Differential effects of recombinant interleukin-1 alpha and beta on Leydig cell function

Effect of IL-1β on the Development of Spermatogenesis In Vitro in Normal and Busulfan-Treated Immature Mice

Gonadotoxic agents could impair spermatogenesis and may lead to male infertility. The present study aimed to evaluate the effect of IL-1β on the development of spermatogenesis from cells isolated from seminiferous tubules (STs) of normal and busulfan-treated immature mice in vitro. Cells were cultured in a 3D in vitro culture system for 5 weeks. We examined the development of cells from the different stages of spermatogenesis by immunofluorescence staining or qPCR analyses. Factors of Sertoli and Leydig cells were examined by qPCR analysis. We showed that busulfan (BU) treatment significantly reduced the expression of testicular IL-1β in the treated mice compared to the control group (CT). Cultures of cells from normal and busulfan-treated immature mice induced the development of pre-meiotic (Vasa), meiotic (Boule), and post-meiotic (acrosin) cells. However, the percentage of developed Boule and acrosin cells was significantly lower in cultures of busulfan-treated mice compared to normal mice. Adding IL-1β to both cultures significantly increased the percentages of Vasa, Boule, and acrosin cells compared to their controls. However, the percentage of Boule and acrosin cells was significantly lower from cultures of busulfan-treated mice that were treated with IL-1β compared to cultures treated with IL-1β from normal mice. Furthermore, addition of IL-1β to cultures from normal mice significantly increased only the expression of androgen receptor and transferrin but no other factors of Sertoli cells compared to their CT. However, the addition of IL-1β to cultures from busulfan-treated mice significantly increased only the expression of androgen-binding protein and the FSH receptor compared to their CT. Adding IL-1β to cultures of normal mice did not affect the expression of 3βHSD compared to the CT, but it significantly reduced its expression in cultures from busulfan-treated mice compared to the CT. Our findings demonstrate the development of different stages of spermatogenesis in vitro from busulfan-treated mice and that IL-1β could potentiate this development in vitro.

Hormonal control of Sertoli cell metabolism regulates spermatogenesis

Hormonal regulation is essential to spermatogenesis. Sertoli cells (SCs) have functions that reach far beyond the physical support of germ cells, as they are responsible for creating the adequate ionic and metabolic environment for germ cell development. Thus, much attention has been given to the metabolic functioning of SCs. During spermatogenesis, germ cells are provided with suitable metabolic substrates, in a set of events mediated by SCs. Multiple signaling cascades regulate SC function and several of these signaling pathways are hormone-dependent and cell-specific. Within the seminiferous tubules, only SCs possess receptors for some hormones rendering them major targets for the hormonal signaling that regulates spermatogenesis. Although the mechanisms by which SCs fulfill their own and germ cells metabolic needs are mostly studied in vitro, SC metabolism is unquestionably a regulation point for germ cell development and the hormonal control of these processes is required for a normal spermatogenesis.

Interleukin 1 alpha (IL1A) is a novel regulator of the blood-testis barrier in the rat

Throughout spermatogenesis, leptotene spermatocytes must traverse the blood-testis barrier (BTB) at stages VIII-XI to gain entry into the adluminal compartment for continued development. However, the mechanism underlying BTB restructuring remains somewhat elusive. In this study, interleukin 1 alpha (IL1A) was administered intratesticularly to adult rats in order to assess its effects on spermatogenesis. IL1A was shown to perturb Sertoli-germ cell adhesion, resulting in germ cell loss from approximately 50% of seminiferous tubules by 15 days posttreatment. Equally important, the functional integrity of the BTB was compromised when inulin-fluorescein isothiocyanate was detected in the adluminal compartment of the seminiferous epithelium following its administration via the jugular vein. Interestingly, IL1A did not affect the steady-state levels of proteins that confer BTB function, namely OCLN, CLDN1, F11R, TJP1, and CDH2. Instead, the localizations of OCLN, F11R, and TJP1 in the seminiferous epithelium were altered; these proteins appeared to move away from sites of cell-cell contact. Moreover, IL1A was shown to perturb the orderly arrangement of filamentous actin at the BTB and apical ectoplasmic specialization with distinct areas illustrating loss of actin filaments. Taken collectively, these results suggest that IL1A-induced BTB disruption is not mediated via the reduction of target protein levels. Instead, IL1A's primary cellular target appears to be the Sertoli cell actin cytoskeleton. It is possible that localized production of IL1A by Sertoli and/or germ cells in vivo results in BTB restructuring, and this may facilitate the movement of leptotene spermatocytes across the BTB.

Chemical neuroimmunology: health in a nutshell bidirectional communication between immune and stress (limbic-hypothalamic-pituitary-adrenal) systems

Stress is a ubiquitous and pervasive part of modern life that is frequently blamed for causing a plethora of diseases and other discomforting medical conditions. All higher organisms, including humans, experience stress in the form of a wide variety of stressors that range from environmental pollutants and drugs to traumatic events or self-induced trauma. Stressors registered by the central nervous system (CNS) generate physiological stress responses in the body (periphery) by means of the limbic-hypothalamic-pituitary-adrenal (LHPA) axis. This LHPA axis operates through the use of chemical messengers such as the stress hormones corticotropin-releasing hormone (CRH) and glucocorticoids (GCs). Under conditions of frequent exposure to acute stress and/or chronic, long-term exposure to stress, the LHPA axis becomes dysfunctional and in the process frequently overproduces both CRH and GCs, which results in many mild to severely toxic side effects. Bidirectional communication between the LHPA axis and immune/inflammatory systems can dramatically potentiate these side effects and create environments in the CNS and periphery ripe for the triggering and/or promotion of tissue degeneration and disease. This review aims to present as far as possible a molecular view of the processes involved so as to provide a bridge from the diffuse range of studies on molecular structure and receptor interactions to the burgeoning biological and medical literature that describes the empirical interplay between stress and disease. We hope that our review of this fast-growing field, which we christen chemical neuroimmunology, will give a clear indication of the striking range and depth of current molecular, cellular and medical evidence linking stress hormones to degeneration and disease. In so doing, we hope to provide encouragement for others to become interested in this critical and far-reaching field of research, which is very much at the heart of many important disease processes and very much a critical part of the crucial interface between chemistry and biology.

