1 Institute of Maternal and Child Research (IDIMI), School Of Medicine, University Of Chile, `San Borja Arriaran' Clinical Hospital, and 2 Department Of Obstetrics and Gynecology, School of Medicine, University of Chile, Santiago, Chile
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Abstract |
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Key words: endometrial receptivity/endometrial stromal epithelial cells/flow cytometry/integrins/unexplained infertility
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Introduction |
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The 1,
4,
V and ß3 integrin molecules are cyclically expressed in the endometrium during the menstrual cycle (Lessey et al., 1992
; Tabibzadeh, 1992
). These molecules have been proposed as in-situ biochemical markers of endometrial receptivity during the implantation window (Lessey et al., 1994
, 1995
, 1996a
). The regulation of the expression of these markers and their role in the molecular mechanism of human implantation are virtually unknown (Creus et al., 1998
; Marions et al., 1998
; Simón et al., 1998
; Sulz et al., 1998
). Inside endometrial tissue, the actions of ovarian steroids, modulated by a variety of growth factors and cytokines, lead the expression of the cycle-dependent integrins (Grosskinsky et al., 1996
; Lessey et al., 1996b
; Simón et al., 1996
).
In vitro, the Ishikawa cells do express most of the normal endometrial epithelial integrins and are a useful model in studying steroid-mediated events in human endometrial epithelium (Lessey et al., 1996c; Somkuti et al., 1997
). The same steroidogenic controlling signals could up-regulate the simultaneous expression of the ß3 integrin in the human Fallopian tube epithelium and in the endometrium (Sulz et al., 1998
). In addition, the up-regulation of the ß3 expression by endometrial epithelial cells co-cultured with competent human embryos could be mediated by the interleukin 1ß (IL-1ß) system, which is present in both the embryo and the endometrium (Simón et al., 1997
).
In vivo, the expression of 4 and ß3 integrins has been positively correlated with endometrial development and could be down-regulated by antiprogestin treatment, while the expression of the
Vß3 integrin dimer was found to be independent of these factors and could be triggered by cytokines (Marions et al., 1998
). However, other investigators reported that
1,
4 and ß3 integrins were not dependent on endometrial maturation in infertile women. The expression of
Vß3 was closely related to the endometrial dating but its relationship to fertility was not definitely established (Creus et al., 1998
). Contradictory data have also been published for the expression of the
Vß3 integrin in the endometrium of women with and without endometriosis (Lessey and Young, 1997
; Creus et al., 1998
; Hii and Rogers, 1998
; Lessey and Castelbaum, 1998
).
The present study describes the flow cytometric assessment of the integrins within the endometrium, including the concentrations of 1,
4,
V and ß3 throughout the menstrual cycle in fertile women and patients with unexplained infertility. Here we describe for the first time the quantitative expression of endometrial stromal and epithelial integrins in both groups of women throughout the menstrual cycle.
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Materials and methods |
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Homogeneous dispersions of endometrial cells
All chemicals and culture media were obtained from Sigma Chemical Co. (St Louis, MO, USA) and from Worthington Biochemical Corporation, NJ, USA. Endometrial biopsies were digested in a two-step design to prepare cellular dispersions for flow cytometry. The procedure to isolate endometrial stromal cells (ESC) utilized 100150 mg of wet endometrial tissue that was treated with collagenase I (0.1%)deoxyribonuclease I (DNase, 0.005%) dissolved in Dulbecco's modified Eagle's medium (DMEM) during 90 min at 37°C (Satyaswaroop et al., 1979; Simón et al., 1993
). Following sedimentation of glandular structures and separation of ESC, the glands were purified of ESC and macrophage contaminants by incubation at 37°C in a Falcon flask. Thus, a second enzymatic digestion was performed to isolate the individual endometrial epithelial cells (EEC) from the glands for flow cytometric measurements. Briefly, the glands were digested with trypsin (0.25%)EDTA (0.03%)DNase (0.1%) for 10 min at 37°C. Subsequently EEC were washed with DMEMfetal bovine serum (FBS, 2%) and filtered out through a 37 µm mesh sieve which retained undigested tissue. Stromal and epithelial cell dispersions were counted in a haemocytometer and cell viability was assessed using the Trypan Blue exclusion method. Means of viability for ESC and EEC were 85 and 80% respectively. Polyclonal antibodies to vimentin (Vm) and cytokeratin (Ck) were used to examine the homogeneity of ESC (Vm+) and EEC (Ck+) in cell smears of cellular dispersions. The maximum cross-contamination found between the endometrial cells (ESCEEC) was <1%. Preliminary experiments were conducted to test whether collagenase or trypsin treatment provoked an important loss of membrane-bound integrins in EEC and ESC. For these purposes, the digestion conditions were mimicked on ESC and EEC cultured in vitro. Following the initial separation, the endometrial cells were cultured for 4 days in a conditioned medium (Simón et al., 1993
). Therefore, cells were detached with trypsin (0.025 %)-EDTA (1 mM) for 5 min at room temperature. After washing, the cell suspensions were incubated with enzymatic solutions as described above. Integrins were determined by flow cytometry. The control experiment was represented by the suspensions of endometrial cells detached in routine conditions without further enzymatic treatment. No differences of integrin concentrations were found between controls and protease-treated cells.
