Download Soluble adhesion molecules in serum throughout the menstrual cycle

Human Reproduction Vol.17, No.9 pp. 2272–2278, 2002
Soluble adhesion molecules in serum throughout the
menstrual cycle
Nigel Bonello1 and Robert J.Norman
Reproductive Medicine Unit, Department of Obstetrics and Gynaecology, The University of Adelaide, The Queen Elizabeth Hospital,
Woodville, SA 5011, Australia
1To
whom correspondence should be addressed. E-mail: [email protected]
BACKGROUND: The female reproductive and immune systems are integrally linked with respect to shared cellular
and molecular mediators. Cell adhesion molecules (CAMs) involved in leukocyte–endothelial interactions, e.g.
intercellular adhesion molecule-1 (ICAM-1), vascular cell adhesion molecule-1 (VCAM-1) and E-selectin, are
regulated by sex steroids when expressed by cultured endothelium, while uterine and ovarian CAM expression
appears to be cyclically or gonadotrophin-regulated. METHODS AND RESULTS: To determine if these effects
translate into changes in soluble CAMs (sICAM-1, sVCAM-1 and sE-selectin) levels in peripheral blood, normally
cycling women received regular venous sampling throughout a complete menstrual cycle. Soluble ICAM-1 levels
were maximal in the early and mid-follicular stages, progressively decreased throughout the remainder of the cycle
and were significantly reduced in the late luteal stage (P < 0.001). Levels of sVCAM-1 fluctuated during the
follicular phase and mid-cycle, but also declined in the late luteal phase (P < 0.01), whereas sE-selectin concentration
did not vary markedly across the menstrual cycle. Plasma hormone and urinary hormone metabolite levels
confirmed precise cycle tracking and revealed an inverse relationship between sICAM-1 and estradiol (r ⍧ –0.38,
P < 0.005). A negative correlation was also apparent between sVCAM-1 and circulating monocyte cell numbers
(r ⍧ –0.47, P < 0.001). CONCLUSIONS: The normal cyclic variation in peripheral sICAM-1 and sVCAM-1 levels
reported here may reflect uterine and/or ovarian tissue remodelling events, and is of particular importance if
soluble CAM levels are utilized as biological markers of certain disease states in women of reproductive age.
Key words: adhesion molecule/menstrual cycle/sE-selectin/sICAM-1/sVCAM-1
Introduction
The scientific literature abounds with evidence linking physiological events of the female reproductive system, including
ovulation, luteal regression, menstruation and parturition, with
inflammatory processes in terms of shared cellular and molecular mediators and the mechanisms involved (Brännström and
Norman, 1993; Bonello et al., 1996; Norman et al., 1997;
Simón et al., 1998). This interaction of the classic reproductive
and immune networks becomes further apparent when specifically considering an initial molecular linkage between the
systems; cell adhesion molecules (CAMs) that participate in
leukocyte–endothelial interactions.
Members of the immunoglobulin superfamily of CAMs,
intercellular and vascular cell adhesion molecule types 1
(ICAM-1 and VCAM-1), as well as the selectin family member,
E-selectin, are cytokine-inducible, or in certain cell types,
constitutively expressed but cytokine-up-regulatable (e.g.
ICAM-1), single chain transmembrane glycoproteins expressed
upon stimulated endothelium, or in the case of ICAM-1 and
VCAM-1, also on haematopoietic and non-haematopoietic
(including epithelial, dendritic and fibroblast) cells of various
lineages (Carlos and Harlan, 1994; Malik and Lo, 1996).
