Primiparous Mice Research Articles

Effects of hyperthyroidism and diabetes mellitus on spermatogenesis in peri- and post-pubertal mice.

Diabetes and thyroid dysfunction often co-exist. One autoimmune disorder always invites another and it has been reported that such co-morbid ailments always become detrimental to the health of the patients. In our previous work, we elucidated the interactions of diabetes and hypothyroidism on testicular development and spermatogenesis. However, the present study illuminates the interface between diabetes and hyperthyroidism, where 16 ICR pregnant primiparous mice were used and subsequently 48 male pups were randomly selected (n=12/group) and separated into 4 groups: control (C), diabetic (D), diabetic + hyperthyroidism (DH) and hyperthyroidism (H). Computerized sperm analyses showed significant reductions in count by 20% and increases of 15% in D and H animals, respectively, vs. controls. However, rapid progressive sperm motility was significantly lower only in D (30%) compared with C mice. Our histomorphometric investigation depicted damaging effects on testicular and epididymal tissues; the stroma adjacent to the seminiferous tubules of the D mice revealed edematous fluid and unstructured material. However, in the epididymis, germ cell diminution contraction of tubules, compacted principal and clear cells, lipid vacuolization, atypical cellular connections, exfoliated epithelial cells, and round spermatids were conspicuous in DH mice. Collectively, our experiment was undertaken to ultimately better recognize male reproductive disorders in diabetic-hyperthyroid patients.

Multiparity and Aging Impact Chondrogenic and Osteogenic Potential at Symphyseal Enthesis: New Insights into Interpubic Joint Remodeling

Pregnancy and childbirth cause adaptations to the birth canal to allow for delivery and fast recovery. To accommodate delivery through the birth canal, the pubic symphysis undergoes changes that lead to the interpubic ligament (IpL) and enthesis formation in primiparous mice. However, successive deliveries influence joint recovery. We aimed to understand tissue morphology and chondrogenic and osteogenic potential at symphyseal enthesis during pregnancy and postpartum in primiparous and multiparous senescent female mice. Morphological and molecular differences were found at the symphyseal enthesis among the study groups. Despite the apparent incapacity to restore cartilage in multiparous senescent animals, the symphyseal enthesis cells are active. However, these cells have reduced expression of chondrogenic and osteogenic markers and are immersed in densely packed collagen fibers contiguous to the persistent IpL. These findings may indicate alterations of key molecules in the progenitor cell population maintenance of the chondrocytic and osteogenic lineages at the symphyseal enthesis in multiparous senescent animals, possibly compromising the mouse joint histoarchitecture recovery. This sheds light on the distention of the birth canal and the pelvic floor that may play a role in pubic symphysis diastasis (PSD) and pelvic organ prolapse (POP), both in orthopedic and urogynecological practice in women.

VEGFR2 Expression Is Differently Modulated by Parity and Nulliparity in Mouse Ovary.

Parity and nulliparity exert opposite effects on women's health, as parity is considered a protective factor for several reproductive diseases. This study is aimed at determining if ovarian VEGF and VEGFR2 expression are differently modulated in the ovaries of parous and nulliparous mice. To this end primiparous and nulliparous fertile mice were sacrificed at postovulatory stage. Whole ovaries, corpus luteum, and residual stromal tissues were analyzed to assess VEGF/VEGFR2 expression levels. Ovarian mRNA amounts of Vegfa (120 and 164) and Vegfr2 were comparable between primiparous and nulliparous mice; both isoforms and receptor were accumulated mainly in corpus luteum tissues. VEGF 120 and 164 protein accumulation and distribution mirrored that of mRNA. Conversely, VEGFR2 protein content was significantly higher in ovaries of nulliparous mice and was more efficiently phosphorylated in ovaries of primiparous mice. In both groups, VEGFR2 was preferentially expressed in corpus luteum, while its phosphorylated form was equally distributed in two somatic compartments. We suggest that parity influences VEGFR2/phospho-VEGFR2 expression and tissue distribution. This difference could be part of a more complex mechanism that at least in mice is activated after the first pregnancy and likely aims to preserve female health.

