Immunosuppressive activity of bovine seminal plasma on bovine lymphocytes in vitro

Reproductive immunology in viviparous mammals: evolutionary paradox of interactions among immune mechanisms and autologous or allogeneic gametes and semiallogeneic foetuses

Literally, reproductive immunology was born in bovine on-farm reproduction where seminal experiments intended for developing methods for embryo transfer in cattle were performed. Actually, these experiments led to two of major concepts and fundamental principles of reproductive immunology using the bovine species as a model for biomedical research, namely the concept of acquired immunological tolerance and the paradox of the semiallogeneic bovine foetus whereby such organism can develop within an immunologically competent host. Peter Medawar, a scientist who together with Frank Macfarlande Burnet shared the 1960 Nobel Prize in physiology or medicine for discovery of acquired immunological tolerance, while studying dizygotic cattle twins, thereby giving birth to reproductive immunology. Also, these findings significantly influenced development of organ transplants and showed that using farm animals as models for studying transplantation immunology had general relevance for mammalian biology and health including those of humans. However, the interest for further research of the fascinating maternal immune influences on pregnancy and perinatal outcomes and of the prevention and treatment of immunologically mediated reproductive disorders in viviparous mammals of veterinary relevance by veterinary immunologists and reproductive clinicians have been very scarce regarding the application of nonspecific immunomodulatory agents for prevention and treatment of subfertility and infertility in pigs and cattle, but still broadening knowledge in this area and hold great potential for improving such therapy in the future. The aim of the current overview is to provide up-to-date information and explaining/translating relevant immunology phenomena into veterinary practice for specialists and scientists/clinicians in reproduction of animals.

Review: The potential of seminal fluid mediated paternal-maternal communication to optimise pregnancy success

Artificial insemination has been a landmark procedure in improving animal agriculture over the past 150 years. The utility of artificial insemination has facilitated a rapid improvement in animal genetics across agricultural species, leading to improvements of growth, health and productivity in poultry, swine, equine and cattle species. The utility of artificial insemination, as with all assisted reproductive technologies side-steps thousands of years of evolution that has led to the development of physiological systems to ensure the transmission of genetics from generation to generation. The perceived manipulation of these physiological systems as a consequence of assisted reproduction are points of interest in which research could potentially improve the success of these technologies. Indeed, seminal fluid is either removed or substantially diluted when semen is prepared for artificial insemination in domestic species. Although seminal fluid is not a requirement for pregnancy, could the removal of seminal fluid from the ejaculate have negative consequences on reproductive outcomes that could be improved to further the economic benefit of artificial insemination? One such potential influence of seminal fluid on reproduction stems from the question; how does the allogeneic foetus survive gestation in the face of the maternal immune system? Observation of the maternal immune system during pregnancy has noted maternal immune tolerance to paternal-specific antigens; a mechanism by which the maternal immune system tolerates specific paternal antigens expressed on the foetus. In species like human or rodent, implantation occurs days after fertilisation and as such the mechanisms to establish antigen-specific tolerance must be initiated very early during pregnancy. We and others propose that these mechanisms are initiated at the time of insemination when paternal antigens are first introduced to the maternal immune system. It is unclear whether such mechanisms would also be involved in domestic species, such as cattle, where implantation occurs weeks later in gestation. A new paradigm detailing the importance of paternal-maternal communication at the time of insemination is becoming evident as it relates to maternal tolerance to foetal antigen and ultimately pregnancy success.

Seminal fluid and reproduction: much more than previously thought

The influence of seminal plasma on the cytokine and immune uterine environment is well characterised in mice and humans, while the effects of disruption to uterine seminal plasma exposure on pregnancy and offspring health is becoming more clearly understood. The cellular and molecular environment of the uterus during the pre- and peri-implantation period of early pregnancy is critical for implantation success and optimal foetal and placental development. Perturbations to this environment not only have consequences for the success of pregnancy and neonatal health and viability, but can also drive adverse health outcomes in the offspring after birth, particularly the development of metabolic disorders such as obesity, hypertension and insulin resistance. It is now reported that an absence of seminal plasma at conception in mice promotes increased fat accumulation, altered metabolism and hypertension in offspring. The evidence reviewed here demonstrates that seminal plasma is not simply a transport medium for sperm, but acts also as a key regulator of the female tract environment providing optimal support for the developing embryo and benefiting future health of offspring.

Immunology and fertility in the bovine

Antibodies are powerful tools for unlocking normal physiological problems of both qualitative and quantitative nature that affect fertility. In addition, when antibodies are generated due to abnormal situations, fertility is depressed or completely inhibited for varying periods of time. Antibodies to sperm have demonstrated sperm membrane transformations that occur during spermatogenesis and spermiogenesis, the role of the blood-testis barrier, and the role of secretion and absorption in acquisition of sperm fertilizability. Antibodies to ovary have demonstrated factors controlling oocyte maturation, folliculogenesis, and the transudation of macromolecules into the follicle, Fallopian tubes, and uterus that affect capacitation, the acrosome reaction, sperm-oocyte interaction, fertilization, and implantation. Most hormone assays today are immune assays. Antibodies also can purposely suppress fertility (immunocontraception). Fertility problems can result from inappropriate antibody formation to sperm, oocytes, pregnancy products, or hormones. Fertility problems include auto-immune aspermatogenic orchitis, auto agglutination of sperm, autoimmune oophoritis, allergy to semen or egg yolk semen extenders, isoimmunization of female to sperm, fertilization failure, and embryo mortality due to maternal-fetal incompatibility.