Role of testicular interstitial macrophages in regulating testosterone release in hyperprolactinemia

Hyperprolactinemia-induced hypogonadism has been linked to a dysfunction of the hypothalamus-pituitary-testis axis. The direct inhibitory effects of prolactin on the testicular release of testosterone have also been demonstrated, though their mechanisms remain unclear. Incubation of rat testicular interstitial cells (TICs) with prolactin stimulated the release of testosterone. TICs from rats with anterior pituitary-grafting-induced hyperprolactinemia release lower amounts of testosterone than controls. However, Leydig cells isolated from anterior pituitary-grafted rats release a greater amount of testosterone. These paradoxical observations have remained unexplained. This study examined the roles of testicular interstitial macrophages and of their product, tumor necrosis factor-alpha (TNF-alpha), in regulating Leydig cells under condition of hyperprolactinemia. Hyperprolactinemia was induced by grafting two anterior pituitary glands of rats under the renal capsule. Control animals were grafted with rat cortex tissue. The rats were sacrificed 6 weeks later. TICs and macrophages, and Leydig cells were isolated for in vitro incubation and drugs challenge. Testosterone released by testicular interstitial or Leydig cells was measured by radioimmunoassay. TNF-alpha concentration in the medium of TICs or macrophages was measured by enzyme-linked immunosorbent assay (ELISA). A dose-dependent stimulation of TNF-alpha secretion in the medium of TICs or macrophages by the prolactin challenge was observed. Higher amounts of TNF-alpha were released by TICs in the anterior pituitary-grafted rats than in the control group. In contrast, the release of TNF-alpha by testicular interstitial macrophages isolated from the anterior pituitary- and cortex-grafted groups was quantitatively similar. Challenge with human chorionic gonadotropin did not modify the TNF-alpha release by testicular interstitial macrophages in either group. Challenge of Leydig cells with TNF-alpha inhibited their release of testosterone stimulated by human chorionic gonadotropin, but not their basal testosterone release. These different patterns of testosterone release in TICs versus Leydig cells cultures in anterior pituitary-grafted rats may be due to the influence of testicular interstitial macrophages. These observations correlate with in vivo conditions, where prolactin increases the release of TNF-alpha by testicular interstitial macrophages, which, in turn, decreases the human chorionic gonadotropin-stimulated release of testosterone by Leydig cells. In summary, hyperprolactinemia-induced hypogonadism involves a mechanism of prolactin-originated, macrophage-mediated inhibitory regulation of testosterone release by Leydig cells. TNF-alpha, one of the cytokines secreted by macrophages, may play a key role in this mechanism.

Modulation of goldfish testicular testosterone production in vitro by tumor necrosis factor alpha, interleukin-1beta, and macrophage conditioned media

The relevance of immune-endocrine interactions to the regulation of testicular steroidogenesis in teleosts is virtually unexplored. The objectives of the present study were: 1) to investigate the effects of murine cytokines, tumor necrosis factor-alpha (TNFalpha) and interleukin-1beta (IL-1beta), and trout (Oncorhynchus mykiss) macrophage conditioned media (MCM) on testosterone (T) production by goldfish (Carassius auratus) testis pieces in vitro; and 2) to identify the site(s) of the inhibitory action of TNFalpha on hCG-stimulated T formation. TNFalpha (0-100 ng/ml) affected basal T production differentially depending on the gonadosomatic index (GSI) value of the fish. TNFalpha stimulated basal T of fish with a relatively low GSI (average 1.99), but inhibited T production by testis of fish with a higher GSI (average 5.14). The remaining studies used fish with only high GSI values. IL-1beta (0-10 ng/ml) inhibited basal T production, while MCM (0-25% v/v) had no effect. The cytokines significantly inhibited hCG-stimulated T production at all doses tested, whereas MCM was inhibitory only at the lower doses of 2.5-5% v/v. TNFalpha did not affect basal or hCG-stimulated cAMP levels, but did inhibit forskolin (0.5 microM; adenylate cyclase activator) and 8-bromo-cAMP (0.15 mM; cAMP analog) stimulated T levels. The inhibitory actions of TNFalpha on T production were greatly reduced by treatment of testis with 25-hydroxycholesterol (1 and 10 microg/ml), pregnenolone (50 and 100 ng/ml), and 17 alpha-hydroxypregesterone (50 ng/ml). TNFalpha caused a moderate decrease in pregnenolone (100 ng/ml)-stimulated T production. Together, these data demonstrate that regulatory actions of TNFalpha may occur at multiple sites within the steroid biosynthetic pathway, but the major effect appears to be related to cholesterol availability in the mitochondria. In conclusion, the results of this study implicate macrophage-derived factors in the regulation of teleost testicular androgen biosynthesis.

Involvement of intratesticular IL-1 system in the regulation of Sertoli cell functions

The Interleukin-1 (IL-1) system has been suggested to be involved in the cell-cell cross talk within the testis. To investigate the testicular autocrine, paracrine and endocrine factors involved in the regulation of Sertoli cell functions, we have examined the capacity of Sertoli cell cultures, from immature mice, to produce IL-1alpha, IL-1beta and IL-1 receptor antagonist (IL-1ra) under in vitro cultures and in the presence of testicular physiological and pathological factors. Our investigation revealed that Sertoli cells produce large amounts of IL-1alpha, IL-1ra but not IL-1beta under basal culture conditions, as examined by ELISA and immunohistochemical staining. Liposaccharides (LPS), as well as IL-1alpha and IL-1beta were found to stimulate IL-1alpha and IL-1ra, but not IL-1beta production, in Sertoli cells from immature mice. Maximum concentration of IL-1alpha and of IL-1ra was observed after 2 and 8 h after the stimulation, respectively. The addition of IL-1ra to Sertoli cells did not alter their capacity to constitutively produce IL-1alpha. However, the stimulatory effects of recombinant IL-1alpha on IL-1alpha production by Sertoli cells were reversed by the concomitant addition of recombinant IL-1ra. FSH is capable to induce IL-1ra production in Sertoli cells in a dose-dependent manner but not IL-1alpha or IL-1beta. As expected, Sertoli cell cultures were also shown to constitutively secrete transferrin. Stimulation of these cultures with IL-1alpha, IL-1beta significantly increased their capacity to secrete transferrin. Addition of IL-1ra to unstimulated Sertoli cell cultures did not affect their capacity to secrete transferrin. Stimulation of Sertoli cell cultures with a combination of both IL-1alpha and FSH or IL-1beta and FSH showed additive effect between IL-1 and FSH in their capacity to induce transferrin secretion by these cells. However, stimulation of Sertoli cells with a combination of both IL-1ra and FSH did not affect their capacity to secrete transferrin as compared with FSH-stimulated cultures. Our results with Sertoli cells, in addition to previous data on Lydig cell and germ cells, may suggest the involvement of the IL-1 system in testicular paracrine/autocrine regulation, which could be involved in the regulation of spermatogenesis and spermiogenesis processes and male fertility.

