250
Journal of Andrology, Vol. 25, No. 2, March/April 2004
Copyright American Society of Andrology
Inflammatory Cytokine Concentrations Are Elevated in
Seminal Plasma of Men With Spinal Cord Injuries
SARMISTHA BASU,* TEODORO C. ABALLA,* SEAN M. FERRELL,* CHARLES M. LYNNE,*, AND
NANCY L. BRACKETT*
From the *Miami Project to Cure Paralysis and the Department of Urology, University of Miami School of
Medicine, Miami, Florida.
ABSTRACT: The semen of most men with spinal cord injury (SCI)
contains sperm with abnormally low motility. Studies suggest that
the seminal plasma is the source of this condition. The seminal plas-
ma of men with SCI contains an abnormally high number of white
blood cells (WBC), specifically, activated T cells. It is known that
activated T cells secrete cytokines and elevated concentrations of
cytokines can be harmful to sperm. It is not known if the seminal
plasma of men with SCI contains elevated concentrations of cyto-
kines. The purpose of this study was to determine if the seminal
plasma of men with SCI contained elevated concentrations of cyto-
kines. Using the method of enzyme-linked immunosorbant assay
(ELISA), ten cytokines were measured in the seminal plasma of men
with SCI as well as healthy non-SCI control subjects. The cytokines
of interest were grouped according to Th1 effector functions: inter-
leukin 1 beta, interleukin 2, interleukin 12, tumor necrosis factor al-
pha, tumor necrosis factor beta, interferon gamma (IL1 , IL2, IL12,
TNF , TNF , INF , respectively) and Th2 effector functions: inter-
leukin 4, interleukin 6, interleukin 10, transforming growth factor beta
1 (IL4, IL6, IL10, TGF 1, respectively). The results showed a pre-
dominance of Th1 versus Th2 cytokine production in the seminal
plasma of men with SCI compared with that of control subjects. This
finding suggests an immunologic basis for infertility as a possible
avenue of investigation in these men.
Key words: Sperm, infertility, semen, T cells, Th1, Th2.
J Androl 2004;25:250­254
Men with SCI have a unique type of infertility. They
suffer from neurogenic ejaculatory dysfunction and
abnormal semen parameters. Their semen often contains
an abnormally low concentration of motile sperm (Ohl et
al, 1992; Sonksen and Biering-Sorensen, 1992; Brackett
et al, 1998). The cause of this condition in men with SCI
remains unexplained, and no specific remedies have been
developed. Wheelchair confinement, bladder catheteriza-
tion, endocrine imbalances, the inability to ejaculate, or
the years postinjury all appear unrelated to the etiology
of this semen abnormality (Brackett et al, 1996b). Inter-
estingly, a soluble factor in the seminal plasma of men
with SCI inhibits sperm motility of normal men within
five minutes of contact (Brackett et al, 1996a). Further-
more, when the sperm of men with SCI have not en-
countered the seminal plasma (ie, the sperm have been
extracted from the vas deferens), the motility is near nor-
mal (Brackett et al, 2000). The nature and source of the
factor in the seminal plasma that causes the drop in sperm
motility of SCI men is uncharacterized. Accompanying
Supported by the Christopher Reeve Paralysis Foundation, the State of
Florida Specific Appropriations, and the Miami Project to Cure Paralysis.
Correspondence to: Dr Nancy L Brackett, The Miami Project to Cure
Paralysis, University of Miami School of Medicine, PO Box 016960, R-
48, Miami, FL 33101 (e-mail: NBrackett@miami.edu).
Received for publication July 9, 2003; accepted for publication Sep-
tember 30, 2003.
this finding is our additional observation that the semen
of men with SCI contains an abnormally high number of
white blood cells, specifically, activated T cells (Basu et
al, 2002). It is known that activated T cells secrete cy-
tokines, and elevated concentrations of cytokines can be
harmful to sperm (Dousset et al, 1997; Matalliotakis et
al, 1998a; Matalliotakis et al, 1998b; Abbas et al, 2000).
It is not known if the seminal plasma of men with SCI
contains elevated concentrations of cytokines. The pur-
pose of this study was to determine if the seminal plasma
of men with SCI contains elevated concentrations of cy-
tokines that might be associated with a Th1 versus Th2
immune pathway. Th1 and Th2 are two subsets of helper
T cells that are characterized by the production of cyto-
kine groups, which determine or augment different im-
mune responses. For example, IFN is a key cytokine
associated with Th1 differentiation and a cell-mediated
immune response, while IL4 and IL5 are associated with
Th2 differentiation and a humoral or antigen-mediated
immune response (ie, stimulating and augmenting B-cell
activity) (Abbas et al, 2000).
