Human IgG lacking effector functions demonstrate lower FcRn-binding and reduced transplacental transport.

We have previously generated human IgG1 antibodies that were engineered for reduced binding to the classical Fcγ receptors (FcγRI-III) and C1q, thereby eliminating their destructive effector functions (constant region G1Δnab). In their potential use as blocking agents, favorable binding to the neonatal Fc receptor (FcRn) is important to preserve the long half-life typical of IgG. An ability to cross the placenta, which is also mediated, at least in part, by FcRn is desirable in some indications, such as feto-maternal alloimmune disorders. Here, we show that G1Δnab mutants retain pH-dependent binding to human FcRn but that the amino acid alterations reduce the affinity of the IgG1:FcRn interaction by 2.0-fold and 1.6-fold for the two antibodies investigated. The transport of the modified G1Δnab mutants across monolayers of human cell lines expressing FcRn was approximately 75% of the wild-type, except that no difference was observed with human umbilical vein endothelial cells. G1Δnab mutation also reduced transport in an ex vivo placenta model. In conclusion, we demonstrate that, although the G1Δnab mutations are away from the FcRn-binding site, they have long-distance effects, modulating FcRn binding and transcellular transport. Our findings have implications for the design of therapeutic human IgG with tailored effector functions.

Glucocorticoid exposure and tissue gene expression of 11beta HSD-1, 11beta HSD-2, and glucocorticoid receptor in a porcine model of differential fetal growth.

Glucocorticoids play a critical role in fetal development, but inappropriate exposure is associated with reduced fetal growth. We investigated cortisol exposure and supply in a porcine model of differential fetal growth. This model compares the smallest fetus of a litter with an average-sized sibling at three stages of gestation. At day 45, small fetuses had reduced plasma cortisol (16.8 +/- 3.4 ng/ml) relative to average fetuses (34.4 +/- 3.4 ng/ml, P < 0.001). At day 65 levels had reduced in small and average fetuses to similar concentrations (5.7 +/- 1.0 vs 4.8 +/- 0.5 ng/ml, P = 0.128). By day 100, elevated levels were found in small fetuses (10.7 +/- 1.5 vs 7.6 +/- 0.7 ng/ml, P < 0.001). Maternal plasma cortisol was unchanged over gestation (day 45, 56.7 +/- 21.6 ng/ml; day 65, 57.8 +/- 14.4 ng/ml; day 100, 55.7 +/- 6.5 ng/ml). We examined the cause of altered cortisol by investigating the fetal hypothalamic-pituitary-adrenal axis through the measurement of adrenocorticotropic hormone and assessing exposure to maternal cortisol by quantifying placental 11beta-hydroxysteroid dehydrogenase-isoform 2 (11beta HSD-2) gene expression. These data suggest that altered cortisol supply was of fetal origin. We examined organ glucocorticoid (GC) metabolism by the measurement of GC receptor (GR) and 11beta-hydroxysteroid dehydrogenase-isoform 1 (11beta HSD-1) gene expression. We found that fetal organs have different temporal patterns of 11beta HSD-1 and GR expression, with the liver particularly sensitive to cortisol in late gestation. This study examines GC exposure in naturally occurring differential growth and simultaneously explores tissue GC sensitivity and handling, at three key stages of gestation.

The effect of fetal pig size and stage of gestation on tissue fatty acid metabolism and profile.

The fetus requires an adequate supply of fatty acids for optimum growth and development. It has been hypothesized that reduced activity of enzymes of fatty acid metabolism could contribute to inadequate fetal growth. In a porcine model of differential fetal growth we examined heart and liver fatty acid synthase, delta5-desaturase and delta6-desaturase gene expression and measured hepatic fatty acid profile to assess long-chain polyunsaturated fatty acid status. On gestation days 45, 65 and 100 sows were killed and tissues extracted from an average-sized fetus and the smallest fetus from each litter. As early as day 45, considerable hepatic delta5- and delta6-desaturase was detected, and this expression significantly increased as gestation progressed. In contrast, cardiac desaturase expression remained stable with time. Fatty acid synthase expression was greatest at day 65 in the liver, but was not expressed in the heart. Overall, the smallest fetus did not exhibit reduced tissue delta5- or delta6-desaturase expression or compromised polyunsaturated fatty acid status at any stage. In fact, small fetuses expressed more cardiac delta5-desaturase than their average-sized siblings, possibly in response to a stress to the heart. It is clear from this study that fatty acid metabolism changes markedly as gestation progresses, and reduced fatty acid supply does not cause inadequate growth in this porcine model of fetal development.

Placental transport of leucine in a porcine model of low birth weight.

Low birth weight is a major factor in neonatal morbidity and mortality in humans and domestic species and is a predictor of physiological disorders in adulthood. This study utilised the naturally occurring variation in pig fetal size within a uterus to test the hypothesis that placental amino acid transport capability is associated with fetal growth. Leucine uptake by trophoblast vesicles prepared from placentas supplying an average-sized fetus and the smallest fetus in the uterus was assessed. On days 45 and 65 of gestation, uptake of leucine by the porcine placenta was predominantly sodium independent and was inhibited by the non-metabolised leucine analogue 2-amino-2-norbornane-carboxylic acid, indicating that uptake occurs via system L. By day 100 the uptake of leucine by placentas supplying average-sized fetuses had changed from being predominantly sodium independent to involving both sodium-dependent (system B0) and -independent (system L) pathways. This change was not seen in placentas supplying the smallest fetus, which continued to display predominantly sodium-independent uptake. In conclusion, these data show gestational- and fetal size-dependent changes in the transport of leucine across the porcine placenta.