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The Journal of Clinical Endocrinology & Metabolism Vol. 82, No. 5 1426-1433
Copyright © 1997 by The Endocrine Society


Experimental Studies

Human Leydig Cells and Sertoli Cells Are Producers of Interleukins-1 and -61

Corinne Cudicini2, Hervé Lejeune, Edith Gomez, Eugène Bosmans, François Ballet, José Saez and Bernard Jégou

Groupe D’Etude de la Reproduction Chez le Mâle (GERM) INSERM U. 435, Université de Rennes I, Campus de Beaulieu (C.C., E.G., B.J.), 35042 Rennes, Bretagne; Rhône-Poulenc Rorer, Département de la Sécurité du Médicament, Centre de Recherche de Vitry-Alfortville (C.C., F.B.), 94403 Vitry sur Seine Cedex; INSERM Institut National de Recherche Agronomique INRA U. 418, Hôpital Debrousse (H.L., J.S.), 69322 Lyon Cedex 05, France; and Eurogenetics (E.B.), 3980 Tessenderlo, Belgium

Address all correspondence and requests for reprints to: Bernard Jégou, Groupe d’Etude de la Reproduction Chez le Mâle INSERM U 435, Université de Rennes I, Campus de Beaulieu, 35042 Rennes, Bretagne, France. E-mail: bernard.jegou{at}univrennes1.fr


    Abstract
 Top
 Abstract
 Introduction
 Materials and Methods
 Results
 Discussion
 References
 
Interleukins (IL)-1 and -6 have been shown to be produced by several categories of cells in the rat testis and involved in the paracrine control of testicular function. Evidence of high amounts of IL-1 have been shown in the human testis, but nothing is known about its cellular origin. Furthermore, to our knowledge, the presence of IL-6 in the human testis has not yet been investigated. Therefore, the present study was aimed at identifying IL-1 and -6 expression and production within the human testis, using RT-PCR, bioassays, and enzyme linked immunosorbent assays. We demonstrated that IL-1 and -6 messenger RNA and proteins were produced constitutively in vitro by human Leydig cell- and Sertoli cell-enriched preparations. FSH only stimulated IL-6 production by Sertoli cell-enriched preparations, but increased the release of both IL-1 and -6 in germ cell-depleted Sertoli cell cultures. In addition, lipopolysaccharides and latex beads enhanced the production of both cytokines by Sertoli cell cultures, whereas human chorionic gonadotropin and lipopolysaccharides enhanced the release of both cytokines by Leydig cells. Enzyme linked immunosorbent assays and neutralization experiments revealed that human Sertoli cells produce essentially the {alpha} form of IL-1, whereas both forms, {alpha} and ß, are present in Leydig cells.

The demonstration that human Leydig and Sertoli cells produce IL-1 and -6 under the control of gonadotropin hormones and exogenous factors, opens the possibility to study the involvement of these cytokines in the control of testis function, in normal and pathological conditions in men. 82:


    Introduction
 Top
 Abstract
 Introduction
 Materials and Methods
 Results
 Discussion
 References
 
INTERLEUKIN-1 (IL-1) is a member of the cytokine family having several important biological activities, such as the control of cell proliferation, induction of fever, and stimulation of production of other cytokines (1). IL-1 exists in two forms, the acidic form, IL-1{alpha}, and the neutral form, IL-1ß, and is synthetized by a wide variety of cells (2). They are coded by two different genes (3) but bind to the same receptor (4). Furthermore, the rat testis contains large amounts of an IL-1-like factor (5). In rat and mouse testicular interstitial tissue, Leydig cells and macrophages (6, 7, 8, 9, 10) secrete IL-1, predominantly the IL-1ß form, whereas within the seminiferous tubules, Sertoli cells and possibly germ cells produce IL-1{alpha} (11, 12). Sertoli cell IL-1 secretion increases during sexual maturation and fluctuates during the seminiferous epithelium cycle (11, 13). Furthermore, testicular IL-1 messenger RNA (mRNA) and protein can be regulated by gonadotropin hormones (9, 14) and by known activators of macrophages/monocytes IL-1, such as lipopolysaccharides (LPS) and latex beads (9, 10, 15).

