Immunological role for seminal plasma in insemination and pregnancy.

Insemination confronts the female with paternally derived alloantigens and represents an immunological challenge preceding fertilization and implantation. Current evidence suggests a role for seminal plasma in regulating maternal immunity for insemination and pregnancy. In vitro seminal plasma has been shown to suppress T- and B-cell proliferation, neutrophil and macrophage phagocytic activity, as well as killer cell activity. Seminal plasma interacts with complement components C1 and C3 and contains factors that specifically bind the Fc region of IgG. These in vitro findings suggest possible seminal plasma-suppressive effects on female alloimmune responses after insemination. Seminal plasma also contains allotypic TLX antigens that could prime mothers prior to fertilization. Such priming effects for pregnancy acceptance are supported by improved implantation rates in controlled clinical trials using timed vaginal exposure to semen during in vitro fertilization or gamete intrafallopian transfer treatment cycles.