Differentiated structure and function of primary cultures of monkey oviductal epithelium

Oxygen levels affect oviduct epithelium functions in air-liquid interface culture

Key reproductive events such as fertilization and early embryonic development occur in the lumen of the oviduct. Since investigating these processes in vivo is both technically challenging and ethically sensitive, cell culture models have been established to reproduce the oviductal microenvironment. Compartmentalized culture systems, particularly air-liquid interface cultures (ALI; cells access the culture medium only from the basolateral cell side), result in highly differentiated oviduct epithelial cell cultures. The oxygen (O2) tension within the oviduct is 4-10% across species, and its reduced O2 content is presumed to be important for early reproductive processes. However, cell culture models of the oviduct are typically cultivated without O2 regulation and therefore at about 18% O2. To investigate the impact of O2 levels on oviduct epithelium functions in vitro, we cultured porcine oviduct epithelial cells (POEC) at the ALI using both physiological (5%) and supraphysiological (18%) O2 levels and two different media regimes. Epithelium architecture, barrier function, secretion of oviduct fluid surrogate (OFS), and marker gene expression were comparatively assessed. Under all culture conditions, ALI-POEC formed polarized, ciliated monolayers with appropriate barrier function. Exposure to 18% O2 accelerated epithelial differentiation and significantly increased the apical OFS volume and total protein content. Expression of oviduct genes and the abundance of OVGP1 (oviduct-specific glycoprotein 1) in the OFS were influenced by both O2 tension and medium choice. In conclusion, oviduct epithelial cells can adapt to a supraphysiological O2 environment. This adaptation, however, may alter their capability to replicate in vivo tissue characteristics.

Physiological Action of Progesterone in the Nonhuman Primate Oviduct

Therapies that target progesterone action hold potential as contraceptives and in managing gynecological disorders. Recent literature reviews describe the role of steroid hormones in regulating the mammalian oviduct and document that estrogen is required to stimulate epithelial differentiation into a fully functional ciliated and secretory state. However, these reviews do not specifically address progesterone action in nonhuman primates (NHPs). Primates differ from most other mammals in that estrogen levels are >50 pg/mL during the entire menstrual cycle, except for a brief decline immediately preceding menstruation. Progesterone secreted in the luteal phase suppresses oviductal ciliation and secretion; at the end of the menstrual cycle, the drop in progesterone triggers renewed estrogen-driven tubal cell proliferation ciliation secretory activity. Thus, progesterone, not estrogen, drives fallopian tube cycles. Specific receptors mediate these actions of progesterone, and synthetic progesterone receptor modulators (PRMs) disrupt the normal cyclic regulation of the tube, significantly altering steroid receptor expression, cilia abundance, cilia beat frequency, and the tubal secretory milieu. Addressing the role of progesterone in the NHP oviduct is a critical step in advancing PRMs as pharmaceutical therapies.

Capture and metabolomic analysis of the human endometrial epithelial organoid secretome

Suboptimal uterine fluid (UF) composition can lead to pregnancy loss and likely contributes to offspring susceptibility to chronic adult-onset disorders. However, our understanding of the biochemical composition and mechanisms underpinning UF formation and regulation remain elusive, particularly in humans. To address this challenge, we developed a high-throughput method for intraorganoid fluid (IOF) isolation from human endometrial epithelial organoids. The IOF is biochemically distinct to the extraorganoid fluid (EOF) and cell culture medium as evidenced by the exclusive presence of 17 metabolites in IOF. Similarly, 69 metabolites were unique to EOF, showing asymmetrical apical and basolateral secretion by the in vitro endometrial epithelium, in a manner resembling that observed in vivo. Contrasting the quantitative metabolomic profiles of IOF and EOF revealed donor-specific biochemical signatures of organoids. Subsequent RNA sequencing of these organoids from which IOF and EOF were derived established the capacity to readily perform organoid multiomics in tandem, and suggests that transcriptomic regulation underpins the observed secretory asymmetry. In summary, these data provided by modeling uterine luminal and basolateral fluid formation in vitro offer scope to better understand UF composition and regulation with potential impacts on female fertility and offspring well-being.