One of the important functions of IL-1 is to induce the production of IL-6, another member of the cytokine family, in various cell types (16). Accordingly, within the rat testis, Sertoli cell IL-1 is known to stimulate the production of IL-6 by an autocrine mechanism, through the lipoxygenase pathway (17, 18). Sertoli IL-6 production is, like IL-1 production, stage-dependent and enhanced by LPS and FSH (17, 19). Absent in rat (17, 20) and human germ cells (our unpublished results), IL-6 mRNA and protein are, in contrast, also produced constitutively by rat Leydig cells and positively regulated by IL-1 and human CG (hCG) (20, 21).

Various actions of IL-1 and IL-6 have been observed within the testis, suggesting that these cytokines are important paracrine regulators (6, 19, 22, 23, 24, 25, 26).

In humans, the presence of IL-1 has been evidenced in testicular cytosols (27), but the cellular origin(s) and regulation of its production so far remains unknown. Therefore, the purpose of the present study was to investigate whether the two main somatic cell types of the testis, namely Sertoli and Leydig cells, are sources of IL-1 and -6 in humans, and how these cytokines were regulated. This report presents evidence of the presence of IL-1 and -6 mRNAs and immunoreactive and bioactive proteins in human adult Leydig and Sertoli cell cultures and describes their regulation by gonadotropins, LPS, and latex beads.


    Materials and Methods
 Top
 Abstract
 Introduction
 Materials and Methods
 Results
 Discussion
 References
 
Isolation and culture of human Leydig and Sertoli cells

Testes were removed from five adult men (age, 21–45 yr) in recent cerebral death, at the same time as kidneys were removed for transplantation. This protocol was approved by the Ethical Committee of the University of Lyon, France.

Isolation and culture of human Leydig and Sertoli cells were performed according to a previously described method (28). Cells were plated in 12-well culture dishes at 106 cells/mL per well for Leydig cell preparations and 5–10 cell aggregates 106/mL per well for Sertoli cell preparations (1 aggregate gave 2.7 ± 0.7 plated cells), on extracellular basal membrane from bovine corneal endothelial cells prepared as previously described (29).

The medium was discarded and replaced after 24 h for Sertoli and Leydig cells. In some instances, a hypotonic treatment of the Sertoli cell cultures was performed with a TRIS-HCl buffer solution 20 mmol/L, pH 7.4, for 2.5 min (30) to remove most of the contaminating germ cells (see Results). The cells were further cultured for 24 h before treatment with hCG (10-9 mol/L; Organon, Paris, France) for the Leydig cells, recombinant human FSH (100 mU/mL, kindly provided by The Ares Serono group, Geneva, Switzerland) for the Sertoli cells, or LPS from E. coli (50 µg/mL; Sigma Chemical Co., St. Louis, MO) for both Leydig and Sertoli cells. In some experiments, Sertoli cells were also incubated with latex beads (7 x 108/mL; Sigma) for 24 h. At the end of the incubation, the media were collected, centrifuged, and stored at -20 C until IL-1 and -6 assays were performed, whereas cells destined for RNA preparation were collected and stored at -80 C.

Characterization of human testicular cell preparations. The presence of Sertoli cells in the Leydig culture was checked by light microscopic examination. Human Sertoli cells presented the typical granulations previously described (31). Sertoli cells accounted for less than 1% of the Leydig cell preparation. Seventy to eighty percent of the Percoll purified cells were positive for 3ß-hydroxysteroid dehydrogenase {Delta}4-{Delta}5 isomerase (3ß-HSD) histochemical coloration (32).

The number of Leydig cells contaminating the Sertoli cell-enriched fraction was assessed by the 3ß-HSD histochemical coloration and found to vary between 3–6%.

The proportion of germ cells in the Sertoli cell preparations was decreased by the various washing steps of the cultures. The number of germ cells remaining in the Sertoli cell preparations averaged 8–12% at the time the cells were exposed to FSH, LPS, or latex beads. The hypotonic shock lowered this number to 1–5%. The viability of plated human Leydig and Sertoli cells, as checked by trypan blue exclusion, was > 95% at the different times of culture.

Immunocytochemical identification of macrophages. Macrophages were identified in the testicular cell preparations by immunocytochemistry with the monoclonal mouse antihuman monocyte CD14 antibody, as primary antibody in an alkaline phosphatase antialkaline phosphatase staining technique (DAKO S.A., Trappes, France). An aliquot of the Leydig and Sertoli cell-enriched preparations (105 cells in 100 µL) was cytofuged onto polylysin-coated glass slides, acetone fixed, and stored at -70 C until used. Immunocytochemical staining was performed according to manufacturer’s instructions, the anti-CD 14 was used at a dilution of 1:20. Ficoll-isolated human blood leukocytes were used as positive (stained red) control; reactions performed on testicular cells without the primary antibody were considered negative control. Hematoxylin counterstaining was performed. Macrophages (CD14+ cells) accounted for less than 0.1% of the cells in the Sertoli cell preparations and 4–8% of the cells in the Leydig cell preparations.

