BACKGROUND:Male fertility investigation is currently limited to semen analysis. However, the origins of abnormal sperm parameters are not well-understood, and normal sperm do not assure fertility in men. Improved pathophysiological and prognostic insight might be achieved utilising additional measures of male reproductive tract function. Cytokine and chemokine levels in seminal plasma (SP) may be relevant, but evidence on their clinical significance is unclear. The utility of measuring SP cytokines remains uncertain, and no consensus exists on which cytokines are most informative. OBJECTIVE AND RATIONALE:To perform a systematic review and meta-analysis on the association between fertility status and concentration of seminal plasma cytokines in men. The sixth edition of the WHO laboratory manual for the examination and processing of human semen raises the prospect of evaluating cytokines in SP as part of an extended examination. We performed a systematic search and meta-analysis to assess whether the current literature is sufficient to identify cytokines present in human SP that exhibit a relationship with fertility status in men. SEARCH METHODS:We searched PubMed, Web of Science, Scopus, and Embase from inception until April 2025, using keywords pertaining to seminal fluid and cytokines, restricted to humans and the English language. Original data with values reported as concentration of cytokines in SP of men clearly defined as infertile, compared to a discernible population of fertile/normozoospermic healthy control men, were included. A total of 5737 studies were identified, with 2737 duplicates removed. Title and abstract screening were performed for 3000 studies, then 291 studies underwent full-text screening, and 68 studies progressed to quality assessment using the NHLBI-NIH quality assessment tool and 52 studies underwent data extraction. OUTCOMES:We identified 52 research articles published from 1993 to 2025 that quantified at least one cytokine in the seminal plasma of 8153 men, after 19 studies of poor quality and/or containing serious flaws were excluded. Data on 30 cytokines in the SP of healthy control and infertile men were extracted and included in narrative synthesis. Compared to fertile controls, infertile men had elevated concentrations of IL6 (SMD 0.39, 95% CI; 0.14-0.64, I2 = 80.7%), TNFA (SMD 0.13, 95% CI; 0.00-0.25, I2 = 4.3%), and CXCL8 (SMD 0.24, 95% CI; 0.06-0.43, I2 = 0.0%) in seminal plasma. IL6 reported a high degree of heterogeneity between studies, whilst CXCL8 and TNFA reported low heterogeneity. No significant moderator effects due to study quality or composition of the control cohort were identified. WIDER IMPLICATIONS:With one in six couples experiencing infertility worldwide and a male factor identified as a primary or contributing cause in up to 50% of cases, there is a strong imperative to develop a better understanding of the pathophysiology of male infertility. This analysis identifies an association between infertility and elevated SP IL6, CXCL8, and TNFA, but whether these pro-inflammatory cytokines reflect events affecting fertility or are simply markers of transient inflammation and/or cofactors of fertility status remains to be determined. Greater precision in quantifying seminal plasma cytokines will be attained, and additional informative cytokines may be identified, by utilising standardised technical approaches in future studies. REGISTRATION NUMBER:CRD42023398438.

Seminal plasma is a pivotal regulator of reproductive success that contributes to fertility and fecundity beyond its traditionally recognized function as a vehicle for spermatozoa. Rich in soluble and extracellular vesicle-encased signaling molecules, seminal plasma influences sperm integrity and function, whilst simultaneously driving profound physiological changes in the female reproductive tract. These functions are broadly conserved across vertebrate and invertebrate species and help to optimize fertilization and create an immunological environment that supports implantation and fetal development. Perturbation of seminal plasma composition or ablation of its effects can affect fertility, the progression of pregnancy and even the long-term health of offspring. Given these far‑reaching effects, the responsiveness of seminal plasma composition to environmental exposures and influences has become an important focus of research. Studies across species using a variety of different physiological perturbations or environmental exposures have shown modification to the abundance and activities of soluble and extracellular vesicle-derived seminal plasma signaling molecules. Exposures to toxins, nutritional deficiency, metabolic disturbance, and infection-associated inflammation have each been shown to affect seminal plasma components with consequences for sperm function, female reproductive tract responses, embryo development, and offspring health. Collectively, these findings position seminal plasma, in addition to spermatozoa, as an important mediator of paternal environmental influences, offering a biological means through which males convey information on their physiological state to their mates and influence reproductive success across generations.

