Progesterone promotes the acrosome reaction in capacitated human spermatozoa as judged by flow cytometry and CD46 staining.

The acrosome reaction is a necessary prerequisite for spermatozoa to acquire fertilizing ability. Several different moieties appear to promote the acrosome reaction through different pathways, including solubilized zona pellucidae, recombinant zona protein ZP3, follicular fluid, calcium ionophores, and mannosylated bovine serum albumin (BSA). Although many investigators have presented evidence that progesterone also promotes the acrosome reaction through the mediation of a non-genomic cell membrane receptor, this concept has been challenged. Other workers have suggested that progesterone does not promote an acrosome reaction in human spermatozoa, as judged by the detection of CD46, a complement regulatory protein present on the inner acrosome membrane, through flow cytometric analysis of large numbers of spermatozoa. Prior investigations were criticized by the limited numbers of spermatozoa enumerated visually, the use of non-specific staining techniques, and the failure to eliminate dead spermatozoa during the scoring of the acrosome reaction. We have repeated these experiments, using both a supravital dye to eliminate dead spermatozoa from flow cytometric analysis, and anti-CD46 monoclonal antibody to score acrosome-reacted spermatozoa. Care was taken to validate the adequacy of capacitation conditions, which were proven by the ability of spermatozoa to acrosome react in response to mannosylated BSA and to penetrate zona-free hamster eggs. Confocal microscopy was used to confirm that CD46 immunostaining was limited to the acrosomal region of the spermatozoon head. Our results indicate that progesterone does promote an acrosome reaction within capacitated spermatozoa.

Evidence that a functional fertilin-like ADAM plays a role in human sperm-oolemmal interactions.

Fertilin is a protein initially identified in guinea pig spermatozoa; it is the prototype of a larger family of conserved, proteins designated as a disintegrin and a metalloproteinase (ADAM). These heterodimers which consist of alpha and beta subunits, containing metalloproteinase-like and disintegrin-like domains, appear to play a role in mammalian fertilization. Peptides derived from the disintegrin domains of two ADAMs, fertilin and cyritestin, interfere with gamete adhesion and sperm-egg membrane fusion in non-human species. It has been suggested that fertilin-beta binds to an oolemmal integrin, and it is proposed that the tripeptide FEE (Phe-Glu-Glu) is the integrin recognition sequence in human fertilin-beta. We evaluated whether fertilin beta plays a role in human fertilization by studying the effects of a linear octapeptide containing the FEE sequence, SFEECDLP, and a scrambled octapeptide with the same amino acids, SFPCEDEL, on the incorporation of human spermatozoa by human zona-free eggs. The effects of G4120, a potent RGD-containing (Arg-Gly-Asp) thioether-bridged cyclic peptide which blocks both fibronectin and vitronectin receptors, and the relationship between FEE- and RGD-receptor interactions on sperm-egg interactions were also studied. The FEE-containing peptide, but not the scrampled peptide, inhibited sperm adhesion to oocytes and their penetration, over the range 1-5 microM. The inhibition induced by SFEECDLP was reversible and occurred only in the presence of peptide itself. The G4120 peptide exhibited 10-fold less inhibitory effects on sperm adhesion and penetration than did SFEECDLP. When combined, SFEECDLP and G4120 exhibited strong inhibition of both adhesion and penetration at concentrations that individually had been ineffective, suggesting co-operation between the two receptor-ligand interactions during fertilization. We propose that a fertilin-like molecule is functionally active on human spermatozoa and that its interaction with an oolemmal integrin receptor plays a role in fertilization in humans.

An investigation of the latency period between sperm oolemmal adhesion and oocyte penetration.