A dog oviduct-on-a-chip model of serous tubal intraepithelial carcinoma

Ovarian cancer is the fifth cause of cancer-related mortality in women, with an expected 5-year survival rate of only 47%. High-grade serous carcinoma (HGSC), an epithelial cancer phenotype, is the most common malignant ovarian cancer. It is known that the precursors of HGSC originate from secretory epithelial cells within the Fallopian tube, which first develops as serous tubal intraepithelial carcinoma (STIC). Here, we used gene editing by CRISPR-Cas9 to knock out the oncogene p53 in dog oviductal epithelia cultured in a dynamic microfluidic chip to create an in vitro model that recapitulated human STIC. Similar to human STIC, the gene-edited oviduct-on-a-chip, exhibited loss of cell polarization and had reduced ciliation, increased cell atypia and proliferation, with multilayered epithelium, increased Ki67, PAX8 and Myc and decreased PTEN and RB1 mRNA expression. This study provides a biomimetic in vitro model to study STIC progression and to identify potential biomarkers for early detection of HGSC.

Air-liquid interface cell culture: From airway epithelium to the female reproductive tract

The air-liquid interface (ALI) approach is primarily used to mimic respiratory tract epithelia in vitro. It is also known to support excellent differentiation of 3D multilayered skin models. To establish an ALI culture, epithelial cells are seeded into compartmentalized culture systems on porous filter supports or gel substrata. After an initial propagation period, the culture medium is removed from the apical side of the epithelium, exposing the cells to the surrounding air. Therefore, nutritive supply to the cells is warranted only by the basolateral cell pole. Under these conditions, the epithelial cells differentiate and regain full baso-apical polarity. Some types of epithelia even generate in vivo-like apical fluid or mucus. Interestingly, the ALI culture approach has also been shown to support morphological and functional differentiation of epithelial cells that are not normally exposed to ambient air in vivo. This review aims at giving a brief overview on the characteristics of ALI cultures in general and ALI models of female reproductive tract epithelia in particular. We discuss the applicability of ALI models for the investigation of the early embryonic microenvironment and for its implications in assisted reproductive technologies.

Steroids affect gene expression, ciliary activity, glucose uptake, progesterone receptor expression and immunoreactive steroidogenic protein expression in equine oviduct explants in vitro

The oviduct undergoes dramatic functional and morphological changes throughout the oestrous cycle of the mare. To unravel the effects of steroids on the morphology, functionality and gene expression of the equine oviduct, an in vitro oviduct explant culture system was stimulated with physiological concentrations of progesterone and 17β-oestradiol. Four conditions were compared: unsupplemented preovulatory explants, preovulatory explants that were stimulated with postovulatory hormone concentrations, unsupplemented postovulatory explants and postovulatory explants that were stimulated with preovulatory hormone concentrations. The modulating effects of both steroids on oviduct explants were investigated and the following parameters examined: (1) ciliary activity, (2) glucose consumption and lactate production pattern, (3) ultrastructure, (4) mRNA expression of embryotrophic genes, (5) steroidogenic capacities of oviductal explants and (6) progesterone receptor expression. The present paper shows that the equine oviduct is an organ with potential steroidogenic capacities, which is highly responsive to local changes in progesterone and 17β-oestradiol concentrations at the level of morphology, functionality and gene expression of the oviduct. These data provide a basis to study the importance of endocrine and paracrine signalling during early embryonic development in the horse.

Improved bovine embryo production in an oviduct-on-a-chip system: prevention of poly-spermic fertilization and parthenogenic activation

The oviduct provides the natural micro-environment for gamete interaction, fertilization and early embryo development in mammals, such as the cow. In conventional culture systems, bovine oviduct epithelial cells (BOEC) undergo a rapid loss of essential differentiated cell properties; we aimed to develop a more physiological in vitro oviduct culture system capable of supporting fertilization. U-shaped chambers were produced using stereo-lithography and mounted with polycarbonate membranes, which were used as culture inserts for primary BOECs. Cells were grown to confluence and cultured at an air-liquid interface for 4 to 6 weeks and subsequently either fixed for immune staining, incubated with sperm cells for live-cell imaging, or used in an oocyte penetration study. Confluent BOEC cultures maintained polarization and differentiation status for at least 6 weeks. When sperm and oocytes were introduced into the system, the BOECs supported oocyte penetration in the absence of artificial sperm capacitation factors while also preventing polyspermy and parthenogenic activation, both of which occur in classical in vitro fertilization systems. Moreover, this "oviduct-on-a-chip" allowed live imaging of sperm-oviduct epithelium binding and release. Taken together, we describe for the first time the use of 3D-printing as a step further on bio-mimicking the oviduct, with polarized and differentiated BOECs in a tubular shape that can be perfused or manipulated, which is suitable for live imaging and supports in vitro fertilization.