Induction of transferrin secretion in murine Sertoli cells by FSH and IL-1: the possibility of different mechanism(s) of regulation

In the present study we examined the capacity of interleukin-1 (IL-1) alpha, beta, interleukin-1 receptor antagonist (IL-1ra) and follicle stimulating hormone (FSH) to induce transferrin secretion by Sertoli cells under in vitro conditions. Primary Sertoli cell (SC) cultures from immature mice secreted constitutively transferrin. Stimulation of these cultures with IL-1alpha, IL-1beta significantly increas\d their capacity to secrete transferrin. Addition of IL-1ra to unstimulated SC cultures did not affect their capacity to secrete transferrin. Stimulation of SC cultures with a combination of both IL-1alpha and FSH or IL-1beta and FSH showed additive effect between IL-1 and FSH in their capacity to induce transferrin secretion by these cells. However, stimulation of Sertoli cells with a combination of both IL-1ra and FSH did not affect their capacity to secrete transferrin compared with FSH-stimulated cultures. Our results may suggest the involvement of testicular paracrine/autocrine factors (IL-1) and endocrine (FSH) factors in the regulation of transferrin secretion by SC. This capacity seems to be differently regulated by these factors. Thus, IL-1alpha and beta may directly affect physiological functions of the testis; which may suggest their involvement in the regulation of spermatogenesis and spermiogenesis processes and male fertility.

Interleukin-1 is a potent growth factor for immature rat sertoli cells

Testes from rats of different maturational ages were explored for presence of paracrine sertoli cell growth factors. Pubertal and adult testes contained a 17 kDa protein, with potent stimulatory effect on immature Sertoli cell multiplication in vitro. The bioactivity of this protein was mimicked by rat interleukin-1 (IL-1) and neutralized by IL-1 receptor antagonist. A receptor-mediated action was further supported by the demonstration of IL-1 receptor type I mRNA and protein expression in the cultured sertoli cells and in intact immature rat testes. IL-1alpha showed higher efficacy in stimulating proliferation than IL-1beta and follicle-stimulating hormone (FSH), and displayed synergistic action in combination with FSH. As IL-1alpha is constitutively produced by the rat testis and IL-1beta readily inducible by proinflammatory stimuli, our results suggest that IL-1 may serve as a growth factor for Sertoli cells under physiological and pathophysiological conditions.

Age-dependent stimulation of Leydig cell steroidogenesis by interleukin-1 isoforms

Different isoforms of testicular interleukin-1 (IL-1) were analysed to determine whether there were differences in the ability to modulate rat Leydig cell steroidogenesis in vitro. Rat 17K IL-1alpha and IL-1beta, 32K IL-1alpha precursor (32proIL-1alpha) and a 24K splice variant (24proIL-1alpha) stimulated testosterone production by Leydig cells from 40- but not 80-day-old rats. The potency of the isoforms was IL-1alpha>IL-1beta>32proIL-1alpha>24proIL-1alpha, IL-1alpha being 50-fold more potent than IL-1beta. IL-1 receptor antagonist reversed the effects and IL-1 receptor type I mRNA was expressed by the responding Leydig cells, indicating a receptor mediated action. Inhibition of PKA and Ca(2+) channels abolished IL-1-induced steroidogenesis, while inhibition of PKC had no significant effect. Except for 24proIL-1alpha which was stimulatory, all IL-1 isoforms suppressed hCG-driven testosterone production. This inhibitory effect was abolished by androstendione, suggesting that P450c17 was suppressed by IL-1. Our results indicate that IL-1 plays a paracrine role in the regulation of Leydig cell steroidogenesis.

Induction of interleukin-1alpha production in murine Sertoli cells by interleukin-1

In the present study we examined the involvement of interleukin (IL)-1alpha, -1beta, FSH, and lipopolysaccharide (LPS) in the regulation of IL-1alpha and -1beta production by Sertoli cells under in vitro conditions. Sertoli cell cultures from immature mice produced constitutively basal levels of intracellular IL-1alpha. Stimulation of Sertoli cell cultures with LPS (5 microgram/ml) resulted in a maximal production of intracellular IL-1alpha 2 h after the stimulation. Thereafter, these levels decreased but remained significantly higher within 24 h after stimulation than those in control cultures. The effect of LPS on IL-1alpha production was dose dependent. FSH did not show any effect on intracellular IL-1alpha production by Sertoli cells. IL-1alpha could not be detected in supernatants of unstimulated or stimulated Sertoli cell cultures. Sertoli cell cultures stimulated with recombinant IL-1alpha induced optimal intracellular levels of IL-1alpha within 2 h of stimulation. These levels remained high 24 h after stimulation. However, stimulation of Sertoli cell cultures with IL-1beta induced a peak of IL-1alpha production 8 h after stimulation. These levels decreased 24 h after the stimulation but were still found to be significantly higher than those in control cultures. The addition of IL-1 receptor antagonist (IL-1ra) to Sertoli cell cultures did not significantly alter their capacity to produce IL-1alpha. However, the stimulatory effects of recombinant IL-1alpha on IL-1alpha production by Sertoli cell cultures were reversed by the concomitant addition of recombinant IL-1ra. No immunoreactive IL-1beta could be detected in lysates or conditioned media of immature murine Sertoli cells under any of the stimulatory conditions outlined. Our results may suggest the involvement of physiological (IL-1) and pathophysiological factors (LPS) in the regulation of spermatogenesis and spermiogenesis processes and male fertility.

Constitutive expression of interleukin-1alpha messenger ribonucleic acid in rat Sertoli cells is dependent upon interaction with germ cells

Interleukin-1 (IL-1), a proinflammatory cytokine originally isolated as a product of activated mononuclear phagocytes, consists of two distinct agonist proteins, IL-1alpha and IL-1beta, of which IL-1beta is the major inducible IL-1 protein produced by macrophages. We show here that mRNA of IL-1alpha, but not IL-1beta, is constitutively expressed by the intact rat testis and localize the transcript to Sertoli cells as confirmed by a novel squash technique. The expression is developmentally regulated and appears only after postnatal day 20 in the rat testis, corresponding to onset of puberty. IL-1alpha mRNA shows a stage-dependent expression pattern during the cycle of the seminiferous epithelium. It is low or absent in stage VII, but present in all other stages of the cycle. The same stage-dependent distribution was also observed at the protein level when bioactive IL-1 was measured in extracts of accurately defined one millimeter segments of seminiferous tubules. No IL-1alpha mRNA was detected in adult rat testes after germ cell depletion by fetal irradiation or cytostatic drug treatment. Because stage VII is the only segment of the seminiferous tubules lacking DNA replication, we propose that IL-1alpha is involved in this event during mitosis and meiosis of spermatogenesis and that its expression is dependent upon interactions between Sertoli cells and germ cells.

