The results could eventually influence recommendations regarding how often to engage in sexual intercourse for couples trying to get pregnant. It could also potentially influence treatment for people with autoimmune disorders, according to an IU press release.
The conclusions are reported in papers published in the journal Fertility and Sterility and the journal Physiology and Behavior.
The lead author on both papers was Tierney Lorenz, a visiting research scientist at the Kinsey Institute for Research in Sex, Gender and Reproduction. Julia R. Heiman, a professor in the Department of Psychological and Brain Sciences and Gregory E. Demas, a professor in the Department of Biology, co-authored 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 chances of getting pregnant, even during so-called ‘non-fertile’ periods, although it’s unclear how this works,” Lorenz said in the release. “This research is the first to show that the sexual activity may cause the body to promote types of immunity that support conception.”
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 immune system regulation in women who are sexually active versus women who are sexually abstinent, according to the release.
The results are based on 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.
In the first paper, Lorenz and colleagues reported sexually active women experienced greater changes in helper T cells, and in the proteins that T cells use to communicate. In the second paper, they reported the differences in antibody levels between the two groups, according to the release.
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 white blood cells and play an important role fighting off foreign invaders in the body.
“The female body needs to navigate a tricky dilemma,” Lorenz said in the release. “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 might otherwise interpret as “foreign invaders,” such as the presence of sperm or emerging embryo.
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, according to the release.
Higher levels of type 1 helper T cells were found in these same women during the follicular phase in the menstrual cycle, 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 higher levels 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 in the release. “The sexually active women’s immune systems were preparing in advance to the mere possibility of pregnancy.”
Both studies contribute to the idea 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.
A recognition that sexual activity can cause natural fluctuations in blood test results could be useful to physicians treating patients with immune disorders, Lorenz said in the release.
Alyson Malinger
