Experimental autoimmune orchitis as a model of immunological male infertility

The role of immune cell death in spermatogenesis and male fertility

The male reproductive system provides a distinctive shield to the immune system, safeguarding germ cells (GCs) from autoimmune harm. The testis in mammals creates a unique immunological setting due to its exceptional immune privilege and potent local innate immunity. which can result from a number of different circumstances, including disorders of the pituitary gland, GC aplasia, and immunological elements. Apoptosis, or programmed cell death (PCD), is essential for mammalian spermatogenesis to maintain and ensure an appropriate number of GCs that correspond with the supporting capability of the Sertoli cells. Apoptosis is substantial in controlling the number of GCs in the testis throughout spermatogenesis, and any dysregulation of this process has been linked to male infertility. There is a number of evidence about the potential of PCD in designing novel therapeutic approaches in the treatment of infertility. A detailed understanding of PCD and the processes that underlie immunological infertility can contribute to the progress in designing strategies to prevent and treat male infertility. This review will provide a summary of the role of immune cell death in male reproduction and infertility and describe the therapeutic strategies and agents for treatment based on immune cell death.

Impaired Spermatogenesis in Infertile Patients with Orchitis and Experimental Autoimmune Orchitis in Rats

Experimental autoimmune orchitis (EAO) is a well-established rodent model of organ-specific autoimmunity associated with infertility in which the testis immunohistopathology has been extensively studied. In contrast, analysis of testis biopsies from infertile patients associated with inflammation has been more limited. In this work, testicular biopsies from patients with idiopathic non-obstructive azoospermia diagnosed with hypospermatogenesis (HypoSp) [mild: n = 9, and severe: n = 11], with obstructive azoospermia and complete Sp (spermatogenesis) (control group, C, n = 9), and from Sertoli cell-only syndrome (SCOS, n = 9) were analyzed for the presence of immune cells, spermatogonia and Sertoli cell (SCs) alterations, and reproductive hormones levels. These parameters were compared with those obtained in rats with EAO. The presence of increased CD45+ cells in the seminiferous tubules (STs) wall and lumen in severe HypoSp is associated with increased numbers of apoptotic meiotic germ cells and decreased populations of undifferentiated and differentiated spermatogonia. The SCs showed an immature profile with the highest expression of AMH in patients with SCOS and severe HypoSp. In SCOS patients, the amount of SCs/ST and Ki67+ SCs/ST increased and correlated with high serum FSH levels and CD45+ cells. In the severe phase of EAO, immune cell infiltration and apoptosis of meiotic germ cells increased and the number of undifferentiated and differentiated spermatogonia was lowest, as previously reported. Here, we found that orchitis leads to reduced sperm number, viability, and motility. SCs were mature (AMH-) but increased in number, with Ki67+ observed in severely damaged STs and associated with the highest levels of FSH and inflammatory cells. Our findings demonstrate that in a scenario where a chronic inflammatory process is underway, FSH levels, immune cell infiltration, and immature phenotypes of SCs are associated with severe changes in spermatogenesis, leading to azoospermia. Furthermore, AMH and Ki67 expression in SCs is a distinctive marker of severe alterations of STs in human orchitis.

Complementing Testicular Immune Regulation: The Relationship between Sertoli Cells, Complement, and the Immune Response

Sertoli cells within the testis are instrumental in providing an environment for spermatogenesis and protecting the developing germ cells from detrimental immune responses which could affect fertility. Though these immune responses consist of many immune processes, this review focuses on the understudied complement system. Complement consists of 50+ proteins including regulatory proteins, immune receptors, and a cascade of proteolytic cleavages resulting in target cell destruction. In the testis, Sertoli cells protect the germ cells from autoimmune destruction by creating an immunoregulatory environment. Most studies on Sertoli cells and complement have been conducted in transplantation models, which are effective in studying immune regulation during robust rejection responses. In grafts, Sertoli cells survive activated complement, have decreased deposition of complement fragments, and express many complement inhibitors. Moreover, the grafts have delayed infiltration of immune cells and contain increased infiltration of immunosuppressive regulatory T cells as compared to rejecting grafts. Additionally, anti-sperm antibodies and lymphocyte infiltration have been detected in up to 50% and 30% of infertile testes, respectively. This review seeks to provide an updated overview of the complement system, describe its relationship with immune cells, and explain how Sertoli cells may regulate complement in immunoprotection. Identifying the mechanism Sertoli cells use to protect themselves and germ cells against complement and immune destruction is relevant for male reproduction, autoimmunity, and transplantation.