Lipidic nanoparticles (LNPs) hold strong potential for cervicovaginal drug delivery, yet their behaviour in complex mucosal environments remains poorly understood, limiting rational design. Here, we systematically investigate five LNP formulations spanning lamellar (Lα) and non-lamellar (cubic and hexagonal) mesophases to establish composition-structure-function relationships under biologically relevant conditions. Using small-angle X-ray scattering, cryo-TEM, proteomics, flow cytometry, confocal microscopy, and cytotoxicity assays, we evaluate physicochemical properties, protein corona formation, cellular uptake, and structural dynamics in simulated vaginal fluid (SVF). Lipid composition emerged as the dominant determinant of nanoparticle behaviour, governing protein corona composition, cytotoxicity, and cellular internalisation, superseding contributions from nanostructure or surface stabilisation. Monoolein-based systems exhibited high protein affinity and enriched corona formation, whereas PEGylated lamellar liposomes showed reduced protein binding and high cellular uptake (>91%) with minimal cytotoxicity. In contrast, phytantriol formulations displayed pronounced toxicity and limited adaptive behaviour. Mucin modulated cellular uptake in a concentration-dependent manner, suppressing internalisation at low doses while enhancing uptake at higher concentrations for non-lamellar systems, indicating an active regulatory role in nanoparticle-cell interactions. In physiologically relevant environments, lipid composition also dictated structural responses: phytantriol-based LNPs remained structurally stable across pH 4.1-7.8, whereas monoolein/oleic acid systems underwent pH and ion dependent transitions that altered internal geometry and are expected to influence release behaviour. Collectively, these results demonstrate that nanoparticle identity and function in mucosal environments are defined by the interplay between lipid composition, protein adsorption, and environmental conditions. This work establishes design principles for cervicovaginal drug delivery, highlighting the need to integrate composition, interfacial behaviour, and environmental responsiveness to achieve effective mucosal nanocarriers.

Preparation of spermatozoa with optimal developmental competence remains a challenge in assisted reproduction. Conventional techniques based on sperm motility and morphology fail to adequately remove sperm with DNA damage. Here, we report development of a microfluidic device with a functionalized surface, inspired by the physiological processes of immune cell-mediated sperm selection in the female reproductive tract. A plasma-polymerized polyoxazoline (PPOx) film is applied to glass channel slides by deposition of 2-methyl-2-oxazoline, to establish a stable, biocompatible interface confirmed by X-ray Photoelectron Spectroscopy (XPS), ellipsometry, and sperm culture assays. To selectively eliminate pre-apoptotic and apoptotic spermatozoa wherein DNA damage is common, anti-phosphatidylserine (Anti-PS) antibody is immobilized to the PPOx-coated surface proximal to the channel slide inlet, while the sperm chemoattractant progesterone is adsorbed near the outlet. To optimize selective functionality, the surface topography is tailored by covalent immobilization of gold nanoparticles and addition of microchannels. Sperm recovered after processing whole liquified semen consistently exhibit high motility and morphology, and low apoptosis-associated membrane damage, with <1% showing DNA fragmentation. Compared with conventional swim-up or other microfluidic approaches, the device yields sperm with improved quality, offering a simple one-step sperm selection strategy with potential for application in human and animal assisted reproduction.