Designing 3-Dimensional In Vitro Oviduct Culture Systems to Study Mammalian Fertilization and Embryo Production

The oviduct was long considered a largely passive conduit for gametes and embryos. However, an increasing number of studies into oviduct physiology have demonstrated that it specifically and significantly influences gamete interaction, fertilization and early embryo development. While oviduct epithelial cell (OEC) function has been examined during maintenance in conventional tissue culture dishes, cells seeded into these two-dimensional (2-D) conditions suffer a rapid loss of differentiated OEC characteristics, such as ciliation and secretory activity. Recently, three-dimensional (3-D) cell culture systems have been developed that make use of cell inserts to create basolateral and apical medium compartments with a confluent epithelial cell layer at the interface. Using such 3-D culture systems, OECs can be triggered to redevelop typical differentiated cell properties and levels of tissue organization can be developed that are not possible in a 2-D culture. 3-D culture systems can be further refined using new micro-engineering techniques (including microfluidics and 3-D printing) which can be used to produce ‘organs-on-chips’, i.e. live 3-D cultures that bio-mimic the oviduct. In this review, concepts for designing bio-mimic 3-D oviduct cultures are presented. The increased possibilities and concomitant challenges when trying to more closely investigate oviduct physiology, gamete activation, fertilization and embryo production are discussed.

Transepithelial electrical resistance (TEER): a functional parameter to monitor the quality of oviduct epithelial cells cultured on filter supports

Cultivation of oviduct epithelial cells on porous filters fosters in vivo-like morphology and functionality. However, due to the optical properties of the filter materials and the cells’ columnar shape, cell quality is hard to assess via light microscopy. In this study, we aim to evaluate transepithelial electrical resistance (TEER) measurement as a prognostic quality indicator for the cultivation of porcine oviduct epithelial cells (POEC). POEC were maintained in four different types of media for 3 and 6 w to achieve diverse culture qualities, and TEER was measured before processing samples for histology. Culture quality was scored using morphological criteria (presence of cilia, confluence and cell polarity). We furthermore analyzed the correlation between cellular height (as a measure of apical–basal polarization) and TEER in fully differentiated routine cultures (biological variation) and in cultures with altered cellular height due to hormonal stimulation. Fully differentiated cultures possessed a moderate TEER between 500 and 1100 Ω*cm². Only 5 % of cultures which exhibited TEER values in this defined range had poor quality. Sub-differentiated cultures showed either very low or excessively high TEER. We unveiled a highly significant (P < 0.0001) negative linear correlation between TEER and epithelial height in well-differentiated cultures (both routine and hormone stimulated group). This may point toward the interaction between tight junction assembly and epithelial apical–basal polarization. In conclusion, TEER is a straightforward quality indicator which could be routinely used to monitor the differentiation status of oviduct epithelial cells in vitro.

Bovine oviductal epithelial cells: long term culture characterization and impact of insulin on cell morphology

In vitro models that resemble cell function in vivo are needed to understand oviduct physiology. This study aimed to assess cell functions and insulin effects on bovine oviductal epithelial cells (BOECs) cultured in an air-liquid interface. BOECs (n=6) were grown in conditioned Ham's F12, DMEM or Ham's F12/DMEM with 10% fetal calf serum (FCS) for 3 weeks. After selecting the most suitable medium (Ham's F12), increasing insulin concentrations (1 ng/mL, 20 ng/mL and 5 μg/mL) were applied, and cell morphology and trans-epithelial electrical resistance (TEER; n=4) were evaluated after 3 and 6 weeks. Keratin immunohistochemistry and mRNA expression of oviductal glycoprotein 1 (OVGP1) and progesterone receptor (PGR) were conducted (n=4) to assess cell differentiation. BOECs grown without insulin supplementation or with 1 ng/mL of insulin displayed polarization and secretory activity. However, cells exhibited only 50% of the height of their in vivo counterparts. Cultures supplemented with 20 ng/mL insulin showed the highest quality, but the 5 μg/mL concentration induced massive growth. TEER correlated negatively with insulin concentration (r=-0.459; p=0.009). OVGP1 and PGR transcripts were still detectable after 3 and 6 weeks. Cellular localization of keratins closely resembled that of BOECs in vivo. Cultures showed heterogeneous expression of PGR and OVGP1 in response to estradiol (10 pg/mL). In summary, BOECs grown for long term in an air-liquid interface expressed markers of cell differentiation. Additionally, insulin supplementation (20 ng/mL) improved the cell morphology in vitro.