Lack of placental transfer of certolizumab pegol during pregnancy: Results from crib, a prospective, postmarketing, multicenter, pharmacokinetic study

Although substantial evidence has demonstrated that parity and 17β-estradiol (E2) reduce mammary carcinogenesis, it is not clear how this protection is conferred. Thus, we examined the effects of parity and E2 treatment in the mammary glands of ovariectomized 15 week-old virgin mice, 15 week-old primiparous mice, and 9 month-old retired breeders. E2 treatment significantly increased lipid peroxidation, protein carbonylation, and protein nitrosylation in the virgin mice, but not in the age-matched primiparous mice or retired breeders. Mammary gland expression of the oxidative stress response protein Cu/Zn superoxide dismutase was consistently reduced in all of the E2-treated mice regardless of parity. Expression of the oxidative stress and DNA repair protein apurinic endonuclease (Ape1) was significantly increased only in the mammary glands of the E2-treated retired breeders. These findings suggest that E2 and parity help to reduce mammary oncogenesis by maintaining the structure and function of proteins, lipids, and DNA.

17β-Estradiol alters oxidative damage and oxidative stress response protein expression in the mouse mammary gland

Although substantial evidence has demonstrated that parity and 17β-estradiol (E2) reduce mammary carcinogenesis, it is not clear how this protection is conferred. Thus, we examined the effects of parity and E2 treatment in the mammary glands of ovariectomized 15 week-old virgin mice, 15 week-old primiparous mice, and 9 month-old retired breeders. E2 treatment significantly increased lipid peroxidation, protein carbonylation, and protein nitrosylation in the virgin mice, but not in the age-matched primiparous mice or retired breeders. Mammary gland expression of the oxidative stress response protein Cu/Zn superoxide dismutase was consistently reduced in all of the E2-treated mice regardless of parity. Expression of the oxidative stress and DNA repair protein apurinic endonuclease (Ape1) was significantly increased only in the mammary glands of the E2-treated retired breeders. These findings suggest that E2 and parity help to reduce mammary oncogenesis by maintaining the structure and function of proteins, lipids, and DNA.

Abstract 217: Cardiac Dysfunction in Offspring of Obese Multiparous Females

Emerging evidence indicates that maternal events prior to birth have a powerful impact on the risk for age-related diseases. Indeed, mothers who are obese during pregnancy confer an increased risk on their offspring for developmental programming of metabolic diseases. An often-overlooked risk factor for female obesity, and thus developmental programming, is multiparity. We have developed a novel mouse model in which multiparous mice become obese and develop severe inflammation − mirroring the pathology of obese multiparous humans. We have previously reported that the adult offspring of multiparous mice exhibit increased adiposity and a reduction in expression levels of genes associated with energy expenditure when fed low fat diets, despite similar food consumption. Recent studies show that these defects are associated with reduced energy expenditure and reduced mitochondrial function in hepatocytes of these mice compared to adult offspring of primiparous mice. Since a change in mitochondrial function in cardiomyocytes can lead to abnormal heart function, we fed male offspring a high fat diet (41% calories; milk fat) to stress the metabolic system. All mice accrued the same amount of fat on the high fat diets. We then and measured cardiac function using an echocardiogram. We found that there were significant differences in the ejection time, left ventricle mass, fractional shortening, and importantly in stroke volume and cardiac output of male offspring from females in their 1 st vs 4 th (multiparous) pregnancy. No differences in heart rate and aorta diameter were observed. These data suggest that the offspring of obese multiparous females are more prone to develop reduced cardiac function on a high fat diet, possibly indicating that maternal environment may be a novel risk factor for heart disease.

Reproductive Experience Affects Parental Retrieval Behaviour Associated with Increased Plasma Oxytocin Levels in Wild‐Type and Cd38‐Knockout Mice