Seminal fluid is more than a vehicle for sperm transport. It contains a complex mix of immune-regulatory cytokines that, together with other bioactive factors, influence sperm maturation and survival, and interact with female reproductive tract cells and tissues to facilitate conception and stimulate female receptivity to pregnancy. Cytokines synthesized in the seminal vesicles, prostate, and other male accessory glands come into contact with sperm at ejaculation, and upon intromission are delivered to the cervix and uterus in soluble form, as cargo of seminal extracellular vesicles, or in physical association with sperm. The relative concentrations of different cytokines vary between individual men and can fluctuate over time - in response to local and systemic viral or bacterial infection, acute and chronic inflammatory and metabolic disorders, such as varicocele, prostatitis and diabetes, and environmental exposures including heat stress, chemical toxin exposures, and smoking. Although seminal fluid cytokines in healthy men promote fertility through permissive effects on embryo development and implantation, elevated abundance of certain proinflammatory cytokines is linked with infertility and subfertility. Emerging insight on the identity and biological functions of key permissive and inhibitory seminal fluid cytokines indicates potential clinical applications in evaluating and managing male and female infertility, and for developing improved assisted reproduction techniques. However, knowledge gaps on the significance of cytokines in reproductive biology and pathophysiology, the most informative cytokines to measure and their normal ranges, and technical challenges regarding optimal assay platforms and protocols, first must be overcome.

Declining reproductive health and fertility are global public health issues affecting an estimated 15% of reproductive-aged couples worldwide. The reasons for declining fertility are complex. However, a male contribution is thought to occur in ∼50% of infertile couples. Deficits in sperm number and/or function are undeniably a major cause of infertility, but compelling evidence suggests that additional factors in the male ejaculate also play an influential and underappreciated role. In this review, we focus specifically on extracellular vesicles within human seminal plasma and explore their emerging roles in reproduction and fertility. These seminal extracellular vesicles (SEVs) are nano-sized membrane structures secreted by various cell lineages in virtually all regions of the male reproductive tract and exert key roles in intercellular communication. Consideration is given to the well-characterized effects of SEVs in supporting sperm as they transit through the female reproductive tract and their ability to modulate the immune environment within the female reproductive tract. Building on these important roles, we also detail the emerging links between dysregulated SEV production and male fertility status, and highlight the potential utility of leveraging these vesicles to improve fertility and reproductive outcomes in infertile couples. Altogether, this review highlights how expanding knowledge of SEVs provides a new perspective on the complexity of seminal fluid physiology and the underlying aetiology of male infertility.

Asthma is the most common respiratory condition during pregnancy and increases the risks of adverse pregnancy and perinatal outcomes. Asthma symptoms change in similar to 60% of pregnancies, but whether this is due to pregnancy itself is unclear. We tested the hypothesis that physiological changes during pregnancy worsen asthma severity in an ovine experimental model of allergic asthma. Three-year-old Merino ewes were randomly allocated to either control or allergic asthma groups. Asthma was induced through sensitisation and repeated airway challenge with house dust mite allergen. We compared airway function, circulating cytokine profile and airway immune response to allergen challenge throughout the study and airway structure between groups, in non-pregnant (control n = 8, asthma n = 9), singleton-pregnant (control n = 5, asthma n = 8) and twin-pregnant ewes (control n = 6, asthma n = 9). Within non-pregnant animals, transpulmonary pressure at Day 132 of the study was 37% higher in asthmatic than control ewes (P = 0.031), but not different between treatments in singleton-pregnant (P = 0.594) or twin-pregnant (P = 0.074) ewes. Between premating and Day 132, dynamic compliance decreased more in asthmatic than control ewes (P = 0.040), and this change did not differ between litter sizes (P = 0.096). Neither asthma nor pregnancy affected eosinophils in bronchoalveolar lavage or lung tissue. There was no evidence of lung airway remodelling in the cohort. The results of this study suggest that pregnancy does not increase asthma symptoms or severity of mild asthma.

Seminal fluid introduced into the female reproductive tract following unprotected coitus initiates an inflammation-like response in the cervical tissues that stimulates immune tolerance to male seminal fluid alloantigens and promotes immune adaptation for pregnancy. This response commences when seminal fluid factors induce genes encoding pro-inflammatory cytokines and chemokines including CSF2, IL6, and CXCL8, that in turn cause recruitment of macrophages, dendritic cells, and T cells into the epithelial and stromal layers. Various signaling agents present in seminal plasma provoke the post-coital pro-inflammatory activation and regulate the quality of immune response. However, the factors identified to date do not account for all the biological activity within seminal fluid, implying sperm-associated factors may also contribute. In this chapter, we report methods for evaluating the effects of human seminal fluid components (seminal plasma and sperm) on the female reproductive tract immune response in primary and immortalized ectocervical epithelial cells in vitro.