Flow cytometric measurements of endometrial integrins
Specific monoclonal antibodies were used to determine the expression of integrins in ESC and EEC by flow cytometry: anti 1 (anti CD49a, clone TS 2/7), anti
1 (anti CD49d, clone B5 G10) and anti ß3 (anti CD61, clone SS A6) were kindly donated by Dr B.A.Lessey, University of North Carolina, NC, USA (for references see Lessey et al., 1992). Anti
V (anti CD51, clone VNR 147) was purchased from GIBCO BRL Products, Gaithersburg, MD, USA. Anti-human leukocitary antigen-I (anti HLA-I, clone w6/32), anti CD45-phycoeritryn (PE) conjugated and fluorescein isothiocyanate (FITC)-conjugated rabbit-antimouse IgG [F(ab')2] were obtained from Dako Corporation, Carpinteria, CA, USA. All the following incubation steps were performed in an ice-bath during 30 min. A total of 2x105 to 5x105 cells (ESC or EEC) dispersed in 100 µl of phosphate-buffered saline (PBS)2% FBS were incubated with the primary antibodies directed towards integrins. After washing with 500 µl of PBS-FBS, the cells were treated with the FITC-conjugate. Subsequently, the cells were incubated with the anti-CD45-PE to eliminate the leukocytes from the cytometric analysis. Red blood cells were eliminated by incubation with a lysing solution (Lysing Solution, Becton Dickinson, San Diego, CA, USA) for 5 min. A negative control with unspecific immunoglobulin G (IgG)-isotype-matched monoclonal antibody for each label and a positive control with anti-human leukocyte antigen (HLA were introduced in each determination. Flow cytometric measurements were taken in a FASCcan Flow Cytometer (Becton Dickinson) using the CONSORT 32 II Version 2.0 software for data acquisition and analysis. Concentrations of integrins were expressed in relative fluorescence units (RFU). One RFU was defined as the ratio (F/Fo) of the mean of fluorescence (F) obtained from the labelled integrins and the background of the mean of fluorescence of the negative control (Fo).
Immunohistochemistry
Acetone-fixed cryostat sections from endometrial biopsies were immunostained for integrin detection. Samples were incubated for 1 h at room temperature with anti-integrin monoclonal antibodies (described above), and stained with streptavidinbiotinhorse radish peroxidase system (Dako LSAB kit system). Negative controls were incubated with irrelevant mouse monoclonal antibodies instead of primary antibodies. Cryostat sections stained by amine-ethyl-carbazol (AEC) enzymatic product and counter-stained with haematoxylin were evaluated on a Nikon microscope.
Statistical analysis
The comparison of integrin concentrations in the endometria of fertile and infertile patients throughout the menstrual cycle was assessed by the non-parametric MannWhitney test. All data are presented as mean ±SEM. Statistical significance was considered to be P < 0.05.
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Results |
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Figure 1A shows the concentration of stromal integrins in fertile women. The stromal
1 integrin subunit was the highest expressed throughout the menstrual cycle (P < 0.05). The maximum concentration of
1 integrin was during the mid-secretory phase (610 days after ovulation), reaching a plateau in the late secretory phase (1214 days after ovulation). Among the stromal integrin subunits,
1 exhibited the highest variability of concentration.
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The 4-ESC exhibited a different expression pattern as it was higher in the early secretory phase as compared to the mid-secretory phase (P < 0.05; Figure 1A
).