Isolation and culture of human blood monocyte-derived macrophages

Human blood monocyte-derived macrophages were prepared according to the method described by Audran et al. (33). Macrophage purity, analyzed with a Coulter Counter ZM (Coulter, Marseilles, France), was consistently 95% and cell viability over 95%, as judged by trypan blue staining. Macrophages were seeded at 5 x 106/mL in Iscove-modified Dulbecco’s medium and stimulated in culture for 90 min in the presence of 1 µg/mL LPS before being collected for RNA preparation and RT-PCR analysis.

Preparation of total RNA and RT-PCR analysis

Total RNA was extracted from human blood macrophages and from human Leydig and Sertoli cell cultures, as described previously (34). First-strand complementary DNAs (cDNAs) were synthesized from 2.5 µg total RNA, with 10 ng/µL random hexanucleotides primers (Pharmacia Biotech, Saclay, France) and 200 U of Moloney-murine leukemia virus reverse transcriptase (Gibco BRL, Life Technologies, Eragny, France), in a Tris-HCl-MgCl2 reaction buffer containing 0.5 mmol/L of each deoxynucleotide triphosphate (Boehringher Mannheim, Meylan, France), 10 mmol/L dithiothreitol, and 40 U of RNasin (Promega, Charbonnières, France) in a final volume of 20 µL. The reverse transcriptase reaction was performed for 1 h at 37 C, and the reaction volume was then brought up to 50 µL (cDNAs RT+). Reverse transcriptase negative controls were performed in parallel, using the same RNA samples without Moloney-murine leukemia virus reverse transcriptase in the reaction medium (cDNAs RT-). After RT of RNA, 3 µL of the resulting cDNA (RT+) was used for PCR, using four couples of oligonucleotide primers (Clontech Laboratories, Ozyme, Montigny-Le-Bretonneux, France) corresponding to positions 1038/1067 and 1876/1905 for the human ß-actin sequence (35), 205/228 and 744/768 for the human IL-1{alpha} sequence (3), 285/314 and 587/616 for the human IL-1ß sequence (3), and 34/56 and 640/661 for the human IL-6 sequence (36). As negative controls, PCRs were carried out on cDNA RT-. PCR was performed on a Biometra trio-thermoblock TB1 DNA Thermal cycler (Biometra Göttingen, Germany) (94 C, 5 min followed by 35 cycles, 94 C, 1 min; 60 C, 1 min; 72 C, 2 min; and finally 72 C, 10 min). Ten microliters of the PCR products were run on a 1% agarose gel with ethidium bromide and photographed under UV light. To verify the specificity of the amplified PCR products visualized, we purified them to perform specific enzymatic digestion (Geneclean II kit, Bio 101, La Jolla, CA) as follows: the 564 bp IL-1{alpha} product was cut by EcoRI; the 332 pb IL-1ß product was cut by HindIII, and the 628 bp IL-6 product was cut by Sau3AI. These three enzymes were chosen because they have only one restriction site in the sequences amplified, as shown by the analysis of their restriction maps (Server Bisance, CITI 2, Paris, France).

Bioassays of IL-1 and -6

IL-1 was quantified in the culture media using the murine thymocyte proliferation assay (18, 37). The female mice C3H/HeJ used in the assay were purchased from Charles River, Wiga, Sulzfeld, Germany. One unit of IL-1 was defined as the quantity of tested material required to double [3H]thymidine incorporation into thymocytes when compared with phytohemagglutinin (PHA; DIFCO, Detroit, MI)-stimulated cultures, PHA being a comitogen factor added to all the assay. In our assay, 1 U IL-1 corresponds to 0.32 ± 0.10 ng.

IL-6 was measured using the specific IL-6-dependent 7TD1 mouse hybridoma cell line proliferation assay (17, 38). In this assay, 1 U was defined as the IL-6 concentration that gave half-maximal proliferation and corresponds to 1 ± 0.27 pg of IL-6.