The seminal vesicle is the largest male accessory sex gland and makes the greatest contribution to the seminal plasma in most mammalian species, including human. Factors secreted from the seminal vesicle facilitate reproduction in two ways. Firstly, they assist in delivery of the sperm into the female reproductive tract and promote sperm retention, viability and function during transit of sperm to the site of fertilization. Secondly, seminal vesicle secretions interact with female tissues after coitus to influence female reproductive physiology and improve the chances of conception, embryo development and reproductive success.

Seminal extracellular vesicles (SEVs) carry a diverse array of bioactive molecules, including proteins, lipids, and nucleic acids, which influence sperm function and have potential to modulate the female reproductive tract immune response after intromission. However, the full spectrum of SEV cargo involved in these processes remains incompletely defined. Here, we employed label-free quantitative high-resolution mass spectrometry to characterize the human SEV proteome, identifying 5079 associated proteins. These proteins were shown to likely originate from multiple regions of the male reproductive tract, notably the seminal vesicles and prostate, providing evidence for heterogeneous tissue origins of SEVs. Bioinformatic analysis revealed enrichment in sperm- and immune-related functions, as well as functions linked to protein translation. Notably, we identified several proteins with established roles in sperm physiology and immune signaling that had not previously been linked with SEV function. These included; Adenylate kinase isoenzyme (AK)2/9, and Calcium-binding tyrosine-phosphorylation regulated protein (CABYR), implicated in sperm motility, and immune regulators such as the Toll-like receptor 4 ligand, High mobility group protein B1 (HMGB1), and the Nuclear factor kappa-light-chain-enhancer of activated B cells (NFκB) inhibitor epsilon (NFκBIE). Altogether, these findings expand the known SEV proteome and highlight proteins that may influence both male and female reproductive capacity.

After intromission of seminal fluid at mating in mammals, the seminal fluid interacts with the lining of the female reproductive tract and elicits a female immune response. This response is triggered by signals in seminal fluid (carried by both the sperm and seminal plasma components) that bind receptors on female tract epithelial cells, causing a change in their transcriptional program to upregulate expression of pro-inflammatory cytokines and chemokines. The ensuing leukocyte recruitment and immune activation facilitates conception, embryo development, and progression of pregnancy. In this chapter, we report methods for evaluating effects of seminal fluid and its components (seminal plasma and sperm) on the female reproductive tract immune response in mice.

Despite statements to the effect that you cannot measure serum cytokines, there have been numerous studies attempting to use serum cytokine measurements as biomarkers of disease activity and severity, relating to infection, autoimmunity, acute and chronic inflammatory diseases, and cancer. The approach is thwarted by assay inaccuracies, sensitivity and standardisation. This extends to the lack of information on serum sample handling and storage. Further setbacks are encountered from the lack of ability to generate appropriate normal intervals and cut-offs relevant to disease prognosis.

