Intracerebroventricular administration of a single small dose of hrIL-1 beta is sufficient to initiate murine pregnancy failure

Immunological prevention of spontaneous early embryo resorption is mediated by non-specific immunosimulation

PROBLEM

Spontaneous early embryo resorption following implantation occurs in many species, but little is known regarding the causes or the prevention of early pregnancy failure. Embryo and fetal loss have widely been assumed to be due to maternal allospecific immune rejection. Alloimmunization therapy with paternal tissues has been successfully used in human and murine pregnancies to prevent early embryo demise. The mechanisms of this treatment have been assumed to be the induction of antigen specific, fetal "graft" enhancing antibodies and suppressor cells. The purpose of this study was to investigate the validity of this assumption.

METHOD

To investigate these general assumptions, female CBA/J mice were immunized with either specific or nonspecific antigens prior to mating with DBA/2 or Balb/c males. Further, a model system for the study of bacterial lipopolysaccharide (LPS) induced abortion was used to demonstrate the nature of antigen specific immune protection against abortion.

RESULTS

Whereas the administration of 1 microgram of LPS to CFW female x CFW male pregnant mice on day 7 of gestation induced complete fetal resorption, prior immunization with 20 micrograms of LPS completely prevented LPS induced abortion as long as the anti-LPS antibody titers remained above a threshold value of about 1/500. Therefore, early embryo loss could be induced by a bacterial infection and could be prevented by appropriate immunity to abortogenic factors. However, due to the short half-life of IgM antibodies, immunity to LPS was short-lived and the protective effect of LPS immunization against LPS induced abortion waned after 5 wk. Through the use of the CBA/J female x DBA/2 male model system to study spontaneous early embryo loss, previous vaccination of CBA/J female mice with Balb/c spleen cells expressing paternal MHC antigens, complete Freund's adjuvant (CFA) or LPS, all decreased the incidence of spontaneous resorption in subsequent pregnancies. Similarly, a previous mating with a Balb/c male prevented spontaneous embryo loss for a period of up to 6 wk. However, none of the immunotherapeutic vaccinations or matings had a permanent effect on CBA/J female x DBA/2 male embryo survival, which one would have expected if specific immune mediators were involved.

CONCLUSION

The results of this study indicated that the decrease in the incidence of spontaneous embryo resorption following alloimmunization was more likely to be due to nonspecific immunomodulatory effects on the immune system of the female mice, as opposed to specific antipaternal immunity. This may, in part, explain the placebo effects observed for alloimmunization therapy for human habitual pregnancy loss. The relevance of these results to the development of immunotherapy strategies for the prevention of habitual abortion is discussed.

The thymus in pregnancy: the interplay of neural, endocrine and immune influences

This article discusses the dramatic events that accompany thymic involution during pregnancy, and traces the possible immune, neural and endocrine interactions that may occur. Ann Clarke and Marion Kendall present accumulating evidence that activity, not inactivity, is a feature of the thymus at this time. Whilst the cortex shrinks, the medulla enlarges and rearranges to create a microenvironment containing increased numbers of mature thymocytes. It is suggested that these recently derived T cells may contribute to the unique populations of cells with suppressive function that appear during pregnancy, and thereby contribute to the immune suppression of the mother to paternal and fetal antigens. In addition, the pregnancy-associated cortical involution of the thymus may reflect the deletion of clones with potential reactivity to paternal and/or fetal antigens.

Evaluation of the role of exogenous pathogens on the incidence of embryo loss during early pregnancy in mice

The mating of CBA/j female mice (H2k) by DBA/2j male mice (H2d) typically results in an elevated incidence of spontaneous embryo loss thus providing an ideal genetically controlled laboratory model for the study of the factors causing early embryo loss during pregnancy. There is now considerable data on the cells and factors involved in fetal resorption but little is known about the events which activate this process. While the activation of the maternal response to the fetal implant could have endogenous or genetic origins, a role for exogenous factors including microbial pathogens could also be involved. In order to investigate these possibilities, the reproductive success of CBA/j female x DBA/2j male matings in a conventional animal care facility were compared with matings in a specific pathogen free (SPF) animal facility. All animals housed under these conditions were routinely screened by immunoassay and culture, for the presence of a number of viral and bacterial pathogens of mice. The incidence of spontaneous embryo loss in specific pathogen free CBA female mice mated by DBA and other male strains was found to be virtually identical to that of CBA female mice infected with multiple viral pathogens and housed under otherwise identical conditions (non-SPF). However, the numbers of implantation per pregnancy was significantly greater in an SPF facility. Therefore, exposure of mating mice to exogenous viral and bacterial pathogens did not appear to alter the overall incidence of spontaneous embryo resorption. It was concluded that the immunomodulatory effects of infection by common murine pathogens neither augmented nor reduced post-implantation embryo losses.

Stress-triggered abortion in mice prevented by alloimmunization

PROBLEM

To determine if immunotherapy can prevent abortion triggered by mechanisms that in humans may be treatable by psychotherapy.

METHOD

The effects of alloimmunization against paternal strain antigens were tested in pregnant mice subjected to stress.

RESULTS

Restraint stress boosted the resorption rate assessed on day 13.5 of pregnancy in DBA/2-mated C3H/HeJ mice with an optimal effect on day 4.5 of pregnancy, and premating alloimmunization greatly reduced the effect. By contrast, CBA/J and A/J mice proved resistant to abortion boosting by restraint stress. A/J mice mated to DBA/2 or C3H/HeJ males showed reduced fertility, perhaps due to failure of pregnancy immediately after the stress, but this was not corrected by alloimmunization with either DBA/2 [class I + class II major histocompatibility complex (MHC) immunogen] or C3H/HeJ (class I MHC immunogen) splenocytes. There was a reduction in the endogenous resorption rate, however, and implantation number was slightly increased by preimmunization using DBA/2 cells. The abortion rate could be boosted, however, by ultrasonic noise stress of high abortion rate CBA/J, and preimmunization using BALB/c (H-2d) splenocytes protected. A similar boosting of loss in low abortion rate BALB/k mice was ameliorated (albeit not completely) by preimmunization with allogenic paternal but not syngeneic splenocytes.

CONCLUSIONS

Immunotherapy may protect against a variety of potential triggers of spontaneous abortion, including those that may be amenable to psychological remedies, and possible mechanisms are discussed.