Materials and Methods
Subjects
Subjects were 31 men with spinal cord injury in good general
health. All were research volunteers participating in an IRB-
251Basu et al  Elevation of Semen Cytokines in SCI Men
Comparison of sperm count and motility between men with spinal
cord injury (SCI) and control subjects
Parameter
Total Sperm Count in
Antegrade Ejaculate
( 106
)
Percent Sperm
Motility
Control subjects
SCI subjects
Significance
243.2 55.8
60.8 12.2
P .001
66.9 4.0
29.6 4.8
P .001
approved protocol of the Male Fertility Research Program of the
Miami Project to Cure Paralysis at the University of Miami
School of Medicine, Miami, Florida. As assessed by the Uni-
versity of Miami Neurospinal Index (Klose et al, 1980), the lev-
els of injury were C3 to C7 in 15 patients, T1 to T5 in 10
patients, and T6 to T10 in 6 patients. Eighty percent of the par-
ticipants had incomplete lesions, and 20% had incomplete le-
sions. Their mean age was 32 2.1 years (range 27­42). Their
mean years postinjury was 8.1 0.9 (range 2­19). Control sub-
jects were 12 healthy, non-SCI men, with no history of infertil-
ity. Their mean age was 30.7 3.6 years (range 25­47 years).
No SCI or control subject had taken any medication known to
interfere with fertility within 6 months prior to their participation
in this study.
Semen Analysis
A semen analysis was performed on each fresh semen specimen
using World Health Organization (World Health Organization,
1999) criteria. All semen analyses were performed by the same
technician.
Semen Collection
In SCI subjects, antegrade semen specimens were collected by
the standard method of penile vibratory stimulation (Brackett,
1999). Retrograde ejaculates and electroejaculates were not used
in this study because these procedures have been shown to alter
semen quality (Brackett and Lynne, 2000). When possible, up
to 3 semen specimens were collected from each SCI subject to
achieve a final volume of 2 mL semen per subject, which was
the minimum volume necessary to perform all cytokine assays.
Multiple semen collections from the same SCI subject occurred
at 2- to 4-week intervals, with no additional ejaculations between
semen collections. Each semen specimen was centrifuged at 400
g for 10 minutes at room temperature to obtain the seminal
plasma fraction. The protease inhibitor, phenyl methyl sulphonyl
fluoride (PMSF), was added to the seminal plasma to a final
concentration of 0.5 mM (Gruschwitz et al, 1996). The PMSF-
treated seminal plasma fractions were then stored in 1.5 mL
microfuge tubes at 80 C until use. Control subjects collected
their semen specimens by masturbation following 3 to 7 days of
abstinence from ejaculation. Semen specimens from control sub-
jects were processed in the same manner as semen specimens
from SCI subjects.
Cytokine Determination in Seminal Plasma
The following 10 cytokines were measured in the seminal plas-
ma of SCI and control subjects: IL1 , IL2, IL12, TNF , TNF ,
INF , IL4, IL6, IL10, TGF 1. Because the volume of ejaculate
available from each subject was limited, in some instances mul-
tiple ejaculates from the same subject were collected and pooled.
Even so, since duplicate determinations of each assay were per-
formed, it was not possible to assay all 10 cytokines in each
subject. Frozen seminal plasma was thawed at room temperature
immediately prior to cytokine determination. Quantitation of
these cytokines was done using ELISA kits (R&D Systems, Min-
neapolis, Minn). Briefly, a solid phase enzyme immunoassay em-
ploying the multiple antibody sandwich principle was applied.
The microtiter plate was coated with antihuman monoclonal an-
tibody specific for the cytokines. The immobilized antibody
binds any cytokine present in the seminal plasma. A goat poly-
clonal antibody was added to which streptavidine-peroxidase
was bound to biotin. The chromogen used was tetramethyl ben-
zidine, the reaction stopped by using 2N H2SO4. Optical density
readings were performed at 450 nm and corrected at 540 nm
using a Wallac ELISA reader.
Cytokine Determination in Blood Serum
As a follow-up experiment to finding elevated semen cytokine
concentrations in SCI subjects, cytokine concentrations were
measured in the blood serum of SCI subjects to determine if the
elevations were a local or systemic effect. Blood serum was not
collected from control subjects since elevated semen cytokine
concentrations were not observed in control subjects.
