Sexual activity causes immune system changes that increase chances of conception

October 5, 2015, Indiana University
Women, Immunity and Sexual Health infographic. Designed by Milana Katic, IU Communications.

Research from Indiana University has found that sexual activity triggers physiological changes in the body that increase a woman's chances of getting pregnant, even outside the window of ovulation.

The results could eventually influence recommendations regarding how often to engage in sexual intercourse for couples trying to get pregnant. It could also potentially impact treatment for people with autoimmune disorders.

The conclusions are reported in papers recently published in the journal Fertility and Sterility and the journal Physiology and Behavior.

The lead author on both papers is Tierney Lorenz, a visiting research scientist at the Kinsey Institute. Julia R. Heiman, a professor in the Department of Psychological and Brain Sciences, and Gregory E. Demas, a professor in the Department of Biology, are also co-authors on the study.

All three researchers are also affiliated with the Center for Integrative Study of Animal Behavior at IU Bloomington. Heiman is also affiliated with the Kinsey Institute, where she previously served as director.

"It's a common recommendation that partners trying to have a baby should engage in regular intercourse to increase the woman's changes of getting pregnant—even during so-called 'non-fertile' periods—although it's unclear how this works," Lorenz said. "This research is the first to show that the sexual activity may cause the body to promote types of immunity that support conception.

"It's a new answer to an old riddle: How does sex that doesn't happen during the fertile window still improve fertility?"

A few earlier studies show changes in immune function during pregnancy and after childbirth and changes in immunity across the menstrual cycle. But the IU research is the first to show that sexual activity plays a role in these changes with clear differences found in regulation in women who are sexually active versus women who are sexually abstinent.

The results are based upon information from participants in the Kinsey Institute's WISH Study—Women, Immunity and Sexual Health—which collected data across the menstrual cycle in 30 healthy women, about half of whom were sexually active and half of whom were sexually abstinent. Heiman and Demas are co-investigators on the study.

In the first paper, Lorenz and colleagues report sexually active women experienced greater changes in helper T , and the proteins that T cells use to communicate. In the second paper, they report differences in antibody levels between the two groups.

Helper T cells manage the body's immune response in part by activating the cells that destroy invading microbes in the body. The antibodies—also known as immunoglobulins—are secreted by and play an important role fighting off foreign invaders in the body.

"The female body needs to navigate a tricky dilemma," Lorenz said. "In order to protect itself, the body needs to defend against foreign invaders. But if it applies that logic to sperm or a fetus, then pregnancy can't occur. The shifts in immunity that women experience may be a response to this problem."

There are several types of helper T cells and immunoglobulins. Type 1 helper T cells assist the body with defense against outside threats. Type 2 helper T cells help the body accept those aspects of pregnancy the body may otherwise interpret as "foreign invaders," such the presence of sperm or emerging embryo.

Similarly, immunoglobulin A antibodies—typically found in the mucous of the female reproductive tract—can interfere with the movement of sperm and other aspects of fertilization. Immunoglobulin G antibodies—typically found in the blood—fight disease without interfering with the uterus.

Lorenz and colleagues found significantly higher levels of type 2 helper T cells in sexually active, non-pregnant women during the luteal phase of the menstrual cycle, a period when the uterine lining thickens in preparation for pregnancy. Higher levels of type 1 helper t cells were found these same women during the follicular phase in the , a period when the ovaries' follicles are maturing.

They also found sexually active women experienced similar changes in immunoglobulins, with higher levels of immunoglobulin G during the luteal phase and of immunoglobulin A during the follicular phase.

Neither shifts in immunity were observed in the sexually abstinent women.

"We're actually seeing the immune system responding to a social behavior: sexual activity," Lorenz said. "The sexually active women's immune systems were preparing in advance to the mere possibility of pregnancy."

Both studies contribute to a growing body of evidence that the immune system isn't a passive system that waits to react to outside threats, but a highly proactive system that changes in response to external cues, such as the physical environment and social behavior.

The studies may also shed light on previous research that found unexplained fluctuations in immune response in women. A recognition that can cause natural fluctuations in blood tests results could be useful to physicians treating patients with immune disorders, Lorenz said.

Explore further: Hormone fluctuations disrupt sleep of perimenopausal women

More information: Fertility and Sterility - … ii/S0015028215018853

Physiology and Behavior - … ii/S0031938415301153

Related Stories

Hormone fluctuations disrupt sleep of perimenopausal women

June 16, 2015
Women in the early phases of menopause are more likely to have trouble sleeping during certain points in the menstrual cycle, according to a new study published in the Endocrine Society's Journal of Clinical Endocrinology ...

Less sleep may mean less sex after menopause

September 30, 2015
(HealthDay)—Too little sleep may lead to too little intimacy for postmenopausal women, a new study finds.

What effect does music TV have on the sexual behavior of teenage boys and girls?

March 19, 2015
There is no doubt that teenage boys and girls are swayed and shaped by music TV. For example, sexually active youth of both genders, after watching music TV, think their peers are sexually active, too. Moreover, when girls ...

Female immune response could hold key to new cancer therapies

May 22, 2015
An understanding of natural immune suppression mechanisms in the female reproductive tract could lead to new ways to combat cancer.

Breastfeeding women and sex: Higher sex drive or relationship management?

April 6, 2015
New mothers in the Philippines spend more time in the bedroom with their partner in the first few weeks after giving birth than they did before they became pregnant. This might be a type of survival strategy to keep the relationships ...

Investigators find window of vulnerability for STIs to infect female reproductive tract

March 16, 2015
Charles R. Wira, PhD, and colleagues at Dartmouth's Geisel School of Medicine have presented a comprehensive review of the role of sex hormones in the geography of the female reproductive tract and evidence supporting a "window ...

Recommended for you

US drug overdose deaths surge amid fentanyl scourge

August 16, 2018
US drug overdose deaths surged to nearly 72,000 last year, as addicts increasingly turn to extremely powerful synthetic opioid fentanyl as the supply of prescription painkillers has tightened.

Phantom odors: One American in 15 smells odors that aren't there, study finds

August 16, 2018
Imagine the foul smell of an ash tray or burning hair. Now imagine if these kinds of smells were present in your life, but without a source. A new study finds that 1 in 15 Americans (or 6.5 percent) over the age of 40 experiences ...

Widespread declines in life expectancy across high income countries coincide with rising young adult, midlife mortality

August 15, 2018
The ongoing opioid epidemic in the United States is a key contributor to the most recent declines in life expectancy, suggests a study published by The BMJ today.

Parental life span predicts daughters living to 90 without chronic disease or disability

August 15, 2018
Researchers at the University of California San Diego School of Medicine report that women whose mothers lived to at least age 90 were more likely to also live to 90, free of serious diseases and disabilities.

Diets high in vegetables and fish may lower risk of multiple sclerosis

August 15, 2018
People who consume a diet high in vegetables and fish may have a reduced risk of multiple sclerosis, new research led by Curtin University has found.

Can sleeping too much lead to an early death?

August 15, 2018
A recent study in the Journal of the American Heart Association has led to headlines that will make you rethink your Saturday morning sleep in.


Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.