The transition to motherhood results in a number of hormonal, neurological and behavioural changes necessary to ensure offspring growth. Once motherhood is established, further neurological and behavioural changes may result in long-term memory in mothering. Recent research has shown that postpartum motherhood enhances both nurturing behaviour and oxytocin activities. The transmembrane glycoprotein, CD38, is expressed on many neuronal cells and has been shown to play a role in social behaviours through stimulating the release of oxytocin in the hypothalamus. The present study was performed to investigate the effects of reproductive experience (primi- and multiparity, dams and sires) on the degree of parental behaviour, such as retrieval. Comparisons were performed between wild-type (Cd38 (+/+) ) and Cd38 knockout (Cd38 (-/-) ) mice of the ICR strain. Multiparous Cd38 (-/-) dams retrieved pups much faster than primiparous mice, whereas there were no significant differences between primi- and multiparous Cd38 (+/+) dams. Plasma oxytocin levels were significantly increased in multiparous dams of both genotypes. In addition, oxytocin levels in the hypothalamus and pituitary were lower in Cd38 (-/-) than in wild-type mice. ADP-ribosyl cyclase activity in the hypothalamus, but not in the pituitary, was slightly increased in Cd38 (+/+) dams. In an identical test, 40% of first-time Cd38 (+/+) sires showed retrieval. The time required to retrieval was shorter in second-time Cd38 (+/+) sires. Both first- and second-time Cd38 (-/-) sires showed only 10% retrieval behaviour. These results indicate that parental behaviour is improved by reproductive experience, especially in Cd38 (-/-) dams, and suggest that these effects may be a result of increased oxytocin levels.

Multiparity increases trophoblast invasion and vascular endothelial growth factor expression at the maternal–fetal interface in mice

To analyze immunomodulating effects related to parity status, we studied trophoblast invasion grade, placental expression and systemic concentration of VEGF and its receptor Flt-1 in normal fertile (CBA/JxBALB/c) mice and abortion-prone (CBA/JxDBA/2) H-2(d)xH-2(k) mice. BALB/c or DBA/2 mated CBA/J females were, respectively, divided into the following groups: primiparous young (3.0+/-0.5 months old); primiparous old (8.5+/-0.5 months old) and multiparous old (8.5+/-0.5 months old, with 4 pregnancies). Immunohistochemical analysis of term placentae from both multiparous groups revealed various layers of invasive trophoblast tissue, identified as cytokeratin+/vimentin- cells, in contrast to the single layer detected in the placentae of primiparous animals, indicating that multiparity increases trophoblast invasion regardless of the success of the pregnancy outcome. Invasive trophoblast tissue from primiparous CBA/JxDBA/2 placentae showed diminished VEGF expression in comparison with the normal fertile group, while both multiparous groups demonstrated high expression of VEGF in the invasive trophoblast tissue. Placental expression of Flt-1 was similar in all groups. However, the primiparous CBA/JxBALB/c group showed the highest plasma concentration of sFlt-1 at term, while both multiparous groups demonstrated low circulating levels. No differences in circulating VEGF levels were observed among the groups. These results demonstrate an increase in trophoblast invasion tissue and expression of VEGF in the maternal-fetal interface in multiparous mice compared to primiparous mice. Moreover, the placenta appears to be able to regulate the circulating levels of VEGF by releasing sFlt-1.

The Effects of Dietary Protein Levels on Milk Protein Levels and Postnatal Growth in Laboratory Mice (Mus musculus)

Changes in diet quality may be as important as changes in energy availability in the reproductive success of small mammals. The effect of dietary protein on fitness of females is most likely mediated by changes in yield or composition of milk. Mus musculus was used as a model to test whether dietary protein restriction leads to changes in milk composition. Primiparous mice were fed a 10% or 20% casein-based diet through 2 consecutive reproductive attempts. There was no effect of diet on food consumption or litter size. However, a reduction in dietary protein led to the production of milk with a 12% decrease in protein content and decreased both prenatal and postnatal growth of young. The impact of low levels of dietary protein on milk protein was greater with the increased reproductive demands of concurrent pregnancy and lactation. Significant variation in the protein content of milk was seen among females on the 20% casein-based diet, but not among females on the 10% casein-based diet. Further work is needed to determine the physiological mechanisms that lactating mice might possess to compensate for changes in dietary protein levels, and to determine if the effect of decreased diet quality on the reproductive success of small mammals is similar to the effect of energy availability.

Permanently increased conductance of the murine uterine arcade after the first pregnancy

Mechanical forces due to increased blood flow during the first pregnancy might induce a permanently higher conductance of the uterine arcade. Number of endothelial and smooth muscle cells, cross-sectional area and wall thickness of the uterine artery were measured in nulliparous mice (n = 11) and until the 93rd day after parturition in primiparous mice (n = 44). Inner diameter and wall area were calculated. Three months after the first pregnancy, uterine artery wall thickness was not altered compared to nulliparous mice. In contrast, inner diameter increased 1.6-fold, wall area 1.5-fold and the numbers of endothelial and smooth muscle cells increased 1.5 times. These changes were completely stable during the whole observation period. The increased blood flow during the first pregnancy might be a mandatory mechanical stimulus for uterine arcade maturation. This physiological maturation process could result in abortion explaining the higher prevalence of unexplained pregnancy losses in primiparous women.