One serum specimen was collected from each of 12 randomly
selected SCI subjects. Blood was collected by venipuncture into
vacutainer tubes, allowed to clot for 15 minutes, then centrifuged
at 400 g for 15 minutes to obtain serum. Serum specimens
were treated similarly to seminal plasma, that is, serum was
treated with PMSF, then frozen at 80 C until use. The presence
of cytokines IL1 , IL6, and TNF was determined using ELISA
as described above for cytokine determination in the seminal
plasma.
Statistical Analysis
Group means were compared by analysis of variance. Fisher
exact test was used in one instance to assess the significance of
the finding that control subjects contained no IFN in their sem-
inal plasma versus SCI subjects who contained a broad range of
this cytokine (0­141.13 pg/mL) in their seminal plasma.
Results
Semen Analysis
Similar to numerous previous studies (Linsenmeyer,
1991; Ohl et al, 1992; Sonksen and Biering-Sorensen,
1992; Brackett et al, 1998), semen parameters were im-
paired in men with SCI compared with control subjects
(Table).
Cytokine Determination in the Seminal Plasma
Of the cytokines typically elaborated by the Th1 subset
of helper T cells, concentrations of IL1 , IL12, and TNF
were significantly elevated in the seminal plasma of SCI
252 Journal of Andrology  March/April 2004
Figure 1. Mean concentrations of Th1 cytokines were compared in the
seminal plasma of SCI subjects and control subjects. n number of
subjects analyzed in each group for each cytokine. * Fisher exact test
(see ``Results'' section).
Figure 2. Mean concentrations of Th2 cytokines were compared in the
seminal plasma of SCI subjects and control subjects. n number of
subjects analyzed in each group for each cytokine.
subjects compared with control subjects (Figure 1). IL2
and TNF were not present in the seminal plasma of SCI
or control subjects. Likewise, IFN was not present in the
seminal plasma of any control subject but was present in
the seminal plasma of two thirds of the SCI subjects. Al-
though the difference in mean concentrations of IFN in
SCI versus control subjects did not reach statistical sig-
nificance (probably due to the wide range of IFN con-
centrations in the SCI group: 0.0­141.13 pg/mL), the oc-
currence of this finding was significant when analyzed by
the Fisher exact test (P .05).
Of the cytokines typically elaborated by the Th2 subset
of helper T cells, only IL6 was significantly elevated in
the seminal plasma of SCI subjects compared with control
subjects (Figure 2). There was no difference between SCI
and control subjects in the concentrations of IL10. Con-
centrations of IL4 and TGF 1 were significantly de-
creased in the seminal plasma of SCI versus control sub-
jects.
Cytokine Concentrations in Blood Sera
IL1 , IL6, and TNF were not detected in the serum of
men with SCI (data not shown).
Discussion
The results of this study show that the seminal plasma
concentrations of IL1 , IL12, IL6, and TNF were sig-
nificantly higher, whereas concentrations of IL4 and
TGF 1 were significantly lower in the seminal plasma of
men with SCI compared with healthy non-SCI men. The
presence of IFN in the seminal plasma of SCI men
where none was found in controls was likewise signifi-
cant. Proinflammatory cytokines have been detected in
the semen of men with inflammation-related infertility
(Shimoya et al, 1993; Naz and Kaplan, 1994; Rajasekaran
et al, 1995; Huleihel et al, 1996); however, these studies
have been conducted only in infertile non-SCI men. Our
study examined the SCI male population. As with pre-
vious studies, semen parameters were found to be abnor-
mal in the SCI group. No detectable levels of IL1 , IL6,
or TNF were found in the blood sera of SCI subjects,
suggesting that the observed inflammatory response was
restricted to the urogenital tract.
Cytokines rarely act in isolation, but rather in a network
of other cytokines, many of which may be inhibitory or
immunoregulatory. Two such cytokines, IL4 and TGF 1
were found to be lower in the seminal plasma of SCI men.
TGF is a cytokine with autocrine and paracrine actions
in the testis with potent immunoregulatory and anti-in-
flammatory activity (Loras et al, 1999). IL4 inhibits the
production of a wide range of cytokines from stimulated
monocytes (Mire-Sluis and Thorpe, 1998). One study
(Naz and Evans, 1998) noted that IL12 was higher in
fertile versus infertile men and was correlated with sperm
count, but not sperm motility. Our study, however,
showed increased concentrations of IL12 in seminal plas-
ma of men with SCI (12.5 pg/mL) compared with those
of controls (5.0 pg/mL).