Altered expression of inflammation-associated genes in oviductal cells following follicular fluid exposure: implications for ovarian carcinogenesis

Evidence indicates that high-grade serous ovarian carcinoma (HGSOC) may originate from lesions within the distal fallopian tube epithelium (FTE). Our previous studies indicate that fallopian tube epithelial cells from carriers of germline mutations in breast cancer susceptibility genes exhibit a pro-inflammatory gene expression signature during the luteal phase, suggesting that delayed resolution of postovulatory inflammatory signaling may contribute to predisposition to this ovarian cancer histotype. To determine whether exposure of tubal epithelial cells to periovulatory follicular fluid alters expression of inflammation-associated genes, we used an ex vivo culture system of bovine oviductal epithelial cells. Oviductal cells grown on collagen IV-coated transwell membranes assumed a cobblestone appearance and immunocytochemistry for FoxJ1 and Pax8 indicated that both ciliated and secretory epithelial cells were maintained in the cultures. Oviductal cells were exposed to human follicular fluid or culture medium for 24 h following which total cellular RNA was extracted at various time points. Expression of genes associated with inflammation was determined by quantitative real-time RT-PCR. Exposure to follicular fluid transiently increased the transcript levels of interleukin 8 (IL8) and cyclooxygenase 2 (PTGS2), and decreased the expression of mitochondrial superoxide dismutase (SOD2), glutathione peroxidase 3 (GPX3), disabled homolog 2 (DAB2), and glucocorticoid receptor (NR3C1). Tumor necrosis factor (TNF) and IL6 levels were also decreased while those of nicotinomide phosphoribosyltransferase (NAMPT) were unaffected. This study demonstrates that periovulatory follicular fluid can act directly upon oviductal epithelial cells to alter gene expression that might contribute to early carcinogenic events. Furthermore, these findings illustrate the potential use of bovine oviductal cells to study signaling events implicated in ovarian carcinogenesis.

In vitro mimicking of estrous cycle stages in porcine oviduct epithelium cells: estradiol and progesterone regulate differentiation, gene expression, and cellular function

Throughout the estrous cycle the oviduct epithelium undergoes dramatic morphological and functional changes. To elucidate cyclic cellular events and associated regulation mechanisms of 17beta estradiol (E2) and progesterone (P4), we mimicked estrous cycle stages in vitro using a culture system of primary porcine oviduct epithelium cells (POEC). Cells were polarized in an air/liquid interface and then treated with E2 and P4 for physiological time periods: In experiment 1, high concentration of P4 with low concentration of E2 for 10 days resembled diestrus; in experiment 2, following the previous diestrus, sequential high E2 with low P4 for 2.5 days represented estrus. Histomorphometry and electron microscopy showed cyclic changes in cellular height, cell population, and cilia density under the influence of hormone stimulation. Transepithelial electrical resistance was high in simulated diestrus but reduced in estrus. Thus, E2 and P4 affect cellular polarity, transformation of ciliated and secretory cells, as well as electrical conductivity of oviduct epithelium. Simulation of diestrus led to significant decrease in expression of hormone receptors (PGR and ESR1) and other epithelial markers (MUC16, OVGP1, and HSP90B1), while sequential simulated estrus caused an increase in these markers. The hormonal regulation of some marker genes was clearly time-dependent. Furthermore, POEC showed increased sperm-binding capacity in simulated estrus. In this study, we also present a novel approach based on the AndroVision software, which can be routinely utilized as a parameter for ciliary activity, and for the first time, we showed fluid movement patterns along the epithelium lining in vitro.

Long-term culture of primary porcine oviduct epithelial cells: validation of a comprehensive in vitro model for reproductive science

Recently, we established a protocol for the cultivation of primary porcine oviduct epithelial cells (POEC), which promoted tissue-like morphology for a prolonged culture period. The present study focuses on developing this model into a comprehensive, standardized culture system, as a candidate tool for reproductive toxicity testing and basic research. We cultivated POEC isolated from 25 animals in our culture system for both 3 and 6 weeks and systematically analyzed effects of medium conditioning, supplementation with standardized sera, and culture duration in both freshly isolated and cryopreserved cells. The differentiation status was evaluated via histomorphometry, transepithelial electrical resistance (TEER) measurement, and expression analyses. The culture system possessed high reproducibility, more than 95% of cultures achieved a fully differentiated phenotype. Cells recapitulated in vivo-like morphology and ultrastructure from 3 to 6 weeks. Cryopreservation of the cells prior to cultivation did not affect culture quality of POEC. Employment of conditioned medium ensured optimal promotion of POEC differentiation, and different standardized sera induced fully differentiated phenotypes. Consistent TEER establishment indicated the presence and maintenance of cell type-specific intercellular junctions. The functionality of POEC was proven by consistent mucin secretion and stable expression of selected markers over the whole culture duration. We conclude that POEC are suitable for experiments from 3 weeks up to at least 6 weeks of culture. Therefore, this culture system could be used for in vitro estrous cycle simulation and long-term investigation of toxic effects on oviduct epithelium.