In clinical studies of the ability of capacitated human sperm to penetrate zona-free hamster eggs, we have previously observed that the ratio of oolemmal adherent to penetrating sperm varied between men. Sperm incorporation did not occur immediately following gamete adhesion and not all adherent sperm penetrated the egg. To further investigate this phenomenon, comparisons were made of the kinetics of gamete adhesion, membrane fusion, and sperm incorporation of capacitated mouse and human spermatozoa by zona-free hamster eggs and of mouse sperm by zona-free mouse and hamster eggs. Eggs were inseminated with either capacitated human or mouse sperm or combinations of both, washed out of sperm suspension after initial gamete adherence, and further incubated in sperm-free medium. Gamete membrane fusion was judged by dye transfer of Hoechst 33342 and sperm entry of the cortical ooplasm by observation of expanded sperm heads within acridine orange stained eggs. Oolemmal adherent mouse and human sperm fused with and penetrated zona-free hamster eggs at different times whether eggs were inseminated in parallel or with combinations of sperm of both species. Oolemmal adherent mouse sperm penetrated zona-free hamster eggs prior to their penetration of zona-free mouse eggs. Ultrastructural studies of zona-free human eggs inseminated with human sperm confirmed prior observations with hamster eggs that only acrosome-reacted human sperm adhere to the oolemma. These results have lead us to postulate that sperm entry into the egg may occur through a "zipper" mechanism involving the ligation of local gamete receptors similar to the incorporation of target particles by phagocytes and suggest that not all oolemmal adherent human sperm are capable of being incorporated although they have undergone an acrosome reaction.

Gonadotropins do not induce antiphospholipid antibodies.

PROBLEM: To determine whether the increased incidence of antiphospholipid antibodies (APAs) in women undergoing assisted reproduction might be secondary to superovulation with gonadotropins, predisposing women to an abnormal immune response and thus inducing APAs. METHOD OF STUDY: Women undergoing assisted reproduction with gonadotropins for the first time were selected and tested before the initiation of the stimulation cycle, during the cycle, and at the end of the cycle (group 1). Women who had undergone gonadotropin stimulation at least 60 days earlier (group 2) and normal, nonpregnant, fertile women (group 3) also were evaluated. Serum samples were assayed by the enzyme-linked immunosorbent assay method. RESULTS: Ten (20%) of 50 women in group 1 were positive for APAs. The 10 women who were positive for APAs remained positive throughout the treatment cycle. Positive antibodies were identified in 12 (24%) of 50 women in group 2, not significantly different from group 1 (P = 0.81). Antibodies were present in 2 of 50 normal fertile control subjects, significantly less frequently than in group 1 (P < 0.03) and in group 2 (P < 0.01). CONCLUSIONS: These data suggest that gonadotropin administration and/or the ovarian response to stimulation does not predispose women to the induction of APAs. Moreover, the incidence of APAs in this population, which is higher than that found in normal fertile women, cannot be explained by cycle-induced events.

Prostaglandins induce calcium influx in human spermatozoa.

Progesterone, prostaglandin and follicular fluid are reported to enhance the acrosome reaction through the influx of extracellular calcium into the cytoplasm of human spermatozoa. Prostaglandins are present within the male reproductive tract, and high concentrations of prostaglandins exist in seminal fluid. In order to investigate the mechanisms by which prostaglandins enhance the acrosome reaction through calcium influx, the intracellular calcium response induced by progesterone, prostaglandin E1 (PGE1), prostaglandin E2 (PGE2) and follicular fluid was measured using fura-2. PGE1 and PGE2 promoted calcium influx dose dependently through dihydropyridine insensitive calcium channels. Refractoriness of the elevation of intracellular Ca2+ concentration ([Ca2+]i) to a second stimulus occurred when 60 microg/ml PGE1 was administered 100 s after the prior administration of 60 microg/ml of PGE1, and similarly when 1 microg/ml of progesterone was administered 100 s after the prior administration of 1 microg/ml of progesterone. Refractoriness also occurred when 60 microg/ml PGE1 was administered after the prior addition of 60 microg/ml PGE2, but did not occur between PGE1 and progesterone. Pertussis toxin (PTX) did not modify the changes in [Ca2+]i after the addition of PGE1 or PGE2. In conclusion, PGE1 and PGE2 promoted calcium influx through PTX-insensitive calcium channels which appeared to be recognized by a common receptor different from that of progesterone.

Measurement of vitronectin content of human spermatozoa and vitronectin concentration within seminal fluid.