Abstract Seminal fluid extracellular vesicles (SFEVs) have previously been shown to interact with spermatozoa and influence their fertilisation capacity. Here, we sought to extend these studies by exploring the functional consequences of SFEV interactions with human spermatozoa. SFEVs were isolated from the seminal fluid of normozoospermic donors prior to assessing the kinetics of sperm-SFEV binding in vitro, as well as the effects of these interactions on sperm capacitation, acrosomal exocytosis, and motility profile. Biotin-labelled SFEV proteins were transferred primarily to the flagellum of spermatozoa within minutes of co-incubation, although additional foci of SFEV biotinylated proteins also labelled the mid-piece and head domain. Functional analyses of high-quality spermatozoa collected following liquefaction revealed that SFEVs did not influence sperm motility during incubation at pH 5, yet SFEVs induced subtle increases in total and progressive motility in sperm incubated with SFEVs at pH 7. Additional investigation of sperm motility kinematic parameters revealed that SFEVs significantly decreased beat cross frequency and increased distance straight line, linearity, straightness, straight line velocity, and wobble. SFEVs did not influence sperm capacitation status or the ability of sperm to undergo acrosomal exocytosis. Functional assessment of both high- and low-quality spermatozoa collected prior to liquefaction showed limited SFEV influence, with these vesicles inducing only subtle decreases in beat cross frequency in spermatozoa of both groups. These findings raise the prospect that, aside from subtle effects on sperm motility, the encapsulated SFEV cargo may be destined for physiological targets other than the male germline, notably the female reproductive tract. Lay Summary A male’s influence over the biological processes of pregnancy extends beyond the provision of sperm. Molecular signals present in the ejaculate can influence the likelihood of pregnancy and healthy pregnancy progression, but the identity and function of these signals remain unclear. In this study, we wanted to understand if nano-sized particles present in the male ejaculate, called seminal fluid extracellular vesicles, can assist sperm in traversing the female reproductive tract to access the egg. To explore this, we isolated seminal fluid extracellular vesicles from human semen and incubated them with sperm. Our data showed that seminal fluid extracellular vesicles act to transfer molecular information to sperm, but this resulted in only subtle changes to the movement of sperm. Graphical abstract

Summary: Regulatory T (Treg) cell defects are implicated in disorders of embryo implantation and placental development, but the origins of Treg cell dysfunction are unknown. Here, we comprehensively analyzed the phenotypes and transcriptional profile of peripheral blood Treg cells in individuals with early pregnancy failure (EPF). Compared to fertile subjects, EPF subjects had 32% fewer total Treg cells and 54% fewer CD45RA+CCR7+ naive Treg cells among CD4+ T cells, an altered Treg cell phenotype with reduced transcription factor FOXP3 and suppressive marker CTLA4 expression, and lower Treg:Th1 and Treg:Th17 ratios. RNA sequencing demonstrated an aberrant gene expression profile, with upregulation of pro-inflammatory genes including CSF2, IL4, IL17A, IL21, and IFNG in EPF Treg cells. In silico analysis revealed 25% of the Treg cell dysregulated genes are targets of FOXP3. We conclude that EPF is associated with systemic Treg cell defects arising due to disrupted FOXP3 transcriptional control and loss of lineage fidelity.

