The vaginal immune system fluctuates depending on the stage of the menstrual cycle

The vaginal immune system fluctuates depending on the stage of the menstrual cycle

The concentration of key immune signaling molecules in the vagina undergoes “clear and consistent” fluctuations throughout the menstrual cycle, a UW Medicine-led team reports in a study published today in the journal BMC Medicine.

The findings could help researchers better understand the role of the immune system in fertility and guide scientists' efforts to develop vaccines and treatments for infectious diseases.

A meta-analysis of 32 studies showed that the immune system in the vagina varies depending on the stage of the menstrual cycle. The analysis identified 53 different messages that immune cells sent to each other.

Cells in the body communicate with each other by producing molecules called cytokines, which can tell other immune cells that "there's an infection here" or "don't worry, everything's OK," said lead author Sean Hughes, an obstetrics and gynecology researcher at the University of Washington School of Medicine.

The main goal of the study is to gain a global overview of immune-related communication in the vagina and cervix during the menstrual cycle, Hughes said. One of the more consistent results of the study was that cytokines "call" macrophages to the vaginal area more during the period before the release of the egg from the ovary (follicular phase) and less after the release of the egg (luteal phase), i.e. when conception occurs.

In practical terms, this discovery suggests that researchers should consider the menstrual cycle stage of patients or study participants when testing a new vaccine or conducting other research, Hughes said.

"The decreases we observed in many cytokines during the luteal phase are consistent with previous claims that immunity declines during the luteal phase. This is likely due to an easier embryo implantation," the authors write. “To compensate, it appears that antimicrobial factors such as beta-defensins increase during the luteal phase.”

Scientists need to design their studies so that all participants are measured at the same stage of the cycle.”

Dr. Florian Hladik, senior author, UW research professor of obstetrics and gynecology

The study provides a strong indication of what happens during the cycle, Hughes said.

"We now have the 'what' information for 53 different cytokines. For each one, we need to figure out why this happens and how this relates to sexually transmitted diseases and pregnancy."

Overall, the difference between the follicular and luteal phases could mean that vaccinations and other interventions would be more effective in one phase than another, Hughes suggested.

Source:

University of Washington School of Medicine/UW Medicine

Reference:

Hughes, SM, et al. (2022) Changes in cervicovaginal immune mediator concentrations during the menstrual cycle: a systematic review and meta-analysis of individual patient data. BMC Medicine. doi.org/10.1186/s12916-022-02532-9.

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