Testicular activin and follistatin levels are elevated during the course of experimental autoimmune epididymo-orchitis in mice

Alleviating 3-MCPD-induced male reproductive toxicity: Mechanistic insights and resveratrol intervention

3-Monochloropropane-1, 2-diol (3-MCPD), a food-borne contaminant, is widely regarded as the primary cause of male infertility. At present, identifying a method to improve/reduce the male reproductive toxicity caused by 3-MCPD is important. In our study, we explored the potential application of resveratrol (RSV) in mitigating the adverse effects of 3-MCPD. Using 7-week-old Sprague-Dawley (SD) rats as animal models, we investigated the impacts and underlying mechanisms of 3-MCPD and RSV on reproductive function. The administration of 3-MCPD led to significant reductions in testicular and epididymal weights, as well as disruptions in spermatogenesis and histological abnormalities. However, co-treatment with RSV and 3-MCPD mitigated these adverse effects. In vitro study, RSV exhibited the ability to reverse the decline in Leydig and Sertoli cell populations inflicted by 3-MCPD treatment. Mechanistically, RSV reduced endoplasmic reticulum stress (PARP), inflammasome activation (NLRP3), and autophagy-mediated lysosome dysfunction (p62 and LC3BII) induced by 3-MCPD. In addition, 3-MCPD treatment increased the expression level of steroidogenesis-related proteins, steroidogenic acute regulatory (StAR) and CYP11A1, but RSV normalized StAR expression. Moreover, 3-MCPD-induced pro-inflammatory responses were counteracted by RSV treatment, with the cytokine reduction and modulation of CD206 expression, a marker of macrophage activation. These findings indicate that RSV attenuates 3-MCPD-induced reproductive toxicity, highlighting its application potential as an adjuvant agent for male reproductive health.

Regulatory T cells play a crucial role in maintaining sperm tolerance and male fertility

Regulatory T cells (Tregs) modulate tissue homeostatic processes and immune responses. Understanding tissue-Treg biology will contribute to developing precision-targeting treatment strategies. Here, we show that Tregs maintain the tolerogenic state of the testis and epididymis, where sperm are produced and mature. We found that Treg depletion induces severe autoimmune orchitis and epididymitis, manifested by an exacerbated immune cell infiltration [CD4 T cells, monocytes, and mononuclear phagocytes (MPs)] and the development of antisperm antibodies (ASA). In Treg-depleted mice, MPs increased projections toward the epididymal lumen as well as invading the lumen. ASA-bound sperm enhance sperm agglutination and might facilitate sperm phagocytosis. Tolerance breakdown impaired epididymal epithelial function and altered extracellular vesicle cargo, both of which play crucial roles in the acquisition of sperm fertilizing ability and subsequent embryo development. The affected mice had reduced sperm number and motility and severe fertility defects. Deciphering these immunoregulatory mechanisms may help to design new strategies to treat male infertility, as well as to identify potential targets for immunocontraception.

A review on immunological aspects in male reproduction: An immune cells and cytokines

The male reproductive system, particularly the male gamete, offers a unique barrier to the immune system. The growing germ cells in the testis need to be shielded from autoimmune damage. Hence the testis has to establish and sustain an immune-privileged milieu. Sertoli cells create this safe space, protected by the blood-testis barrier. Cytokines are a type of immune reaction that can positively and negatively affect male reproductive health. Inflammation, disease, and obesity are just a few physiological conditions for which cytokines mediate signals. They interact with steroidogenesis, shaping the adrenals and testes to produce the hormones needed for survival. In particular pathological condition, including autoimmune disorders, contains high levels of the same cytokines in semen that play an essential role in the immunomodulation of the male gonad. This review focuses on understanding the immunological role of cytokines in the control and development of male reproduction. Also, in maintaining male reproductive health and diseases linked with their aberrant function in the testis.

Interleukin-17A knockout or self-recovery alleviated autoimmune reaction induced by fluoride in mouse testis

Fluoride (F) is usually treated as a hazardous material, and F-caused public health problem has attracted global attention. Previous studies demonstrate that interleukin-17A (IL-17A) plays a crucial role in F-elicited autoimmune orchitis and self-recovery reverses F-induced testicular toxicity to some extent, but these basic mechanisms remain unclear. Thus, we established a 180 d F exposure model of wild type (WT) mice and IL-17A knockout mice (C57BL/6 J background), and 60 d & 120 d self-recovery model based on F exposure model of WT mice, and used various techniques like qRT-PCR, western blot, immunohistochemistry and ELISA to further explore the mechanism of F-induced autoimmune reaction, the role of IL-17A in it and the reversibility of F-caused toxicity in testis. The results indicated that F exposure for 180 d caused the decreased sperm quality, the damaged testis histopathology, the enhanced mRNA and protein expression levels of inflammatory cytokines, the changes of autoantibody such as the appearance and increased content of anti-testicular autoantibodies in sera and the autoantibody deposition in testis, the alterations of autoimmune related genes containing the decreased mRNA and protein expressions of AIRE and FOXP3 with an increase of MHCII, and the reduced protein expressions of CTLA4, and the activation of IL-17A signaling cascade like the elevated mRNA and protein expressions of IL-17A, Act1, NF-κB, AP-1 and CEBPβ, and the increased protein expressions of IL-17RC, with a decrease of IκBα. After IL-17A knockout, 29 of 35 F-induced changes were alleviated. In two self-recovery models, all F-caused differences except fluorine concentration in femur were gradually restored in a time-dependent manner. This study concluded that IL-17A knockout or self-recovery attenuated F-induced testicular injury and decrease of sperm quality through alleviating autoimmune reaction which was involved with the activation of IL-17A pathway, the damage of self-tolerance and the enhancement of antigen presentation.