BACKGROUND:The last decade has seen increased research on the relationship between diet and male fertility, but there are no clearly defined nutritional recommendations for men in the preconception period to support clinical fertility outcomes. OBJECTIVE AND RATIONALE:The purpose of this scoping review is to examine the extent and range of research undertaken to evaluate the effect(s) of diet in the preconception period on male clinical fertility and reproductive outcomes. SEARCH METHODS:Four electronic databases (MEDLINE and EMBASE via Ovid, CAB Direct, and CINAHL via EBSCO) were searched from inception to July 2023 for randomized controlled trials (RCTs) and observational studies (prospective/retrospective, case-control, and cross-sectional). Intervention studies in male participants or couples aiming to achieve dietary or nutritional change, or non-intervention studies examining dietary or nutritional components (whole diets, dietary patterns, food groups or individual foods) in the preconception period were included. Controls were defined as any comparison group for RCTs, and any/no comparison for observational studies. Primary outcomes of interest included the effect(s) of male preconception diet on clinical outcomes such as conception (natural or via ART), pregnancy rates and live birth rates. Secondary outcomes included time to conception and sperm parameters. OUTCOMES:A total of 37 studies were eligible, including one RCT and 36 observational studies (prospective, cross-sectional, and case-control studies; four studies in non-ART populations) published between 2008 and 2023. Eight reported clinical outcomes, 26 reported on secondary outcomes, and three reported on both. The RCT did not assess clinical outcomes but found that tomato juice may benefit sperm motility. In observational studies, some evidence suggested that increasing fish or reducing sugar-sweetened beverages, processed meat or total fat may improve fecundability. Evidence for other clinical outcomes, such as pregnancy rates or live birth rates, showed no relationship with cereals, soy and dairy, and inconsistent relationships with consuming red meat or a 'healthy diet' pattern. For improved sperm parameters, limited evidence supported increasing fish, fats/fatty acids, carbohydrates and dairy, and reducing processed meat, while the evidence for fruits, vegetables, cereals, legumes, eggs, red meat and protein was inconsistent. Healthy diet patterns in general were shown to improve sperm health. WIDER IMPLICATIONS:Specific dietary recommendations for improving male fertility are precluded by the lack of reporting on clinical pregnancy outcomes, heterogeneity of the available literature and the paucity of RCTs to determine causation or to rule out reverse causation. There may be some benefit from increasing fish, adopting a healthy dietary pattern, and reducing consumption of sugar-sweetened beverages and processed meat, but it is unclear whether these benefits extend beyond sperm parameters to improve clinical fertility. More studies exploring whole diets rather than singular foods or nutritional components in the context of male fertility are encouraged, particularly by means of RCTs where feasible. Further assessment of core fertility outcomes is warranted and requires careful planning in high-quality prospective studies and RCTs. These studies can lay the groundwork for targeted dietary guidelines and enhance the prospects of successful fertility outcomes for men in the preconception period. Systematic search of preconception diet suggests that increasing fish and reducing sugary drinks, processed meats and total fat may improve male fertility, while consuming healthy diets, fish, fats/fatty acids, carbohydrates and dairy and reducing processed meat can improve sperm health.

Conventionally it was believed seminal fluid had just one biological function, to support delivery of spermatozoa into the female tract, thereby facilitating fertilisation of the oocyte. There is increasing evidence indicating seminal fluid plays a more complex role, with studies conducted in mice revealing a critical effect of seminal fluid in initiating inflammatory changes in the female reproductive tract important for the establishment of immune tolerance that is required for successful pregnancy to occur. This tolerogenic immune environment is established at coitus prior to and at the time of conception, when contact with the conceiving male partner's seminal fluid primes the female immune response. Immune tolerance is induced when seminal fluid delivers an array of signalling molecules that interact with the female reproductive tissues. The actions of immune cells responding to these signals in the cervix, uterus and ovary facilitate the likelihood of successful conception and pregnancy, by promoting clearance of seminal debris and microbes, inducing regulatory T cells to modulate the female immune response to male histocompatibility antigens, and conditioning the uterine environment in preparation for embryo implantation. In humans, this response is not as well characterised, however clinical studies have shown seminal fluid contact following intercourse provokes an adaptive immune response within the cervical tissues of women, and the transport of spermatozoa to the higher tract suggests a potential role in affecting the endometrial lining of the uterus directly. Further, seminal fluid exposure has been linked with both acute and cumulative benefits to pregnancy outcome, suggesting the immune response is physiologically important, long-lasting, and additive. Epidemiological studies show that pregnancy pathologies leading to prematurity and low birth weight occur more frequently in women where exposure to partner's semen is limited or where seminal signalling is compromised. However, basic understanding of the female reproductive tract response to seminal fluid signals remains incomplete, limiting our capacity to develop diagnostics and design therapeutic interventions for women where faulty immune tolerance is a likely cause of reproductive dysfunction. This could provide a hitherto unknown mechanism to influence endometrial receptivity for embryo implantation and regulation of female fertility as seen in rodent species.