OBJECTIVE: Vitronectin previously has been extracted from human spermatozoa and messenger RNA (mRNA) encoding vitronectin localized by reverse transcriptase in situ polymerase chain reaction (PCR) to spermatocytes of human testis. In the present experiments, we have established ranges for the content of vitronectin in living human spermatozoa and vitronectin concentration within seminal fluid of human ejaculates. DESIGN: Seminal fluid was obtained by centrifugation and motile sperm selected by swim-up from men with normal and abnormal ejaculates, according to World Health Organization criteria, for vitronectin determinations. SETTING: Academic research environment. MAIN OUTCOME MEASURE(S): Seminal fluid vitronectin concentrations were measured by ELISA and sperm vitronectin content by polyacrylamide gel electrophoresis and semiquantitative Western blots. RESULT(S): Vitronectin seminal fluid concentration was 1.35 +/- 1.0 mg/mL (mean +/- SD) for normospermic samples (n = 26) and 0.78 +/- 0.4 mg/mL for azoospermic specimens (n = 6). Vitronectin sperm content ranged from 1 to 15 ng/10(6) motile cells (n = 20). Both high- and low-molecular-weight material was observed. Sperm content of vitronectin did not vary with sperm morphology. CONCLUSION(S): These results suggest that spermatozoa represent a major source of seminal fluid vitronectin, but that a secondary source exists, perhaps through transudation from serum.

Detection using antisperm monoclonal antibodies of shared epitopes expressed by human spermatozoa and oocytes.

OBJECTIVE: To determine whether human spermatozoa and oocytes share common antigenic epitopes, supporting the hypothesis that their cross-linking by antisperm antibodies present in the clinical sera of infertile couples could promote sperm adhesion to the oolemma. DESIGN: Human and hamster eggs were studied for the presence of antigens recognized by a panel of World Health Organization Task Force monoclonal antibodies (mAbs) originally raised against human spermatozoa. A new technique was devised, using frozen sections of paraformaldehyde-fixed individual human and hamster eggs, to screen rapidly antisperm mAbs for egg reactivity. Living zona-free human and hamster eggs then were exposed to Covaspheres (Duke Scientific, Palo Alto, CA) coupled with these mAbs to document the presence of reactive epitopes on the oolemma. SETTING: Academic research environment. MAIN OUTCOME MEASURE(S): Indirect immunofluorescence and Covasphere rosetting. RESULT(S): Eleven of 37 antisperm mAbs tested reacted with fixed hamster eggs and 10 reacted with human eggs. Five of 6 mAbs reactive with both fixed eggs also reacted with the oolemma of living, zona-free eggs. CONCLUSION(S): Common antigenic epitopes, some of which are shared with somatic tissues, exist on the oolemma of human eggs and on the plasma membrane of human spermatozoa.

Is vitronectin the velcro that binds the gametes together?

Evidence has been presented that the adhesion of human spermatozoa to the oolemma is mediated by integrins recognizing the Arg-Gly-Asp sequence (RGD). Fibronectin and vitronectin, glycoproteins that contain functional RGD sequences, are both present on human spermatozoa, and integrins that recognize these ligands have been detected on spermatozoa and eggs. In this work, we studied the effects of oligopeptides specifically designed to block fibronectin or vitronectin receptors on the interaction of human spermatozoa with zona-free hamster oocytes. GRGDdSP, a peptide blocking cell attachment to fibronectin, was without effect, while GdRGDSP, which blocks both fibronectin and vitronectin receptors, significantly inhibited the binding of human spermatozoa to the oolemma of zona-free hamster eggs, in a concentration-dependent manner, over a range 1-100 microM. As these experiments suggested that a vitronectin receptor plays a role in sperm-oolemmal adhesion, we performed a series of experiments studying the effects of exogenous vitronectin, when added to spermatozoa and oocytes, on gamete interactions. Sperm-oolemmal adherence, as well as sperm aggregation, was promoted by vitronectin, over range of 2.2 nM to 1 microM, but only in the presence of calcium ions. We propose that vitronectin released during the sperm acrosome reaction is recognized by both gametes and plays a role in their adhesion.

P-selectin is expressed on the oolemma of human and hamster oocytes following sperm adhesion and is also detected on the equatorial region of acrosome-reacted human spermatozoa.

Selectins are a family of adhesive molecules, involved in the interactions between leukocytes and endothelium and in platelet adhesion. P-selectin, one of the members of this family, is stored in alpha-granules and dense granules of platelets as well as in Weibel-Palade bodies of endothelial cells, and it is rapidly redistributed to the cell surface after activation. It recognizes carbohydrate structures as ligands, in particular sialyl-Lewis(x), which is part of the CD15 antigen. In this work we studied P-selectin expression on gametes. While zona-free human and hamster oocytes did not react with a monoclonal antibody directed against P-selectin, oocytes from both species displayed a reactivity with this antibody following their contact with human spermatozoa, as demonstrated both by covasphere binding and indirect immunofluorescence. Artificial activation of zona-intact human oocytes by means of the calcium lonophore A23187 induced the expression on the oolemma of a moiety reacting with anti-P-selectin antibody as well. P-selectin also appeared to be expressed on the sperm surface following the acrosome reaction, as demonstrated by a flow cytometric study of reactivity of spermatozoa with the anti-P-selectin antibody, using the expression of CD46 as a marker of the acrosome reaction. The localization of the P-selectin moiety on the equatorial region of the plasma membrane of acrosome reacted spermatozoa was confirmed by transmission electron microscopy using immunogold labelling. We suggest that P-selectin might be involved in gamete interactions.

