Invasive trophoblast in the genus Equus

The effect of skin allografting on the equine endometrial cup reaction

This research tested the hypothesis that immunological sensitization of mares by skin allografting, followed by the establishment of pregnancy using semen from the skin-graft donor, would give rise to secondary immune responses to the developing horse conceptus, resulting in an earlier demise of the fetally derived endometrial cups. Maiden mares received skin allografts from a stallion homozygous for Major Histocompatibility Complex (MHC) antigens and/or equivalent autografts and were subsequently mated to the skin-graft donor stallion during the next two breeding seasons. Mares that had been immunologically primed to the foreign MHC class I antigens of the skin-graft donor stallion developed strong secondary antibody responses early in their first pregnancies, whereas autografted mares made weak primary antibody responses in their first pregnancies and strong secondary responses in their second pregnancies. In contrast, histological examination of the endometrial cups after surgical pregnancy termination at Day 60 of gestation revealed no discernible differences between allografted and autografted mares, and there were no significant differences in the concentrations and/or duration of secretion of the endometrial cup-specific hormone, equine chorionic gonadotrophin (eCG), between allografted and autografted mares, nor in either group between first and second pregnancies. The vigorous antibody response observed in the pregnant allografted mares supported the first part of our hypothesis, providing evidence of systemic immunological priming. However, there was a lack of an equivalent heightened cellular response to the endometrial cups. These findings provided strong evidence for an asymmetric immune response to the conceptus, characterized by strong humoral immunity and a dampened cellular response.

Modulation of Allospecific CTL Responses During Pregnancy in Equids: An Immunological Barrier to Interspecies Matings?

Maternal immune recognition of the developing conceptus in equine pregnancy is characterized by the strongest and most consistent alloantibody response described in any species, a response directed almost exclusively against paternal MHC class I Ags. This work investigated the cellular immune response to paternal MHC Ags in pregnant and nonpregnant horses and donkeys, and in horses carrying interspecies hybrid mule conceptuses. We observed profound decreases in classical, MHC-restricted, CTL activity to allogeneic paternal cells in peripheral blood lymphocytes from both horse mares and donkey jennets carrying intraspecies pregnancies, compared with cells from nonpregnant controls. This is the first evidence in a randomly bred species for a generalized systemic shift of immune reactivity away from cellular and toward humoral immunity during pregnancy. Surprisingly, mares carrying interspecies hybrid mule conceptuses did not exhibit this transient, pregnancy-associated decrease in CTL activity. The failure of interspecies pregnancy to down-regulate cellular immune responses may be a heretofore-unrecognized, subtle barrier to reproductive success between species.

The effect of horse placental tissue extracts and equine chorionic gonadotrophin on the proliferation of horse lymphocytes stimulated in vitro

Commercial preparations of equine chorionic gonadotrophin (eCG) and extracts of horse placenta taken at 80 days gestation were incorporated into mixed lymphocyte culture and mitogen stimulation assays of horse peripheral blood mononuclear cells. A dose-related inhibition of lymphocyte proliferation, indicative of immunosuppressive activity, was observed in both systems, both with commercial eCG preparations and tissue extracts. Negligible inhibitory activity was observed with an extract of term placenta. The inhibitory activity of the placental samples was not related to their eCG content as measured by immunoassay. The fact that one pregnant horn allantochorion extract containing 50 IU/ml of eCG showed an identical dose-dependent lymphoproliferation-inhibitory activity to an extract of a second such allantochorion containing only 1.7 IU/ml of eCG suggests that this hormone does not inhibit lymphocyte proliferation and that commercially available eCG contains inhibitory contaminants.

Differential modulation of the in vitro lymphocyte activation pathways by soluble and solubilized placental substances

Soluble and detergent-solubilized placental extracts were studied for their modulatory effects upon the proliferation of lymphocytes stimulated by various activating agents. It was shown that soluble placental extract (SPE) exerted an inhibitory effect on the lymphoproliferation triggered by alloantigen or LPS but not by Con A or the combined action of PMA + calcium ionophore A 23187. This effect was also observed with SPE precipitated by 30% of ammonium sulfate (SPE30). On the other hand, a solubilized placental extract (SzPE) that was obtained by using octyl-beta-D-glucopyranoside inhibited the stimulation triggered by alloantigen, LPS, and Con A but did not affect the protein kinase C pathway. The modulatory effects were observed not only when SPE (or SPE30) and SzPE were added at the time of culture initiation but also at 24 h before or after the activating agents. Preincubation with SPE30 or SzPE immobilized on plastic surface, however, transduced an enhanced lymphoproliferative response to alloantigen and mitogen Con A but not to LPS. The above results suggest that placental substances exerted their modulatory effects by interfering mainly with the antigen or mitogen lymphoproliferation pathways.

Vaccination against spontaneous abortion in mice by preimmunization with an anti-idiotypic antibody

CBA/J females mated with DBA/2 display a high level of fetal wastage which can be corrected by anti-Balb/c vaccination. A batch of CBA/J anti-(CBA/J anti-Balb/c) antiserum was raised. This serum was characterized as anti-idiotypic by various techniques, including a solid-phase radioimmunoassay. Such a serum proved to confer protection against resorptions when injected into CBA/J mice mated with DBA/2. However, the kinetics of the effect pointed to the need for administration in early pregnancy for successful protection. The significance of these data, and the possible mechanism(s) by which the serum acts, are discussed.

Environmental influences on immunologically associated spontaneous abortion in CBA/J mice

CBA/J female mice mated to DBA/2 male mice have a high level of fetal resorption. The rate of resorption can be influenced by the environment in which the animals are maintained.

Placental immunoregulatory factors

Local immune suppression appears to be a key feature in the success of the fetal allograft. Various placental factors have been described endowed with immunoregulatory activity. Much of the available evidence concerning the biological function and biochemical characteristics of these molecules is reviewed here, as well as the controversial issues surrounding them. In the final section, some outstanding questions relating to these immunoregulators are considered.