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.

Sperm-specific proteins: new implications for diagnostic development and cancer immunotherapy

Spermatozoa are comprised of many unique proteins not expressed elsewhere. Sperm-specific proteins are first expressed at puberty, after the development of immune tolerance to self-antigens, and have been assumed to remain confined inside the seminiferous tubules, protected from immune cell recognition by various mechanisms of testicular immune privilege. However, new data has shown that sperm-specific proteins are released by the tubules into the surrounding interstitial fluid; from here they can contact immune cells, potentially promote immune tolerance, and enter the circulation. These new findings have clinical implications for diagnostics and therapeutics targeted at a specific class of proteins known as cancer-testis antigens (CTA), the opportunity to identify new communication pathways in the testis, and to discover new ways to monitor testis function.

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.

Ethyl pyruvate, a versatile protector in inflammation and autoimmunity

Ethyl pyruvate (EP) has potent influence on redox processes, cellular metabolism, and inflammation. It has been intensively studied in numerous animal models of systemic and organ-specific disorders whose pathogenesis involves a strong immune component. Here, basic chemical and biological properties of EP are discussed, with an emphasis on its redox and metabolic activity. Further, its influence on myeloid and T cells is considered, as well as on intracellular signaling beyond its effect on immune cells. Also, the effects of EP on animal models of chronic inflammatory and autoimmune disorders are presented. Finally, a possibility to apply EP as a treatment for such diseases in humans is discussed. Scientific papers cited in this review were identified using the PubMed search engine that relies on the MEDLINE database. The reference list covers the most important findings in the field in the past twenty years.

Gallic acid ameliorates di-(2-ethylhexyl) phthalate-induced testicular injury in adult mice

Background: Di-(2-ethylhexyl) phthalate (DEHP) is a well-known endocrine-disrupting compound inducing degeneration of testes. Gallic acid (GA) is a polyphenol with various pharmacological properties, including antioxidant and anti-inflammatory effects.Purpose: This research evaluated effects of different doses of GA on DEHP-induced testicular injury in adult mice.Research Design: Male mice were randomly divided into five groups and treated with agents for two weeks; group (I) received normal saline and corn oil (5 mL/kg/day, p. o.), group (II) received DEHP (2 g/kg/day, dissolved in corn oil, p. o.), groups (III, IV, and V) received DEHP + GA (25, 50, and 100 mg/kg/day, p. o.). Body and testes weights, serum testosterone, luteinizing hormone (LH), and follicle-stimulating hormone (FSH) levels were evaluated. The number of sperms and sperm motility and viability were analyzed in the cauda epididymis. Histological changes, oxidative/nitrosative stress markers, and inflammatory cytokines levels were examined in testes.Results: Body and testes weights, the number of spermatogonia, primary spermatocyte and early spermatid, and late spermatid and sperm vitality, and progressive motility were significantly reduced in mice exposed to DEHP. Serum testosterone level decreased and serum LH and FSH levels increased in DEHP-exposed mice. These alterations were associated with the increased oxidative stress level and inflammatory responses in testicular tissue. Treatment with GA (50 and 100 mg/kg/day) attenuated DEHP-induced alterations in oxidative stress markers and inflammatory cytokines and reversed abnormality in sperm characteristic and number, tissue structure, and serum hormones levels.Conclusions: Results indicated that GA might be a promising agent against male gonadal toxicity induced by endocrine disrupting chemicals including DEHP.

Aspirin Alleviates Particulate Matter Induced Asymptomatic Orchitis of Mice via Suppression of cGAS-STING Signaling

As an important source of air pollutant, airborne particulate matter (PM) has become a major threat to public health. Orchitis is characterized by acute or chronic testicular inflammation and is a primary cause of male infertility. Although accumulating evidence indicates that PM exposure is associated with increased male infertility rates, the mechanism by which PM is involved is not well understood. Here, we found that short-term PM exposure activated NF-κB signaling in mouse Leydig cells and testes and leading to asymptomatic orchitis. Analyzing the mitochondrial abundance and cGAMP levels in PM exposed mouse Leydig cells, we found that PM exposure induced mitochondrial injury and mtDNA release, leading to inflammation via the cGAS-STING axis. We also found that aspirin-induced acetylation of cGAS inhibited the inflammation in mice after PM exposure, especially in the testes. Moreover, aspirin pretreatment rescued offspring growth in PM-exposed mice. In summary, our study not only provides evidence that PM-induced asymptomatic orchitis in mice may be amenable to aspirin pre-treatment by acetylating cGAS, but also provides a potential explanation for male infertility caused by air pollutants.

