The uterine immune axis holds the key to solving major problems in female reproductive health, including infertility, many pathologies of pregnancy, and sexually transmitted disease. The molecular determinants of tolerance and immunity in the reproductive tract are now being identified, and the governing principles are similar to those in other mucosal tissues. Cytokines are implicated as pivotal regulators at important 'decision-making' points in each phase of the induction and elicitation of a response. Indeed, the flexibility to deal appropriately with antigens as disparate as infectious micro-organisms, spermatozoa and the conceptus is likely to be attributable to the sophistication of the cytokine network in driving immune deviation. A better understanding of the factors controlling the development of immune activity in the uterus, particularly the significance of the inductive cytokine environment in determining the destiny of T-lymphocyte responses, will assist the rational design of new therapeutic strategies to treat immune-based reproductive disorders.
SA Robertson, VJ Mau, IG Young, and KI Matthaei
Interleukin 5 is expressed in type 2 T lymphocytes and has a key role in driving the differentiation, recruitment and activation of eosinophils. Mice with a null mutation in the interleukin 5 gene (IL-5 -/- mice) have altered type 2 immune responses and severely depleted eosinophil populations. In the present study, the effect of interleukin 5 deficiency on the abundant population of eosinophils present in the female reproductive tract was investigated, and the reproductive performance in C57Bl/6 IL-5 -/- mice was measured. Endometrial eosinophils, detected on the basis of their endogenous peroxidase activity, were reduced in number by four-sevenfold during the oestrous cycle and in early pregnancy in IL-5 -/- mice. Eosinophils present in the cervix and decidual tissues at the time of parturition were similarly diminished. The temporal fluctuations in eosinophil recruitment and localization within these tissues were otherwise unchanged, indicating that interleukin 5 is not a necessary chemotactic agent in the female reproductive tract. Oestrous cycles were moderately greater in duration in IL-5 -/- mice (mean +/- SD = 5.6 +/- 1.0 days in IL-5 -/- mice versus 5.0 +/- 0.8 days in IL-5 +/+ mice), owing to an extended period in oestrus (2.7 +/- 0.9 days per cycle in IL-5 -/- mice versus 1.8 +/- 0.7 in IL-5 +/+ mice). The interval between placing females with males and the finding of copulatory plugs was reduced significantly in interleukin 5-deficient mice. Implantation rates and subsequent fetal development were comparable in IL-5 -/- and IL-5 +/+ mice, irrespective of whether pregnancies were sired by syngeneic (C57Bl/6) or allogeneic (CBA or Balb/c) males, apart from a 10% increase in placental size and a 6.5% decrease in placental∶fetal ratio seen on day 17 in pregnancies sired by CBA males. Parturition and post-partum uterine repair were not compromised in interleukin 5-deficient mice, as judged by the length of gestation, and the outcomes of pregnancies initiated at post-partum oestrus. The birth weights and growth trajectories of pups were significantly influenced by interleukin 5 status, with small but significant increases in the weights of IL-5 -/- pups, particularly C57Bl/6 and CBA F(1) animals, remaining evident until adulthood. These data are consistent with the view that eosinophils have a role in endometrial tissue remodelling associated with the oestrous cycle, but indicate that the events of pregnancy and parturition proceed quite normally in the absence of maternal and fetal interleukin 5. However, strain-dependent effects of interleukin 5 deficiency on placental growth and function and subsequent weight gain in the newborn indicate that this cytokine may act through the maternal or fetal immune axis to exert subtle influences on reproductive outcome.
RB Gilchrist, DB Rowe, LJ Ritter, SA Robertson, RJ Norman, and DT Armstrong
Granulocyte-macrophage colony-stimulating factor (GM-CSF), a cytokine secreted by lymphohaemopoietic and other cell lineages, is known to influence ovarian cyclicity and embryo development. The aim of this study was to examine the effect of GM-CSF on ovarian follicular cell function using GM-CSF-deficient (GM -/-) mice. Immature GM -/- and GM +/+ mice were stimulated with eCG, and cumulus-oocyte complexes and mural granulosa cells were collected 48 h later. Expression of GM-CSF receptor (GM-CSFR) alpha and beta mRNA subunits by cumulus-oocyte complexes and mural granulosa cells was examined using RT-PCR. Cumulus-oocyte complexes from both genotypes were found to express mRNA for the GM-CSFRalpha-subunit only, while the mural granulosa cells expressed both the alpha and beta receptor subunits. Cumulus-oocyte complexes recovered from GM -/- mice had approximately twice the number of cumulus cells per cumulus-oocyte complex than did those of GM +/+ mice (P < 0.05), even though the growth-promoting activity of denuded GM -/- oocytes was found to be equivalent to that of wild-type oocytes. GM-CSF deficiency was associated with marginally increased DNA synthesis in cumulus cells and significantly (P < 0.05) lower progesterone production by mural granulosa cells recovered from GM -/- compared with those recovered from GM +/+ mice. The addition of rec-mGM-CSF in vitro did not affect DNA synthesis in either cell type or progesterone production by mural granulosa cells, irrespective of GM-CSF status. There was no effect of GM-CSF deficiency on the capacity of FSH and insulin-like growth factor I to stimulate DNA synthesis in cumulus-oocyte complexes (approximately 15- and threefold, respectively) and in mural granulosa cells (approximately two- and threefold, respectively). Taken together, these data show that GM-CSF influences events associated with follicular maturation in mice. The effects of GM-CSF are not exerted directly in granulosa or cumulus cells, but appear to be mediated indirectly, perhaps through the agency of steroidogenesis-regulating secretions of local macrophage populations residing in the theca.