Role of cytokines in testicular function

Inflammatory disease has been established to affect male reproductive function and fertility. Relevant inflammatory diseases include general and chronic infectious diseases as well as localized acute or chronic infections of the male genitourinary tract. Male accessory gland infections account for almost 15% of all cases of male infertility seen in infertility clinics while fertility usually is not a clinical objective among patients with acute systemic infections such as Gram-negative sepsis. Infections of the male accessory glands frequently are associated with increased counts of white blood cells in semen and elevated levels of proinflammatory cytokines in semen and the testis. There is a mounting body of evidence that demonstrates the importance of cytokines and chemokines in the regulation of testicular and glandular function during pathophysiological states as well as under normal physiological conditions when cytokines act as growth and differentiation factors. The purpose of this review is to examine the role of cytokines in the regulation of steroidogenesis and spermatogenesis in the testis under physiological and pathophysiological conditions and considers clinical investigations that help to improve the evaluation and treatment of male infertility.

Rodent Leydig cell tumorigenesis: a review of the physiology, pathology, mechanisms, and relevance to humans

Leydig cells (LCs) are the cells of the testis that have as their primary function the production of testosterone. LCs are a common target of compounds tested in rodent carcinogenicity bioassays. The number of reviews on Leydig cell tumors (LCTs) has increased in recent years because of its common occurrence in rodent bioassays and the importance in assessing the relevance of this tumor type to humans. To date, there have been no comprehensive reviews to identify all the compounds that have been shown to induce LCTs in rodents or has any review systematically evaluated the epidemiology data to determine whether humans were at increased risk for developing LCTs from exposure to these agents. This review attempts to fill these deficiencies in the literature by comparing the cytology and ontogeny of the LC, as well as the endocrine and paracrine regulation of both normal and tumorigenic LCs. In addition, the pathology of LCTs in rodents and humans is compared, compounds that induce LC hyperplasia or tumors are enumerated, and the human relevance of chemical-induced LCTs is discussed. There are plausible mechanisms for the chemical induction of LCTs, as typified by agonists of estrogen, gonadotropin releasing hormone (GnRH), and dopamine receptors, androgen receptor antagonists, and inhibitors of 5alpha-reductase, testosterone biosynthesis, and aromatase. Most of these ultimately involve elevation in serum luteinizing hormone (LH) and/or LC responsiveness to LH as proximate mediators. It is expected that further work will uncover additional mechanisms by which LCTs may arise, especially the role of growth factors in modulating LC tumorigenesis. Regarding human relevance, the pathways for regulation of the hypothalamo-pituitary-testis (HPT) axis of rats and humans are similar, such that compounds that either decrease testosterone or estradiol levels or their recognition will increase LH levels. Hence, compounds that induce LCTs in rats by disruption of the HPT axis pose a risk to human health, except for possibly two classes of compounds (GnRH and dopamine agonists). Because GnRH and prolactin receptors are either not expressed or are expressed at very low levels in the testes in humans, the induction of LCTs in rats by GnRH and dopamine agonists would appear not to be relevant to humans; however, the potential relevance to humans of the remaining five pathways of LCT induction cannot be ruled out. Therefore, the central issue becomes what is the relative sensitivity between rat and human LCs in their response to increased LH levels; specifically, is the proliferative stimulus initiated by increased levels of LH attenuated, similar, or enhanced in human vs. rat LCs? There are several lines of evidence that suggest that human LCs are quantitatively less sensitive than rats in their proliferative response to LH, and hence in their sensitivity to chemically induced LCTs. This evidence includes the following: (1) the human incidence of LCTs is much lower than in rodents even when corrected for detection bias; (2) several comparative differences exist between rat and human LCs that may contribute, at least in part, to the greater susceptibility of the rat to both spontaneous and xenobiotic-induced LCTs; (3) endocrine disease states in man (such as androgen-insensitivity syndrome and familial male precocious puberty) underscore the marked comparative differences that exist between rats and man in the responsiveness of their LC's to proliferative stimuli; and (4) several human epidemiology studies are available on a number of compounds that induce LCTs in rats (1,3-butadiene, cadmium, ethanol, lactose, lead, nicotine) that demonstrate no association between human exposure to these compounds and induction of LC hyperplasia or adenomas. (ABSTRACT TRUNCATED)

Expression and regulation of interferon-gamma-inducible protein 10 gene in rat Leydig cells

In the present study, we report the cloning of a gene that is differentially expressed in normal adult rat Leydig cells and whose expression is inhibited by hCG but is induced by interferon-gamma (IFNgamma). DNA sequence analysis identified this gene as rat IFNgamma-inducible protein 10 (IP-10), a member of the -C-X-C- chemokine superfamily of proinflammatory cytokines. High levels of IP-10 messenger RNA (mRNA) were constitutively expressed in freshly isolated and primary cultured Leydig cells. hCG inhibited this expression in a dose-dependent manner. The addition of 1 ng/ml hCG inhibited IP-10 mRNA levels more than 80%. Conversely, IP-10 mRNA levels were markedly increased in response to murine interleukin-1alpha, murine tumor necrosis factor-alpha, and murine IFNgamma by 3.3-, 10-, and 26-fold, respectively. Concomitant addition of murine interleukin-1alpha, murine tumor necrosis factor-alpha, and murine IFNgamma synergistically increased IP-10 mRNA levels by 58-fold. Furthermore, in addition to one previously described rat IP-10 mRNA transcript (1.5 kb), another larger transcript (2.7 kb) was identified by Northern blot in rat Leydig cells. After screening a rat testis complementary DNA library, we obtained a partial structural gene and an intron sequence, which possibly originated from the larger transcript of rat IP-10 mRNA. Histochemical and immunocytochemical staining revealed that purified cells were positive for 3beta-hydroxysteroid dehydrogenase and IP-10, confirming that IP-10 is indeed present in Leydig cells. IP-10 antisense oligonucleotides enhanced basal and hCG-induced testosterone formation. This suggests that endogenous IP-10 has an inhibitory effect on Leydig cell steroidogenesis. In conclusion, IP-10 is expressed in rat Leydig cells and may have paracrine and autocrine effects on testicular function.