Profile of endometrial integrin subunits in EEC of fertile women
The number of fertile endometria evaluated in each phase was as follows: late proliferative (n = 5; except 1 and ß3 which were n = 3 and n = 4 respectively); early secretory (n = 9); mid-secretory phase or implantation window (n = 9); and late secretory phase (n = 4).
Figure 1B shows the concentrations of the integrin subunits in the epithelium of fertile women throughout the menstrual cycle. The epithelial
1 integrin was the highest expressed. A significant increase was observed in
1-EEC during the late secretory phase (P < 0.05; see Figure 1B
). This finding could be related to the over-expression of
1 by epithelial glands found in the inner mass of the functionalis endometrium.
The ß3- and V-EEC subunits were expressed either during the late proliferative or the secretory phase (see Figure 1B
). The concentrations were similar for
V and ß3 until the early secretory phase. Epithelial
V and ß3 (P < 0.05) increased significantly at the time of the implantation window (6 to 10 days after ovulation; P < 0.05). However, from the implantation window to the late secretory phase, the ß3-EEC concentrations were higher than
V-EEC (P < 0.05).
The 4-EEC was poorly detected during the proliferative phase. Slightly higher concentrations were noted after ovulation but were almost undetectable at the time of the implantation window (P < 0.05; see Figure 1B
).
Overall, the pattern of integrin expression at the time of the implantation window in fertile women was characterized by an over-expression of epithelial 1 and ß3, a slight increase in
V expression and an under-expression of
4 integrin subunits.
Profile of endometrial integrin subunits in ESC of women with unexplained infertility
The number of infertile women evaluated in each phase of the menstrual cycle was as follows: late proliferative (n = 4); early secretory (n = 4); mid-secretory or implantation window (n = 13); and late secretory phase (n = 5).
Figure 2 shows the comparison between the concentrations of the stromal integrin subunits in infertile and fertile women throughout the menstrual cycle. The stromal
1 integrin was detected in the endometria of infertile women throughout the menstrual cycle (see Figure 2A
). A trend towards a slightly lower concentration of
1-ESC was observed in infertile women during the late proliferative and mid-secretory phases. However,
1-ESC concentrations in infertile women were significantly lower (P < 0.05) during the late secretory phase (Figure 2A
).
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The V-ESC (Figure 2C
) and ß3-ESC (Figure 2D
) showed expression patterns similar to those determined for fertile women.
The immunohistochemical staining of stromal integrins was similar for fertile and infertile women. A weak to moderate signal was found for 4-ESC and was consistent with the flow cytometric measurements. Interestingly, the higher sensitivity of flow cytometric analysis led to the discovery of significant differences in the
4-ESC expression between fertile and infertile women during the peri-ovulatory days. Stromal
1 and ß3 in fertile and infertile women showed a similar immunohistochemical staining intensity, contrary to the findings in the immunohistochemical evaluation of ß3-EEC that showed evident differences between stained fertile and non-stained infertile endometria (see Figure 3
).
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Figure 4 depicts the pattern of the concentrations of epithelial integrin subunits in infertile and fertile women throughout the menstrual cycle. The concentrations of
1-,
4- and
V-EEC subunits (Figure 4
, panels A, B and C respectively) in infertile patients were not significantly different from those calculated in EEC of fertile women from the proliferative to the mid-secretory phases. However, a trend was found in infertile women towards lower
1-EEC concentrations in post-ovulatory days. The concentrations of epithelial
1 were significantly lower in infertile women in the late secretory phase (P < 0.05; see Figure 4A
).
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Slightly lower V-EEC concentrations were observed during the peri-ovulatory days in infertile patients as compared to fertile women (see Figure 4C
). Interestingly, similar concentrations for the epithelial
V were observed in both groups of women at the time of the implantation window. However, during the late secretory phase, the
V-EEC in infertile patients has a significantly lower expression (P < 0.05).
It is interesting to note that the main differences between infertile and fertile women were observed in regard to the epithelial-ß3 subunit. During the late proliferative phase, the concentration of ß3-EEC in infertile women was slightly higher than in fertile women. On the contrary, during the secretory phase the concentrations of the epithelial ß3 were always lower in infertile women than in fertile women. Significantly lower concentrations of the ß3-EEC (P < 0.05) were observed in infertile women at the time of the implantation window and in the late secretory phase (Figure 4D). However, at the time of the implantation window, two infertile patients (2 of 13) expressed ß3 concentrations similar to those of fertile women.