Microbiology and immune mechanisms associated with male infertility

Up to 50% of infertility is caused by the male side. Varicocele, orchitis, prostatitis, oligospermia, asthenospermia, and azoospermia are common causes of impaired male reproductive function and male infertility. In recent years, more and more studies have shown that microorganisms play an increasingly important role in the occurrence of these diseases. This review will discuss the microbiological changes associated with male infertility from the perspective of etiology, and how microorganisms affect the normal function of the male reproductive system through immune mechanisms. Linking male infertility with microbiome and immunomics can help us recognize the immune response under different disease states, providing more targeted immune target therapy for these diseases, and even the possibility of combined immunotherapy and microbial therapy for male infertility.

Cell-Based Therapy Approaches in Treatment of Non-obstructive Azoospermia

The rate of infertility has globally increased in recent years for a variety of reasons. One of the main causes of infertility in men is azoospermia that is defined by the absence of sperm in the ejaculate and classified into two categories: obstructive azoospermia and non-obstructive azoospermia. In non-obstructive azoospermia, genital ducts are not obstructed, but the testicles do not produce sperm at all, due to various reasons. Non-obstructive azoospermia in most cases has no therapeutic options other than assisted reproductive techniques, which in most cases require sperm donors. Here we discuss cell-based therapy approaches to restore fertility in men with non-obstructive azoospermia including cell-based therapies of non-obstructive azoospermia using regenerative medicine and cell-based therapies of non-obstructive azoospermia by paracrine and anti-inflammatory pathway, technical and ethical challenges for using different cell sources and alternative options will be described, and then the more effectual approaches will be mentioned as future trends.

Probing the Potential Mechanism of Quercetin and Kaempferol against Heat Stress-Induced Sertoli Cell Injury: Through Integrating Network Pharmacology and Experimental Validation

Quercetin and kaempferol are flavonoids widely present in fruits, vegetables, and medicinal plants. They have attracted much attention due to their antioxidant, anti-inflammatory, anticancer, antibacterial, and neuroprotective properties. As the guarantee cells in direct contact with germ cells, Sertoli cells exert the role of support, nutrition, and protection in spermatogenesis. In the current study, network pharmacology was used to explore the targets and signaling pathways of quercetin and kaempferol in treating spermatogenic disorders. In vitro experiments were integrated to verify the results of quercetin and kaempferol against heat stress-induced Sertoli cell injury. The online platform was used to analyze the GO biological pathway and KEGG pathway. The results of the network pharmacology showed that quercetin and kaempferol intervention in spermatogenesis disorders were mostly targeting the oxidative response to oxidative stress, the ROS metabolic process and the NFκB pathway. The results of the cell experiment showed that Quercetin and kaempferol can prevent the decline of cell viability induced by heat stress, reduce the expression levels of HSP70 and ROS in Sertoli cells, reduce p-NF-κB-p65 and p-IκB levels, up-regulate the expression of occludin, vimentin and F-actin in Sertoli cells, and protect cell structure. Our research is the first to demonstrate that quercetin and kaempferol may exert effects in resisting the injury of cell viability and structure under heat stress.

The potential impact of COVID-19 on male reproductive health

The SARS-CoV-2 virus continues to overwhelm health care systems impairing human to human social and economic interactions. Invasion or damage to the male reproductive system is one of the documented outcomes of viral infection. Existing studies have reported that SARS-CoV-2 may contribute to this loss in relation to inflammatory responses and the formation of cytokine storms in COVID-19 patients. Although direct infection of the testes and entry of SARS-CoV-2 into semen as well as subsequent consequences on the male reproductive system need to be studied more systematically, warnings from two organising ASRM and SART for prospective parents when infected with SARS-CoV-2 should be considered. In the context of an increasingly complex pandemic, this review provides preliminary examples of the potential impact of COVID-19 on male reproductive health and guidance for prospective parents currently infected with or recovering from SARS-CoV-2.

Implications of regulatory T cells in non-lymphoid tissue physiology and pathophysiology

Treg cells have been initially described as gatekeepers for the control of autoimmunity, as they can actively suppress the activity of other immune cells. However, their role goes beyond this as Treg cells further control immune responses during infections and tumor development. Furthermore, Treg cells can acquire additional properties for e.g., the control of tissue homeostasis. This is instructed by a specific differentiation program and the acquisition of effector properties unique to Treg cells in non-lymphoid tissues. These tissue Treg cells can further adapt to their tissue environment and acquire distinct functional properties through specific transcription factors activated by a combination of tissue derived factors, including tissue-specific antigens and cytokines. In this review, we will focus on recent findings extending our current understanding of the role and differentiation of these tissue Treg cells. As such we will highlight the importance of tissue Treg cells for tissue maintenance, regeneration, and repair in adipose tissue, muscle, CNS, liver, kidney, reproductive organs, and the lung.

Hypertension Induces Gonadal Macrophage Imbalance, Inflammation, Lymphangiogenesis, and Dysfunction

Hypertension (HTN) is associated with gonadal dysfunction and impaired reproductive health in both men and women.  An imbalance in the systemic and renal pro-inflammatory (M1)/anti-inflammatory (M2) macrophage ratio, increased inflammation, and inflammation-associated lymphangiogenesis have been observed in animals with HTN.  However, the impact of HTN on gonadal macrophages, inflammation, and lymphatics remains obscure. We hypothesized that salt-sensitive HTN (SSHTN) and HTN alters gonadal macrophage polarization, which is associated with inflammation, inflammation-associated lymphangiogenesis and reproductive dysfunction. Flow cytometry analyses revealed a significant increase in M1 macrophages in the testes of SSHTN and nitric oxide synthase inhibition-induced HTN (LHTN) mice, with a concurrent decrease in M2 macrophages in SSHTN mice yet an increase in M2 macrophages in LHTN mice.  Ovaries from SSHTN mice exhibited increase in M1 and a decrease in M2 macrophages, while ovaries from LHTN mice had a significant increase in M2 and a decrease in M1 macrophages. Gene expression patterns of pro-inflammatory cytokines revealed gonadal inflammation in all hypertensive mice.  Increased lymphatic vessel density in the gonads of both male and female hypertensive mice was confirmed by immunofluorescence staining for LYVE-1. HTN adversely affected the expression pattern of steroidogenic enzymes, hormone receptors, and secretory proteins in both the testes and ovaries.  In line with these results, male hypertensive mice also presented with decreased sperm concentration, and increased percentage of sperm with abnormal morphology, damaged acrosome, and non-functional mitochondrial activity. These data demonstrate that HTN alters gonadal macrophage polarization, which is associated with gonadal inflammation, inflammation-associated lymphangiogenesis, and dysfunction.