Modulation of Leydig cell testosterone production by secretory products of macrophages

Unstimulated macrophages from testes inhibited the production of testosterone by Leydig cells from adult, but not immature, Sprague-Dawley rats (significant after 48 h). Similar results were observed with unstimulated macrophage-conditioned media, suggesting that the observed effect was mediated by one or more secretory products. None of these substances was interleukin-1, since macrophage supernatants tested negative in an interleukin-1 alpha and interleukin-1 beta sensitive, thymocyte assay. Interleukin-6 was detected by a B cell proliferation assay. After stimulation by LPS, testicular macrophages enhanced testosterone production by Leydig cells from adult and immature rats. This enhancement was dose-dependent and required low concentrations (but over 2.5%) of conditioned media. Interleukin-1 and interleukin-6 activities were detected in LPS-stimulated macrophage supernatants. Supernatants of LPS-stimulated, human monocytes had similar effects on Leydig cells. They were rich in interleukin-1, interleukin-1 receptor antagonist and interleukin-6. The present study suggests that, in adult rats, testicular macrophages modulate Leydig cell steroidogenesis by secretory products whose secretion depends on the physiological state of macrophages. The factor or factors responsible for stimulation are not species-specific. The effect cannot be accounted for by variations in the concentration of the above mentioned interleukins in macrophage supernatants.

Identification of IL-6 as one of the important cytokines responsible for the ability of mononuclear cells to stimulate Sertoli cell functions

There is increasing evidence that locally produced cytokines may play an important role in the control of testicular function. In a previous report we demonstrated that medium conditioned by activated human peripheral blood mononuclear cells (PBMC-CM), which is a rich source of cytokines, has extremely potent effects on Sertoli cell transferrin and cGMP secretion. Part of this activity could be explained by interleukin-1beta (IL-1beta) but additional cytokines were evidently involved. In the present study we tried to characterize and purify additional components active on Sertoli cells from PBMC-CM. To this end PBMC-CM was subjected to a purification procedure involving successively: adsorption to silicic acid, affinity chromatography with an antiserum recognizing a mixture of cytokines except IL-1beta, gel-filtration, reversed-phase HPLC and cation-exchange FPLC. Throughout this protocol a Sertoli cell bioassay was used to monitor the effects on transferrin and cGMP production. After cation-exchange FPLC, SDS-PAGE using silver staining showed a single protein band in the bioactive fractions. NH2-terminal amino-acid sequencing revealed that the active principle(s) in this band corresponded to four truncated forms of IL-6 missing the first 13, 14, 17 and 18 N-terminal amino-acids, respectively. The truncated IL-6 molecules were as active as intact IL-6 in the Sertoli cell bioassay. Since neither IL-1beta nor IL-6 alone or in combination could account for the extremely potent effect of PBMC-CM, we tested a series of additional cytokines (IL-1alpha, INF-alpha, IL-4, TGF-beta, IFN-gamma) alone and in combination with IL-1beta and IL-6. These data suggest that IL-1beta, IL-6 and TNF-alpha display more than additive effects on Sertoli cell transferrin and cGMP secretion and that the combination of these cytokines may explain the major part of the effects observed with crude PBMC-CM. The observation that the latter effects could be observed with murine as well as human IL-1beta, IL-6 and TNF-alpha further supports the potential physiological relevance of these findings.

Vectorial production of interleukin 1 and interleukin 6 by rat Sertoli cells cultured in a dual culture compartment system

The bidirectional production of interleukin-1 (IL-1) and IL-6 by Sertoli cells and its regulation by inflammatory and physiological stimuli has been studied using a dual compartment culture system allowing the study of Sertoli cell apical and basal secretory activities. Another Sertoli cell activity, the vectorial transferrin production was also studied in all culture conditions. A low constitutive IL-1 production appeared equally distributed between both poles, while IL-6 and transferrin constitutive production was predominantly directed apically. Two activators of macrophages, lipopolysaccharides and zymosan, were found to induce marked increases of IL-1 in the compartment where they had been added: basal if added to the lower compartment and vice versa. In contrast, after a basal stimulation, IL-6 production was mainly increased in the upper compartment that corresponds to a Sertoli cell apical flux. In this system, IL-1 and IL-6 levels were not modified by FSH; they were not also affected by residual bodies and latex beads, probably due to the fact that, in the bicameral system, phagocytosis is restricted to the Sertoli cells situated at the surface of the inner compartment. IL-1beta, but not IL-1alpha, induced IL-6 secretion in the compartment of stimulation. In conclusion, the present study demonstrates that vectorial secretory patterns of IL-1 and IL-6 production greatly differ and that these cytokines are also differently regulated. These results suggest that Sertoli IL-1 and IL-6 have different targets within the testis and that, in normal and pathophysiological conditions, both the tubular and the interstitial compartments may be influenced by the action of these paracrine factors.

Decreased plasma gonadotropin and testosterone levels in arthritic rats: are corticosteroids involved?

Infectious and inflammatory diseases are often accompanied by abnormal reproductive functions, and the present working hypothesis is that proteins (called cytokines or interleukins, ILs) released by activated immune cells are at least in part responsible for these neuroendocrine changes. In order to test this hypothesis, we need paradigms of immune pathologies in which concentrations of cytokines are increased, and those of hormones of the hypothalamic-pituitary-gonadal (HPG) axis are blunted. We chose a rodent model of arthritis, adjuvant-induced arthritis (AIA), in which rats show elevated plasma IL-6 and decreased testosterone (T) concentrations. We describe here the first phase of our studies, in which we determined whether gonadotropin release was also altered, whether this change was responsible for the low T levels, and whether elevated corticosterone participated in the decreased activity of the HPG axis.AIA is induced by the intramuscular injection ofMycobacterium butyricum (MBB) into the tail base of the rat, with swelling of the limbs occurring 11-12 days later. We observed significant decreases in LH and FSH secretion of castrated AIA male rats, suggesting that altered gonadotropin output was independent of the gonads. The absence of significant alterations in GnRH gene expression in the hypothalamus of AIA rats, as well as only modest declines in pituitary responsiveness to GnRH, indicate that these mechanisms are not primarily responsible for the blunted gonadotropin concentrations. Intact AIA rats exhibited a dramatic decline in T levels, but no concimitant rise in LH concentrations. The observation that gonadotropin secretion does not increase despite significantly reduced T levels suggests the presence of an unidentified defect within the GnRH neuronal circuitry that prevents the gonadotrophs to respond to decreased steroid feedback. Testicular responsiveness to hCG was significantly blunted in AIA rats, and this decrease was not reversed by acute blockade of nitric oxide formation or of prostaglandin synthesis. Interestingly, the onset of these hormonal changes preceded the appearance of symptoms (limb swelling), as well as the decrease in body weight that accompanies visible joint enlargement. On the other hand, blunted T secretion coincided with rising levels of ACTH and corticosterone. This suggested that adrenal steroids might be responsible for the decrease in LH and T values, but this hypothesis did not prove valid. Indeed, we observed that adrenalectomized AIA animals implanted with corticosterone pellets retained their low T levels. Furthermore, clamping corticosterone levels was only moderately effective in reversing the inhibitory influence of the arthritic process on LH secretion.In the absence of significant alterations in GnRH gene expression, it is possible that low Gn levels are secondary to an abnormal pattern in GnRH pulse amplitude and/or frequency. While the decrease in plasma LH concentrations may play a role in the dramatically lowered plasma T values, it is more likely that the inability of the testes to respond to gonadotropin is of significance. While we cannot rule out the participation of perceived stress at the onset of the changes in pituitary and testicular function of AIA rats, we hypothesize that cytokines released by the inflamed tissues, an event that may well precede the appearance of overt swelling, are responsible for the activation of the HPA axis and independently, for the decreased activity of the HPG axis. The AIA model may therefore provide an experimental paradigm in which to test hypotheses related to the cross-talk between the immune system and reproductive parameters.