Bovine oviductal monolayers cultured under three-dimension conditions secrete factors able to release spermatozoa adhering to the tubal reservoir in vitro

Different in vitro models have been developed to understand the interaction of gametes and embryos with the maternal reproductive tract. We recently showed that bovine oviductal monolayers three-dimensionally cultured in Gray's medium on collagen-coated microporous polycarbonate inserts under liquid-air interface conditions are well polarized, develop cilia, remain viable for at least 3 weeks postconfluence, and mantain the viability of bound spermatozoa significantly better than bidimensionally cultured monolayers. Herein, we used these culture conditions to understand whether: (1) spermatozoa adhering to three-dimensionally cultured oviductal monolayers can be released by heparin or penicillamine as previously shown with bidimensionally cultured oviductal monolayers and explants; and (2) media conditioned by three-dimensionally cultured oviductal monolayers were able to release spermatozoa adhering to oviductal explants. Findings demonstrated that (1) spermatozoa adhering to three-dimensionally cultured oviductal monolayers are readily released by heparin and penicillamine, (2) media conditioned by three-dimensionally cultured oviductal monolayers are able to release spermatozoa bound to oviductal explants, (3) do not depress sperm motility and viability, (4) they improve sperm kinetics, and (5) promote binding to the zona pellucida. In conclusion, in vitro data suggest that the release of spermatozoa adhering to the oviductal reservoir in vivo can be triggered by factors secreted by the oviduct itself that induce sperm capacitation.

Long-term viability and differentiation of bovine oviductal monolayers: bidimensional versus three-dimensional culture

Different in vitro models have been developed to study the interaction of gametes and embryos with the maternal tract. In cattle, the interaction of the oviduct with gametes and embryos have been classically studied using oviductal explants or monolayers (OMs). Explants are well differentiated but have to be used within 24 h after collection, whereas OMs can be used for a longer time after cell confluence but dedifferentiate during culture, losing cell polarity and ciliation. Herein, OMs were cultured either in M199 plus 10% fetal calf serum or in a semidefined culture medium (Gray's medium), in an immersed condition on collagen-coated coated microporous polyester or polycarbonate inserts under air-liquid interface conditions. The influence of culture conditions on long-term viability and differentiation of OMs was evaluated through scanning electron microscopy, localization of centrin and tubulin at the confocal laser scanning microscope, and assessment of maintenance of viability of sperm bound to OMs. Findings demonstrated that OMs cultured in an immersed condition with Gray's medium retain a better morphology, do not exhibit signs of crisis at least until 3 wks postconfluence, and maintain the viability of bound sperm significantly better than parallel OMs cultured in M199 plus 10% fetal calf serum. OM culture with Gray's medium in air-liquid interface conditions on porous inserts promotes cell polarity, ciliation, and maintenance of bound sperm viability at least until 3 wks postconfluence. In conclusion, oviduct culture in Gray's medium in an immersed or air-liquid condition allows long-term culture and, in the latter case, also ciliation of bovine OMs, and may represent in vitro systems that mimick more closely the biological processes modulated by the oviduct in vivo.

Primary ex vivo cultures of human fallopian tube epithelium as a model for serous ovarian carcinogenesis

Recent studies suggest that some serous ovarian carcinomas (SOCs) arise from the fallopian tube (FT) epithelium rather than the ovarian surface epithelium. This hypothesis places emphasis on the FT secretory epithelial cell as a cell-of-origin. Herein, we report the development of a novel ex vivo primary human FT epithelium culture system that faithfully recapitulates the in vivo epithelium, as shown by morphological, ultrastructural and immunophenotypic analyses. Mass spectrometry-based proteomics reveal that these cultures secrete proteins previously identified as biomarkers for ovarian cancer. We also use this culture system to study the response of the FT epithelium to genotoxic stress and find that the secretory cells exhibit a distinct response to DNA damage when compared with neighboring ciliated cells. The secretory cells show a limited ability to resolve the damage over time, potentially leaving them more susceptible to accumulation of additional mutagenic injury. This divergent response is confirmed with in situ studies using tissue samples, further supporting the use of this ex vivo culture system to investigate FT epithelial pathobiology. We anticipate that this novel culture system will facilitate the study of SOC pathogenesis, and propose that similar culture systems could be developed for other organ site-specific epithelia.