Olfactory recognition of infants in laboratory mice: Role of noradrenergic mechanisms

Noradrenaline depletion of the olfactory bulbs induces cannibalism at parturition in primiparous mice, without producing anosmia or impairment of maternal behaviour. Similar lesions made in multiparous experienced females do not result in cannibalism. The present studies investigated 1) whether a 30-min exposure to pups or to distal cues from pups given to virgin females before noradrenaline depletion of the olfactory bulbs overcame the impairment in recognition at first parturition, and 2) whether noradrenaline-depleted females allowed to care for their pups for the 24 h following parturition showed a failure in recognition on a second parturition. Experiment 1 showed that exposure to distal cues from pups enabled the females to successfully recognize pups at parturition in comparison to naive females. However, neither the exposure to pup cues nor the fully interactive experience with pups overcame the disruptive effect on recognition at birth of the noradrenaline depletion. In Experiment 2, we found that olfactory recognition was impaired in noradrenaline-depleted females on second parturition, in spite of the mothering experience with their own pups.

Distribution of the Lysosomal Enzyme Aryl Sulfatase in Murine Mammary Tissue Through Pregnancy, Lactation, and Involution

Mammary tissue from 44 primiparous mice at various stages of pregnancy, lactation, and involution were stained for aryl sulfatase (lysosomal marker enzyme) activity and prepared for electron microscopy. Stereological techniques were used to determine the distribution of lysosomes per unit of cytoplasmic area in mammary epithelial cells. The number of primary lysosomes (containing only enzyme) was stable throughout the study, except for a temporary increase following parturition. Secondary lysosomes (containing substrate undergoing active digestion) designated as either telolysosomes or dense bodies were more frequent in mammary epithelial cells from animals in the late involution and early pregnancy stages than in lactating animals. However, telolysosomes did increase temporarily at the onset of lactation and casein micelles were identified within secondary lysosomes throughout the lactation stage. The frequencies for endoplasmic reticulum and Golgi apparatus containing aryl sulfatase reaction product were highest in secretory cells, when these structures were predominant. Shifts in lysosomal populations throughout the study suggests that lysosomes may have an active role within the mammary epithelial cells during differentiation and secretion as well as during involution.

Anticollagen antibody responses in DBA/1 (H-2 q) mice associated with type II collagen-induced arthritis and the effect of pregnancy

We have previously shown that DBA/1 mice immunized with heterologous type II collagen showed remission of the subsequent collagen-induced arthritis (CIA) when pregnant, but experienced exacerbation postpartum. Measurement of anticollagen antibody (aCa) responses by ELISA in primiparous mice immunized at day 1 of pregnancy revealed no significant difference compared to aCa titres in virgin animals, apart from slightly increased titres following the primary immunisation. When mice received collagen challenge during early pregnancy, however, the date at which maximal antibody titres was reached was delayed by 5 days. Pregnancy initiated following the intraperitoneal boost caused a ten-fold suppression in aCa titres with a rise post-partum. Measurements of aCa levels in individuals which showed fetal resorption indicated that suppression of humoral responses was dependent on the presence of a viable conceptus. Antibody titres declined in all animals after a period of time, which was more prolonged in multigravidae where aCa titres were higher than in nulliparous and primiparous mice. The results show that although pregnancy alters aCa responses during the course of gestation, no long-term modification of humoral immunity occurs, an observation in agreement with the clinical findings in these mice and in humans.

Quantitative and functional change in T cells of primiparous mice following injection of benzo(a)pyrene at the second trimester of pregnancy.