Rat seminiferous tubular culture medium contains a biological factor that inhibits Leydig cell steroidogenesis: its purification and mechanism of action

Seminiferous tubules prepared from adult rats cultured for 48 h in serum-free conditions produce multiple biological factors that modulate Leydig cell steroidogenic function in vitro. Using gel filtration chromatography, it was shown that seminiferous tubular culture medium (STCM) contained at least three inhibitory activities designated AI, AII, and AIII that inhibited testosterone production by purified Leydig cells. The factor that induced AIII activity, designated Leydig cell inhibitor (LCI), was further purified to apparent homogeneity by sequential HPLC using gel permeation, C8-, C18-, C2/C18-reversed-phase, and microbore anion exchange columns. When this batch of purified factor was resolved by SDS-PAGE under reducing conditions, only a single silver stained band with an apparent M(r) of 21,000 was detected. Protein sequence analysis using about 100 pmol of purified LCI revealed that its N-terminus was blocked. Incubation of this highly purified factor with Percoll gradient purified Leydig cells induced a dose-dependent inhibition of hCG-stimulated testosterone production. LCI inhibited the basal testosterone production and hCG-stimulated cAMP production by Leydig cell dose-dependently. It also inhibited the forskolin- and cholera toxin-stimulated testosterone and cAMP production but had no apparent effect on the binding of 125I-labeled hCG to LH receptors. These data suggest that this LCI exerts its inhibitory action at steps beyond the LH receptors but prior to the cAMP formation by affecting the adenylate cyclase activity directly or indirectly through inhibition of the stimulatory G-protein (Gs-protein); however, it is also possible that it decreases the coupling of the receptors to the Gs-protein. LCI also inhibited the conversion of exogenously added 22R-hydroxycholesterol, pregnenolone, progesterone, and 17 alpha-hydroxyprogesterone to testosterone. However, it had no effect on the conversion of dehydroepiandrostenedione and androstenedione to testosterone. These data strongly suggest that LCI affects the steroidogenic enzymes metabolizing cholesterol to testosterone, the cytochrome P-450 side-chain cleavage (P-450SCC), and cytochrome P-450 17 alpha-hydroxylase/17,20-lyase (P-450C17). However, it has no effect on the 3 beta-hydroxysteroid dehydrogenase (3 beta-HSD) and 17 beta-hydroxysteroid dehydrogenase (17 beta-HSD) enzyme activities. Based on the results of the present study, it is apparent that this LCI is distinct from other known potent Leydig cells inhibitors such as interleukin-1 (IL-1) and transforming growth factor-beta (TGF-beta). The LCI appears to involve in the paracrine regulation of Leydig cell function.

Recombinant murine tumor necrosis factor-alpha inhibits cholesterol side-chain cleavage cytochrome P450 and insulin-like growth factor-I gene expression in rat Leydig cells

The purpose of the present study was to evaluate the effects of murine recombinant tumor necrosis factor-alpha (TNF-alpha) on rat Leydig cell function. In primary cultures of Leydig cells, we found that in the presence of hCG (10 ng/ml), testosterone levels were markedly elevated, 69.3 +/- 3.1 ng/10(6) cells/h (mean + SE). TNF-alpha in a concentration of 1 ng/ml markedly inhibited testosterone biosynthesis (a 69% reduction; p < 0.01) and 100 ng/ml of TNF-alpha almost completely inhibited testosterone formation (p < 0.001). TNF-alpha (10 ng/ml) inhibited hCG (0.1, 1 and 10 ng/ml)-induced testosterone formation by 63%, 67% and 61%, respectively. TNF-alpha (10 ng/ml) also markedly inhibited 8-bromo cAMP-induced testosterone formation from 76 +/- 9 ng/10(6) cells/h to 4.9 ng/10(6) cells/h. This indicates that the major effect of TNF-alpha is at steps beyond LH receptor site. To further evaluate the site(s) of action of TNF-alpha, we evaluated its effect on the conversion of precursor steroids to testosterone. We found that the addition of 20-hydroxy-cholesterol could not reverse inhibitory effects of TNF-alpha on hCG-induced testosterone formation. TNF-alpha had no effect on the conversions of pregnenolone, 17-OH-pregnenolone, DHEA and androstenedione to testosterone. This indicates that the major effect of TNF-alpha is at the key steroidogenic enzyme, P450scc. We reported previously that human recombinant TNF-alpha had no effect on hCG-induced testosterone formation but did enhance the inhibitory effects of human recombinant IL-1beta. In the present study, we demonstrated that both murine TNF-alpha and human IL-1beta were potent inhibitors of hCG-induced testosterone formation. IL-1beta alone in concentrations of 0.1, 1 and 10 ng/ml inhibited testosterone formation by 45%, 62% and 91%, respectively, in the presence of TNF-alpha (10 ng/ml), IL-1beta in a concentration as low as 0.1 ng/ml completely blocked hCG-induced testosterone formation. We next evaluated the effect of TNF-alpha on P450scc gene expression. There was no constitutively expressed P450scc mRNA in Leydig cells after 24 h in culture. In response to hCG, there was a 33-fold increase in the P450scc mRNA level. Both TNF-alpha and IL-1beta inhibited hCG-induced expression of P450scc mRNA. Finally, the effect of TNF-alpha on IGF-I gene expression was investigated since IGF-I enhances Leydig cell androgen formation and IGF-I gene is expressed in high levels in Leydig cells. TNF-alpha inhibited both large (7.4 kb) and small species (0.8-1.2 kb) IGF-I mRNA levels in a dose-dependent manner. In conclusion, murine TNF-alpha is a potent inhibitor of Leydig cell function. TNF-alpha inhibited both P450scc and IGF-I mRNA gene expression.