2272
During inflammatory reactions, these membrane-bound CAMs
sequentially interact with their respective leukocyte ligands
(selectins with carbohydrate counter-receptors; proceeded by
ICAM-1 and VCAM-1 with the integrins Mac-1/LFA-1 and
VLA-4 respectively), resulting in the margination and firm
attachment of leukocytes upon endothelium, necessary for
subsequent leukocyte extravasation, chemoattraction and
activation within surrounding inflamed tissue (Butcher, 1991;
Carlos and Harlan, 1994). Such CAMs are also shed from the
cell, most likely through proteolytic cleavage (Budnik et al.,
1996; Meager et al., 1996), and are present as circulating (i.e.
soluble: sICAM-1, sVCAM-1 and sE-selectin) forms in plasma
and other biological fluids, where studies show that they retain
biological activity with regard to ligand binding and activation,
thereby potentially hindering leukocyte–endothelial interactions (Lobb et al., 1991; Rothlein et al., 1991). Soluble
CAM level alterations have also been proposed as indicators
of numerous disease conditions (Gearing and Newman, 1993),
including disorders of the female reproductive system, such
as endometriosis, pre-eclampsia and ovarian hyperstimulation
syndrome (Higgins et al., 1998; Daniel et al., 1999; Abramov
et al., 2001; Vinatier et al., 2001).
© European Society of Human Reproduction and Embryology
Menstrual cyclicity of soluble adhesion molecules
Various studies have revealed the presence of ICAM-1,
VCAM-1 or E-selectin protein and/or mRNA in the human
and rat ovary (Campbell et al., 1995; Bonello and Norman,
1997; Viganò et al., 1997; Suzuki et al., 1998; Ratcliffe et al.,
1999; Olson and Townson, 2000), where peak expression
occurs at recognized periods of maximal leukocyte density,
during ovulation and/or luteal regression (Brännström and
Norman, 1993; Bonello and Norman, 1997; Norman et al.,
1997; Suzuki et al., 1998; Olson and Townson, 2000). Similarly
in the uterus, stage-dependent cell type- and site-specific
protein expression of ICAM-1, VCAM-1 and E-selectin is
observable (Tawia et al., 1993; Tabibzadeh et al., 1994;
Thomson et al., 1999a), with greatest ICAM-1 or E-selectin
expression occurring at times of intensive leukocyte infiltration,
during menstruation or parturition (Poropatich et al., 1987;
Starkey et al., 1991; Tawia et al., 1993; Thomson et al.,
1999a,b). Ovarian and uterine cells also shed sICAM-1, with
some evidence for cycle-stage variations in production. Soluble
ICAM-1 is secreted by cultured luteinized granulosa cells
(Viganò et al., 1997), is detectable with sVCAM-1 in follicular
fluid (Viganò et al., 1998; Benifla et al., 2001) and constitutively produced by cultured endometrial stromal cells, more
so from proliferative rather than secretory phase-retrieved cells
(Somigliana et al., 1996). Furthermore, in-vitro studies show
that estrogen modulates cytokine-induced/hyperinduced cell
expression of ICAM-1, VCAM-1 and E-selectin in a cell typeand cytokine-dependent manner (Cid et al., 1994; CaulinGlaser et al., 1996; Dickens et al., 1999). Hormone replacement
therapy (HRT) investigations and studies with pre-menopausal
participants indicate that relationships may also exist between
peripheral blood steroid hormone concentrations and circulating CAM levels (Jilma et al., 1996; Koh et al., 1997; Cushman
et al., 1999; Daniel et al., 1999; Van Baal et al., 1999; Zanger
et al., 2000).
Considering the cyclic variations in expression of ovarian
and uterine cell-bound leukocyte–endothelial CAMs, regulation
of endothelium-expressed CAMs in culture by steroids which
are cyclic in vivo and the documented menstrual cyclicity of
sICAM-1 in endometrial stromal supernatants, the present
study was undertaken to establish whether sICAM-1,
sVCAM-1 and sE-selectin in serum undergo alterations in
immunodetectable levels across the menstrual cycle. Further
objectives were to determine if any observed menstrual cyclicity in soluble CAM levels may be associated with: (i)
cycling steroid hormones; (i) changes in leukocytic ligandbinding potential as measured by tracking peripheral blood
leukocytes; or (i) cyclically occurring reproductive tissue
degradation and repair events, such as menstruation and/or
ovulation.
