Neutrophils Dominate the Cervical Immune Cell Population in Pregnancy and Their Transcriptome Correlates With the Microbial Vaginal Environment

Abstract

The cervicovaginal environment in pregnancy is proposed to influence risk of spontaneous preterm birth. The environment is shaped both by the resident microbiota and local inflammation driven by the host response (epithelia, immune cells and mucous). The contributions of the microbiota, metabolome and host defence peptides have been investigated, but less is known about the immune cell populations and how they may respond to the vaginal environment. Here we investigated the maternal immune cell populations at the cervicovaginal interface in early to mid-pregnancy (10–24 weeks of gestation, samples from N = 46 women), we confirmed neutrophils as the predominant cell type and characterised associations between the cervical neutrophil transcriptome and the cervicovaginal metagenome (N = 9 women). In this exploratory study, the neutrophil cell proportion was affected by gestation at sampling but not by birth outcome or ethnicity. Following RNA sequencing (RNA-seq) of a subset of neutrophil enriched cells, principal component analysis of the transcriptome profiles indicated that cells from seven women clustered closely together these women had a less diverse cervicovaginal microbiota than the remaining three women. Expression of genes involved in neutrophil mediated immunity, activation, degranulation, and other immune functions correlated negatively with Gardnerella vaginalis abundance and positively with Lactobacillus iners abundance; microbes previously associated with birth outcome. The finding that neutrophils are the dominant immune cell type in the cervix during pregnancy and that the cervical neutrophil transcriptome of pregnant women may be modified in response to the microbial cervicovaginal environment, or vice versa, establishes the rationale for investigating associations between the innate immune response, cervical shortening and spontaneous preterm birth and the underlying mechanisms.

Single-cell RNA sequencing of cervical exfoliated cells reveals potential biomarkers and cellular pathogenesis in cervical carcinogenesis

“…Although, we had excluded the patients suffering the acute vulvovaginal candidiasis and bacterial vaginosis. Our finding supported the previous reports claiming neutrophils acted as the dominant immune cell type in the cervix [ 56 – 58 ]. The percentage of neutrophils was different with samples collected from biopsies [ 59 ].…”

The Role of Neutrophils in Pregnancy, Term and Preterm Labour

“…Evidence is emerging supporting the role of microbial-induced inflammation in modifying risk, with higher cervical-vaginal concentrations of cytokines such as IL-8, IL-6 and IL-1β and complement proteins C3b, C5 and C5a seen in association with in these high-risk vaginal microbial signatures [ 102 , 103 , 104 ]. It is plausible, that the predominant leukocyte influencing the local immune milieu is the neutrophil, with early studies beginning to support this [ 105 , 106 , 107 ].…”

“…No statistically significant differences were seen in neutrophil concentrations between women who delivered preterm compared to at term, however the numbers of preterm deliveries were small (n = 18). Mohd Zaki et al have also reported that neutrophils are the predominant leukocyte population at the cervical-vaginal interface of women at high risk of preterm birth [ 105 ]. No significant differences were seen in neutrophil concentrations between women who delivered at term compared to preterm, however the study was likely to be underpowered for this outcome as only six women delivered preterm.…”

Torquetenovirus in pregnancy: Correlation with vaginal microbiome, metabolome and pro-inflammatory cytokines

“…Since TTV replication preferentially occurs in activated lymphoid cells (Brundin et al, 2020), and immune system activation is at its lowest level in case of a L. crispatus-dominated vaginal microbiome (Witkin and Linhares, 2017), we can speculate that the absence/decrease of TTV is linked to the reduction of lymphoid cells or their pro-inflammatory molecules when L. crispatus is predominant. On the contrary, the presence of L. iners is associated with a higher expression of genes involved in leukocyte mediated immunity and activation (Mohd Zaki et al, 2022), being potentially associated with higher levels of TTV in the vaginal environment.…”