By Jennifer Bass (M.P.H.)
The Birds And The Bees…And Helper T’s?
Ok, we all know that sexual activity is usually a prerequisite to becoming pregnant. Of course there are other ways to fertilize an egg to result in conception, but most people rely onthe time-honored method of intercourse. And if pregnancy is the goal, then intercourse should happen around the woman’s fertile window, when ovulation is about to occur. But there is more to the story…
New research from Kinsey Institute shows that women who are sexually active throughout their menstrual cycle may be creating a more friendly environment for conception. And it all has to do with immunity. Think about it, how does the body allow for a foreign substance (ie, sperm) to enter without attacking it like an invader, as it would when fighting off a cold? The key is a shift in immunity around ovulation.
Two studies were conducted by Kinsey Institute research scientist Tierney Lorenz, Indiana University Bloomington (IUB) psychology professor and Kinsey affiliate Julia Heiman, and IUB biology professor Gregory Demas. As part of their Women, Immunity and Sexual Health research, blood and saliva samples were collected over the course of a month from 30 healthy pre-menopausal and hormonally unregulated women. Fourteen of the women were sexually active and 16 were sexually abstinent. In the first study the samples were analyzed for number of helper T cells and then were exposed to E. coli bacteria. In the second study the samples were analyzed for number of immunoglobulin antibodies in mucus and blood. The effectiveness of their immune response was measured through the number of bacteria remaining after an incubation period.
Lorenz and her colleagues found that levels of two types of helper T cells and immunoglobulins varied across the menstrual cycle, with ovulation emerging as a key turning point. Prior to ovulation the women had higher levels of Type 1 helper t cells and immunoglobulin A antibodies, which protect the body against outside invaders and prevent sperm movement in the uterus. After ovulation the women had higher levels of Type 2 cells which allow the body to accept certain foreign bodies such as sperm and embryo and immunoglobulin B antibodies that fight invaders elsewhere in the body but are not present in the uterus. Notably, these shifts in immune function were not found in sexually abstinent women.
So, What Does This Mean?
Lorenz explains, “We’re actually seeing the immune system responding to a social behavior: sexual activity. The sexually active women’s immune systems were preparingin advance to the mere possibility of pregnancy.” Thus the immune system is not static but rather a complex dynamic system that responds to our environments, including whether our weekend plans are Netflix and sweatpants or ‘Netflix and chill.’
This shift in immune response is adaptive because it allows potential sperm to survive. “Otherwise, a super strong immunity would lead to sperm attack, and that would be the end of the human species!” according to Lorenz.
This research also helps explain why a piece of advice commonly given to couples trying to get pregnant is effective. “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. This research suggests that regular sex helps by triggering the woman’s immune response to allow sperm once she has ovulated. Conversely, if you only have sex around the fertile window, the immune response may not shift and the body may be more likely to attack sperm and any successfully fertilized egg, which you don’t want if you are hoping to get pregnant.
Lorenz and her research team are next examining how sexual activity affects inflammation, a risk factor in depression and heart disease. Stay tuned!