Effects of stallion seminal plasma on hydrogen peroxide release by leukocytes exposed to spermatozoa and bacteria

The ability of stallion seminal plasma to modify phagocytosis of spermatozoa and Streptococcus zooepidemicus was examined. Phagocytosis was monitored indirectly as the H2O2 produced by peripheral blood leukocytes after addition of spermatozoa or bacteria. Hydrogen peroxide production after addition of ejaculated spermatozoa was greater (P less than 0.01) than after addition of epididymal sperm. Furthermore, pre-incubation of epididymal sperm with 6.25-50% seminal plasma caused a dose-dependent increase in subsequent H2O2 production by leukocytes (P less than 0.05). In addition, equine serum was capable of opsonizing epididymal and ejaculated sperm. Seminal plasma also directly stimulated phagocyte function because leukocytes preincubated with 12.5% or 25% seminal plasma released more H2O2 after addition of S. zooepidemicus than control leukocytes (P less than 0.05). It is suggested that the opsonization of spermatozoa and the direct stimulation of phagocytes by seminal plasma may represent mechanisms for clearing spermatozoa and bacteria from the reproduction tract.

Individual variation in immunosuppressive activity of bovine seminal plasma on concanavalin A-stimulated bovine T lymphocytes in vitro

Individual dialyzed seminal plasma samples from 21 bulls in routine artificial breeding service were tested for their immunosuppressive activity on in vitro induced blastogenesis of bovine lymphocytes from 3 nonpregnant cows. Concanavalin A was used to induce blastogenesis and thymidine uptake was monitored. Dialyzed seminal plasma from 15 of 21 bulls inhibited deoxyribonucleic acid synthesis response to concanavalin with cow A lymphocytes, and 21 of 21 were immunosuppressive to lymphocytes from cows B and C. Degree of immunosuppression varied according to bull and cow, ranging from 0 to 100%. The lower the percentage response of the lymphocytes to concanavalin stimulation, the less their inhibition by dialyzed seminal plasma. The degree of immunosuppression produced by a bull's dialyzed seminal plasma was not highly related either to amount of protein in the seminal plasma or to the bull's 60 to 90-d nonreturn rate.

Effect of estrual stage on complement activity in bovine follicular fluid

Ovaries were excised from 112 cows during specific stages of the estrous cycle and from cows with follicular cysts. Follicular fluid was collected from the largest follicle at estrus (d 1), metestrus (d 2 to 4), early diestrus (d 5 to 8), mid diestrus (d 9 to 14), late diestrus (d 15 to 18), proestrus (d 19 to 21), and from follicular cysts. Complement was measured with a standard hemolytic assay. Complement in follicular fluid varied with stage of cycle and was two to five times higher at estrus than at diestrus. Complement in follicular fluid was 5 to 22-fold higher than in blood serum. Blood complement was not influenced by stage of cycle. Cystic follicular fluid had complement amounts similar to that of metestrus follicles. The relationships of complement to ovulation, sperm maturation, fertilization, and sperm removal from the tract are discussed.

Immunosuppressive activity of bovine follicular fluid on bovine T lymphocytes in vitro

Follicular fluid from bovine follicles at various stages of the estrous cycle and cysts were tested in vitro for immunosuppressive activity. Mitogen-stimulated lymphocyte assays and the mixed lymphocyte reaction were used as test procedures and thymidine uptake was monitored. Follicular fluid and cyst fluid inhibited the deoxyribonucleic acid synthesis response of bovine lymphocytes to mitogenic and antigenic stimulation. The nature of the suppression varied with the mitogen or antigen assay used, with the estrual stage, with size of follicle within the diestrual stage, and with the type of ovarian cyst. Blood sera from estrual or diestrual cows were not immunosuppressive. Heating (56 degrees C for 30 min) follicular fluid from normal follicles and cysts destroyed most of its suppressive activity toward Concanavalin A-stimulated lymphocytes but did not suppress that in luteal cyst fluid. The suppressive activity in follicular fluid toward phytohemagglutinin-stimulated lymphocytes was more stable to heat than that against Concanavalin A-stimulated lymphocytes. Because the immunosuppressive activity in follicular fluid was heat labile, estrogen, progesterone, and other steroids were not the active suppressive molecules. Proposed roles for these immunosuppressive substances are hypothesized in preventing autoantibody formation to the zona pellucida and in the inflammatory reaction leading to ovulation.

Identification of an immunosuppressive protein in bovine seminal plasma with activity against bovine lymphocytes

Seminal plasma was determined to have immunosuppressive activities in vitro on Concanavalin A-induced blastogenesis of bovine lymphocytes. This immunosuppressive activity was isolated and characterized using a pool of seminal plasma from five bulls. The immunosuppressive activity was associated with seminal plasma proteins of less than 50,000 daltons and also with those of approximately 150,000 daltons. The 150,000-dalton proteins were precipitable at 33% saturation with ammonium sulfate and with an antibody to a Sephadex G-200 chromatographic fraction of seminal plasma. The immunosuppressive activity of the less than 50,000 dalton proteins was lost upon chromatography on Sephadex G-25. This suggests that interaction of several components of low molecular weight might be necessary for this inhibitory activity to be expressed.