In a recent study published in Clinical Microbiology, a group of researchers investigated the impact of changes in gut microbiota and metabolites on immune function during pregnancy by comparing gut microbiota, stool and plasma metabolites, as well as cytokines in pregnant and non-pregnant women.
Pregnancy leads to significant changes in hormone levels, body structure, and immune function, which are essential for fetal development. The role of the gut microbiome in immune regulation during pregnancy is increasingly recognized. Studies suggest that it influences pregnancy outcomes and conditions such as preeclampsia through changes in microbial composition and interactions with immune cells.
However, the detailed mechanisms remain unclear. Metabolites primarily mediate the relationship between the microbiome and the immune system, highlighting areas for further research to understand pregnancy-related immune adaptations and develop new therapeutic strategies.
About the Study
The study, conducted between February 2019 and August 2020 at the First Affiliated Hospital of Jinan University, recruited 30 pregnant and 15 non-pregnant women to examine the interactions between gut microbiota, metabolites, and immune function.
Eligible pregnant participants were between 18 and 34 years old, had naturally conceived singleton pregnancies, and had a pre-pregnancy body mass index (BMI) of 18.5 to 21.9 kg/m2, excluding those with pregnancy complications or immune disorders. The control group consisted of healthy women matching the age and BMI of the pregnant group, with neither group taking probiotics or antibiotics in the six months prior to the study.
Stool and blood samples were collected from pregnant women in late third trimester and non-pregnant women on the 14th day of their menstrual cycle. Stool samples were collected using sterile techniques and stored at -80 °C, while blood samples were processed to separate the serum for storage under the same conditions.
The study utilized gene sequencing of ribosomal 16S ribonucleic acid (rRNA) to analyze gut microbiota, with DNA extracted and sequenced to identify microbial species. A combination of Random Forest analysis and Weighted Gene Co-expression Network Analysis (WGCNA) was used to differentiate microbial profiles between groups.
The untargeted liquid chromatography-tandem mass spectrometry (LC-MS/MS) metabolomics analyzed stool and plasma samples to identify metabolic changes, with quality control measures in place to ensure data reliability. The metabolomic data were processed and analyzed to identify significant differences and assign them to biological signaling pathways using the Kyoto Encyclopedia of Genes and Genomes (KEGG) database.
Plasma cytokines were measured using a multiplex bead assay to assess differences in immune function between the groups. Lastly, the study integrated microbial, metabolomic, and cytokine analysis data through statistical and visualization tools to examine possible correlations and mediation effects in the multi-omics analysis.
The study revealed no significant differences in average age or pre-pregnancy BMI between the two groups. Immunoprofiling showed that pregnant participants had lower levels of pro-inflammatory cytokines and higher levels of certain anti-inflammatory cytokines compared to the control participants, indicating a shift toward immune suppression during pregnancy.
The study also examined gut microbiota and found different microbial compositions between pregnant and non-pregnant women. Pregnant women exhibited higher diversity in operational taxonomic units (OTUs) and differences in the frequency of specific bacterial strains.
Using Random Forest models and WGCNA methods, the researchers identified microbial modules that negatively correlated with pro-inflammatory cytokines, suggesting that certain gut bacterial groups consistently influence inflammation reduction during pregnancy.
In particular, bacteria such as Bifidobacterium and Ruminococcus, known for their anti-inflammatory properties, were more prevalent in pregnant women and negatively correlated with pro-inflammatory cytokines.
Metabolic analysis of stool and plasma samples using untargeted LC-MS revealed significant metabolic changes during pregnancy. Different metabolites, especially lipids and bile acids, were identified, with many showing downregulation in pregnant women.
These included arachidonic acid and various bile acids, known to be associated with inflammation. The analysis highlighted the significant role of bile acid metabolism during pregnancy.
Correlation studies between metabolites and cytokines showed that certain enriched metabolites in pregnant women negatively correlated with pro-inflammatory cytokines, indicating their involvement in modulating immune responses.
The study also examined the relationships between gut microbiota, metabolites, and cytokines, and found that metabolites could mediate the relationship between microbiota and the immune system.
Directed mediation analysis identified specific connections between microbes, metabolites, and cytokines, suggesting that certain gut microbes could influence cytokine levels by modulating metabolite concentrations. For example, Ruminococcus callidus and other bacteria might reduce pro-inflammatory cytokines by influencing specific metabolites such as desoxycholic acid and arachidonic acid levels.