The vaginal immune system may indicate the best time to get vaccinated

A study led by the University of Washington School of Medicine published today in the journal BMC Medicine reported that during the menstrual cycle, the level of key immune signaling molecules in the vagina "experienced clear and consistent" fluctuations
.

The findings may 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 within the vagina fluctuates depending on the menstrual cycle
.
The analysis identified 53 different messages sent by immune cells to each other
.

Sean Hughes, a research scientist in obstetrics and gynecology at the University of Washington School of Medicine and lead author of the study, said that cells in the body communicate with each other by making a molecule called cytokines, which can tell other immune cells "there's an infection here" or "don't worry, everything is fine
.
"

Hughes said the main purpose of the study was to construct a global view
of immune-related communication in the vagina and cervix during the menstrual cycle.
One of the more consistent findings of the study was that cytokines "summoned" macrophages to the vaginal region more often before the egg was released from the ovary (follicle phase), and less
after the egg release (luteal phase), that is, when conception occurred.

In fact, Hughes said, the findings suggest that researchers should consider the menstrual cycle stages
of patients or study participants when testing new vaccines or conducting other investigations.

"The decline in many cytokines we observed in the luteal phase is consistent with previous claims that immunity weakens
in the luteal phase.
This may just make the embryo easier to implant," the authors wrote
.
"As compensation, antimicrobial factors, such as β-defensins, appear to increase
in the luteal phase.
"

"Scientists need to design their studies to ensure that all participants are measured at the same stage of the cycle," said senior author Florian Hladik, Ph.
D.
, a professor of obstetrics and gynecology research at
the University of Washington.

Hughes said the study provides a powerful reference point
for what happens in the study cycle.

"We now have 'what' information
for 53 different cytokines.
For every problem, we need to find out the cause, and how this relates
to sexually transmitted diseases and pregnancy.
”

Overall, the difference between the follicular phase and the luteal phase may mean that vaccinations and other interventions are more effective in one phase than the other, Hughes said
.