Materials and methods
Subjects
Ten nulliparous, healthy volunteers (mean age 27.0 years; range 23–
35) with regular menstrual cycles and no history of reproductive or
immune system-related disorders were recruited to the study. A
detailed questionnaire completed before study commencement showed
that no subjects had taken hormonal contraception for 艌3 months
previously, none was receiving pharmacological treatment and all
were non- or light smokers (⬍5 cigarettes/day). Subjects’ mean body
mass index (BMI) and menstrual cycle length were determined to be
21.4 kg/m2 (range 18.7–29.2) and 27.7 days (range 23–35) respectively, and good general health was confirmed through physical
examination (pulse rate, blood pressure) and laboratory tests (liver
function, urea and electrolytes). This project was approved by the
North-West Adelaide Health Service Ethics of Human Research
Committee and informed consent was obtained from all subjects prior
to study participation.
Sample collection
Subjects received regular morning venous blood sampling throughout
one complete menstrual cycle and collected mid-stream urine in
Urine-Monovet tubes (Sarstedt, Germany) every morning from day 5
until the completion of the study cycle. Blood samples (10–15 ml)
were portioned. One sample was allowed to clot in serum tubes
coated with clot retraction accelerator, centrifuged at 1500 g (4°C)
and stored at –80°C, until multiple-assayed in at least duplicate for
sICAM-1, sVCAM-1 and sE-selectin. The other portion was used to
track cycle stage by assaying plasma collected following centrifugation
(10 min, 4°C, 1500 g), for estradiol, progesterone, LH and FSH.
Cycle stage was further defined by assaying urine samples, maintained
at 4°C, for LH and the principle urinary metabolites of progesterone
and estrogen; pregnanediol glucuronide (5β-pregnane-3α, 20α-diol
glucuronide) (PdG) and oestrone glucuronide [1,3,5(10) estrien-3-ol17-one glucuronide] (E1G) respectively. Based upon cycle length and
hormone/metabolite levels during the study, serum samples were
grouped into early [EF, –12.8 ⫾ 1.2 (mean ⫾ SEM) days in relation
to the day of the LH surge], mid- (MF, –6.9 ⫾ 0.9) and late (LF,
–2.4 ⫾ 0.3) follicular phase, time of the LH peak (LH, by convention
day 0), approximate time of ovulation (OV, ⫹1 ⫾ 0.3) and early
(EL, ⫹3.4 ⫾ 0.3), mid- (ML, ⫹7.3 ⫾ 0.5) and late (LL, ⫹11.4 ⫾
0.3) luteal phase.
Laboratory measures
Serum sICAM-1 and sE-selectin were measured using enzyme-linked
immunosorbent assay kits purchased from Hycult Biotechnology
(Uden, The Netherlands), with intra-/inter-assay coefficients of variation (CV) ⬍9%/11% and ⬍8%/10% for each kit respectively.
sVCAM-1 was assayed using kits supplied by Cayman Chemical Co.
(Ann Arbor, MI, USA) where the intra-assay CV was ⬍5.9% and
the inter-assay CV ⬍10.2%. Plasma estradiol, progesterone, FSH and
LH (including urinary LH) levels were assayed using the ACS-180
analyser and associated assay kits (Chiron Diagnostics, East Walpole,
MA, USA). Measurement of urinary PdG and E1G levels was by
homogeneous enzyme immunoassay, according to a published method
(Brown et al., 1988) with test materials supplied by St Michael’s
Natural Family Planning (University of Melbourne, VIC, Australia).
Excreted levels of PdG and E1G were expressed relative to creatinine
excretion, with creatinine estimated using the Beckman Creatinine
Analyser 2 (Beckman Instruments, Galway, Ireland). Leukocyte
subtype counts were calculated using whole blood samples and a
standard gating Coulter Counter program (Coulter Electronics Corp.,
Miami, FL, USA), within 30 min of blood sample collection.