The principal differences in the expression of epithelial integrin subunits between infertile and fertile women were observed during the implantation window for the ß3 and during the late secretory phase for the 1,
V and ß3.
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Discussion |
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Most of the data for the pattern of integrin expression in endometria have been determined by immunohistochemical studies, and integrin concentrations have been assessed semi-quantitatively according to the degree of positive staining or the HSCORE approach (Lessey et al., 1992, 1994
; Tabibzadeh, 1992
). Immunochemistry is an essential technique in determining the tissue and cellular localization of integrins in the endometrium (Klentzeris et al., 1993
; Lessey et al., 1994
, 1995
). However, the expression of cellular antigens in whole organs and tissue could be quantitatively examined by flow cytometry (Serna et al., 1998
). Flow cytometry has been used to assess integrin expression in endometrial stromal cells in vitro (Grosskinsky et al., 1996
), Ishikawa cells (Castelbaum et al., 1997
) and to evaluate the expression of the ß3-integrin subunit in endometrial epithelial cells co-cultured with human blastocyst (Simón et al., 1997
).
In the present investigation, flow cytometry was used to determine the concentration of integrin molecules in homogeneous cellular dispersions isolated directly from endometrial biopsies. The main differences found in the expression of the 1,
4,
V and ß3 integrin subunits in the endometria of fertile and infertile women throughout the menstrual cycle are schematically represented in Figure 5
. The patients have a wide range of age, but eligible subjects were homogeneous in both groups. Consequently, the variations in integrin expression observed in these groups should be related to infertility and not to age difference.
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The epithelial 4-integrin subunit (
4ß1, a fibronectin receptor) had a low expression in fertile and infertile women throughout the menstrual cycle. Flow cytometric analysis detected a tendency for the expression of the epithelial
4 to increase in infertile women during the implantation window (see Figure 5
). A similar increase in the epithelial glandular
4ß1 expression has been observed in women treated with oral contraceptives (Somkuti et al., 1996
).
A moderate expression of the stromal 4 integrin in fertile women during the different phases of the menstrual cycle has been described (Tabibzadeh, 1992
; Lessey et al., 1994
; Marions et al., 1998
). The flow cytometric measurements in our study for the stromal
4 integrin demonstrated the under-expression of this molecule in infertile patients during the late proliferative and early secretory phases. Although the immunohistochemical staining of this integrin was moderate, it related closely to the flow cytometry determinations (data not shown). These observations suggest changes in the pattern of expression of this adhesion molecule in the stroma of women with unexplained infertility.
The expression of the V integrin subunit, a component of the vitronectin receptor (
Vß3), was different from the expression of its molecular partner, the ß3 integrin subunit. The
V integrin was under-expressed only in the endometrial epithelium of infertile women during the late secretory phase. This integrin could be constitutively expressed in the endometrial epithelium, as was found in the Ishikawa cells (Widra et al., 1997
). In addition to ß3, the
V subunit could also be the molecular partner for diverse ß subunits, i.e. ß1 and ß5ß8 (Lessey and Young, 1997
). An investigation is pending of the implications of the under-expression of the
V and
1 endometrial epithelial integrins in infertile women during the late secretory phase (see Figure 5
).
The epithelial ß3 integrin subunit has been proposed as the more reliable biochemical marker for failure in endometrial receptivity (Lessey et al., 1995). Oral contraceptive use has been associated with a decrease in glandular
Vß3 expression (Somkuti et al., 1996
). Nevertheless, the expression of the glandular
Vß3 did not vary throughout the menstrual cycle in fertile women or in patients with endometriosis (Creus et al., 1998
; Hii and Rogers, 1998
). The expression of the ß3 integrin subunit was not affected in normal and out-phase endometria of infertile women, contrary to the
Vß3 integrin dimer (Creus et al., 1998
). The epithelial ß3 integrin was under-expressed in fertile women treated with antiprogestin, but expression of the epithelial
vß3 molecule was constant (Marions et al., 1998
). Diverse methodologies or the specificity of antibodies used might be responsible for these differences (Lessey and Castelbaum, 1998
).
Using flow cytometry, it has been confirmed that the epithelial ß3 subunit was significantly higher in fertile women at the time of the implantation window (see Figure 5). Infertile women expressed lower epithelial ß3 from the mid-secretory phase. Defects in epithelial ß3 expression have been postulated as a cause of infertility (Lessey et al., 1995
).