The ameliorative effect of ellagic acid on di-(2-ethylhexyl) phthalate-induced testicular structural alterations, oxidative stress, inflammation and sperm damages in adult mice

BACKGROUND

Phthalates such as di (2-ethylhexyl) phthalate (DEHP) are well known exogenous substances, disrupting reproductive system function and structure. The current research demonstrated the effect of ellagic acid (EA) on DEHP-induced testicular injury in mice.

METHODS

Thirty-five healthy adult male mice were randomly divided to five groups; normal saline receiving group, DEHP (2 g/kg/day, dissolved in corn oil, p.o.) receiving group, DEHP (2 g/kg/day, dissolved in corn oil, p.o.) and EA receiving groups (25, 50 and 100 mg/kg/day, p.o.). Treatment duration of animals was 14 days. Body and testes weights and sperm characteristics and histological changes of testes were evaluated. Serum testosterone, luteinizing hormone (LH) and follicle-stimulating hormone (FSH) levels were analyzed. In the testicular tissue, oxidative/nitrosative stress markers and inflammatory cytokine levels were measured.

RESULTS

Ellagic acid significantly reduced DEHP-induced reduction of body and testes weights. The DEHP-induced reduction of spermatogonia, primary spermatocyte and sertoli cells numbers as well as reduction of sperm vitality and progressive motility were reversed by EA. Furthermore, EA inhibited DEHP-induced alterations in serum hormone levels. These effects were associated with the reduction of DEHP-induced increased level of oxidative stress and inflammatory responses.

CONCLUSIONS

Ellagic acid considerably inhibits testicular toxicity of DEHP through reducing oxidative/nitrosative stress and inflammatory responses. Our data suggest that EA may be considered as a promising agent to inhibit male reproductive toxicity induced by endocrine disrupting chemicals such as DEHP.

Sperm proteins and cancer-testis antigens are released by the seminiferous tubules in mice and men

Sperm develop from puberty in the seminiferous tubules, inside the blood-testis barrier to prevent their recognition as "non-self" by the immune system, and it is widely assumed that human sperm-specific proteins cannot access the circulatory or immune systems. Sperm-specific proteins aberrantly expressed in cancer, known as cancer-testis antigens (CTAs), are often pursued as cancer biomarkers and therapeutic targets based on the assumption they are neoantigens absent from the circulation in healthy men. Here, we identify a wide range of germ cell-derived and sperm-specific proteins, including multiple CTAs, that are selectively deposited by the Sertoli cells of the adult mouse and human seminiferous tubules into testicular interstitial fluid (TIF) that is "outside" the blood-testis barrier. From TIF, the proteins can access the circulatory- and immune systems. Disruption of spermatogenesis decreases the abundance of these proteins in mouse TIF, and a sperm-specific CTA is significantly decreased in TIF from infertile men, suggesting that exposure of certain CTAs to the immune system could depend on fertility status. The results provide a rationale for the development of blood-based tests useful in the management of male infertility and indicate CTA candidates for cancer immunotherapy and biomarker development that could show sex-specific and male-fertility-related responses.

Immunologic Environment of the Testis

Mammalian spermatogenesis is a carefully orchestrated male germ cell differentiation process by which spermatogonia differentiate to spermatozoa in the testis. A highly organized testicular microenvironment is therefore necessary to support spermatogenesis. Regarding immunologic aspects, the testis adapts a specialized immune environment for the protection of male germ cells and testicular functions. The mammalian testis possesses two immunologic features: (1) it is an immunoprivileged organ where immunogenic germ cells do not induce deleterious immune responses under physiologic conditions; and (2) it creates its own effective innate defense system against microbial infection. Various pathologic conditions may disrupt testicular immune homeostasis, thereby resulting in a detrimental immune response and perturbing testicular functions, one of the etiologic factors of male infertility. Understanding the mechanisms underlying immunoregulation in the testis can aid in establishing strategies for the prevention and therapy of immunologic testicular dysfunction and male infertility. This chapter focuses on the mechanisms underlying immune privilege, local innate immunity, and immunologic diseases 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.