Progeny from benzo(a)pyrene (BP) exposed (150 micrograms/g body weight) primiparous mothers, injected during the second trimester of pregnancy, are severely compromised immunologically. In view of maternal-fetal associations, we studied, during pregnancy and postpartum, the quantitative and functional status of the maternal T cell population in the thymus and/or spleen. In the thymus, there is an exacerbated depression in the amounts of thymocytes, (theta +, Lyt 1+, Lyt 2+ cells) during pregnancy relative to the corn oil-injected controls, which is sustained postpartum. In the spleen, while there are inconsistencies in the level of theta + cells, The Lyt 1+ are depressed postpartum relative to virgins, but the Lyt 2+ are enhanced during pregnancy and postpartum, reaching levels greater than 700-fold of controls. In controls, while the number of Lyt 1+ cells was higher than BP-exposed mice or virgins during pregnancy, they virtually disappeared postpartum. A similar but reversed image is mirrored by the Lyt 2+ cells, i.e., they were virtually absent during pregnancy but increased postpartum. Splenic allogeneic and syngeneic mixed lymphocyte responses were subnormal. The data show that BP disrupts the maternal T cell repertoire, leading to an accumulation of Lyt 1-2+ cells, and suggest that splenic disruption may be due to changes in the differentiation potential of T precursor cells. These changes not only are most likely to affect maternal defenses, but also may have a direct bearing on the establishment of progeny immune status.

Functional differentiation of virgin mouse mammary epithelium in explant culture is dependent upon extracellular proline.

Depletion of proline from insulin, hydrocortisone, and prolactin-containing medium prior to incubating virgin mouse mammary explants prevents both DNA synthesis and functional differentiation in the mammary epithelial cells; however, DNA synthesis in the mammary stroma and total incorporation of radioactive amino acids into total protein appears to continue without hindrance. Removal of glycine instead of proline had no deleterious effect on either DNA replication in the hormone-stimulated epithelium or in its functional differentiation. Functional differentiation was determined by the induction of casein and alpha-lactalbumin synthesis in the insulin, hydrocortisone, and prolactin (IFPrl)-treated explant cultures. As a control, the induction of mouse mammary tumor virus (MMTV) gene expression, a corticosteroid-regulated function, was also measured. Neither the absence of proline or glycine prevented the glucocorticoid stimulation of MMTV gene expression. In contrast to mammary tissue from virgin mice, explants from nonpregnant primiparous mice responded fully to IFPrl stimulation with respect to DNA, casein, and alpha-lactalbumin synthesis in medium depleted of proline. These data suggest that the uncommitted epithelium of virgin mouse mammary glands requires the presence of exogenous proline in order to respond to lactogenic hormonal signals. We have demonstrated earlier that DNA synthesis is a prerequisite of functional differentiation in virgin mouse mammary explants (Smith and Vonderhaar, 1981, Dev. Biol., 88:167-179; Vonderhaar and Smith, 1982, J. Cell Sci, 53:97-114), although cytological differentiation proceeded unencumbered in explants prevented from synthesizing DNA. Here, without proline, neither cytological nor functional differentiation can be induced; this suggests that proline provides an essential metabolic interlock in the acquisition of lactogenic hormone responsiveness in uncommitted mouse mammary tissue.

Quantitative and Functional Change in T Cells of Primiparous Mice Following Injection of Benzo(a)Pyrene at the Second Trimester of Pregnancy

AbstractProgeny from benzo(a)pyrene (BP) mposed (150 ug/g body weight) primiparous mothers, injected during the second trimester of pregnancy, are severely compromised immunologically. In view of maternal-fetal associations, we studied, during pregnancy and postpartum, the quantitative and functional status of the maternal T cell population in the thymus and/or spleen. In the thymus, there is an exacerbated depression in the amounts of thymocytes, (tH+, Lyt 1+, Lyt 2+ cells) during pregnancy relative to the corn oil-injected controls, which is sustained postpartum. In the spleen, while there are inconsistencies in the level of θ+ cells, The Lyt 1+ are depressed postpartum relative to virgins, but the Lyt 2+ are enhanced during pregnancy and postpartum, reaching levels <700-fold of controls. In controls, while the number of Lyt 1+ cells was higher than BP-exposed mice or virgins during pregnancy, they virtually disappeared postpartum. A similar but reversed image is mirrored by the Lyt 2+ cells, i.e., they...