The expression of alpha v, alpha 5, beta 1, and beta 3 integrin chains on ejaculated human spermatozoa varies with their functional state.

Evidence has been presented suggesting the involvement of integrins and their ligands in mammalian fertilization. In this study we asked whether the alpha 5, alpha v, beta 1 and beta 3 integrin chains, which form receptors for fibronectin and vitronectin, are present on human spermatozoa. Fresh ejaculate spermatozoa and capacitated spermatozoa, before and after a calcium ionophore (A23187)-induced acrosome reaction, were either fixed and their reaction with anti-integrin monoclonal antibodies detected by immunoperoxidase staining or studied without fixation, using cytofluorimetric scanning. Expression of specific integrin chains varied with the functional state of spermatozoa. The alpha 5 chain was not detected on fresh living spermatozoa, but was present on capacitated spermatozoa, whether fixed or living. The pattern of beta 1 expression on living spermatozoa paralleled that of alpha 5. No further increase in the expression of either alpha 5 or beta 1 was observed following an ionophore-promoted acrosome reaction. In contrast, alpha v was detected on neither fresh, living ejaculate spermatozoa, nor following capacitation (< 10% reactive). The percentage of alpha v positive cells increased substantially following ionophore exposure. Expression of beta 3 was similar to alpha v, and the percentage of cells displaying beta 3 correlated with the proportion of spermatozoa that had undergone an acrosome reaction, following ionophore exposure. These results indicate that the expression of integrins on spermatozoa is dynamic, varying with their functional state and that integrin receptors for fibronectin (alpha 5 beta 1) become apparent on the spermatozoan surface during capacitation and vitronectin (alpha v beta 3) following the acrosome reaction.

Echistatin, a disintegrin, inhibits sperm-oolemmal adhesion but not oocyte penetration.

OBJECTIVE: To study the effects of echistatin, a disintegrin known to block the binding of fibronectin (FN) and vitronectin to their respective integrin receptors, alpha 5 beta 1 and alpha v beta 3, on the adhesion of human spermatozoa to the oolemma of zona-free hamster eggs and their subsequent penetration. DESIGN: Motile capacitated human spermatozoa and zona-free hamster eggs were coincubated in the presence of echistatin or in its absence and observed at short serial intervals. Whole mounts of these eggs, washed out of sperm suspension and stained with acridine orange, were scored for numbers of oolemmal adherent and penetrating sperm. SETTING: University Hospital laboratories. PATIENTS: Known fertile semen donors. MAIN OUTCOME MEASURES: Numbers of spermatozoa adherent to the oolemma and those penetrating the oocyte. RESULTS: Sperm adherence to the oolemma was reduced significantly at micromolar concentrations of echistatin, in a concentration-dependent manner. In contrast, echistatin did not inhibit the penetration of oocytes by sperm that had become adherent to the oolemma despite the presence of echistatin. CONCLUSION: We propose that two processes occur in the binding of sperm to the oolemma, one that is echistatin sensitive and possibly involving the integrin receptors that recognize FN and vitronectin, and a second process, resistant to echistatin, that leads to gamete membrane fusion.

PCR-amplified vitronectin mRNA localizes in situ to spermatocytes and round spermatids in the human testis.

Vitronectin is an adhesion protein present within the acrosomal cap region of human spermatozoa and is liberated during the acrosome reaction. The purpose of this study was to determine if vitronectin mRNA was synthesized in the male genital tract using the reverse transcriptase in-situ polymerase chain reaction (PCR) technique. Twelve genital tract tissues, which included six testes, one showing Sertoli cells only and one from a 3 year old boy, as well as sections from the prostate, seminal vesicles, and epididymis, were analysed for vitronectin transcripts. PCR-amplified vitronectin cDNA was detected in the seminiferous tubules of the four adult testes that showed normal spermatogenesis and localized to the spermatocytes and round spermatids. PCR-amplified vitronectin cDNA was not detected in the tissues of the prostate, epididymis, and seminal vesicles from the men whose testes did contain the message, nor in the testes with Sertoli cells only or that of the prepubertal boy. It is concluded that, in the male genital tract, vitronectin is transcribed exclusively in the germ cells at the spermatocyte and round spermatid stages. This demonstrates that the translated protein present in the spermatozoon is being produced in situ. Further study is needed to determine the role of this protein in the dynamics of sperm-oocyte interaction.