In conclusion, temporal and spatial differences of expression of the cycle-dependent integrins were found between fertile and infertile endometria. We underline the importance of the quantitative measurement of the endometrial integrins, particularly the epithelial ß3 subunit, during the implantation window. In addition, the lower concentration of the stromal 1ß1 integrin detected in women with unexplained infertility suggests that this adhesion molecule may be involved in the interaction between stromal and trophoblast cells. The pattern of integrin concentrations in the endometrium, quantified by flow cytometry, could contribute to infertility or fertility regulation assessment.
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Acknowledgments |
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Notes |
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References |
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Bilalis, D.A., Klentzeris, L.D. and Fleming, S. (1996) Immunohistochemical localization of extra-cellular matrix proteins in luteal phase endometrium of fertile and infertile patients. Hum. Reprod., 11, 27132718.[Abstract]
Castelbaum, A.J., Ying, L., Somkuti, S.G. et al. (1997) Characterization of the integrin expression in a well-differentiated endometrial adenocarcinoma cell line (Ishikawa). J. Clin. Endocrinol. Metab., 82, 136142.
Coutifaris, C., Omigbodum, A. and Coukos, G. (1998) Integrins, endometrial maturation and human embryo implantation. Semin. Reprod. Endocrinol., 16, 219229.[ISI][Medline]
Creus, M., Balasch, J., Ordi, J. et al. (1998) Integrin expression in normal and out-phase endometria. Hum. Reprod., 13, 34603468.[Abstract]
Endometriosis (1993) ACOG. Tech. Bull., 184, 16.
Fay, T.N. and Grudzinskas, J.G. (1991) Human endometrial peptides: a review of their potential role in implantation and placentation. Hum. Reprod., 6, 13111326.[Abstract]
Grosskinsky, C.M., Yowell, C.W., Sun, J.H. et al. (1996) Modulation of integrin expression in endometrial stromal cells in vitro. J. Clin. Endocrinol. Metab., 81, 26472654.[Abstract]
Herman, A. and Lewin, A. (1996) The role of ultrasonography in the evaluation of endometrial receptivity following assisted reproductive treatments: a critical review. Hum. Reprod. Update, 2, 323335.
Hii, LL.P. and Rogers, P.A.W. (1998) Endometrial vascular and glandular expression of vß3 in women with and without endometriosis. Hum. Reprod., 13, 10301035.[Abstract]
Hynes, R.O. (1992) Integrins: versatility, modulation, and signaling in cell adhesion. Cell, 69, 1125.[ISI][Medline]
Kim, H.H. and Hornstein, M.D. (1997) Unexplained infertility: Defining the problem and understanding study design. In Diamond, M.P. and DeCherney, A.H. (eds), Infertility and Reproductive Medicine. Clinics of North America, 8, 487500, W.B.Saunders Company.
Klentzeris, L.D., Bulmer, J.N., Trejdosiewicz, L.K. et al. (1993) Beta-1 integrin cell adhesion molecules in the endometrium of fertile and infertile women. Hum. Reprod., 8, 12231230.[Abstract]
Lanteri, E., Pistritto, M., Bartoloni, G. et al. (1998) Expression of 6 and ß4 integrin subunits on human endometrium throughout the menstrual cycle and during early pregnancy. Fertil. Steril., 69, 3740.[ISI][Medline]
Lessey, B.A. and Young, S.L. (1997) Integrins and other cell adhesion molecules in endometrium and endometriosis. Semin. Reprod. Endocrinol., 15, 291299.[Medline]
Lessey, B.A. and Arnold, J.T. (1998) Paracrine signaling in the endometrium: integrins and the establishment of uterine receptivity. J. Reprod. Immunol., 39, 105116.[ISI][Medline]
Lessey, B.A. and Castelbaum, A.J. (1998) Integrins and endometriosis: fact or artefact? Hum. Reprod., 13, 35783580.[ISI][Medline]
Lessey, B.A., Damjanovich, L., Coutifaris, C. et al. (1992) Integrin adhesion molecules in the human endometrium. Correlation with the normal and abnormal menstrual cycle. J. Clin. Invest., 90, 188195.[ISI][Medline]