BXSB/MpJ-Yaa mouse model of systemic autoimmune disease shows increased apoptotic germ cells in stage XII of the seminiferous epithelial cycle

In mammals, the reproductive system and autoimmunity regulate mutual functions. Importantly, systemic autoimmune diseases are thought to cause male infertility but the underlying pathological mechanism remains unclear. In this study, the morpho-function of the testes in BXSB/MpJ-Yaa mice was analyzed as a representative mouse model for systemic autoimmune diseases to investigate the effect of excessive autoimmunity on spermatogenesis. At 12 and 24 weeks of age, BXSB/MpJ-Yaa mice showed splenomegaly and increased levels of serum autoantibodies, whereas no controls showed a similar autoimmune condition. In histological analysis, the enlarged lumen of the seminiferous tubules accompanied with scarce spermatozoa in the epididymal ducts were observed in some of the BXSB/MpJ-Yaa and BXSB/MpJ mice but not in C57BL/6N mice. Histoplanimetrical analysis revealed significantly increased residual bodies and apoptotic germ cells in the seminiferous tubules in BXSB/MpJ-Yaa testes without apparent inflammation. Notably, in stage XII of the seminiferous epithelial cycles, the apoptotic germ cell number was remarkably increased, showing a significant correlation with the indices of systemic autoimmune disease in BXSB/MpJ-Yaa mice. Furthermore, the Sertoli cell number was reduced at the early disease stage, which likely caused subsequent morphological changes in BXSB/MpJ-Yaa testes. Thus, our histological study revealed the altered morphologies of BXSB/MpJ-Yaa testes, which were not observed in controls and statistical analysis suggested the effects of an autoimmune condition on this phenotype, particularly the apoptosis of meiotic germ cells. BXSB/MpJ-Yaa mice were shown to be an efficient model to study the relationship between systemic autoimmune disease and the local reproductive system.

Protective effect of alpha-lipoic acid on di-(2-ethylhexyl) phthalate-induced testicular toxicity in mice

Phthalates are synthetic chemicals, widely used as plasticizers due to their flexibility in plastics. Human populations may be exposed to phthalates through direct contact or environmental contamination. Most studies have focused on the effects of phthalates on the reproductive tract and have classified these compounds as endocrine disruptors. In this study, we aimed to investigate the possible oxidative damage induced by di-(2-ethylhexyl) phthalate (DEHP) in the mouse testis and to evaluate the regulatory effects of alpha-lipoic acid (LA). For this purpose, forty male mice were divided into four experimental groups. Group I received normal saline (2 mL/kg; p.o.) and corn oil (5 mL/kg; p.o.) as the control group, group II received DEHP (2 g/kg; p.o.), group III received DEHP and LA (20 mg/kg; p.o.), and group IV was treated with LA alone; treatments continued for 2 weeks. The glutathione level (GSH), as well as glutathione peroxidase (GPx), superoxide dismutase (SOD), and catalase (CAT) activities, was determined in mice. In addition, serum concentrations of follicle-stimulating hormone (FSH), luteinizing hormone (LH), testosterone, interleukin-1β (IL-1β), and tumor necrosis factor-alpha (TNF-α) were measured. Nitric oxide (NO) level, malondialdehyde (MDA) level, sperm characteristics, and histological changes of the testes were also evaluated. The results showed that 2 g/kg of DEHP could significantly decrease the sperm motility. Based on our findings, DEHP significantly reduced the production and count of sperms; these toxic effects were associated with alterations in the serum hormone levels. In the DEHP group, a significant reduction was reported in the serum testosterone, FSH, and LH levels. LA improved DEHP-induced changes in hormonal levels and sperm index. According to our findings, treatment with DEHP triggered histopathological changes and oxidative stress, which were normalized by LA pretreatment. In conclusion, DEHP disrupts the testicular function in rats, at least partly through induction of oxidative stress. On the other hand, LA exhibits potential protective effects on testicular toxicity induced by DEHP.