Graphical representation and data analysis
A high degree of inter-subject variability in serum sICAM-1 levels
existed in the present study (CV: 28.9%), as has been encountered
by others (Jilma et al., 1994). Soluble VCAM-1 and sE-selectin
inter-subject variability was also large (mean CV: 19.5 and 50.5%
respectively). Hence, to analyse the sample group’s net changes in
circulating CAMs through the menstrual cycle, without the con-
2273
N.Bonello and R.J.Norman
sampling time intervals (see ‘Sample collection’ above). All statistical
analyses investigating soluble CAM fluctuations with cycle stage
were performed on raw data using repeated measures analysis
of variance and Tukey–Kramer multiple comparison tests. Linear
correlation analysis methods (Pearson’s coefficient) were used to
examine the relationship between levels of soluble CAMs and sex
hormones, white blood cell subsets and other subject variables.
Statistical differences of P 艋 0.05 were considered significant.
Results
Figure 1. Soluble intercellular adhesion molecule-1 (sICAM-1)
levels in serum (mean ⫾ SEM) at each stage of the menstrual
cycle, expressed as ng/ml and as percentage subject mean (see
Materials and methods). Significantly lower values than early
follicular phase reading: *P ⬍ 0.05, **P ⬍ 0.01, ***P ⬍ 0.001.
EF ⫽ early follicular phase; MF ⫽ mid-follicular phase; LF ⫽ late
follicular phase; LH ⫽ LH peak; OV ⫽ ovulation; EL ⫽ early
luteal phase; ML ⫽ mid-luteal phase; LL ⫽ late luteal phase.
Soluble ICAM-1, VCAM-1 and E-selectin
The group mean ⫾ SD serum concentrations of sICAM-1,
sVCAM-1 and sE-selectin across the entire menstrual cycle
were within previously reported limits at 110 ⫾ 32, 690 ⫾
134 and 13 ⫾ 7 ng/ml respectively (Gearing and Newman,
1993). Circulating ICAM-1 levels in peripheral blood peaked
during the early and mid-follicular stages but progressively
declined through mid-cycle and luteal stages by up to 20%
(Figure 1). Levels of sICAM-1 were significantly lower
(P ⬍ 0.05) from the expected time of ovulation onwards,
when compared with the early follicular stage, reaching a
minimum level in the late luteal stage. Every subject exhibited
a reduced late luteal stage sICAM-1 level compared with
her early follicular stage reading. Soluble VCAM-1 levels
fluctuated during the follicular and mid-cycle phases of the
menstrual cycle, before decreasing by a significant degree
(P ⬍ 0.01) during the late luteal stage, in comparison with
the LH peak stage (Figure 2a). Mean levels of sE-selectin did
not vary significantly across the menstrual cycle (Figure 2b).
Gonadotrophins, gonadal steroids and hormone metabolites
All subjects were ovulatory in their respective study cycle and
as a group demonstrated normal menstrual cycles as shown
by typical plasma hormone and urinary metabolite changes,
including a mid-cycle LH peak in blood (Table I) and urine
samples (data not shown). Plasma progesterone and urinary
PdG, as expected, peaked during the mid-luteal stage (Table I).
A significant negative correlation (n ⫽ 73, r ⫽ –0.38,
P ⬍ 0.005) existed between circulating levels of sICAM-1
and estradiol (Figure 3a). This inverse relationship was also
present at the individual early follicular (n ⫽ 10, r ⫽ –0.85,
P ⬍ 0.005) and ovulatory (n ⫽ 10, r ⫽ –0.63, P ⬍ 0.05)
time points.
Figure 2. Soluble (a) vascular cell adhesion molecule-1 (sVCAM-1)
and (b) E-selectin levels in serum (mean ⫾ SEM) at each stage of
the menstrual cycle, expressed as ng/ml and as percentage subject
mean (see Materials and methods). Significantly lower value than
LH peak reading: **P ⬍ 0.01. EF ⫽ early follicular phase;
MF ⫽ mid-follicular phase; LF ⫽ late follicular phase; LH ⫽ LH
peak; OV ⫽ ovulation; EL ⫽ early luteal phase; ML ⫽ mid-luteal
phase; LL ⫽ late luteal phase
founding influence of inter-subject differences, each participant’s
individual cycle stage soluble CAM level was expressed as a
percentage of her mean soluble CAM level across all time points.