Lessey, B.A., Castelbaum, A.J., Buck, C.A. et al. (1994) Further characterization of endometrial integrins during the menstrual cycle and in pregnancy. Fertil. Steril., 62, 497506.[ISI][Medline]
Lessey, B.A., Castelbaum, A.J., Sawin, S.J. and Sun, J. (1995) Integrins as markers of uterine receptivity in women with primary unexplained infertility. Fertil. Steril., 63, 535542.[ISI][Medline]
Lessey, B.A., Ilesanmi, A.O., Lessey, M.A. et al. (1996a) Luminal and glandular endometrial epithelium express integrins differentially throughout the menstrual cycle: implications for implantation, contraception, and infertility. Am. J. Reprod. Immunol., 35, 195204.[ISI][Medline]
Lessey, B.A., Yeh, I., Castelbaum, A.J. et al. (1996b) Endometrial progesterone receptors and markers of uterine receptivity in the implantation window. Fertil. Steril., 65, 477483.[ISI][Medline]
Lessey, B.A., Ilesanmi, A.O., Castelbaum, A.J. et al. (1996c) Characterization of the functional progesterone receptor in an endometrial adenocarcinoma cell line (Ishikawa): progesterone-induced expression of the alpha1 integrin. J. Steroid. Biochem. Mol. Biol., 59, 3139.[ISI][Medline]
Marions, L., Gemzell-Danielsson, K. and Bygdeman, M. (1998) The effect of antiprogestin on integrin expression in human endometrium: an immunohistochemical study. Mol. Hum. Reprod., 4, 491495.[Abstract]
Noyes, R.W., Herting, A.I. and Rock, J. (1950) Dating the endometrial biopsy. Fertil. Steril., 1, 325.[ISI][Medline]
Satyaswaroop, P.G., Bressler, R.S., de la Pena, M.M. and Gurpide, E. (1979) Isolation and culture of human endometrial glands. J. Clin. Endocrinol. Metab., 48, 639641.[Abstract]
Serna, J., Pimentel, B. and de la Rosa, E.J. (1998) Flow cytometric analysis of whole organs and embryos. Curr. Top. Dev. Biol., 36, 211222.[ISI][Medline]
Simón, C., Piquette, G.N., Frances, A. and Polan, M.L. (1993) Localization of interleukin-1 type I receptor and interleukin-1b in human endometrium throughout the menstrual cycle. J. Clin. Endocrinol. Metab., 77, 549555.[Abstract]
Simón, C., Gimeno, M.J., Mercader, A. et al. (1996) Cytokines-adhesion molecules-invasive proteinases. The missing paracrine/autocrine link in embryonic implantation. Mol. Hum. Reprod., 2, 405424.[Abstract]
Simón, C., Gimeno, M.J., Mercader, A. et al. (1997) Embryonic regulation of integrins ß3, 4 and
1 in human endometrial epithelial cells in vitro. J. Clin. Endocrinol. Metab., 82, 26072616.
Simón, C., Moreno, C., Remohi, J. and Pellicer, A. (1998) Molecular interactions between embryo and uterus in the adhesion phase of human implantation. Hum. Reprod., 13 (Suppl. 3), 219232
Somkuti, S.G., Sun, J., Yowell, C.W. et al. (1996) The effect of oral contraceptive pills on markers of endometrial receptivity. Fertil. Steril., 65, 484488.[ISI][Medline]
Somkuti, S.G., Yuan, L., Fritz, M.A. and Lessey, B.A. (1997) Epidermal growth factor and sex steroids dynamically regulate a marker of endometrial receptivity in Ishikawa cells. J. Clin. Endocrinol. Metab., 82, 21922197.
Suekoda, K., Shiokawa, S., Miyazaki, T. et al. (1997) Integrins and reproductive physiology: expression and modulation in fertilization, embryo genesis and implantation. Fertil. Steril., 67, 799811.[ISI][Medline]
Sulz, L., Valenzuela, J.P., Salvatierra, A.M. et al. (1998) The expression of alpha (v) and beta3 integrin subunits in the normal human Fallopian tube epithelium suggests the occurrence of a tubal implantation window. Hum. Reprod., 13, 29162920.
Tabibzadeh, S. (1992) Patterns of expression of integrin molecules in human endometrium throughout the menstrual cycle. Hum. Reprod., 7, 876882.[Abstract]
World Health Organization (1988) Manual Examination of Human Semen. Cambridge University Press, Cambridge.
Widra, E.A., Weeraratna, A., Stepp, M.A. et al. (1997) Modulation of implantation associated integrin expression but not uteroglobin by steroid hormones in an endometrial cell line. Mol. Hum. Reprod., 3, 563568.[Abstract]
Submitted on February 3, 1999; accepted on June 25, 1999.