ObjectiveSeminal plasma cytokines are associated with fertility and reproductive health, but progressing their clinical utility is hampered by absence of reference data on concentration ranges of relevant cytokines in healthy men. We employed a systematic approach to assemble current evidence on the concentrations of immune regulatory cytokines present in seminal plasma (SP) of normozoospermic and/or fertile men and evaluated the impact of different platform methodologies for cytokine quantification. Evidence reviewA systematic literature search was performed utilising PubMed, Web of Science and Scopus. Databases were searched from inception until 30th June 2022 inclusive, using combinations of keywords pertaining to seminal fluid and cytokines, and was restricted to human participants. Original data with values reported as concentration of specific cytokines in SP of men clearly defined as fertile or normozoospermic were extracted from studies written in English. ResultsA total of 3769 publications were initially identified, of which 118 fulfilled the eligibility criteria for inclusion. A total of 51 individual cytokines are detectable in SP of healthy men. The number of studies reporting on each cytokine range from 1 to >20. The reported concentrations for many cytokines linked with fertility status, including IL6, CXCL8/IL8, and TNFA, are highly variable between published studies. This is associated with the different immunoassay methodologies utilised and may be exacerbated by a lack of validation of assays to ensure suitability for SP assessment. Due to the large variation between studies, accurate reference ranges for healthy men cannot be determined from the published data. ConclusionsThe concentrations of cytokines and chemokines detected in SP is inconsistent and highly variable between studies and cohorts, limiting current capacity to define reference ranges for cytokine concentrations in fertile men. The lack of standardisation in methods used to process and store SP, and variation in platforms used to evaluate cytokine abundance, are factors contributing to the observed heterogeneity. To progress the clinical utility of SP cytokine analysis will require standardisation and validation of methodologies so that reference ranges for healthy fertile men can be defined.

Conventional belief has held that the male contribution to pregnancy begins and ends with provision of developmentally competent sperm to fertilise the oocyte and form the embryo. However, an additional function for seminal fluid has emerged - to exert actions on the female tissues that can directly promote or constrain fertility and fecundity through effects on the female immune response and reproductive processes. The immune-regulatory cytokines transforming growth factor-B (TGFB) and E-series prostaglandins in seminal fluid have been identified as key drivers of post-coital inflammation in mice and women. Seminal fluid can also contain interferon-G (IFNG). At high levels, seminal plasma IFNG is linked with idiopathic infertility, independently of sperm parameters. In fertile men and men experiencing idiopathic infertility, we have discovered using logistic regression analysis that IFNG concentration is a robust predictor of fertility status. In in vitro experiments, IFNG suppresses synthesis of pro-tolerance cytokines from ectocervical epithelial cells. Our data identifies IFNG as a potent inhibitor of TGFB-mediated seminal fluid signalling and implicates seminal fluid IFNG content as a determinant of fertility acting through suppression of immune tolerance at coitus in women. Our preclinical studies implicate additional permissive and inhibitory cytokines in seminal plasma, suggesting female sensing of seminal fluid signals can affect immune receptivity to implantation and placental development, having positive or negative effects on pregnancy outcome depending on the balance of signals. A challenge to progress this field is identifying the most informative seminal plasma markers, to build diagnostic tests for male partner seminal plasma quality.

Progesterone (P4) is essential for embryo implantation, but the extent to which the pro-gestational effects of P4 depend on the maternal immune compartment is unknown. Here, we investigate whether regulatory T cells (Treg cells) act to mediate luteal phase P4 effects on uterine receptivity in mice. P4 antagonist RU486 administered to mice on days 1.5 and 3.5 postcoitum to model luteal phase P4 deficiency caused fewer CD4+Foxp3+ Treg cells and impaired Treg functional competence, along with dysfunctional uterine vascular remodeling and perturbed placental development in midgestation. These effects were linked with fetal loss and fetal growth restriction, accompanied by a Th1/CD8-skewed T cell profile. Adoptive transfer at implantation of Treg cells - but not conventional T cells - alleviated fetal loss and fetal growth restriction by mitigating adverse effects of reduced P4 signaling on uterine blood vessel remodeling and placental structure and by restoring maternal T cell imbalance. These findings demonstrate an essential role for Treg cells in mediating P4 effects at implantation and indicate that Treg cells are a sensitive and critical effector mechanism through which P4 drives uterine receptivity to support robust placental development and fetal growth.