The intra- and interassay coefficients of variation were <20 and <28% for the IL-1 bioassay, respectively, and <10% for both for IL-6. All samples from each independent study were run in the same IL-1 or -6 bioassay. IL-1 and -6 were undetectable in media incubated for 24 h at 35 C in extracellular basal membrane-coated culture dishes, without testicular cells.

Neutralization experiments

Because the IL-1 bioassay does not discriminate between the IL-1ß and -1{alpha} forms, we performed neutralization experiments using specific antibodies to identify the type of IL-1 involved in the bioactivities measured.

Various dilutions of human recombinant IL-1{alpha} and -1ß (rhIL-1{alpha} and -ß; Sigma) and of media from Leydig and Sertoli cultures were incubated for 4 h at 37 C with the given concentration of: rabbit antihuman IL-1{alpha} (0.15 mg/mL; a gift from Dr. B. Ferrua, Nice, France); or of murine antihuman IL-1ß neutralizing antibodies (0.01 mg/mL; a gift from Dr. J. Wijdenes, Innotherapie Laboratoires, Besançon, France); or of both anti-IL-1{alpha} and anti-IL-1ß antibodies; or of nonimmune rabbit IgG (0.15 mg/mL); and/or of supernatant of nonimmune hybridoma (0.01 mg/mL) used as controls. At the end of the incubation period, all the samples were bioassayed for IL-1.

In parallel to these experiments, we also established that the antibodies used did not interfere with the proliferation of the thymocytes used for the IL-1 bioassay and displayed the expected effects on rhIL-1 (anti-IL-1{alpha} antibody neutralizing only the activity of rhIL-1{alpha} and anti-IL1ß antibody neutralizing only the activity of rhIL-1ß).

IL-1{alpha}, -1ß, and -6 enzyme linked immunosorbent assays (ELISAs)

Immunoreactive IL-1{alpha}, -1ß, and -6 of Leydig and Sertoli cell culture media were quantified using specific ELISA kits from Eurogenetics (Tessenderlo, Belgium). According to the manufacturer, no cross-reactivity was measured between: IL-1ß, -2, -3, -4, -6, tumor necrosis factor (TNF)-{alpha} or -ß, granulocyte-macrophage colony-stimulating factor (GM-CSF) or granulocyte-colony stimulating factor (G-CSF), and IL-1{alpha} ELISA; IL-1{alpha}, -2, TNF, or interferon-{gamma}, and IL-1ß ELISA; IL-1ß, -2, -3, -4, TNF-{alpha} or -ß, GM-CSF or G-CSF, and IL-6 ELISA. Sensitivity of IL-1{alpha}, -1ß, and -6 ELISA kits were 10, 2, and < 5 pg/mL, respectively. The intraassay variations were <15, 7, and 10% for IL-1{alpha}, -1ß, and -6, respectively.

Because of the great difficulty in obtaining human testis and the small volumes of the culture media available for analysis, ELISAs could not be performed on all samples run in the IL-1 and -6 bioassays. Therefore, to verify the results of the bioassays, ELISA measurements were only performed on a selected number of samples of each experiment.

Statistical analyses

Results are expressed as means ± SEM. Statistical analyses were performed by the use of Student’s t test after ANOVA. Significance was defined as P < 0.05.


    Results
 Top
 Abstract
 Introduction
 Materials and Methods
 Results
 Discussion
 References
 
RT-PCR experiments

Our RT-PCR experiments demonstrated the presence of IL-1{alpha} (564 bp), IL-1ß (332 bp), and IL-6 (628 bp) mRNAs in the Leydig and Sertoli cell preparations (Fig. 1Go). The integrity of our RNA preparations was assessed by the presence of ß-actin mRNAs in blood-activated macrophages and in Leydig and Sertoli cell preparations, as confirmed by the expected specific PCR product (Fig. 1Go). The RT-PCRs performed without reverse transcriptase were always negative, establishing the absence of genomic contamination of our samples (data not shown). The verification of the RT-PCR products IL-1{alpha}, -6, and -1ß by enzymatic digestion are presented in Fig. 2Go and show that the 564-bp IL-1{alpha}, the 332-bp IL-1ß, and the 628-pb IL-6 product-generated fragments (Fig. 2Go) expected from the restriction map analyses of the three sequences studied.