An immunoPET probe to SARS-CoV-2 reveals early infection of the male genital tract in rhesus macaques

The systemic nature of SARS-CoV-2 infection is highly recognized, but poorly characterized. A non-invasive and unbiased method is needed to clarify whole body spatiotemporal dynamics of SARS-CoV-2 infection after transmission. We recently developed a probe based on the anti-SARS-CoV-2 spike antibody CR3022 to study SARS-CoV-2 pathogenesis in vivo. Herein, we describe its use in immunoPET to investigate SARS-CoV-2 infection of three rhesus macaques. Using PET/CT imaging of macaques at different times post-SARS-CoV-2 inoculation, we track the 64Cu-labelled CR3022-F(ab')2 probe targeting the spike protein of SARS-CoV-2 to study the dynamics of infection within the respiratory tract and uncover novel sites of infection. Using this method, we uncovered differences in lung pathology between infection with the WA1 isolate and the delta variant, which were readily corroborated through computed tomography scans. The 64Cu-CR3022-probe also demonstrated dynamic changes occurring between 1- and 2-weeks post-infection. Remarkably, a robust signal was seen in the male genital tract (MGT) of all three animals studied. Infection of the MGT was validated by immunofluorescence imaging of infected cells in the testicular and penile tissue and severe pathology was observed in the testes of one animal at 2-weeks post-infection. The results presented here underscore the utility of using immunoPET to study the dynamics of SARS-CoV-2 infection to understand its pathogenicity and discover new anatomical sites of viral replication. We provide direct evidence for SARS-CoV-2 infection of the MGT in rhesus macaques revealing the possible pathologic outcomes of viral replication at these sites.

An immunoPET probe to SARS-CoV-2 reveals early infection of the male genital tract in rhesus macaques

The systemic nature of SARS-CoV-2 infection is highly recognized, but poorly characterized. A non-invasive and unbiased method is needed to clarify whole body spatiotemporal dynamics of SARS-CoV-2 infection after transmission. We recently developed a probe based on the anti-SARS-CoV-2 spike antibody CR3022 to study SARS-CoV-2 pathogenesis in vivo. Herein, we describe its use in immunoPET to investigate SARS-CoV-2 infection of three rhesus macaques. Using PET/CT imaging of macaques at different times post-SARS-CoV-2 inoculation, we track the 64Cu-labelled CR3022-F(ab')2 probe targeting the spike protein of SARS-CoV-2 to study the dynamics of infection within the respiratory tract and uncover novel sites of infection. Using this method, we uncovered differences in lung pathology between infection with the WA1 isolate and the delta variant, which were readily corroborated through computed tomography scans. The 64Cu-CR3022-probe also demonstrated dynamic changes occurring between 1- and 2-weeks post-infection. Remarkably, a robust signal was seen in the male genital tract (MGT) of all three animals studied. Infection of the MGT was validated by immunofluorescence imaging of infected cells in the testicular and penile tissue and severe pathology was observed in the testes of one animal at 2-weeks post-infection. The results presented here underscore the utility of using immunoPET to study the dynamics of SARS-CoV-2 infection to understand its pathogenicity and discover new anatomical sites of viral replication. We provide direct evidence for SARS-CoV-2 infection of the MGT in rhesus macaques revealing the possible pathologic outcomes of viral replication at these sites.

Diabetes as a potential compounding factor in COVID-19-mediated male subfertility

Recent work indicates that male fertility is compromised by SARS-CoV-2 infection. Direct effects derive from the presence of viral entry receptors (ACE2 and/or CD147) on the surface of testicular cells, such as spermatocytes, Sertoli cells, and Leydig cells. Indirect effects on testis and concentrations of male reproductive hormones derive from (1) virus-stimulated inflammation; (2) viral-induced diabetes, and (3) an interaction between diabetes and inflammation that exacerbates the deleterious effect of each perturbation. Reproductive hormones affected include testosterone, luteinizing hormone, and follicle-stimulating hormone. Reduction of male fertility is also observed with other viral infections, but the global pandemic of COVID-19 makes demographic and public health implications of reduced male fertility of major concern, especially if it occurs in the absence of serious symptoms that would otherwise encourage vaccination. Clinical documentation of COVID-19-associated male subfertility is now warranted to obtain quantitative relationships between infection severity and subfertility; mechanistic studies using animal models may reveal ways to mitigate the problem. In the meantime, the possibility of subfertility due to COVID-19 should enter considerations of vaccine hesitancy by reproductive-age males.