Ovarian cancer pathogenesis: a model in evolution

Ovarian cancer is a deadly disease for which there is no effective means of early detection. Ovarian carcinomas comprise a diverse group of neoplasms, exhibiting a wide range of morphological characteristics, clinical manifestations, genetic alterations, and tumor behaviors. This high degree of heterogeneity presents a major clinical challenge in both diagnosing and treating ovarian cancer. Furthermore, the early events leading to ovarian carcinoma development are poorly understood, thus complicating efforts to develop screening modalities for this disease. Here, we provide an overview of the current models of ovarian cancer pathogenesis, highlighting recent findings implicating the fallopian tube fimbria as a possible site of origin of ovarian carcinomas. The ovarian cancer model will continue to evolve as we learn more about the genetics and etiology of this disease.

Hormonal and purinergic stimulation of bicarbonate secretion in oviducts of rhesus monkey

Because an increase in the HCO(3)(-) concentration of oviductal liquid at midcycle is believed to markedly enhance fertility, we have studied active secretion of HCO(3)(-) across highly differentiated cultures of monkey oviductal epithelium. Cultured cell sheets were mounted in Ussing chambers and bathed in medium containing 25 mM HCO(3)(-). Purinergic agents potently stimulated short-circuit current (I(sc)) with an initial transient response declining within approximately 2 min to a sustained response. The potency sequence of ATP approximately UTP > ADP >> AMP suggested that the I(sc) response was mediated mainly by P2Y(2) receptors. Acetazolamide, an inhibitor of carbonic anhydrase, had little or no effect on baseline I(sc) or the transient response to ATP but abolished the sustained response to ATP. Similar results were obtained on sheets of native epithelium. In pH-stat experiments, the abluminal medium of cell cultures was bathed in HCO(3)(-)-CO(2) medium, and the pH of the unbuffered luminal medium was maintained at approximately 7.4 by addition of strong acid or base. ATP stimulated base secretion, and this was inhibited by acetazolamide. Furthermore, these changes in secretion of base were in good quantitative agreement with the I(sc) responses. When phenol red (an estrogen) was removed from the culture medium, ATP-dependent HCO(3)(-) secretion was markedly reduced but could be restored by treatment with estradiol. Estrogens also markedly increased ciliation of the cultures. These results suggest that the midcycle increase in the HCO(3)(-) concentration of oviductal liquid may be mediated by the effects of estradiol on purinergic pathways or on ATP secretion.

Beta-defensin 126 on the surface of macaque sperm mediates attachment of sperm to oviductal epithelia

Beta-defensin 126 (DEFB126) coats the entire surface of macaque sperm until sperm become capacitated, and the removal of DEFB126 from over the head of sperm is required for sperm-zona recognition. Viable sperm collected from cervix and the uterine lumen of mated female macaques had DEFB126 coating the entire surface, suggesting that DEFB126 is retained on sperm en route to the oviduct. DEFB126 plays a major role in attachment of sperm to oviductal epithelial cells (OECs). Following treatment to either remove or alter DEFB126, sperm were coincubated with explants of OECs, which were assessed for sperm binding following rinsing to remove superficially attached sperm. Sperm treated with either 1 mM caffeine + 1 mM dibutyryl cyclic adenosine monophosphate (dbcAMP) (induces capacitation and complete release of DEFB126 from sperm), 2 mM caffeine (removes DEFB126 from over the head and midpiece but does not induce capacitation), anti-DEFB126 immunoglobulin, or neuraminidase (cleaves sialic acid from terminal positions on glycosylation sites of DEFB126) resulted in similar and significant levels of inhibition of sperm-OEC binding. Preincubation of OECs with soluble DEFB126 also resulted in significantly reduced sperm-OEC binding. Furthermore, reduced OEC binding capability of sperm lacking DEFB126 could be restored by addition of soluble DEFB126 to the sperm surface prior to incubation with OECs. Finally, purified DEFB126, infused into oviducts in situ, associated primarily with the apical membranes of secretory-type epithelial cells. In summary, treatments of macaque sperm that result in either removal, masking, or alteration of DEFB126 result in loss of sperm-OEC binding that is independent of changes in sperm motility. DEFB126 may be directly involved in the formation of a reservoir of sperm in the oviduct of macaques.