eLife: Increased vaginal immune activity after first sexual intercourse

The detected changes can have an important impact on
the risk of sexually transmitted infections (STIs).
But the authors don't yet know whether these changes increase or decrease the risk of
STIs.

Girls and young women aged 15 to 24 are at higher
risk of contracting STIs than older women.
However, it has not been determined whether riskier behavioral choices or physiological factors can explain the increased
risk.

"We measured immune changes before and after sexual activity in young women to determine whether immune changes might play a role in increasing vulnerability to STIs," said
Sean Hughes, lead author of the study and a research scientist in the Department of Obstetrics and Gynecology at the University of Washington School of Medicine in Seattle, USA.

Hughes and his colleagues compared vaginal samples
collected from 95 adolescent women in Kenya before and after sexual intercourse.
They found that during the participants' first year of sexual activity, proteins that control the immune response, including IL-1β, IL-2 and CXCL8, increased
dramatically.
These changes were confirmed not due to pregnancy or having a sexually transmitted infection
.

The team reviewed data collected from two other studies to validate this result
.
One included 93 young women in Belgium and the other included 19 participants
from the United States.
Combined data from the two studies also showed elevated levels of immune control proteins, including IL-1β, IL-2, and CXCL8
, after participants were sexually active.

"The onset of sexual activity is associated with higher levels of immune mediators, but we are uncertain whether the onset of sexual activity led to these changes," said
Florian Hradik, associate senior professor in the Division of Vaccines and Infectious Diseases at Fred Hutchinson Cancer Center in Seattle, Washington.
"Other factors related to the onset of sex, such as socioeconomic status, may also contribute to changes in
the immune system.
"

The consequences of this immune activation are also unclear
.
The immune changes detected in the study may help improve fertility and may also be a protective defense
against sexually transmitted infections.
If this is a defensive attempt, it may inadvertently increase young women's vulnerability to HIV infection because it attracts virus-targeted CD4 T immune cells into the vagina
.
More research is needed to confirm the link between the onset of sexual activity and these immune changes, and to understand their impact
on the sexual health of young women.

Alison Roxby, associate professor of infectious diseases and global health at the University of Washington School of Medicine and co-senior author of the study, said: "More research on the immune changes associated with the onset of sexual activity may help us understand the reasons for the
increased risk of STIs in young women.
" "It may also help us find new ways to
prevent STIs in this vulnerable group.
"