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Figure 1. Expression of ß-actin and IL-1{alpha}, -6, and -1ß mRNAs in human Sertoli and Leydig cells in basal culture conditions. Control (-), negative RT-PCR control reaction performed without cDNA. Activated human blood macrophages were used as positive control for RT-PCR reactions. PCR products were run on a 1% agarose gel with ethidium bromide and photographed under UV light. DNA size markers (L, in bp) are shown the left. PCR product sizes are indicated in brackets.

 


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Figure 2. Restriction analysis of IL-1{alpha}, -6, and -1ß PCR products amplified from human Sertoli cells (A) and Leydig cells (B). PCR product (-); purified PCR product digested by a restriction enzyme (+). IL-1{alpha} PCR product cut by EcoRI generates two fragments of 371 bp and 193 bp; IL-6 PCR product cut by Sau3AI generates two fragments of 449 bp and 179 bp; IL-1ß PCR product cut by HindIII generates two fragments of 221 bp and 112 bp. PCR products digested or undigested were run on a 2% agarose gel with ethidium bromide and photographed under UV light. DNA size markers (L, in bp) are shown the left.

 
Biological activity of IL-1 and -6 in Sertoli cell-enriched culture media

Bioassays revealed that under basal culture conditions Sertoli cell-conditioned media displayed both IL-1 and -6 bioactivity (Fig. 3Go, A and B). Exposure of the Sertoli cells to FSH enhanced IL-6 bioactivity, but not IL-1 production. In contrast, exposure of the cells to LPS or to latex beads greatly increased the production of both cytokines (Fig. 3Go, A and B).



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Figure 3. Bioactive IL-1 and -6 production by human Sertoli cells. Day 3 Sertoli cells were cultured without (control; C) or with FSH (100 mU/mL), LPS (50 µg/mL), or latex beads (7 x 108/mL) for 24 h and IL-1 (A) and IL-6 (B) were assayed in culture media using their respective bioassays (see Materials and Methods). Data presented are means ± SEM of three separate experiments, each performed in triplicate. *, P < 0.05; **, P < 0.01; ***, P < 0.001 compared with respective basal IL-1 and -6 levels (C).

 
Bioactive levels of IL-1 and -6 in hypotonic-treated Sertoli cell culture media

Because recent studies suggested that IL-1 is also probably produced by germ cells (rat, Ref. 12 ; humans, our unpublished observations), and because our Sertoli cell preparations were contaminated by these cells (8–12%), we performed a series of experiments assaying IL-1 in media from cultures in which the number of contaminating germ cells was reduced (1–5% remaining) by hypotonic treatment (30). Under these basal conditions, Sertoli cells still produced IL-1, though at levels that represented about one-third of the levels measured in cultures without hypotonic treatment (Fig. 4AGo vs. 3A). Furthermore, after elimination of germ cells, a significant stimulation of IL-1 bioactivity by FSH was revealed, whereas the strong stimulation by LPS was even enhanced. Unlike IL-1 bioactive levels, IL-6 bioactivity levels were only marginally influenced by the hypotonic treatment (Fig. 4BGo vs. 3B), which is consistent with our previous observations that germ cells do not produce IL-6 (rat, Ref. 17 ; human, our unpublished observations).



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Figure 4. Production of IL-1 and -6 by human Sertoli cells exposed to a hypotonic treatment on day 2 of culture for removing contaminating germ cells. On day 3, cells were exposed or not (control; C) to either FSH (100 mU/mL) or LPS (50 µg/mL) for 24 h, and IL-1 (A) and IL-6 (B) levels were measured in culture media using their respective bioassays (see Materials and Methods). Data presented are means ± SEM of three separate experiments each performed in triplicate. *, P < 0.05; **, P < 0.01; ***, P < 0.001 compared with respective basal IL-1 and -6 levels (C).

 
Biological activity of IL-1 and -6 in Leydig cell culture media

As in Sertoli cells, bioactive IL-1 and -6 were found in conditioned media of human Leydig cell-enriched preparations cultured in basal conditions. Both hCG and LPS were found to stimulate markedly the production of both these cytokines (Fig. 5Go, A and B).



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Figure 5. Bioactive IL-1 and -6 production by human Leydig cells. Day 3 Leydig cells were cultured without (control; C) or with hCG (10-9 mol/L) or LPS (50 µg/mL) for 24 h. IL-1 (A) and IL-6 (B) were assayed in culture media using their respective bioassays (see Materials and Methods). Data presented are means ± SEM of three separate experiments each performed in triplicate. *, P < 0.05; **, P < 0.01; ***, P < 0.001 compared with respective basal IL-1 and -6 levels (C).