Figures 1 and 2 show the combined result of these transformations
alongside absolute soluble CAM levels. The equidistant spacing
between cycle stages in these figures is not indicative of equal
2274
White blood cell subsets
Total white blood cells and constituent subsets were observed
to fluctuate non-significantly across the various stages of the
menstrual cycle (Table II). A significant inverse relationship
(n ⫽ 70, r ⫽ –0.47, P ⬍ 0.001) was shown to exist between
circulating levels of sVCAM-1 and monocyte cell numbers
(Figure 3b). This negative association was also present at the
individual ovulatory (n ⫽ 10, r ⫽ –0.63, P ⬍ 0.05) and late
luteal (n ⫽ 10, r ⫽ –0.76, P ⬍ 0.05) phases of the cycle.
Subject variables
No significant relationships were evident between individual
subjects’ mean menstrual cycle levels of sICAM-1 or
Menstrual cyclicity of soluble adhesion molecules
Table I. Plasma hormone and urinary hormone metabolite levels (mean ⫾ SEM) at each stage of the
menstrual cycle
Stage of cycle
Estradiol
(pmol/l)
Progesterone
(nmol/l)
LH (IU/l)
FSH (IU/l)
E1G/creatinine
ratio
PdG/creatinine
ratio
EF
MF
LF
151
⫾24
2.5
⫾0.3
5.9
⫾0.6
5.7
⫾0.4
–
291
⫾33
1.9
⫾0.3
8.3
⫾1.0
5.7
⫾0.6
7.5
⫾2.9
0.2
⫾0.1
563
⫾54
2.2
⫾0.3
12.9
⫾2.1
4.2
⫾0.2
10.2
⫾2.9
0.2
⫾0.0
–
LH
781
⫾109
3.5
⫾0.5
71.1
⫾13.2
11.2
⫾1.6
19.6
⫾7.8
0.2
⫾0.0
OV
EL
ML
LL
401
⫾53
6.9
⫾1.0
17.9
⫾2.6
7.1
⫾0.7
12.7
⫾5.6
0.3
⫾0.1
367
⫾35
29.7
⫾4.9
9.3
⫾0.8
4.7
⫾0.5
9.2
⫾2.6
0.6
⫾0.1
559
⫾46
50.5
⫾6.3
6.8
⫾0.8
2.8
⫾0.4
13.3
⫾4.5
0.8
⫾0.2
358
⫾64
12.8
⫾3.7
7.4
⫾2.1
3.1
⫾0.3
7.7
⫾2.1
0.5
⫾0.1
Urinary metabolites were measured in the following units: E1G (nmol/l), PdG (µmol/l) and creatinine
(mmol/l).
EF ⫽ early follicular phase; MF ⫽ mid-follicular phase; LF ⫽ late follicular phase; LH ⫽ LH peak;
OV ⫽ ovulation; EL ⫽ early luteal phase; ML ⫽ mid-luteal phase; LL ⫽ late luteal phase; PdG ⫽
pregnanediol glucuronide; E1G ⫽ oestrone glucuronide.
Table II. Leukocyte counts (mean ⫾ SEM) at each stage of the menstrual cycle, expressed as ⫻106 cells/ml
peripheral blood
Stage of cycle
Total WBC
Neutrophils
Lymphocytes
Monocytes
Eosinophils
Basophils
EF
MF
LF
LH
OV
EL
ML
LL
7.9
⫾0.5
4.9
⫾0.5
2.0
⫾0.1
0.6
⫾0.1
0.2
⫾0.1
0.1
⫾0.0
6.8
⫾0.5
3.7
⫾0.2
2.2
⫾0.2
0.5
⫾0.1
0.2
⫾0.0
0.1
⫾0.0
7.9
⫾0.5
4.7
⫾0.4
2.2
⫾0.2
0.6
⫾0.1
0.2
⫾0.0
0.1
⫾0.0
7.7
⫾0.7
4.8
⫾0.3
2.0
⫾0.2
0.6
⫾0.1
0.1
⫾0.0
0.1
⫾0.0
8.0
⫾0.6
4.9
⫾0.4
2.1
⫾0.2
0.6
⫾0.1
0.2
⫾0.0
0.1
⫾0.0
8.1
⫾0.5
4.9
⫾0.4
2.1
⫾0.1
0.7
⫾0.1
0.2
⫾0.1
0.1
⫾0.0
7.4
⫾0.6
4.4
⫾0.3
2.0
⫾0.2
0.5
⫾0.1
0.2
⫾0.1
0.1
⫾0.0
7.3
⫾0.3
4.2
⫾0.3
2.1
⫾0.2
0.6
⫾0.0
0.2
⫾0.1
0.1
⫾0.0
EF ⫽ early follicular phase; MF ⫽ mid-follicular phase; LF ⫽ late follicular phase; LH ⫽ LH peak;
OV ⫽ ovulation; EL ⫽ early luteal phase; ML ⫽ mid-luteal phase; LL ⫽ late luteal phase; WBC ⫽ white
blood cells.