Fluoride Induces Autoimmune Orchitis Involved with Enhanced IL-17A Secretion in Mice Testis

Fluoride (F) widely exists in the water and food. Recent studies reported that F induced testicular toxicity via inflammation reaction. This study was aimed to explore the mechanism of F-induced inflammation in testis. 100 healthy male mice (BALB/cJ strain) were randomly divided into five groups including: control, experimental autoimmune orchitis (EAO), and three F groups (25, 50, and 100 mg/L sodium fluoride (NaF)). After 150 d, the results showed a significant increase in testicular cytokines levels including of IL-17A, IL-6, IFN-γ, and TNF-α in NaF and EAO groups compared with control group. Interestingly, the presence of specific antisperm autoantibodies in antitesticular autoantibodies and the notable recruitment of immunocyte (T cells and dendritic cells) were also observed in NaF and EAO groups. In addition, findings showed that in NaF and EAO groups macrophages and T cells both significantly secreted IL-17A, and the protein and mRNA levels of cytokines (IL-6 and TGF-β) were significantly increased. From these results, it can be concluded that autoimmune orchitis and IL-17A are implicated in F-induced testicular inflammation.

Effects of Chemotherapy and Radiotherapy on Spermatogenesis: The Role of Testicular Immunology

Substantial improvements in cancer treatment have resulted in longer survival and increased quality of life in cancer survivors with minimized long-term toxicity. However, infertility and gonadal dysfunction continue to be recognized as adverse effects of anticancer therapy. In particular, alkylating agents and irradiation induce testicular damage that results in prolonged azoospermia. Although damage to and recovery of spermatogenesis after cancer treatment have been extensively studied, there is little information regarding the role of differences in testicular immunology in cancer treatment-induced male infertility. In this review, we briefly summarize available rodent and human data on immunological differences in chemotherapy or radiotherapy.

The mucosal surfaces of both eyes are immunologically linked by a neurogenic inflammatory reflex involving TRPV1 and substance P

Immunological interdependence between the two eyes has been reported for the cornea and the retina but not for the ocular mucosal surface. Intriguingly, patients frequently report ocular surface-related symptoms in the other eye after unilateral ocular surgery. Here we show how unilateral eye injuries in mice affect the mucosal immune response of the opposite ocular surface. We report that, despite the lack of lymphatic cross-drainage, a neurogenic inflammatory reflex in the contralateral conjunctiva is sufficient to increase, first, epithelial nuclear factor kappa B signaling, then, dendritic cell maturation, and finally, expansion of effector, instead of regulatory, T cells in the draining lymph node, leading to disrupted ocular mucosal tolerance. We also show that damage to ocular surface nerves is required. Using pharmacological inhibitors and agonists, we identified transient receptor potential vanilloid 1 (TRPV1) channel as the receptor sensing tissue damage in the injured eye and substance P released in the opposite ocular surface as the effector of the sympathetic response. Finally, blocking either step prevented subsequent ocular allergic reactions in the opposite eye in a unilateral corneal alkali burn model. This study demonstrates that both ocular surfaces are immunologically linked and suggests potential therapeutic targets for intervention.

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.

Regulatory Functions of MicroRNAs in Male Reproductive Health: A New Approach to Understanding Male Infertility

MicroRNAs (miRNAs) are a novel class of small noncoding RNAs (ncRNAs) that play critical roles in regulation of gene expression, especially at posttranscriptional level. Over the past decade, the degree to which miRNAs are involved in male infertility has become clear. They are expressed in a cell- or phase-specific manner during spermatogenesis and play crucial role in male reproductive health. Therefore, dysregulation of miRNAs in testicular cells can be considered as a molecular basis for reproductive failure and male infertility. The abnormal expression pattern of miRNAs can be transmitted to the offspring via assisted reproductive techniques (ART) and results in the birth of children with a higher risk of infertility, congenital abnormalities, and morbidity. This review expounds on the miRNAs reported to play essential roles in somatic cells development, germ cells differentiation, steroidogenesis, normal spermatogenesis, sperm maturation, and male infertility, as well as emphasizes their importance as minimally invasive biomarkers of male infertility.