Studies by Estrada et al (1997) and Paradisi et al (1996)
showed that IFN had a somewhat detrimental effect on
sperm motility and viability. In our study, IFN was pre-
sent in the seminal plasma of 8 of the 12 SCI men tested
for this cytokine and in none of the control subjects tested
(P .05).
The concentrations of IL1 , IL6, and TNF were great-
ly elevated in seminal plasma of men with SCI. Presence
of IL1 in human seminal plasma and its influence in
253Basu et al  Elevation of Semen Cytokines in SCI Men
membrane peroxidation and fertility has been reported
(Buch et al, 1994). Various studies have shown that IL1
in very high concentrations can have an adverse affect on
sperm motility and fertilization (Naz, 1985; Anderson and
Hill, 1988). However, the direct influence of cytokines
such as IL1 and TNF is a topic of controversy (Hill et
al, 1987; Haney et al, 1992). Studies have also shown an
inverse correlation between sperm number and motion pa-
rameters and seminal IL6 levels (Naz and Kaplan, 1994).
IL6 is a pleiotrophic cytokine produced by different types
of cells. According to Matalliotakis et al, the prostate ap-
pears to be the main site for origin of IL6 in the semen
(Matalliotakis et al, 1998b).
In vitro studies have shown that recombinant TNF
does not affect human sperm motility (Wincek et al,
1991). The effects of TNF on sperm motility, sperm
penetration, and mouse embryo development was shown
by Hill et al (1987). The cytotoxic effects of TNF are
normally mediated through membrane receptor mecha-
nisms linked to protein synthesis. Many effects are me-
diated by activation of the TNF receptor pathways, in-
cluding nuclear factor kappa B (NF B) activation and in-
duction of apoptotic processes. Our data showed that
TNF was not found in detectable levels in control sub-
jects. Even though its correlation with sperm motility and
viability could not be determined due to absence of TNF
in control subjects, its presence in the seminal plasma of
SCI subjects suggests a possible role in infertility.
Another mechanism of interference with sperm quality
may be an adverse effect on sperm membrane properties
such as lipid peroxidation (Buch et al, 1994). Increased
oxidative stress may additionally modulate the concentra-
tion of these cytokines (Rajasekaran et al, 1995). Reactive
oxygen species (ROS) might also play a role in reducing
sperm motility along with cytotoxic cytokines. It has been
shown that semen samples of SCI patients showed high
levels of ROS, which was inversely related to sperm mo-
tility and positively related to polymorphonuclear neutro-
phils (Padron et al, 1997).
The role of abnormal sperm storage in the seminal ves-
icles of SCI men (Ohl et al, 1999) in contributing to the
abnormal levels of cytokines, WBC, and overall sperm
quality is unclear. It is tempting to assign all the abnor-
malities to this possibility. However, repeated frequent
ejaculations (which should minimize the effects of ab-
normal storage) do not seem to change semen quality in
these men (Sonksen et al, 1999).
Whereas cells of the immune system are the major
sources of these cytokines, other cells in the reproductive
tract might be capable of cytokine expression. It has been
suggested that the prostate gland is the site of origin of
IL6 (Matalliotakis et al, 1998b). Studies have suggested
that there are both endogenous and exogenous factors that
might affect sperm motility (Majumder et al, 1990; de
Lamirande and Gagnon, 1993). The precise origin of the
cytokines, however, remains unclear. Presumably they are
produced by WBC present in abnormally high numbers
in the semen of men with SCI (Basu et al, 2002; Trabulsi
et al, 2002). The origin of these WBC is unclear and may
not be related to chronic infection or inflammation. For
example, many men post retroperitoneal lymph node dis-
section (RPLND) share the same abnormal sperm profiles
and ejaculatory dysfunction with men who have SCI but
not the stigmata of bladder dysfunction, UTI, and so forth.
Their commonality with SCI men is autonomic disinner-
vation of the accessory sex glands, a condition whose role
is unclear with respect to immune function and regulation.
Treatment of UTIs does not seem to make a major dif-
ference in the sperm parameters of men with SCI (Ohl et
al, 1992). A biopsy study of the prostate glands of SCI
versus control subjects showed no evidence of any sig-
nificant acute or chronic inflammatory changes in the
prostate glands of SCI men (Randall et al, 2003).