High Throughput scRNA-Seq Provides Insights Into Leydig Cell Senescence Induced by Experimental Autoimmune Orchitis: A Prominent Role of Interstitial Fibrosis and Complement Activation

Leydig cells (Lc), located in the interstitial space of the testis between seminiferous tubules, produce 95% of testosterone in male individuals, which is pivotal for male sexual differentiation, spermatogenesis, and maintenance of the male secondary sex characteristics. Lc are prone to senescence in aging testes, resulting in compromised androgen synthesis capability upon aging. However, little is known about whether Lc undergo senescence in a chronic inflammatory environment. To investigate this question, mouse models of experimental autoimmune orchitis (EAO) were used, and Lc were analyzed by high throughput scRNA-Seq. Data were screened and analyzed by correlating signaling pathways with senescence, apoptosis, androgen synthesis, and cytokine/chemokine signaling pathways. EAO did induce Lc senescence, and Lc senescence in turn antagonized androgen synthesis. Based on the correlation screening of pathways inducing Lc senescence, a plethora of pathways were found to play potential roles in triggering Lc senescence during EAO, among which the Arf6 and angiopoietin receptor pathways were highly correlated with senescence signature. Notably, complement and interstitial fibrosis activated by EAO worsened Lc senescence and strongly antagonized androgen synthesis. Furthermore, most proinflammatory cytokines enhanced both senescence and apoptosis in Lc and spermatogonia (Sg) during EAO, and proinflammatory cytokine antagonism of the glutathione metabolism pathway may be key in inducing cellular senescence during EAO.

Activin A and CCR2 regulate macrophage function in testicular fibrosis caused by experimental autoimmune orchitis

Experimental autoimmune-orchitis (EAO), a rodent model of chronic testicular inflammation and fibrosis, replicates pathogenic changes seen in some cases of human spermatogenic disturbances. During EAO, increased levels of pro-inflammatory and pro-fibrotic mediators such as TNF, CCL2, and activin A are accompanied by infiltration of leukocytes into the testicular parenchyma. Activin A levels correlate with EAO severity, while elevated CCL2 acting through its receptor CCR2 mediates leukocyte trafficking and recruits macrophages. CCR2 + CXCR4 + macrophages producing extracellular matrix proteins contribute widely to fibrogenesis. Furthermore, testicular macrophages (TMs) play a critical role in organ homeostasis. Therefore, we aimed to investigate the role of the activin A/CCL2-CCR2/macrophage axis in the development of testicular fibrosis. Following EAO induction, we observed lower levels of organ damage, collagen deposition, and leukocyte infiltration (including fibronectin⁺, collagen I⁺ and CXCR4⁺ TMs) in Ccr2^-/- mice than in WT mice. Furthermore, levels of Il-10, Ccl2, and the activin A subunit Inhba mRNAs were lower in Ccr2^-/- EAO testes. Notably, fibronectin⁺ TMs were also present in biopsies from patients with impaired spermatogenesis and fibrotic alterations. Overexpression of the activin A antagonist follistatin reduced tissue damage and collagen I⁺ TM accumulation in WT EAO testes, while treating macrophages with activin A in vitro increased the expression of Ccr2, Fn1, Cxcr4, and Mmp2 and enhanced migration along a CCL2 gradient; these effects were abolished by follistatin. Taken together, our data indicate that CCR2 and activin A promote fibrosis during testicular inflammation by regulating macrophage function. Inhibition of CCR2 or activin A protects against damage progression, offering a promising avenue for therapeutic intervention.

Testicular macrophages: development and function in health and disease

Macrophages comprise a heterogeneous immune cell population and display niche-specific phenotypes and functions in almost all organs. Testicular macrophages (TMs) perform essential immune and non-immune functions in the mammalian male gonads. Here, we discuss the most recent findings on TM ontogeny, heterogeneity, and function under steady state and inflammatory conditions. We also highlight new discoveries regarding the functions of macrophages during bacterial and viral infections of the testes and how macrophages may indirectly help the establishment of a reservoir through virus seeding. Understanding TM function and macrophage-related mechanisms of disease might assist in developing new opportunities for intervention in male infertility.

Leydig Cells in Patients with Non-Obstructive Azoospermia: Do They Really Proliferate?

Background: Non-obstructive azoospermia (NOA) is a form of male infertility caused by disorders of the testicular parenchyma and impaired spermatogenesis. This study aimed to investigate the nature of Leydig cell changes in patients with NOA, especially whether their actual proliferation occurred. Methods: 48 testicular biopsies from infertile patients with NOA and 24 testicular biopsies originating from azoospermic patients suffering from obstructive azoospermia (OA) were included in the study. Leydig cells and their possible proliferative activity were analysed by immunohistochemistry and morphometry (stereology). Results: Unlike in the OA group, Leydig cells in NOA patients were sometimes organised into larger clusters and displayed an abundant cytoplasm/hypertrophy. Moreover, significant fibrosis of the interstitial compartment was demonstrated in some NOA samples, often accompanied by inflammatory cells. Stereological analysis showed no increase/proliferation of Leydig cells; on the contrary, these cells decreased in number in the NOA group. Conclusions: The decrease in the number of Leydig cells can be explained by previous inflammatory changes within the testicular interstitium and consequent interstitial fibrosis. The interstitial fibrosis might have a deteriorating effect on Leydig cells.

Bone Status in a Mouse Model of Experimental Autoimmune-Orchitis

Investigations in male patients with fertility disorders revealed a greater risk of osteoporosis. The rodent model of experimental autoimmune-orchitis (EAO) was established to analyze the underlying mechanisms of male infertility and causes of reduced testosterone concentration. Hence, we investigated the impact of testicular dysfunction in EAO on bone status. Male mice were immunized with testicular homogenate in adjuvant to induce EAO (n = 5). Age-matched mice were treated with adjuvant alone (adjuvant, n = 6) or remained untreated (control, n = 7). Fifty days after the first immunization specimens were harvested. Real-time reverse transcription-PCR indicated decreased bone metabolism by alkaline phosphatase and Cathepsin K as well as remodeling of cell-contacts by Connexin-43. Micro computed tomography demonstrated a loss of bone mass and mineralization. These findings were supported by histomorphometric results. Additionally, biomechanical properties of femora in a three-point bending test were significantly altered. In summary, the present study illustrates the induction of osteoporosis in the investigated mouse model. However, results suggest that the major effects on bone status were mainly caused by the complete Freund's adjuvant rather than the autoimmune-orchitis itself. Therefore, the benefit of the EAO model to transfer laboratory findings regarding bone metabolism in context with orchitis into a clinical application is limited.