Human chorionic gonadotropin induces interleukin-1 gene expression in rat Leydig cells in vivo

Luteinizing hormone (LH)/human chorionic gonadotropin (hCG) causes inflammatory-type responses in the testis. In the present study, we evaluated the effects of hCG on Leydig cell interleukin-1 (IL-1) gene expression. Using monoclonal antibody (ED2) staining for macrophages, our Leydig cell preparations had no significant contamination with macrophages. When purified Leydig cells from normal rats were cultured for 24 h and then treated with IL-1 beta (1-100 ng/ml) for 6 h, IL-1 beta induced dose-dependent increases in IL-1 beta mRNA levels. IL-1 beta also induced IL-1 alpha mRNA accumulation; however, the level of IL-1 alpha mRNA was much lower than that of IL-1 beta mRNA. When rats were treated with either saline or hCG (5 units i.p.), hCG markedly induced IL-1 beta mRNA accumulation in purified Leydig cells at 6 h which persisted for over 24 h. However, hCG had no direct effect on purified Leydig cell or crude interstitial cell IL-1 mRNA levels. Our results suggest that inflammatory effects of hCG in vivo may be mediated by increased IL-1 gene expression in Leydig cells.

Effects of tumor necrosis factor on the hypothalamic-pituitary-testicular axis in healthy men

Tumor necrosis factor (TNF) has been implicated as a mediator of many diseases associated with alterations in hypothalamic-pituitary-testicular (HPT) function. To assess the effects of TNF on the HPT axis, we performed a saline-controlled cross-over study in six healthy men, sequentially measuring serum concentrations of gonadotropins, testosterone, and sex hormone-binding globulin (SHBG) after a bolus intravenous injection of recombinant human TNF (50 micrograms/m2). TNF induced an early and transient increase in serum luteinizing hormone (LH) levels from 6.0 +/- 1.0 to a maximum of 8.0 +/- 1.0 U/L after 30 minutes (P < .005), whereas the concentrations of follicle-stimulating hormone (FSH) remained unchanged. The increase in LH concentrations was followed by a transient decrease in serum testosterone levels from 18.2 +/- 0.3 to 9.1 +/- 1.2 nmol/L after 4 hours (P < .0001). Remarkably, LH levels had returned to control values when the testosterone level reached its nadir. SHBG levels were not affected by TNF. Our results suggest that TNF affects the HPT axis at multiple levels and may be involved either directly or indirectly in the decrease in circulating testosterone concentrations in systemic illnesses.

The role of cytokines in the regulation of Leydig cell P450c17 gene expression

Cytokines produced by immune-activated testicular interstitial macrophages (TIMs) may play a fundamental role in the local control mechanisms of testosterone biosynthesis in Leydig cells. We investigated whether in vivo immune-activation of TIMs can modulate Leydig cell steroidogenesis. To immune activate TIMs in vivo, mice were injected intraperitoneally (i.p.) with lipopolysaccharide (LPS, 6 mg/kg). TIMs and Leydig cells were purified for RNA analysis. LPS treatment resulted in a 47-fold increase in interleukin-1β (IL-1β) mRNA in TIMs. P450c17 mRNA levels in the Leydig cells from the same animals, decreased to less than 10% compared to control. The effect of LPS on IL-1β and P450c17 mRNA levels was reversible on both TIMs and Leydig cells, respectively. To determine if the effect of LPS on P450c17 was mediated by a possible decrease in pituitary LH secretion, mice were co-injected with LPS and hCG. Treatment with hCG did not change the effect observed with LPS alone, in TIMs or in Leydig cells. In vitro, LPS treatment of TIMs resulted in marked induction of IL-1β mRNA expression. In parallel, in vitro treatment of Leydig cells with recombinant IL-1 resulted in a dose-dependent inhibition of P450c17 mRNA expression and testosterone production. These data demonstrate that LPS treatment, in vivo and in vitro, induced IL-1 gene expression in TIMs, and that IL-1 inhibits P450c17 mRNA in vitro. Therefore, we suggest that immune-activation of TIMs might have caused the observed inhibition of P450c17 gene expression in Leydig cells in vivo.

Multiple amino acid substitutions suggest a structural basis for the separation of biological activity and receptor binding in a mutant interleukin-1 beta protein

Receptor binding and biological activity properties of human interleukin-1 beta can be dissociated by mutating a single amino acid, arginine 127, to glycine (IL-1 beta R----G) [Gehrke et al. (1990) J. Biol. Chem. 265, 5922-5925]. The mechanism underlying the reduced biological activity has been examined by replacing arginine 127 with several other amino acids, followed by determination of biological activity using a T-helper cell proliferation assay. Mutant IL-1 beta proteins containing lysine, glutamic acid, tryptophan, or alanine in place of arginine 127 maintain biological activity. These data strongly suggest that IL-1 beta biological activity is not directly dependent upon the specific properties of charge, hydrophobicity/hydrophilicity, or side-chain group presented by the residue at position 127. Molecular modeling analyses indicate that the structural integrity of the antiparallel beta-strand 1/12 pair is disturbed in the glycine 127 mutant protein. Collapse of beta-strand 1 into a hydrated space between strands 1, 2, and 4 could structurally alter a cleft in IL-1 beta that contains a cluster of highly conserved amino acids, including a key aspartic acid residue [Ju et al. (1991) Proc. Natl. Acad. Sci. U.S.A. 88, 2658-2662]. Mutagenesis data and the differential activities of the IL-1 beta R----G and IL-1 receptor antagonist proteins in stimulating early and late gene expression [Conca et al. (1991) J. Biol. Chem. 266, 16265-16268] suggest that multiple receptor-ligand contacts, exclusive of those required for receptor binding, are required for the stimulation of full IL-1 biological activity.

