The mechanisms underlying the protection of the human embryo/fetus from the maternal immune response are poorly understood. Substantial evidence indicates that carbohydrate recognition plays a primary role in the sequestration of leukocytes during inflammatory processes, lymphocyte homing, and initial gamete binding. Our previous studies suggest a possible convergence in the types of carbohydrate sequences recognized during initial human gamete binding and immune/inflammatory cell interactions. Our more recent findings indicate that oligosaccharides participating in such processes are also associated with soluble glycoconjugates found in the human placenta, amniotic fluid, and decidua. We theorize that such glycoconjugates may abrogate the maternal immune/inflammatory response by blocking the primary adhesive interactions required for the expression of such activities. Foreign embryonic cells may also be protected by surface expression of oligosaccharide sequences that suppress immune effector cell action in a manner not dependent upon classical major histocompatibility (MHC) recognition. Glycoconjugates expressing selectin ligands may also manifest a potent contraceptive effect that may also be beneficial for both the mother and the developing embryo/fetus. This hypothesis provides a preliminary framework for understanding how temporally and spatially restricted immunosuppressive effects could be expressed in utero that protect the human embryo/fetus during this period of human development.

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Insulin-like growth factor-I (IGF-I) enhances and epidermal growth factor (EGF) inhibits gonadotrophin-induced aromatization in granulosa cells. Our previous studies have shown that human ovarian granulosa cells synthesize insulin-like growth factor-binding protein-1 (IGFBP-1) which inhibits IGF-stimulated DNA synthesis. The present study addresses the effect of EGF and gonadotrophins in the regulation of IGFBP-1 release by human granulosa cells cultured in serum-free medium. At concentrations of 1-100 micrograms/l EGF was found to stimulate IGFBP-1 secretion. This was not due to cell proliferation, as the viable cell count remained unaffected. Growth hormone and gonadotrophins had no effect on IGFBP-1 secretion when added alone to culture medium. These results suggest that EGF regulates IGFBP-1 secretion in human granulosa-luteal cells.

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In this time-resolved immunofluorometric assay for the 34-kDa somatomedin-binding protein (SmBP), affinity-purified polyclonal antibodies are used, along with solid-phase separation of bound and free analyte. The first antibody is bound to polystyrene microtiter wells; the second is labeled with europium(III) chelate. The detection limit of the method is 0.25 microgram/L, much lower than that (about 8 micrograms/L) for radioimmunoassay. By immunofluorometric assay, SmBP is detectable, and could be accurately quantified, in the serum of all 88 individuals we tested, whereas by radioimmunoassay a third of the samples had concentrations below the detection limit. When SmBP was detectable by both methods, the concentrations measured by the two techniques correlated well (r = 0.98).

Local regulation of insulin-like growth factor binding protein-1 (IGFBP-1) production in the human ovarian follicle was investigated using cultured human granulosa-luteal cells. Both insulin-like growth factor-I (IGF-I) and follicle-stimulating hormone (FSH) exerted a dual effect on granulosa cells: while estradiol (E2) production was increased by both stimulants, the addition of either of the two hormones led to a reduction in IGFBP-1 secretion by more than 50%. Inhibition of IGFBP-1 production in response to IGF-I was dose-dependent,with the highest effect observed at 5 nM IGF-I. A significant correlation was found between the increase in E2 and inhibition of IGFBP-1 secretion in response to IGF-I. These observations may suggest a novel mechanism, at the follicular level, by which FSH and IGF-I amplify the IGF-I effect in the ovarian follicular cells.

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