Two populations of self-maintaining monocyte-independent macrophages exist in adult epididymis and testis

Macrophages are the principal immune cells of the epididymis and testis, but their origins, heterogeneity, development, and maintenance are not well understood. Here, we describe distinct populations of epididymal and testicular macrophages that display an organ-specific cellular identity. Combining in vivo fate-mapping, chimeric and parabiotic mouse models with in-depth cellular analyses, we found that CD64^hiMHCII^lo and CD64^loMHCII^hi macrophage populations of epididymis and testis arise sequentially from yolk sac erythro-myeloid progenitors, embryonic hematopoiesis, and nascent neonatal monocytes. While monocytes were the major developmental source of both epididymal and testicular macrophages, both populations self-maintain in the steady-state independent of bone marrow hematopoietic precursors. However, after radiation-induced macrophage ablation or during infection, bone marrow-derived circulating monocytes are recruited to the epididymis and testis, giving rise to inflammatory macrophages that promote tissue damage. These results define the layered ontogeny, maintenance and inflammatory response of macrophage populations in the male reproductive organs.

Hypertension and reproductive dysfunction: a possible role of inflammation and inflammation-associated lymphangiogenesis in gonads

Hypertension is one of the most prevalent diseases that leads to end organ damage especially affecting the heart, kidney, brain, and eyes. Numerous studies have evaluated the association between hypertension and impaired sexual health, in both men and women. The detrimental effects of hypertension in men includes erectile dysfunction, decrease in semen volume, sperm count and motility, and abnormal sperm morphology. Similarly, hypertensive females exhibit decreased vaginal lubrication, reduced orgasm, and several complications in pregnancy leading to fetal and maternal morbidity and mortality. The adverse effect of hypertension on male and female fertility is attributed to hormonal imbalance and changes in the gonadal vasculature. However, mechanistic studies investigating the impact of hypertension on gonads in more detail on a molecular basis remain scarce. Hence, the aim of the current review is to address and summarize the effects of hypertension on reproductive health, and highlight the importance of research on the effects of hypertension on gonadal inflammation and lymphatics.

T Lymphocytes and Testicular Immunity: A New Insight into Immune Regulation in Testes

The immune privilege of the testes is necessary to prevent immune attacks to gamete-specific antigens and paternal major histocompatibility complex (MHC) antigens, allowing for normal spermatogenesis. However, infection and inflammation of the male genital tract can break the immune tolerance and represent a significant cause of male infertility. Different T cell subsets have been identified in mammalian testes, which may be involved in the maintenance of immune tolerance and pathogenic immune responses in testicular infection and inflammation. We reviewed the evidence in the published literature on different T subtypes (regulatory T cells, helper T cells, cytotoxic T cells, γδ T cells, and natural killer T cells) in human and animal testes that support their regulatory roles in infertility and the orchitis pathology. While many in vitro studies have indicated the regulation potential of functional T cell subsets and their possible interaction with Sertoli cells, Leydig cells, and spermatogenesis, both under physiological and pathological processes, there have been no in situ studies to date. Nevertheless, the normal distribution and function of T cell subsets are essential for the immune privilege of the testes and intact spermatogenesis, and T cell-mediated immune response drives testicular inflammation. The distinct function of different T cell subsets in testicular homeostasis and the orchitis pathology suggests a considerable potential of targeting specific T cell subsets for therapies targeting chronic orchitis and immune infertility.

Successful activation of rat T lymphocytes by sperm specific antigens in vitro

Autoimmune orchitis is a condition related to cellular immunity. A disease model involving transfer of T lymphocytes activated by known antigens would be useful for defining pathogenical molecules. Since no method for activating rat T cells using specific antigens is available, we started the study to develop the method. T cells were collected from draining lymph nodes of immunized rats, then co-cultured with syngeneic splenocytes as antigen-presenting cells (APC) in antigen-supplemented medium (= stimulation). The cells were then incubated in medium without antigens and APC (= resting). Repetitive stimulation and resting increased the number of the T cells more than 100-fold. The antigen-specific activation was demonstrated by cell proliferation assay and ELISA assay for interferon gamma. Flow cytometry revealed that > 95% of the cells expressed tumor necrosis factor alpha, a cytokine responsible for autoimmune orchitis. The present method will provide a new procedure to evaluate antigenicity of sperm molecules.

Elevated CCL2 causes Leydig cell malfunction in metabolic syndrome

Metabolic syndrome (MetS), which is associated with chronic inflammation, predisposes males to hypogonadism and subfertility. The underlying mechanism of these pathologies remains poorly understood. Homozygous leptin-resistant obese db/db mice are characterized by small testes, low testicular testosterone, and a reduced number of Leydig cells. Here we report that IL-1β, CCL2 (also known as MCP-1), and corticosterone concentrations were increased in the testes of db/db mice relative to those in WT controls. Cultured murine and human Leydig cells responded to cytokine stress with increased CCL2 release and apoptotic signals. Chemical inhibition of CCL2 rescued Leydig cell function in vitro and in db/db mice. Consistently, we found that Ccl2-deficient mice fed with a high-energy diet were protected from testicular dysfunction compared with similarly fed WT mice. Finally, a cohort of infertile men with a history of MetS showed that reduction of CCL2 plasma levels could be achieved by weight loss and was clearly associated with recovery from hypogonadism. Taken together, we conclude that CCL2-mediated chronic inflammation is, to a large extent, responsible for the subfertility in MetS by causing damage to Leydig cells.