Isolation and culture of testicular macrophages from a seasonally breeding species, Phodopus sungorus. Evidence for functional differences between macrophages from active and regressed testes

We have developed an isolation and cultivation protocol for testicular macrophages from the seasonally breeding Siberian hamster, Phodopus sungorus which allows serum-free culture. Macrophages were isolated from the active testes of adult Phodopus kept in long photoperiod (LD, 18hL:6hD), and from the inactive testes of animals with gonadal regression induced by exposure to a short photoperiod (SD, 6hL;18hD; for 10 weeks). The isolated cells were identified as macrophages by (a) electron microscopy, (b) non-specific phagocytosis, and (c) the presence of Fc-receptors. Treatment of the cultures with oFSH (at 0.5 and 1 micrograms ml-1 for 1 and 4 days) significantly stimulated lactate secretion by testicular macrophages from LD hamsters, as expected from studies in the rat. In marked contrast, oFSH did not affect lactate secretion by testicular macrophages from SD hamsters, or by peritoneal macrophages. To test possible macrophage-Leydig cell interactions, the influence of testicular macrophage-conditioned medium (TM-CM) from FSH-responsive LD macrophage cultures was assessed and compared with the effect of peritoneal macrophage-conditioned medium (PM-CM) on testosterone production by testicular parenchyma from LD hamsters. Unexpectedly, and in contrast to previous reports in rats, testosterone production by testes was inhibited significantly by TM-CM from cultures pretreated with either 0.1 or 0.5 micrograms FSH ml-1. FSH alone stimulated testosterone production (due either to LH contamination or to possible paracrine effects). PM-CM from cultures pretreated with FSH did have an inhibitory effect. It is concluded that: (i) There is indirect evidence for the presence of functional FSH receptors on macrophages from the active testes of Phodopus. (ii) Testicular macrophages from inactive testes of Phodopus are not responsive to FSH, implicating impaired macrophage function in the regressed testes of Phodopus exposed to SD. (iii) Testicular macrophages produce a factor which can inhibit testosterone production by incubated testicular tissue.

Cell-cell interactions and the regulation of testis function

Regulatory interactions have been shown to occur between all the testicular cell types considered. The paracrine factors mediating these interactions generally influence either cellular growth or differentiation. The regulation of cellular growth is essential in the developing testis and is required for the maintenance of spermatogenesis in the adult testis. The rapid rate of germinal cell proliferation and the continuous but slowed growth of the peritubular cells and Leydig cells requires the presence of specific growth factors in the adult. Therefore, cell-cell interactions have evolved that involve growth factors such as IGF, TGF-alpha, TGF-beta and NGF. Other growth factors such as FGF or less characterized components like the seminiferous growth factor (SGF) also may be involved in the paracrine regulation of testis cell growth. An alternate cellular parameter to cell growth to consider is the regulation of cellular function and differentiation. A number of endocrine agents and locally produced paracrine factors have been shown to control and maintain testis cell function and differentiation. Cell-cell interactions mediated by factors such as androgens, POMC peptides, and PModS are all primarily directed at the regulation of cellular differentiation. Therefore, the agents which mediate cell-cell interactions in the testis can generally be categorized into factors that regulate cell growth or those which influence cellular differentiation. The specific cell-cell interactions identified will likely be the first of a large number of cellular interactions yet to be investigated. Although a number of potentially important cell-cell interactions have been identified, future research will require the elucidation of the in vivo physiological significance of these interactions. The existence of different cell types and potential cell-cell interactions in a tissue implies that the actions of an endocrine agent on a tissue will not simply involve a single hormone and single cell. The endocrine regulation of testis function will have effects on cell-cell interactions and be affected by local cell-cell interactions. The ability of LH to influence Leydig cell androgen production promotes a cascade of interactions mediated through several cell types to maintain the process of spermatogenesis. FSH actions on Sertoli cells also promote cell-cell interactions that influence germinal cell development, peritubular myoid cell differentiation and Leydig cell function. Therefore, elucidation of the endocrine regulation of testis function requires an understanding of the local cell-cell interactions in the testis.

Recombinant monocyte-derived interleukin-1 receptor antagonist reverses inhibitory effects of interleukin-1 on Leydig cell steroidogenesis

Previously we have reported that interleukin-1 (IL-1) is a potent inhibitor of Leydig cell function. Most recently, IL-1 receptor antagonist (IL-1ra) has been purified, sequenced and cloned. In the present study, we evaluated the recombinant monocyte-derived IL-1ra on the inhibitory effects of IL-1. The addition of recombinant human IL-1ra up to 1000 ng/ml has no discernible effects on human chorionic gonadotropin (hCG)-stimulated testosterone formation in primary cultures of rat Leydig cells. Similar to that reported previously, IL-1 beta caused a dose-dependent inhibition of hCG-induced testosterone. The inhibitory effect of IL-1 beta could be reversed by the concomitant addition of IL-1ra. The amounts of IL-1ra required to reverse the effect of IL-1 were 25-fold higher. Our results suggest that IL-1 is important in modulating Leydig cell function and its effect most likely is mediated by specific IL-1 receptors.

Constitutive production of lymphocyte activating factors by normal tissues in the adult rat

Lymphocyte activating factors (LAFs), e.g., interleukin-1 (IL-1) and IL-1-like factors, have previously been demonstrated outside the immune system in the skin, thymus epithelium, and the human and rat testis. We have studied the presence of LAFs in normal tissues of the adult rat, utilizing a highly IL-1 sensitive murine thymocyte proliferation assay. We have demonstrated high amounts of LAF activity in the tongue, esophagus, proventricular part of the stomach, and the liver. Some activity was also demonstrated in the duodenum, placenta, spleen, Peyer's patches, glandular stomach, and jejunum, but no bioactivity was present in other gastrointestinal, endocrine, lymphoid, or haematopoeitic tissues. We were also unable to detect any LAF activity in the reproductive organs (except for the testis), urinary tract, skeletal and muscular tissues, brain, eyes, salivary glands, or lung. In the esophagus the activity was mainly localized to the mucosa. The LAF activity in the skin was partly inhibited by treatment with a mixture of antibodies against human IL-1 alpha and IL-1 beta. Dose response curves and gel filtration on a Sephacryl S-200 column suggested the presence of a high molecular weight (90,000-100,000 Da) LAF inhibitory factor in the liver. In all positive tissues, the demonstrated LAFs had a molecular weight of 15,000-25,000 Da, as determined by Sephacryl S-200 gel filtration. Of the positive tissues, the skin, tongue, esophagus, and the proventricular part of the stomach all contain stratified squamous epithelium. It is tempting to suggest that the detected LAFs have a similar function in these barrier tissues, e.g., to serve as host defence factors, or, alternatively or additionally, as tissue growth factors.