sVCAM-1 and their age, BMI and length of menstrual cycle
or menstruation (in days) that could account for the variation
in soluble CAMs observed. Similarly, neither sICAM-1 nor
sVCAM-1 levels at early or mid-follicular stages were correlated with subject’s length of menstruation.
Discussion
This is the first report examining changes in serum sICAM-1,
sVCAM-1 and sE-selectin across the natural cycle of healthy,
untreated subjects. It shows that, like their uterine and ovarian
cell-bound counterparts, immunodetectable levels of certain
soluble CAMs also vary, to a modest degree, according to
menstrual/ovarian cycle phase.
The lowered serum sICAM-1 levels observed during the
luteal phase, while subtle and not correlated with progesterone
secretion, were significant and broadly in alignment with
other investigations. First, it was shown that serum sICAM-1
declined during the lifespan of the active corpus luteum in
subjects undergoing IVF procedures, but increased in those
failing to conceive, at a time point corresponding with the
present study’s period of maximal sICAM-1 detection
(Mantzavinos et al., 1996). Secondly, it was demonstrated
that secretory/luteal phase-derived endometrial stromal cells
released significantly less sICAM-1 into culture than proliferative/follicular phase-acquired cells (Somigliana et al., 1996).
While we cannot determine the source of soluble CAM in our
study by their presence in serum alone, the study by Somigliana
et al. implicates the uterus as a potential source of active,
cycle phase-dependent, sICAM-1 secretion and one which
2275
N.Bonello and R.J.Norman
Figure 3. Correlation between (a) soluble intercellular adhesion
molecule-1 (sICAM-1) levels and estradiol concentration
[correlation coefficient (r) ⫽ –0.38, P ⬍ 0.005] and (b) soluble
vascular cell adhesion molecule-1 (sVCAM-1) levels and monocyte
numbers (r ⫽ –0.47, P ⬍ 0.001), in all peripheral blood samples
obtained during one complete menstrual cycle of 10 subjects.
may at least partly account for the diminishing luteal phase
sICAM-1 levels we observed. Alternatively, the uterus may
passively shed increased cell-bound ICAM-1 into the peripheral
circulation, during menstruation, as a result of the generalized
endometrial tissue disruption occurring at this time, while a
lack of constitutive cell surface expression may account for
this effect not being as marked with shed VCAM-1 and
E-selectin. Supporting this concept, maximal sICAM-1 levels
were observed during and just after menstruation, coincident
with the periods of maximal uterine vascular surface CAM
expression and uterine leukocyte density as shown by others
(Poropatich et al., 1987; Starkey et al., 1991; Tawia et al.,
1993; Thomson et al., 1999a). However, there was no correlation between sICAM-1 levels and the duration of menstruation
and no measure was made of the extent of menstrual flow.
Expression of ICAM-1 protein in the vascularized theca of rat
ovaries also declines post-ovulation (Bonello and Norman,
1997), so the ovary is also a candidate organ for cyclic
shedding of CAMs originally bound to the cell surface. Ovarian
CAM expression, similar to the uterus, is largely endothelialderived, although non-vascular cells of the theca and luteinized
granulosa cells also express ICAM-1 (Bonello and Norman,
1997; Viganò et al., 1998). As the soluble form of P-selectin,
another regulator of leukocyte–endothelium interactions, also
progressively declines in serum throughout the normal menstrual cycle (Jilma et al., 1996), the underlying mechanisms
2276
and sources responsible for lowered luteal sICAM-1,
sVCAM-1 and sP-selectin levels may be similar.