Vitronectin is an intrinsic protein of human spermatozoa released during the acrosome reaction.

Evidence has been presented that oolemmal integrins and their ligands on spermatozoa may play a role in gamete interactions leading to fertilization. We previously demonstrated that vitronectin (Vn) could be extracted from fresh human spermatozoa and detected in Western blots, and Vn was observed on the surface of living, capacitated sperm by indirect immunofluorescence. In the present experiments, messenger RNA encoding Vn was detected in human testis poly (A+) RNA using Northern analysis, and Vn was localized within the acrosomal region of ejaculated sperm by immunoperoxidase and immunofluorescence staining. During the acrosome reaction, induced in capacitated spermatozoa by lonomycin, Vn was released into the medium in a calcium-dependent manner. Vn appears to be a specific product of intratesticular spermatozoa that is secreted during the acrosome reaction. These findings suggest that Vn is positioned to play a strategic role in gamete interactions leading to fertilization.

Mammalian oocytes exhibit specific recognition of the RGD (Arg-Gly-Asp) tripeptide and express oolemmal integrins.

Integrins are a family of cell adhesion receptors involved in many cell-cell and cell-matrix interactions. Some of these heterodimeric receptors, such as alpha 5 beta 1 and alpha v beta 1, specifically recognize the amino acid sequence Arg-Gly-Asp (RGD) within their ligands. The RGD sequence is found in fibronectin, vitronectin, and other extracellular matrix proteins. Our results demonstrate that the oolemmas of eggs from human and several other mammalian species contain receptors capable of binding to RGD ligands, and that integrin subunits are expressed by oocytes. Four distinct techniques were utilized to identify the presence of functional integrins on mammalian eggs. RGD-binding receptors were detected on the surfaces of zona-free eggs from all species tested. Covaspheres coated with PepTite-2000, which contains RGD, bound to the eggs and formed rosettes. Rosetting was competitively inhibited by PepTite-2000 and by GRGDTP, a soluble RGD peptide, but not by RGES. An ELISA using polyclonal antibodies directed against the cytoplasmic tails of the integrin subunits identified the integrin subunits alpha 5, beta 1, and alpha v, but not beta 3, in detergent extracts of Syrian hamster eggs. A dot blot confirmed the presence of alpha v in hamster egg lysates. Finally, the integrin subunits alpha 2, alpha 5, alpha 6, but not alpha 4, were detected on the surfaces of zona-free eggs from human and Syrian hamster. Immunobeads coated with monoclonal antibodies specific for alpha 2, alpha 5, and alpha 6 bound to the eggs and formed rosettes.(ABSTRACT TRUNCATED AT 250 WORDS)

Progesterone-evoked increases in sperm [Ca2+]i correlate with the egg penetrating ability of sperm from fertile but not infertile men.

OBJECTIVES: To investigate the relationship between sperm capacitation and intracellular calcium ([Ca2+]i) and to correlate these findings with routine semen parameters and sperm fertilizing ability. DESIGN: Baseline and P-evoked increases in [Ca2+]i of fresh versus capacitated human sperm were measured for known fertile donors and infertile men and compared with the results of semen analysis and in vitro penetration of zona-free hamster eggs. SETTING: Andrology laboratory in a university hospital. PATIENTS: Infertile men undergoing semen analysis. INTERVENTIONS: Capacitation of spermatozoa and exposure of sperm to P (1 microgram/mL). MAIN OUTCOME MEASURES: [Ca2+]i as measured using fura-2, percent zone-free hamster eggs penetrated, and number of penetrating sperm per egg. RESULTS: Steady state [Ca2+]i increased from 74 +/- 32 nM to 166 +/- 97 nM after capacitation, as did P-evoked peak and plateau [Ca2+]i. Deletion of calcium from the assay buffer with ethylene-bis (oxy-ethylenenitriolo) tetraacetic acid abrogated the P-evoked increments. RU486, a P receptor antagonist; reduced the P-evoked response in a dose-dependent manner. Progesterone-evoked calcium responses of sperm varied between different ejaculates of the same fertile donor and correlated with their egg penetrating ability. Sperm from infertile men with abnormal morphology exhibited lower egg penetrating ability and lower mean peak P-evoked [Ca2+]i than morphologically normal sperm. However, free intracellular calcium parameters correlated only weakly with penetrating ability for individual infertile men. CONCLUSION: Progesterone-evoked increases in [Ca2+]i in motile capacitated spermatozoa cannot be used to discriminate between dysfunctional spermatozoa and those capable of penetrating eggs.