Induction of experimental autoimmune orchitis by immunization with xenogenic testicular germ cells in mice

We previously showed that immunization of mice with syngeneic or allogeneic testicular germ cells (TGC) alone induces autoimmune inflammation in the testes without using any adjuvant. In the present study, we examined testicular autoimmune response against xenogenic TGC antigens in mice. The mice were immunized with murine, rat or guinea pig TGC and then the histopathology, delayed type hypersensitivity (DTH) response and humoral autoimmunity were investigated. The results showed that immunization with not only murine but also rat TGC caused experimental autoimmune orchitis (EAO) with hypospermatogenesis in mice, while that with guinea pig TGC could not. The DTH response to murine TGC was significantly elevated in mice that had been immunized with murine or rat but not guinea pig TGC. Serum autoantibody to murine TGC was immunohistochemically detected in the mice immunized with either murine, rat or guinea pig TGC, however, the level of autoantibody detected by ELISA revealed significant elevation when mice were immunized with murine and rat TGC. With the immunoblotting after electrophoresis, the murine TGC proteins at molecular masses around 55kDa and 70kDa can be detected when incubated with sera from m-TGC and r-TGC groups. These results represent the cross-reactivity among TGC of the mouse, the rat and the guinea pig at the levels of humoral immunity and also demonstrate that the rat TGC could elicit significant DTH response to murine TGC with the resultant EAO. This is the first to succeed in EAO induction by the use of xenogenic TGC.

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.

Low-dose exposure to di-(2-ethylhexyl) phthalate (DEHP) increases susceptibility to testicular autoimmunity in mice

Exposure to di-(2-ethylhexyl) phthalate (DEHP) induces spermatogenic disturbance (SD) through oxidative stress, and affects the immune system by acting as an adjuvant. Recently, we reported that in mice, a low dose of DEHP, which did not affect spermatogenesis, was able to alter the testicular immune microenvironment. Experimental autoimmune orchitis (EAO) can be induced by repeated immunization with testicular antigens, and its pathology is characterized by production of autoantibodies and SD. In the present study, we investigated the effect of a low-dose DEHP on the susceptibility of mice to EAO. The exposure to DEHP-containing feed (0.01%) caused a modest functional damage to the blood-testis barrier (BTB) with an increase in testicular number of interferon gamma (IFN-γ)-positive cells and resulted in the production of autoantibodies targeting haploid cells, but did not affect spermatogenesis. While only single immunization with testicular antigens caused very mild EAO, the concurrent DEHP exposure induced severe EAO with significant increases in number of interferon gamma-positive cells and macrophages, as well as lymphocytic infiltration and serum autoantibody titer accompanied by severe SD. To summarize, the exposure of mice to the low-dose DEHP does not induce significant SD, but it may cause an increase in IFN-γ positive cells and modest functional damage to the BTB in the testis. These changes lead to an autoimmune response against haploid cell autoantigens, resulting in increased susceptibility to EAO.

Roles of Toll-like receptors 2 and 4 in mediating experimental autoimmune orchitis induction in mice

The mammalian testis is an immunoprivileged site where male germ cell antigens are immunologically tolerated under physiological conditions. However, some pathological conditions can disrupt the immunoprivileged status and induce autoimmune orchitis, an etiological factor of male infertility. Mechanisms underlying autoimmune orchitis induction are largely unknown. The present study investigated the roles of Toll-like receptor 2 (TLR2) and TLR4 in mediating the induction of experimental autoimmune orchitis (EAO) in mice after immunization with male germ cell antigens emulsified with complete Freund adjuvant. Wild-type mice developed severe EAO after three immunizations, which was characterized by leukocyte infiltration, autoantibody production, and impaired spermatogenesis. Tlr2 or Tlr4 deficient mice showed relatively low susceptibility to EAO induction compared with wild-type mice. Notably, Tlr2 and Tlr4 double knockout mice were almost completely protected from EAO induction. Moreover, we demonstrated that TLR2 was crucial in mediating autoantibody production in response to immunization. The results imply that TLR2 and TLR4 cooperatively mediate EAO induction.