MCP-1/CCL2 upregulation associates with metabolic syndrome–induced male subfertility in both mice and men.

Pathomechanisms of Autoimmune Based Testicular Inflammation

Infection and inflammation of the male reproductive tract are relevant causes of infertility. Inflammatory damage occurs in the special immunosuppressive microenvironment of the testis, a hallmark termed testicular immune privilege, which allows tolerance to neo-antigens from developing germ cells appearing at puberty, long after the establishment of systemic immune tolerance. Experimental autoimmune orchitis (EAO) is a well-established rodent model of chronic testicular inflammation and organ specific autoimmunity that offers a valuable in vivo tool to investigate the pathological and molecular mechanisms leading to the breakdown of the testicular immune privilege. The disease is characterized by the infiltration of the interstitium by immune cells (mainly macrophages, dendritic cells, and T cells), formation of autoantibodies against testicular antigens, production of pro-inflammatory mediators such as NO, MCP1, TNFα, IL6, or activins and dysregulation of steroidogenesis with reduced levels of serum testosterone. EAO leads to sloughing of germ cells, atrophic seminiferous tubules and fibrotic remodeling, parameters all found similarly to changes in human biopsies from infertile patients with inflammatory infiltrates. Interestingly, testosterone supplementation during the course of EAO leads to expansion of the regulatory T cell population and inhibition of disease development. Knowledge of EAO pathogenesis aims to contribute to a better understanding of human testicular autoimmune disease as an essential prerequisite for improved diagnosis and treatment.

Immune Cell Subtypes and Their Function in the Testis

Immunoregulation in the testis is characterized by a balance between immuno-suppression (or immune privilege) and the ability to react to infections and inflammation. In this review, we analyze the phenotypes of the various immune cell subtypes present in the testis, and how their functions change between homeostatic and inflammatory conditions. Starting with testicular macrophages, we explore how this heterogeneous population is shaped by the testicular microenvironment to ensure immune privilege. We then describe how dendritic cells exhibit a tolerogenic status under normal conditions, but proliferate, mature and then stimulate effector T-cell expansion under inflammatory conditions. Finally, we outline the two T-cell populations in the testis: CD4⁺/CD8⁺ αβ T cells and CD4⁺/CD8⁺ Foxp3⁺ regulatory T cells and describe the distribution and function of mast cells. All these cells help modulate innate immunity and regulate the immune response. By improving our understanding of immune cell behavior in the testis under normal and inflammatory conditions, we will be better placed to evaluate testis impairment due to immune mechanisms in affected patients.

Testicular immune cell populations and macrophage polarisation in adult male mice and the influence of altered activin A levels

Detailed morphological characterization of testicular leukocytes in the adult CX₃CR₁^gfp/+ transgenic mouse identified two distinct CX₃CR₁⁺ mononuclear phagocyte (macrophage and dendritic cell) populations: stellate/dendriform cells opposed to the seminiferous tubules (peritubular), and polygonal cells associated with Leydig cells (interstitial). Using confocal microscopy combined with stereological enumeration of CX₃CR₁^gfp/+ cells established that there were twice as many interstitial cells (68%) as peritubular cells (32%). Flow cytometric analyses of interstitial cells from mechanically-dissociated testes identified multiple mononuclear phagocyte subsets based on surface marker expression (CX₃CR₁, F4/80, CD11c). These cells comprised 80% of total intratesticular leukocytes, as identified by CD45 expression. The remaining leukocytes were CD3⁺ (T lymphocytes) and NK1.1⁺ (natural killer cells). Functional phenotype assessment using CD206 (an anti-inflammatory/M2 marker) and MHC class II (an activation marker) identified a potentially tolerogenic CD206⁺MHCII⁺ sub-population (12% of total CD45⁺ cells). Rare testicular subsets of CX₃CR₁⁺CD11c⁺F4/80⁺ (4.3%) mononuclear phagocytes and CD3⁺NK1.1⁺ (3.1%) lymphocytes were also identified for the first time. In order to examine the potential for the immunoregulatory cytokine, activin A to modulate testicular immune cell populations, testes from adult mice with reduced activin A (Inhba^+/-) or elevated activin A (Inha^+/-) were assessed using flow cytometry. Although the proportion of F4/80⁺CD11b⁺ leukocytes (macrophages) was not affected, the frequency of CD206⁺MHCII⁺cells was significantly lower and CD206⁺MHCII^- correspondingly higher in Inha^+/- testes. This shift in expression of MHCII in CD206⁺ macrophages indicates that changes in circulating and/or local activin A influence resident macrophage activation and phenotype and, therefore, the immunological environment of the testis.

Investigation of activin A in inflammatory responses of the testis and its role in the development of testicular fibrosis

STUDY QUESTION

Does activin A contribute to testicular fibrosis under inflammatory conditions?

SUMMARY ANSWER

Our results show that activin A and key fibrotic proteins are increased in human testicular biopsies with leukocytic infiltrates and impaired spermatogenesis and in murine experimental autoimmune orchitis (EAO) and that activin A stimulates fibrotic responses in peritubular cells (PTCs) and NIH 3T3 fibroblasts.

WHAT IS KNOWN ALREADY

Fibrosis is a feature of EAO. Activin A, a regulator of fibrosis, was increased in testes of mice with EAO and its expression correlated with severity of the disease.