Correlation between puberty and the development of autoimmunity to spermatozoa in men with cystic fibrosis.

OBJECTIVE: To test the hypothesis that puberty is a necessary factor in the pathogenesis of autoimmunity to sperm in men with cystic fibrosis (CF), we studied prepubertal and postpubertal males with CF versus an age-matched group of males with type 1 diabetes as controls. DESIGN: Sera from CF and diabetic males treated at University Hospital, State University of New York, Stony Brook, were tested by indirect immunobead binding for antisperm antibodies and by radioimmunoassay for testosterone (T), luteinizing hormone, and follicle-stimulating hormone. The finding of autoantibodies to spermatozoa was correlated with chronological age, as well as with clinical and hormonal pubertal status. RESULTS: Autoimmunity to sperm, as detected by humoral antisperm antibodies, was documented solely in postpubertal males, as judged by hormonal and clinical criteria. Eighty-three percent of sexually mature CF males and 6.3% (1 of 16) diabetic males exhibited autoantibodies to sperm. These antibodies were only detected when serum T levels were > 8.7 nmol/L (250 ng/dL). CONCLUSIONS: These results suggest that puberty, and presumably, active spermatogenesis is a requirement for the development of autoimmunity to sperm in men with CF.

Sperm surface proteins after capacitation. Expression of vitronectin on the spermatozoan head and laminin on the sperm tail.

Several integrins recognize as ligands proteins containing the Arg-Gly-Asp (RGD) sequence, such as fibronectin, vitronectin, and laminin. It has been previously demonstrated that oligopeptides containing the RGD sequence competitively inhibit both the adhesion of hamster and human sperm to zona-free hamster eggs and their subsequent penetration. In addition, the appearance of fibronectin on the surface of living human spermatozoa after capacitation has been demonstrated. In this work, it is shown that spermatozoa incubated overnight under capacitating conditions, but not fresh spermatozoa, also display the RGD-containing proteins vitronectin and laminin. Whereas the expression of fibronectin does not appear to be localized to any specific region of the sperm surface, laminin is present solely on the sperm tail, and vitronectin was detected mostly as an equatorial band on the sperm head. The percent of capacitated spermatozoa within each ejaculate reacting with antivitronectin antibodies (51% to 94%) was similar to that observed with antifibronectin antibodies (72% to 100%) in a series of fertile donors, and in a series of infertile men (7% to 98% for vitronectin versus 5% to 100% for fibronectin). In contrast, the percent of spermatozoa displaying laminin was lower, ranging from 2% to 42% for fertile donors and from 5% to 34% for infertile donors, and was unrelated to the expression of fibronectin or vitronectin. The time of appearance of both fibronectin and vitronectin when spermatozoa were incubated under capacitating conditions varied for different sperm donors, suggesting a difference in the process of their expression between different men. The specificity of antivitronectin antibody binding to human spermatozoa was demonstrated by competitive inhibition with purified human vitronectin. That there was no immunologic reaction between the antivitronectin antibodies used and fibronectin was demonstrated both by the failure of free fibronectin to inhibit antivitronectin antibody binding to spermatozoa, and by Dot blot analysis. A partial cross-reaction of the polyclonal antivitronectin antibody with fibronectin was shown by Western blot analysis, but this phenomenon was not present when the monoclonal antivitronectin antibody was used. In addition, both fibronectin and vitronectin could be extracted from capacitated spermatozoa solubilized in Chaps buffer, as shown by Dot blot and Western blot analysis. These observations suggest that vitronectin and fibronectin expressed on the surface of capacitated human spermatozoa could act as a ligand for specific receptors on the egg, and play a role in sperm-oolemmal adhesion.