 women; 19 of these women delivered <34 weeks and were defined as preterm cases and 35 controls delivered >37 weeks. The median time to birth from sample collection was 13 weeks. No transcripts were significantly associated with preterm birth in a case-control study of matched term and preterm birth (n = 42 women). In the influenza-stimulated samples, expression of IFNL1 was associated with longer time to delivery-the amount of time between sample collection and delivery (n = 54 women). A qPCR analysis confirmed that influenza-induced IFNL expression was associated with longer time to delivery. These data indicate that during pregnancy, ex vivo influenza stimulation results in altered transcriptional response and is associated with time to delivery in cohort of women residing in an area with high preterm birth prevalence.

Keywords: immune; influenza virus; interferon; pregnancy; preterm; time to delivery.

Figure 1

Volcano plots of gene expression comparisons between women who have birth preterm vs. at term in unstimulated (A) and influenza-virus stimulated (B) PBMC samples. No genes were significantly associated with preterm birth after correcting for multiple comparisons.

Figure 2

Virus-induced induction of interferon is associated with the time to delivery. (A) Network analysis with p-values from fitting a model that explains gene expression from time to delivery with gestational age at birth as a covariate. The shape of the nodes represent how these nodes contribute to the overall score of the network. Triangles contribute positively and increase the overall network false discovery rate (FDR), whereas circles contribute negatively and decrease overall FDR. The color gradient represents t-statistics. (A) positive t-statistic means that gene expression increases with approaching delivery. (B) Network analysis as in (A) with the color gradient representing the actual estimated regression coefficients. Confirmatory RT-PCR analysis of IFN-lamba expression was performed on unstimulated PBMCs (C) and on influenza-stimulated PBMCs (D). Expression levels were fit to a linear model with the following covariates: intercept, time to delivery, and gestational age at birth. Shown are fitted time to delivery slopes for unstimulated mock (C) and stimulated H1N1 (D) samples. The slope on the H1N1 stimulated samples is significant (p = 0.002). The y-axis is the residual expression not explained by gestational age at birth.