Changes in epidermal growth factor concentrations of submandibular gland, plasma and urine of normal and sialoadenectomized female mice during various reproductive stages

The concentrations of epidermal growth factor (EGF) were measured by radioimmunoassay in the submandibular gland, plasma and urine of adult female C3H/HeN mice whilst virgin and during pregnancy, lactation and after lactation. During gestation there was a significant increase in the submandibular EGF concentration which was five to seven times higher than that found in virgin mice. The level of EGF in the gland remained high during the period of lactation and even several weeks after lactation. Plasma EGF levels were also increased during the periods of pregnancy, lactation and after lactation when compared with those of virgin mice. These increases were, however, apparent only between 24.00 and 08.00 h, because of circadian variations in circulating EGF. The level of plasma EGF was significantly (P less than 0.05) higher during the 24.00-08.00 h period than during the 12.00-20.00 h period in all stages examined. Concentrations of EGF in the urine of virgin, pregnant, lactating and primiparous mice remained relatively constant, and the levels were much higher than those in the plasma. Similar studies using sialoadenectomized pregnant and lactating mice indicated that the plasma levels of EGF were below the level of sensitivity of the assay (less than 16.5 pmol/l (less than 0.1 ng/ml] even during the 24.00-08.00 h period, whereas urinary EGF remained at high levels which were similar to those of normal pregnant and lactating mice. These results suggest that submandibular EGF contributes to the increase in plasma EGF which occurs after gestation, but is not the major source of the urinary EGF.

Cell proliferation in the embryonic mouse neocortex following acute maternal alcohol intoxication

Experiments were conducted to examine the effects of ‘binge’ or acute maternal alcohol intoxication during the early proliferative phase of embryonic brain development. Primiparous mice received ethanol as 0, 10, 15 or 20% (v/v) aqueous solutions by gavage on days 13, 14 and 15 of gestation. Mean daily doses were 0.0, 2.58, 4.03 and 5.40 ml/kg, respectively. There was no alcohol-related reduction in fetal body weight, length or fixed brain weight. Coronal sections (1 μm) of the dorsal roof of the lateral ventricles over the optic chiasma were examined from nine embryonic day 15 brains for each treatment group. The ventricular surface index of mitotic figures, the number and distribution of non-surface mitotic figures, and the depth of the cortical roof and its constituent layers were determined. There was no alcohol-related difference in any of these parameters. These results are in contrast to those of a previous experiment using the same mouse strain, in which prolonged or chronic maternal alcohol consumption in the drinking water from days 11 to 19 of pregnancy was associated with a reduction in the surface index, a reduction in the depth of the cortical roof and an increase in the non-surface mitotic figures. These latter changes, however, occurred in the presence of reduced body weight. Our observations suggest that during this particular developmental period (corresponding to the second trimester of human pregnancy) alcohol-related reductions in brain growth parallel restrictions in general body growth.

Changes in the term mouse placenta associated with maternal alcohol consumption and fetal growth deficits

Primiparous mice were fed alcohol in their drinking water as 0%, 10%, 15%, or 20% (vv) solutions on days 11 through 18 of gestation. Based on blood alcohol levels and on locomotor and health impairments, these treatment groups represent situations of mild, moderate, and severe alcohol abuse. There were significant alcohol-related fetal growth deficits but no increase in fetal mortality or malformation. Placental weight was reduced with increasing alcohol intake. Histologic examination of the placenta revealed an increase in the frequency and severity of intravascular coagulation of maternal erythrocytes in the labyrinth and advanced degenerative changes in the basal zone of alcohol-exposed placentas. These observations suggest that both the vascular and the endocrine functions of the placenta are compromised in alcohol-consuming dams.

Existence of suppressor cells in the spleen of allogeneic and syngeneic primiparous pregnant mice

Mixed lymphocyte reaction (MLR) and in vitro induction of cytolytic cells against alloantigens were investigated using spleen cells from primiparous mice mated allogeneically or syngeneically. One-way MLR was reduced significantly in degree not only in allogeneic but also in syngeneic pregnant mice. MLR of virgin spleen cells was suppressed when mitomycin C-treated spleen cells taken from syngeneic or allogeneic pregnant mice were added as regulator cells. These suppressive effects disappeared when regulator cells were treated with anti-Thy 1 or anti-Lyt 2 serum plus complement. Generation of cytotoxic lymphocytes from syngeneic or allogeneic pregnancy spleen cells in MLR was depressed compared with that from virgin spleen cells. The addition of pregnancy spleen cells to MLR suppressed in vitro generation of cytotoxic lymphocytes from virgin spleen cells. These results indicated that reduction of in vitro cellular responses of pregnancy spleen cells was due to suppressor cells in the spleens. These cells suppressed non-specifically the reactions to alloantigens and could be detected both in allogeneic and syngeneic primiparous pregnancies.