 
Neutralization of Sertoli and Leydig cell IL-1 bioactivity

The thymocyte proliferation assay used to measure IL-1 bioactivity in this study has been shown to cross-react with several other cytokines (39, 40) and does not discriminate between IL-1{alpha} and -1ß. Nonimmune rabbit IgG and supernatant of nonimmune hybridoma had no neutralizing effect on Sertoli and Leydig cell IL-1 bioactivity (data not shown). In the absence of LPS, the IL-1 activity detected in Sertoli cell-conditioned media was completely neutralized by anti-IL-1{alpha} antiserum, but not affected by anti-IL-1ß antibody (Fig. 6AGo). As shown above (Fig. 3AGo), LPS markedly stimulated Sertoli cell IL-1 activity (Fig. 6AGo). Furthermore, the addition of the anti-IL-1{alpha} antibody alone or in combination with the anti-IL-1ß antibody reduced this activity by approximately 75%; whereas no effect of the anti-IL-1ß antibody used alone was seen. Therefore, most bioactivity detected in Sertoli cell media is attributable to IL-1{alpha}.



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Figure 6. Effects of specific antihuman IL-1{alpha} or antihuman IL-1ß or of both antihuman IL-1{alpha} and -ß antibodies on IL-1 bioactivity detected in culture media of human Sertoli cells (A) and human Leydig cells (B) stimulated or not by LPS (50 µg/mL). A and B, Histograms indicated as PHA give threshold of sensitivity of IL-1 bioassay, whereas values of IL-1 bioactivity in media without antibodies (control values) are indicated by histograms indicated - anti-IL-1. Values are means ± SD of three culture dishes, each assayed in triplicate. *, P < 0.05; **, P < 0.01; ***, P < 0.001.

 
Under basal conditions, a significant inhibition of Leydig cell IL-1 bioactivity was observed with the anti-IL-1{alpha} antibody but not with the anti-IL-1ß antibody (Fig. 6BGo). In LPS-stimulated Leydig cells incubated with the anti-IL-1{alpha} antibody alone, IL-1 levels were 80% of that measured in the controls, but the decrease observed was not statistically significant. A much greater inhibition (40%) was seen when the anti-IL-1ß antibody was used, clearly indicating the presence of IL-1ß. This inhibition was even greater (70%) when both antisera were added together (Fig. 6BGo). It is concluded that most probably, in basal as well as in LPS-stimulated conditions, both IL-1{alpha} and -1ß are present in Leydig cells.

Immunological activity of IL-1 and -6 in Sertoli and Leydig cell culture media

In confirmation of the results of bioactivity presented above (Fig. 3AGo), IL-1{alpha} was detected in the Sertoli cell media and was stimulated by LPS (~ 3- to 5-fold) and latex beads (about 10-fold), but not at all or only marginally by FSH (Fig. 7AGo). The very low IL-1ß activity detected in these media by the ELISA kit did not increase when the Sertoli cell preparations were incubated with FSH, LPS, or latex beads (data not shown). Low IL-1{alpha} production was detected in Leydig cell media (Fig. 7BGo). This production was enhanced by hCG (~ 2-fold) and by LPS (~ 2- to 4-fold). Much higher levels of IL-1ß were measured in these medias, which were increased in the presence of hCG (~ 2-fold) and LPS (~ 3-fold) (Fig. 7CGo).



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Figure 7. Immunoreactive IL-1 production by human Sertoli and Leydig cells. Day 3 Sertoli and Leydig cells were cultured without (control; C) or with FSH (100 mU/mL for Sertoli cells), latex beads (7.108 mL for Sertoli cells), hCG (10-9 mol/L for Leydig cells), or LPS (50 µg/mL) for 24 h. Media were then assayed for IL-1{alpha} (A, Sertoli cells; B, Leydig cells) and IL-1ß (C, Leydig cells), using specific ELISAs (see Materials and Methods). Black and white histograms correspond to two independent experiments performed, and each histogram represents mean of duplicates in each experiment.

 
The results of the IL-6 ELISA were also totally consistent with the previous results of the IL-6 bioassay (Figs. 3BGo and 5BGo): IL-6 was constitutively produced by both Sertoli and Leydig cells and stimulated markedly by FSH (~ 5-fold), LPS (~ 10-fold), and latex beads (~ 15-fold) in Sertoli cell-enriched preparations (Fig. 8AGo) and by hCG (~ 3-fold) and LPS (>2-fold) in Leydig cell-enriched preparations (Fig. 8BGo).