STUDY DESIGN, SIZE, DURATION

This is a cross-sectional and longitudinal study of adult mice immunized with testicular homogenate (TH) in adjuvant to induce EAO, collected at 30 (n = 6), 50 (n = 6) and 80 (n = 5) days after first immunization. Age-matched mice injected with adjuvant alone (n = 14) and untreated mice (n = 15) were included as controls. TH-immunized mice with elevated endogenous follistatin, injected with a non-replicative recombinant adeno-associated viral vector carrying a gene cassette of follistatin (rAAV-FST315; n = 3) or vector with an empty cassette (empty vector controls; n = 2) 30 days prior to the first immunization, as well as appropriate adjuvant (n = 2) and untreated (n = 2) controls, were also examined.Human testicular biopsies showing focal inflammatory lesions associated with impaired spermatogenesis (n = 7) were included. Biopsies showing intact spermatogenesis without inflammation, from obstructive azoospermia patients, served as controls (n = 7).Mouse primary PTC and NIH 3T3 fibroblasts were stimulated with activin A and follistatin 288 (FST288) to investigate the effect of activin A on the expression of fibrotic markers. Production of activin A by mouse primary Sertoli cells (SCs) was also investigated.

PARTICIPANTS/MATERIALS, SETTING, METHODS

Testicular RNA and protein extracts collected from mice at days 30, 50 and 80 after first immunization were used for analysis of fibrotic marker genes and proteins, respectively. Total collagen was assessed by hydroxyproline assay and fibronectin; collagen I, III and IV, α-smooth muscle actin (α-SMA) expression and phosphorylation of suppressor of mothers against decapentaplegic (SMAD) family member 2 were measured by western blot. Immunofluorescence was used to detect fibronectin. Fibronectin (Fn), αSMA (Acta2), collagen I (Col1a2), III (Col3a1) and IV (Col4a1) mRNA in PTC and NIH 3T3 cells treated with activin A and/or FST288 were measured by quantitative RT-PCR (qRT-PCR). Activin A in SC following tumour necrosis factor (TNF) or FST288 stimulation was measured by ELISA. Human testicular biopsies were analysed by qRT-PCR for PTPRC (CD45) and activin A (INHBA), hydroxyproline assay and immunofluorescence.

MAIN RESULTS AND THE ROLE OF CHANCE

Production of activin A by SC was stimulated by 25 and 50 ng/ml TNF (P < 0.01, P < 0.001, respectively) as compared to untreated cells. INHBA mRNA was increased in human testicular biopsies with leukocytic infiltrates and impaired spermatogenesis, compared with control biopsies (P < 0.05), accompanied by increased total collagen (P < 0.01) and fibronectin deposition. Total testicular collagen (P < 0.0001) and fibronectin protein expression (P < 0.05) were also increased in EAO, and fibronectin expression was correlated with the severity of the disease (r = 0.9028). In animals pre-treated with rAAV-FST315 prior to immunization with TH, protein expression of fibronectin was comparable to control. Stimulation of PTC and NIH 3T3 cells with activin A increased fibronectin mRNA (P < 0.05) and the production of collagen I (P < 0.001; P < 0.01) and fibronectin (P < 0.05). Moreover, activin A also increased collagen IV mRNA (P < 0.05) in PTC, while αSMA mRNA (P < 0.01) and protein (P < 0.0001) were significantly increased by activin A in NIH 3T3 cells.

LARGE SCALE DATA

N/A.

LIMITATIONS, REASONS FOR CAUTION

A limited number of human testicular specimens was available for the study. Part of the study was performed in vitro, including NIH 3T3 cells as a surrogate for testicular fibroblasts.

WIDER IMPLICATIONS OF THE FINDINGS

Resident fibroblasts and PTC may contribute to the progression of testicular fibrosis following inflammation, and activin A is implicated as a key mediator of this process.

STUDY FUNDING/COMPETING INTEREST(S)

This work was supported by the National Health and Medical Research Council of Australia, the Victorian Government's Operational Infrastructure Support Program and the International Research Training Group between Justus Liebig University (Giessen) and Monash University (Melbourne) (GRK 1871/1-2) on `Molecular pathogenesis on male reproductive disorders' funded by the Deutsche Forschungsgemeinschaft and Monash University. The authors declare no competing financial interests.

Zika virus tropism during early infection of the testicular interstitium and its role in viral pathogenesis in the testes

Sexual transmission and persistence of Zika virus (ZIKV) in the testes pose new challenges for controlling virus outbreaks and developing live-attenuated vaccines. It has been shown that testicular infection of ZIKV is initiated in the testicular interstitium, followed by spread of the virus in the seminiferous tubules. This leads to testicular damage and/or viral dissemination into the epididymis and eventually into semen. However, it remains unknown which cell types are targeted by ZIKV in the testicular interstitium, and what is the specific order of infectious events leading to ZIKV invasion of the seminiferous tubules. Here, we demonstrate that interstitial leukocytes expressing mir-511-3p microRNA are the initial targets of ZIKV in the testes, and infection of mir-511-3p-expressing cells in the testicular interstitium is necessary for downstream infection of the seminiferous tubules. Mir-511-3p is expressed concurrently with CD206, a marker of lineage 2 (M2) macrophages and monocyte derived dendritic cells (moDCs). Selective restriction of ZIKV infection of CD206-expressing M2 macrophages/moDCs results in the attenuation of macrophage-associated inflammatory responses in vivo and prevents the disruption of the Sertoli cell barrier in vitro. Finally, we show that targeting of viral genome for mir-511-3p significantly attenuates early ZIKV replication not only in the testes, but also in many peripheral organs, including spleen, epididymis, and pancreas. This incriminates M2 macrophages/moDCs as important targets for visceral ZIKV replication following hematogenous dissemination of the virus from the site of infection.

[Orchitis]

Orchitis can be acutely symptomatic or chronically asymptomatic. Among the acute forms is the rarer isolated orchitis, which is of viral origin in most cases as well as the more frequent secondary orchitis, which is usually the result of an ascending bacterial epididymitis. In addition, sterile forms of orchitis are also seen in patients with systemic autoimmune comorbidities. Chronic asymptomatic orchitis is the term used to describe cellular immune infiltrates in the testes, which are observed in approximately 25% of cases of azoospermia during testicular biopsy. The etiopathogenesis of these infiltrates is largely unknown with postinfection and primary pathogen-independent autoimmune reactions being discussed. Animal experimental models of orchitis may be helpful to investigate the immunological mechanisms involved as well as the therapeutic possibilities.