A previous study by our group showed that seminal
plasma from men with SCI rapidly and profoundly re-
duced sperm motility of normal men (Brackett et al,
1996a). Additionally, sperm obtained from the vas defer-
ens of men with SCI had significantly higher motility than
that of their ejaculates (Brackett et al, 2000). Taken to-
gether, these studies indicate that when sperm of men with
SCI comes into direct contact with their seminal plasma,
sperm motility decreases. Further experiments will be re-
quired to prove the exact involvement of cytokines in
reducing sperm motility. However, identification of the
exact cyokines involved in this response will lead to the
development of strategies to neutralize, eliminate, or oth-
erwise combat these substances and their noxious effects.
Conclusion
This study demonstrates elevated concentrations of the
cytokines IL1 , IL6, IL12, IFN , and TNF , and lower
concentrations of IL4 and TGF 1 in the seminal plasma
of men with SCI compared with non-SCI healthy control
subjects. Many of the cytokines were either not detectable
or not present in the seminal plasma of control subjects.
This finding suggests a cell mediated versus a humoral
immunologic basis for infertility as a possible avenue of
investigation in these men.
References
Abbas AK, Lichtman AH, Pober JS, eds. Cellular and Molecular Im-
munology. Philadelphia: WB Saunders; 2000.
Anderson DJ, Hill JA. Cell-mediated immunity in infertility. Am J Rep
Immunol.1988;17:22­30.
Basu S, Lynne CM, Ruiz P, Aballa TC, Ferrell SM, Brackett NL. Cyto-
254 Journal of Andrology  March/April 2004
fluorographic identification of activated T-cell populations in the se-
men of men with spinal cord injuries. J Androl. 2002;23:551­556.
Brackett NL. Semen retrieval by penile vibratory stimulation in men with
spinal cord injury. Hum Reprod Update. 1999;5:216­222.
Brackett NL, Davi RC, Padron OF, Lynne CM. Seminal plasma of spinal
cord injured men inhibits sperm motility of normal men. J Urol.
1996a;155:1632­1635.
Brackett NL, Ferrell SM, Aballa TC, et al. An analysis of 653 trials of
penile vibratory stimulation on men with spinal cord injury. J Urol.
1998;159:1931­1934.
Brackett NL, Lynne CM. The method of assisted ejaculation affects the
outcome of semen quality studies in men with spinal cord injury: a
review. Neurorehab. 2000;15:89­100.
Brackett NL, Lynne CM, Aballa TC, Ferrell SM. Sperm motility from
the vas deferens of spinal cord injured men is higher than from the
ejaculate. J Urol. 2000;164:712­715.
Brackett NL, Nash MS, Lynne CM. Male fertility following spinal cord
injury: facts and fiction. Phys Ther. 1996b;76:1221­1231.
Buch JP, Kolon TF, Maulik N, Kreutzer DL, Das DK. Cytokines stimulate
lipid membrane peroxidation of human sperm. Fertil Steril. 1994;62:
186­188.
de Lamirande E, Gagnon C. A positive role for the superoxide anion in
triggering hyperactivation and capacitation of human spermatozoa. Int
J Androl. 1993;16:21­25.
Dousset B, Hussenet F, Daudin M, Bujan L, Foliguet B, Nabet P. Seminal
cytokine concentrations (IL-1beta, IL-2, IL-6, sR IL-2, sR IL-6), se-
men parameters and blood hormonal status in male infertility. Hum
Reprod. 1997;12:1476­1479.
Estrada LS, Champion HC, Wang R, et al. Effect of tumour necrosis
factor-alpha (TNF-alpha) and interferon-gamma (IFN-gamma) on hu-
man sperm motility, viability and motion parameters. Int J Androl.
1997;20:237­242.
Gruschwitz MS, Brezinschek R, Brezinschek HP. Cytokine levels in the
seminal plasma of infertile males. J Androl. 1996;17:158­163.
Haney AF, Hughes SF, Weinberg JB. The lack of effect of tumor necrosis
factor-alpha, interleukin-1-alpha, and interferon-gamma on human
sperm motility in vitro. J Androl. 1992;13:249­253.
Hill JA, Haimovici F, Politch JA, Anderson DJ. Effects of soluble prod-
ucts of activated lymphocytes and macrophages (lymphokines and
monokines) on human sperm motion parameters. Fertil Steril. 1987;
47:460­465.
Huleihel M, Lunenfeld E, Levy A, Potashnik G, Glezerman M. Distinct
expression levels of cytokines and soluble cytokine receptors in sem-
inal plasma of fertile and infertile men. Ferti Steril. 1996;66:135­139.