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Figure 8. Immunoreactive IL-6 production by human Sertoli cells (A) and Leydig cells (B). Day 3 Sertoli and Leydig cells were cultured without (control; C), with FSH (100 mU/mL for Sertoli cells), or with latex beads (7.108 mL for Sertoli cells), hCG (10-9 mol/L for Leydig cells), or LPS (50 µg/mL) for 24 h. IL-6 was assayed in culture media using a specific ELISA (see Materials and Methods). Black and white histograms correspond to two independent experiments performed, and each histogram represents mean of duplicates in each experiment.

 

    Discussion
 Top
 Abstract
 Introduction
 Materials and Methods
 Results
 Discussion
 References
 
Our results reveal that human Leydig and Sertoli cell-enriched preparations from young adult men express IL-1 and -6 mRNAs constitutively in vitro. These mRNAs are translated into proteins that can be detected in culture media by bioassays and immunoassays. These data are in accordance with previous results obtained in the rat showing that these cytokines are produced by Sertoli cells (11, 17, 18) and Leydig cells (9, 10, 20, 21) and the recent finding of IL-1 mRNA in crude human testicular cell preparations (41).

The results of experiments using specific antibodies and immunoassays led to the conclusion that the IL-1 produced by human Sertoli cells is essentially the IL-1{alpha} type. Although the extremely high sensitivity of RT-PCR allowed the detection of IL-1ß mRNA in the Sertoli cell cultures, the IL-1ß form accounted for a very marginal part of IL-1 immunoactivity in the human Sertoli cell media. Whether the IL-1ß mRNA originated from the very few contaminant macrophages remains to be determined. In contrast, the immunoneutralization experiments performed on Leydig cell media revealed that in both basal and LPS-stimulated conditions, IL-1 bioactivity was not completely abolished by both the anti-IL-1{alpha} and anti-IL-1ß antibodies. This probably indicated that the Leydig cell media contained not only IL-1{alpha} and IL-1ß, the presence of which was demonstrated by the use of the specific antibodies taken separately and by the immunoassays, but also other products interacting with the IL-1 bioassay. We established that IL-6 was not involved in this phenomenon, because addition of a specific antihuman IL-6 antibody to Sertoli and Leydig cell culture media containing the anti-IL-1{alpha} and IL-1ß antibodies did not reduce the residual IL-1 bioactivity observed (data not shown). Moreover, a synergistic effect of IL-2 can be excluded, because human testicular cytosols do not exhibit IL-2 activity (27). In other respects, TNF-{alpha}, not found in media from Sertoli and Leydig cells, could originate from contaminant macrophages and germ cells (8, 42, 43). In a similar manner, GM-CSF, a potent costimulator factor of murine thymocyte proliferation (40), found recently in rat testicular macrophage-conditioned media (8), could contribute to the bioactivity detected in Leydig cell media. Results of IL-6 immunoactivity of our ELISA experiments were also consistent with those obtained with the IL-6 bioassay for both human Sertoli and Leydig cell-enriched cultures.

Our Sertoli cells were only slightly contaminated by macrophages, as assessed by the very low number of CD14+ cells detected in the Sertoli cell-enriched preparations, but they were contaminated by germ cells because of the close anatomical contact existing in vivo between the Sertoli cells and the germ cells (44). Because recent studies have shown that IL-1, but not IL-6, is present in rat and human germ cells (rat, Refs. 12, 17, 20 ; human, our unpublished observations), part of the IL-1 measured in the Sertoli cell-enriched cultures might originate from the germ cells contaminating the culture. This probably explains why production of IL-1, but not that of IL-6, was reduced after hypotonic treatment of Sertoli cells. However, it is also most probable that the decline of IL-1 could also result to some extent from the direct effect of the hypotonic treatment (45). It is well established that FSH action on the seminiferous epithelium is mediated by Sertoli cells (46). Interestingly, whereas in the presence of germ cells FSH was unable to enhance Sertoli cell IL-1 production, a significant FSH-induced stimulation of this production was observed after germ cell removal. This could be caused by the lifting of the inhibitory effect that germ cells exert on Sertoli cell responsiveness to FSH, as evidenced in different species (47).

