The early stages of pregnancy represent a critical period for fetal neurodevelopment, laying the foundation for future psychological well-being (1). Maternal factors, such as the inflammatory intrauterine environment modulated by cytokines and chemokines, significantly shape this trajectory. 

Researchers at Cornell University, led by neuroscientist Miklos Toth, shed light on how chemokine C motif ligand (XCL1), an essential lymphocyte chemoattractant, influenced anxiety and neurodevelopment of the fetus during pregnancy (2). In a mouse model, they observed baseline levels of circulating maternal XCL1 levels throughout pregnancy but noted a brief increase during the mid-gestational period. This surge in XCL1 appeared to be critical for anxiety regulation in the offspring and may serve as a new target in the fight against mental health disorders. 

“We really want to understand what is exchanged between the mother [and the fetus] that might directly and indirectly cause neurodevelopmental problems,” said Toth. “Cytokines keep the mother's immune system in homeostasis, and we never thought that it had anything to do with offspring.” 

Cytokines are signaling molecules that act as the immune system's messengers, orchestrating the host’s responses to pathogens and inflammation. Elevated levels of maternal pro-inflammatory cytokines such as interleukin-1 beta during development have been linked with an increased risk of Huntington’s disease, autism spectrum disorder, and anxiety in offspring. XCL1 is a cytokine produced by CD8+ T cells and natural killer cells and plays a role in antitumor cytotoxic T cell mediated cell death. 

To investigate anxiety, Toth’s group used a mouse model that was heterozygous for the loss of a serotonin 1A receptor (5HT1AR), a receptor known to have a link to anxiety (3). The offspring of these 5HT1AR heterozygous mice had heightened anxiety-like behaviors. In the current study, they wanted to see if maternal inflammation in this anxiety model had an effect on the increased anxiety in the offspring. To their surprise, these 5HT1AR heterozygous mothers had no elevation in pro-inflammatory cytokine levels, which are typically seen in anxiety disorders. RNA sequencing on the 5HT1AR heterozygous mothers revealed a significant downregulation of XCL1 expression compared to wild type mice, suggesting that XCL1 could be regulating offspring anxiety. 

“If the cytokine XCL1 is not produced, then the offspring ends up with a higher psychological abnormality, which is anxiety and fearfulness,” Toth said. “It's very similar to human anxiety.”

They observed consistently low XCL1 levels in wild type mothers throughout gestation, except for a transient surge in XCL1 during gestational days 9 through 10.5. This surge was absent in 5HT1AR heterozygous mothers. To assess how the maternal XCL1 surge affected offspring behavior, the researchers employed the elevated plus maze (EPM) test. This well-established rodent behavior test uses an elevated platform with arms arranged in a plus sign configuration. Walls enclose two opposing arms, while the remaining two arms are open. Rodents have a natural aversion to open spaces and heights, so they typically spend more time in the enclosed arms. But animals with anxiety show even more aversion to open spaces and heights, so they explore those open spaces less than healthy mice.

If the cytokine XCL1 is not produced, then the offspring ends up with a higher psychological abnormality in the mouse, which is anxiety and fearfulness. It's very similar to human anxiety. 
- Miklos Toth, Cornell University

“An anxious human would avoid situations like social anxiety because it's very noisy and very stressful; they would rather sit in the comfort of their home — the mouse is very similar,” said Toth.

The offspring of 5HT1AR heterozygous mothers exhibited a significant increase in the time spent within the enclosed arms compared to control offspring, indicating that anxiety and stress are increased in the progeny of mothers with low XCL1 levels.

To confirm the role of maternal XCL1 on offspring outcomes, the group administered neutralizing anti-XCL1 antibodies to pregnant wild type mice, suppressing the mid-gestation XCL1 surge. Notably, the progeny of these treated mothers also displayed behavioral changes in the EPM test, mirroring the anxiety-like phenotype observed in the offspring of 5HT1AR heterozygous mice. 

“This study really showed how maternal cytokines ultimately alter fetal brain development, something we didn’t ever consider,” said Qingsheng Li, an immunologist at the University of Louisville who was not part of this study. 

These findings may open new avenues for investigating the causes of psychiatric conditions such as anxiety. Toth and his team plan to explore the XCL1 profile in pregnant women and its association with offspring mental health to translate these nonclinical findings into a human context. 

He added, “This really shapes the field of human development that we didn’t think of 20 to 30 years ago and opens up a new field of discovery.” 

References

1. Kwon, H.-K., Choi, G.B. & Huh, J.R. Maternal inflammation and its ramifications on fetal neurodevelopment.Trends Immunol  43, 230–244 (2022).
2. Chen, R.J., Nabila, A., Gal Toth, J., Stuhlmann, H., & Toth, M. The chemokine XCL1 functions as a pregnancy hormone to program offspring innate anxiety.Brain Behav Immun  118, 178–189 (2024).
3. Gleason, G. et al. The serotonin1A receptor gene as a genetic and prenatal maternal environmental factor in anxiety.Proc Natl Acad Sci USA  107, 7592–7597 (2010).