Infectious, inflammatory and 'autoimmune' male factor infertility: how do rodent models inform clinical practice?

BACKGROUND

Infection and inflammation of the reproductive tract are significant causes of male factor infertility. Ascending infections caused by sexually transmitted bacteria or urinary tract pathogens represent the most frequent aetiology of epididymo-orchitis, but viral, haematogenous dissemination is also a contributory factor. Limitations in adequate diagnosis and therapy reflect an obvious need for further understanding of human epididymal and testicular immunopathologies and their contribution to infertility. A major obstacle for advancing our knowledge is the limited access to suitable tissue samples. Similarly, the key events in the inflammatory or autoimmune pathologies affecting human male fertility are poorly amenable to close examination. Moreover, the disease processes generally have occurred long before the patient attends the clinic for fertility assessment. In this regard, data obtained from experimental animal models and respective comparative analyses have shown promise to overcome these restrictions in humans.

OBJECTIVE AND RATIONALE

This narrative review will focus on male fertility disturbances caused by infection and inflammation, and the usefulness of the most frequently applied animal models to study these conditions.

SEARCH METHODS

An extensive search in Medline database was performed without restrictions until January 2018 using the following search terms: 'infection' and/or 'inflammation' and 'testis' and/or 'epididymis', 'infection' and/or 'inflammation' and 'male genital tract', 'male infertility', 'orchitis', 'epididymitis', 'experimental autoimmune' and 'orchitis' or 'epididymitis' or 'epididymo-orchitis', antisperm antibodies', 'vasectomy'. In addition to that, reference lists of primary and review articles were reviewed for additional publications independently by each author. Selected articles were verified by each two separate authors and discrepancies discussed within the team.

OUTCOMES

There is clear evidence that models mimicking testicular and/or epididymal inflammation and infection have been instructive in a better understanding of the mechanisms of disease initiation and progression. In this regard, rodent models of acute bacterial epididymitis best reflect the clinical situation in terms of mimicking the infection pathway, pathogens selected and the damage, such as fibrotic transformation, observed. Similarly, animal models of acute testicular and epididymal inflammation using lipopolysaccharides show impairment of reproduction, endocrine function and histological tissue architecture, also seen in men. Autoimmune responses can be studied in models of experimental autoimmune orchitis (EAO) and vasectomy. In particular, the early stages of EAO development showing inflammatory responses in the form of peritubular lymphocytic infiltrates, thickening of the lamina propria of affected tubules, production of autoantibodies against testicular antigens or secretion of pro-inflammatory mediators, replicate observations in testicular sperm extraction samples of patients with 'mixed atrophy' of spermatogenesis. Vasectomy, in the form of sperm antibodies and chronic inflammation, can also be studied in animal models, providing valuable insights into the human response.

WIDER IMPLICATIONS

This is the first comprehensive review of rodent models of both infectious and autoimmune disease of testis/epididymis, and their clinical implications, i.e. their importance in understanding male infertility related to infectious and non-infectious/autoimmune disease of the reproductive organs.

Induction of experimental autoimmune orchitis in mice: responses to elevated circulating levels of the activin-binding protein, follistatin

Experimental autoimmune orchitis (EAO) is a rodent model of chronic testicular inflammation that mimics the pathology observed in some types of human infertility. In a previous study, testicular expression of the inflammatory/immunoregulatory cytokine, activin A, was elevated in adult mice during the onset of EAO, indicating a potential role in the regulation of the disease. Consequently, we examined the development of EAO in mice with elevated levels of follistatin, an endogenous activin antagonist, as a potential therapeutic approach to testicular inflammation. Prior to EAO induction, mice received a single intramuscular injection of a non-replicative recombinant adeno-associated viral vector carrying a gene cassette of the circulating form of follistatin, FST315 (FST group). Serum follistatin levels were increased 5-fold in the FST group compared with the control empty vector (EV) group at 30 and 50 days of EAO, but intra-testicular levels of follistatin or activin A were not significantly altered. Induction of EAO was reduced, but not prevented, with mild-to-severe damage in 75% of the EV group and 40% of the FST group, at 50 days following immunisation with testicular homogenate. However, the EAO damage score (based on disruption of the blood-testis barrier, apoptosis, testicular damage and fibrosis) and extent of intratesticular inflammation (expression of inflammatory mediators) were directly proportional to the levels of activin A measured in the testis at 50 days. These data implicate activin A in the progression of EAO, thereby providing a potential therapeutic target; however, elevating circulating follistatin levels were not sufficient to prevent EAO development.

Cytokines in Male Fertility and Reproductive Pathologies: Immunoregulation and Beyond

Germline development in vivo is dependent on the environment formed by somatic cells and the differentiation cues they provide; hence, the impact of local factors is highly relevant to the production of sperm. Knowledge of how somatic and germline cells interact is central to achieving biomedical goals relating to restoring, preserving or restricting fertility in humans. This review discusses the growing understanding of how cytokines contribute to testicular function and maintenance of male reproductive health, and to the pathologies associated with their abnormal activity in this organ. Here we consider both cytokines that signal through JAKs and are regulated by SOCS, and those utilizing other pathways, such as the MAP kinases and SMADs. The importance of cytokines in the establishment and maintenance of the testis as an immune-privilege site are described. Current research relating to the involvement of immune cells in testis development and disease is highlighted. This includes new data relating to testicular cancer which reinforce the understanding that tumorigenic cells shape their microenvironment through cytokine actions. Clinical implications in pathologies relating to local inflammation and to immunotherapies are discussed.