Mice lacking Axl and Mer tyrosine kinase receptors are susceptible to experimental autoimmune orchitis induction

The mammalian testis is an immunoprivileged organ where male germ cell autoantigens are immunologically ignored. Both systemic immune tolerance to autoantigens and local immunosuppressive milieu contribute to the testicular immune privilege. Testicular immunosuppression has been intensively studied, but information on systemic immune tolerance to autoantigens is lacking. In the present study, we aimed to determine the role of Axl and Mer receptor tyrosine kinases in maintaining the systemic tolerance to male germ cell antigens using the experimental autoimmune orchitis (EAO) model. Axl and Mer double-knockout (Axl(-/-)Mer(-/-)) mice developed evident EAO after a single immunization with germ cell homogenates emulsified with complete Freund's adjuvant. EAO was characterized by the accumulation of macrophages and T lymphocytes in the testis. Damage to the seminiferous epithelium was also observed. EAO induction was associated with pro-inflammatory cytokine upregulation in the testes, impaired permeability of the blood-testis barrier and generation of autoantibodies against germ cell antigens in Axl(-/-)Mer(-/-) mice. Immunization also induced mild EAO in Axl or Mer single-gene-knockout mice. By contrast, a single immunization failed to induce EAO in wild-type mice. The results indicate that Axl and Mer receptors cooperatively regulate the systemic immune tolerance to male germ cell antigens.

Age- and species-dependent infiltration of macrophages into the testis of rats and mice exposed to mono-(2-Ethylhexyl) phthalate (MEHP)

The mechanism by which noninfectious testicular inflammation results in infertility is poorly understood. Here the infiltration of CD11b+ immunoreactive testicular interstitial cells (neutrophil, macrophages, dendritic cells) in immature (Postnatal Day [PND] 21, 28, and 35) and adult (PND 56) Fischer rats is described at 12, 24, and 48 h after an oral dose of 1 g/kg mono-(2-ethylhexyl) phthalate (MEHP), a well-described Sertoli cell toxicant. Increases of CD11b+ cells are evident 12 h after MEHP exposure in PND 21 and 28 rats. In PND 28 rats, CD11b+ cells remained significantly elevated at 48 h, while in PND 21 rats, it returned to control levels by 24 h. The peak number of CD11b+ cells in PND 35 rat testis is delayed until 24 h, but remains significantly elevated at 48 h. In PND 56 rats, no increase in CD11b+ cells occurs after MEHP exposure. In PND 21, 28, and 35 rats, a significant increase in monocyte chemoattractant protein-1 (MCP-1) by peritubular myoid cells occurs 12 h after MEHP. Interestingly, MEHP treatment of C57BL/6J mice did not incite an infiltration of CD11b+ cells at either PND 21 or 28. The peak level of germ cell apoptosis observed 24 h after MEHP exposure in young rats is not seen in mice at any age or in PND 56 rats. Taken together, these findings implicate MCP-1 released by peritubular myoid cells in provoking the migration of CD11b+ cells into the immature rat testis early after MEHP exposure and point to a role for CD11b+ cells in triggering germ cell apoptosis in an age- and species-dependent manner.

Contribution of IL-12/IL-35 common subunit p35 to maintaining the testicular immune privilege

The testis is an organ with immune privilege. The comprehensive blood–testis barrier formed by Sertoli cells protects autoimmunogenic spermatozoa and spermatids from attack by the body’s immune system. The interleukin (IL)-6/IL-12 family cytokines IL-12 (p35/p40), IL-23 (p19/p40), IL-27 (p28/Epstein-Barr virus−induced gene 3 [EBI3]), and IL-35 (p35/EBI3) play critical roles in the regulation of various immune responses, but their roles in testicular immune privilege are not well understood. In the present study, we investigated whether these cytokines are expressed in the testes and whether they function in the testicular immune privilege by using mice deficient in their subunits. Expression of EBI3 was markedly increased at both mRNA and protein levels in the testes of 10- or 12-week-old wild-type mice as compared with levels in 2-week-old mice, whereas the mRNA expression of p40 was markedly decreased and that of p35 was conserved between these two groups. Lack of EBI3, p35, and IL-12 receptor β2 caused enhanced infiltration of lymphocytes into the testicular interstitium, with increased interferon-γ expression in the testes and autoantibody production against mainly acrosomal regions of spermatids. Spermatogenic disturbance was more frequently observed in the seminiferous tubules, especially when surrounded by infiltrating lymphocytes, of these deficient mice than in those of wild-type mice. In particular, p35-deficient mice showed the most severe spermatogenic disturbance. Immunohistochemical analyses revealed that endothelial cells and peritubular cells in the interstitium were highly positive for p35 at both ages, and CD163⁺ resident macrophages positive for p35 and EBI3, possibly producing IL-35, were also detected in the interstitium of 12-week-old mice but not those of 2-week-old mice. These results suggest that p35 helps in maintaining the testicular immune privilege, in part in an IL-35-dependent manner.