Serum sICAM-1 was negatively correlated with estradiol
levels in this study. This result is comparable with in-vivo
research showing a significant attenuation of sICAM-1 levels
in serum 4 days post-estradiol infusion into male subjects
(Jilma et al., 1994). Furthermore, numerous studies of the
short- and long-term effects of HRT in post-menopausal women
have revealed an association between exogenous estrogen and
reduced soluble CAM levels, usually including sICAM-1 (Koh
et al., 1997; Cushman et al., 1999; Van Baal et al., 1999;
Zanger et al., 2000). Indeed, such evidence has advanced the
case for estradiol’s anti-atherogenic/cardioprotective role being
orchestrated via indirect (e.g. cortisol-mediated) or direct (e.g.
modulation of CAM gene transcription) down-regulation of
endothelial cell-expressed and soluble CAMs (Caulin-Glaser
et al., 1996). It is possible that this relationship between
estradiol and endothelium-derived CAMs manifests itself
across the normal menstrual cycle, at least in the case of
sICAM-1.
Although leukocyte subtypes did not vary significantly
across the menstrual cycle in our study, sVCAM-1 concentration was inversely correlated with blood monocyte cell numbers. Unlike sICAM-1 and sE-selectin, sVCAM-1 is restricted
to binding blood mononuclear cells, as its counter-receptor,
VLA-4, is absent from granulocytes (Carlos and Harlan, 1994).
Unbound, and thereby assay-detectable, sVCAM-1 levels may
therefore be altered with even minor fluctuations in VLA-4
ligand expressing monocyte numbers. This VCAM-1/α4
integrin pathway is regarded as a major regulator of monocyte–
endothelial adhesion under flow conditions and can be inhibited
by raised sVCAM-1 levels (Abe et al., 1998). In the present
study, sE-selectin levels did not vary across the cycle and were
unrelated to gonadal steroids, gonadotrophins or circulating
leukocytes. The different sE-selectin menstrual cycle response,
compared with sICAM-1 and sVCAM-1, may reflect variant
activation of cell types capable of expressing specific combinations of CAMs, or differences in the mechanisms or rate of
soluble CAM cleavage and/or uptake from the circulation. Of
course, molecular immunodetection in peripheral blood does
not necessarily equate to bioactivity and remains dependent
upon factors including molecular synthesis, release and
clearance.
This study’s findings may have immediate relevance in
numerous conditions where soluble CAM levels are currently
utilized, or have been proposed, as biological indicators of
disease state or progression. As we have shown that peripheral
blood levels of certain soluble CAMs fluctuate normally in
accordance with menstrual cycle phase, cycle stage should
perhaps be accounted for when analysing results of soluble
CAM assays in cycling women, particularly in borderline
normal/abnormal cases. Furthermore, future research should
endeavour to build upon the findings of this study by elucidating
the specific source(s) of fluctuating sICAM-1 and sVCAM-1.
The relative contribution of the uterus to the cycling soluble
CAM pool in peripheral blood could be addressed by comparing
uterine vein and peripheral blood soluble CAM levels in
Menstrual cyclicity of soluble adhesion molecules
patients undergoing hysterectomy, while comparisons between
women having undergone total hysterectomy/ovariectomy and
cyclic, hysterectomized women who retain their ovaries, may
clarify the portion of soluble CAMs (if any) derived from
the ovary.
Acknowledgements
We thank Ms Anne Marie Carrera for assay assistance and acknowledge help provided by Helen Alvino and the sisters/staff of the
Reproductive Medicine Unit, Reproductive Endocrine and Main
Haematology Laboratories of TQEH. N.B. was supported by the
Adelaide University Medical Faculty and the Queen Elizabeth Hospital
Research Foundation.
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Submitted on March 2002; accepted on May 8, 2002