In contrast to IL-1, IL-6 secretion was markedly stimulated by FSH, even in the presence of germ cells, as previously observed in the rat (17). The fact that, as in the rat, FSH stimulated both IL-1 and -6 production is a very strong argument to support the hypothesis that Sertoli cells are producers of both of these cytokines in the human testis. However, because of the intrinsic limitations of the techniques presently available to study human Sertoli cell IL-1 activity, it cannot be totally ruled out that a FSH-stimulated Sertoli cell factor could have stimulated a contaminating cell to produce these cytokines, though this appears very improbable, considering the low proportion of contaminants in our Sertoli cell preparations. Endotoxins from gram-negative bacteria, such as LPS from E. coli, are potent activators of cytokine production. They are able to stimulate levels of rat testicular IL-1 and -6 production in vitro (6, 10, 15, 17) and in vivo (6, 7, 48). The present study, showing an LPS-induced increase of the levels of both IL-1 and -6 in human Sertoli cell media are in line with these results. Our results also demonstrate that, as in the rat Sertoli cells (15, 17), phagocytosis of latex beads, which are other activators of macrophage IL-1 production (3), induces a strong stimulation of IL-1 and -6 release by human Sertoli cell-enriched cultures. This effect of latex beads is considered to be analogous with the residual body effect (15, 17).

It has been shown that rat Leydig cells also produce cytokines (9, 10, 20, 21). However, because the interstitium of the testis contains a high proportion of macrophages, the involvement of both Leydig cells and macrophages in cytokine production is probable. Whereas our Sertoli cell preparations were virtually uncontaminated by macrophages, Leydig cell preparations contained 4–8% of CD14+ cells. However, it is notable that hCG does not regulate macrophage function in general and macrophage IL-6 production in particular (6). Therefore, the fact that both IL-1 and -6 production are stimulated by hCG in this study, which was also observed in cultured rat Leydig cells (9, 21), very strongly suggests that human Leydig cells are producers of these cytokines. Even so, as for human Sertoli cells, it cannot totally be excluded that hCG may have stimulated a Leydig cell factor that could have induced production of IL-1 or -6 by one of the cell types contaminating our Leydig cell fraction. In addition to hCG, LPS was found to markedly stimulate IL-1 and -6 release from human Leydig cells.

In the rat, IL-1 has been found to stimulate DNA synthesis in preleptotene spermatocyte and in spermatogonia (22), whereas IL-6 was found to exert the reverse action (19), therefore suggesting major effects of these cytokines in the spermatogenetic process. Furthermore, IL-1 and -6 were also found to modulate Sertoli cell function in vitro (23, 24, 25), and IL-1 was shown to influence Leydig cell function (6), as well as to stimulate Leydig cell DNA synthesis in immature rats (26). Whether similar important IL-1 and -6 paracrine actions occur in the human testis remains to be established.

By providing the first data supporting that human Leydig and Sertoli cells produce IL-1 and -6, and that IL-1 and -6 productions are under the control of physiological (gonadotropin) and immunogenic (LPS) factors, or can be induced by the phagocytosis of latex beads by Sertoli cells, we open the way to the investigation of the role of these cytokines in the autocrine and paracrine regulations of the normal and pathophysiological testicular function in men.


    Acknowledgments
 
We are grateful to Dr. V. Syed for her participation in the preliminary steps of this study, Dr. J. Van Snick (Ludwig Institute for Cancer Research, Brussels, Belgium) for providing the 7TD1 cell line, Dr. P.Y. Le Bail (Institut National de Recherche Agronomique, Rennes, France), and the Centre de Transfusion Sanguine de Rennes (France) for providing the rabbit IgG and supernatant of hybridoma. We thank Mrs. A.M. Touzalin and Mrs. P. Sanchez for their excellent technical assistance.


    Footnotes
 
1 This work was supported by INSERM, Direction de la Recherche et des Etudes Doctorales, Rhône-Poulenc Rorer, Centre Regional pour l’Innovation et Transfert de Technologie-Génie Biologique et Médical Bretagne, Institut National de Recherche Agronomique: Régulations Intragonadiques and the Réseau de recherche clinique INSERM 493010. Back

2 Recipient of a Rhône-Poulenc Rorer fellowship. Back

Received September 19, 1996.

Revised January 15, 1997.

Accepted January 23, 1997.


    References
 Top
 Abstract
 Introduction
 Materials and Methods
 Results
 Discussion
 References
 

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