Immune cell and transcriptomic analysis of the human decidua in term and preterm parturition.

STUDY QUESTION

Is labour, both at term and preterm, associated with alterations in decidual lymphocyte densities and widespread changes to the decidual transcriptome?

SUMMARY ANSWER

The onset of parturition, both at term and preterm, is associated with widespread gene expression changes in the decidua, many of which are related to inflammatory signalling, but is not associated with changes in the number of any of the decidual lymphocyte populations examined.

WHAT IS KNOWN ALREADY

Given its location, directly at the maternal-foetal interface, the decidua is likely to play a pivotal role in the onset of parturition, however, the molecular events occurring in the decidua in association with the onset of labour, both at term and preterm, remain relatively poorly defined. Using flow cytometry and microarray analysis, the present study aimed to investigate changes to the immune cell milieu of the decidua in association with the onset of parturition and define the decidual gene signature associated with term and preterm labour (PTL).

STUDY DESIGN, SIZE, DURATION: This study used decidual samples collected from 36 women across four clinical groups: term (38-42 weeks of gestation) not in labour, TNL; term in labour, TL; preterm (<35 weeks of gestation)not in labour, PTNL; and preterm in labour, PTL.

PARTICIPANTS/MATERIALS, SETTING, METHODS: Decidual lymphocytes were isolated from fresh decidual tissue collected from women in each of our four patient groups and stained with a panel of antibodies (CD45, CD3, CD19, CD56, CD4, CD8 and TCRVα24-Jα18) to investigate lymphocyte populations present in the decidua (TNL, n = 8; TL, n = 7; PTNL, n = 5; PTL, n = 5). RNA was extracted from decidual tissue and subjected to Illumina HT-12v4.0 BeadChip expression microarrays (TNL, n = 11; TL, n = 8; PTNL, n = 7; PTL, n = 10). Quantitative real-time PCR (qRT-PCR) was used to validate the microarray results.

MAIN RESULTS AND THE ROLE OF CHANCE

The relative proportions of decidual lymphocytes (T cells, NK cells, B cells and invariant natural killer (iNKT) cells) were unaffected by either gestation or labour status. However, we found elevated expression of the non-classical MHC-protein, CD1D, in PTL decidua samples (P < 0.05), suggesting the potential for increased activation of decidual invariant NKT (iNKT) cells in PTL. Both term and PTL were associated with widespread gene expression changes, particularly related to inflammatory signalling. Up-regulation of candidate genes in TL (IL-6, PTGS2, ATF3, IER3 and TNFAIP3) and PTL (CXCL8, MARCO, LILRA3 and PLAU) were confirmed by qRT-PCR analysis.

LARGE SCALE DATA

Microarray data are available at www.ebi.ac.uk/arrayexpress under accession number E-MTAB-5353.

LIMITATIONS REASONS FOR CAUTION

Whilst no changes in lymphocyte number were observed across our patient samples, we did not investigate the activation state of any of the immune cell sub-populations examined, therefore, it is possible that the function of these cells may be altered in association with labour onset. Additionally, the results of our transcriptomic analyses are descriptive and at this stage, we cannot prove direct causal link with the up-regulation of any of the genes examined and the onset of either term or PTL.

WIDER IMPLICATIONS OF THE FINDINGS

Our findings demonstrate that the onset of parturition is associated with widespread changes to the decidual transcriptome, and there are distinct gene expression changes associated with term and PTL. We confirmed that an inflammatory signature is present within the decidua, and we also report the up-regulation of several genes involved in regulating the inflammatory response. The identification of genes involved in regulating the inflammatory response may provide novel molecular targets for the development of new, more effective therapies for the prevention of preterm birth (PTB). Such targets are urgently required.

STUDY FUNDING AND COMPETING INTEREST(S): This work was supported by Medical Research Council (grant number MR/L002657/1) and Tommy's, the baby charity. Jane Norman has had research grants from the charity Tommy's and from the National Institute for Health Research on PTB during the lifetime of this project. Jane Norman also sits on a data monitoring committee for GSK for a study on PTB prevention and her institution receives financial recompense for this. The other authors do not have any conflicts of interest to declare.