Immune molecules in the female reproductive path and sperm: relevance to mate choice

Mate choice has been postulated to be MHC-dependent, ensuring the maintenance of polymorphism for species survival. At the molecular level, MHC polymorphism is represented by class-I (MHCI), class-II (MHCII) antigens and their T cell receptors (TCRs). In order to evaluate the presence such immune molecules during male/female interaction, vaginal fluid, vaginal cells, urine, sperm, seminal fluid, cumulus cells, tubal fluid and epithelium were isolated from BALB/c mice and examined for the presence of membrane or soluble MHCI, MHCII, TCRαβ and TCRγδ, using immunofluorescence and ELISA techniques, respectively. These molecules were expressed on sperm and seminal fluid in a sperm quality-dependent manner and in vagina, fallopian tube, cumulus cells and urine in an estrus cycle-dependent manner. Vaginal cells showed increased expression of all molecules tested during estrus, while vaginal fluid showed an increase of TCRγδ and decrease of MHCI and MHCII levels, during estrus. Urine showed only increased concentrations of TCRαβ during estrus. Cumulus cells expressed MHCI, MHCII, TRCγδ but not TCRαβ, while sperm mainly expressed TCRαβ and TRCγδ. All molecules were detected in tubal fluids mostly during estrus, while they were almost undetectable during pregnancy. The vaginal environment was shown to affect sperm motility according to the estrus-cycle, whereas sperm motility was affected by antibodies against these molecules. In conclusion, the presence of complementary immune molecules in the male/female interactive environment, except for revealing novel markers for unexplained infertility, provides for the first time evidence for immune-mediated recognition of the two counterparts, enlightening thus a molecular basis for mate choice.