Klose KJ, Green BA, Smith RS, Adkins RH, MacDonald AM. University
of Miami Neuro-Spinal Index (UMNI): a quantitative method for de-
termining spinal cord function. Paraplegia. 1980;18:331­334.
Linsenmeyer TA. Male infertility following spinal cord injury. J Am
Paraplegic Soc. 1991;14:116­121.
Loras B, Vetele F, El Malki A, Rollet J, Soufir JC, Benahmed M. Seminal
transforming growth factor-beta in normal and infertile men. Hum
Reprod.1999;14:1534­1539.
Majumder GC, Dey CS, Haldar S, Barua M. Biochemical parameters of
initiation and regulation of sperm motility. Arch Androl. 1990;24:
287­303.
Matalliotakis I, Kiriakou D, Fragouli I, Sifakis S, Eliopoulos G, Kou-
mantakis E. Interleukin-6 in seminal plasma of fertile and infertile
men. Arch Androl. 1998a;41:43­50.
Matalliotakis I, Sifakis S, Goumemou A, et al. Cytokine levels in seminal
plasma. Clin Exp Obst Gyn. 1998b;25:58­60.
Mire-Sluis AR, Thorpe R. Laboratory protocols for the quantitation of
cytokines by bioassay using cytokine responsive cell lines. J Immunol
Meth. 1998;211:199­210.
Naz RK: Role of cell mediated immunity in infertility. In: Naz RK, ed.
Immunology of Reproduction. Boca Raton, Fla: CRC Press; 1985:61­
80.
Naz RK, Evans W. Decreased levels of interleukin-12 are not correlated
with leukocyte concentration and superoxide dismutase activity in se-
men of infertile men. Arch Androl. 1998;41:91­96.
Naz RK, Kaplan P. Increased levels of interleukin-6 in seminal plasma
of infertile men. J Androl. 1994;15:220­227.
Ohl DA, Denil J, Fitzgerald-Shelton K, et al. Fertility of spinal cord
injured males: effect of genitourinary infection and bladder manage-
ment on results of electroejaculation. J Am Paraplegic Soc. 1992;15:
53­59.
Ohl DA, Menge A, Jarow J. Seminal vesicle aspiration in spinal cord
injured men: insight into poor semen quality. J Urol. 1999;162:2048­
2051.
Padron OF, Brackett NL, Sharma RK, Lynne CM, Thomas AJ Jr, Agarwal
A. Seminal reactive oxygen species and sperm motility and mor-
phology in men with spinal cord injury. Fertil Steril. 1997;67:1115­
1120.
Paradisi R, Capelli M, Mandini M, Bellavia E, Flamigni C. Increased
levels of interferon-gamma in seminal plasma of infertile men. An-
drologia. 1996;28:157­161.
Rajasekaran M, Hellstrom WJ, Naz RK, Sikka SC. Oxidative stress and
interleukins in seminal plasma during leukocytospermia. Fertil Steril.
1995;64:166­171.
Randall JM, Evans DH, Bird VG, Aballa TC, Lynne CM, Brackett NL.
Leukocytospermia in spinal cord injured patients is not related to
histological inflammatory changes in the prostate. J Urol. 2003;170:
897­900.
Shimoya K, Matsuzaki N, Tsutsui T, Taniguchi T, Saji F, Tanizawa O.
Detection of interleukin-8 (IL-8) in seminal plasma and elevated IL-
8 in seminal plasma of infertile patients with leukospermia. Fertil
Steril. 1993;59:885­888.
Sonksen J, Biering-Sorensen F. Fertility in men with spinal cord or cauda
equina lesions. Semin Neurol. 1992;12:106­114.
Sonksen J, Ohl DA, Giwercman A, Biering-Sorensen F, Skakkebaek NE,
Kristensen JK. Effect of repeated ejaculation on semen quality in
spinal cord injured men. J Urol. 1999;161:1163­1165.
Trabulsi EJ, Shupp-Byrne D, Sedor J, Hirsh IH. Leukocyte subtypes in
electroejaculates of spinal cord injured men. Arch Phys Med Rehabil.
2002;83:31­33.
Wincek TJ, Meyer TK, Meyer MR, Kuehl TJ. Absence of a direct effect
of recombinant tumor necrosis factor-alpha on human sperm function
and murine preimplantation development.[comment]. Fertil Steril.
1991;56:332­339.
World Health Organization. Laboratory Manual for the Examination of
Human Semen and Sperm-Cervical Mucous Interaction. Cambridge,
United Kingdom: Cambridge University Press; 1999.