UropathogenicEscherichia coli(UPEC) induced antimicrobial gene expression in the male reproductive tract of rat: evaluation of the potential of Defensin 21 to limit infection

Defensins: defenders of human reproductive health

BACKGROUND

Reproductive tract infection is an important factor leading to male and female infertility. Among female infertility factors, microbial and viral infections are the main factors affecting female reproductive health and causing tubal infertility, ectopic tubal pregnancy and premature delivery. Among male infertility factors, 13-15% of male infertility is related to infection. Defensins are cationic antibacterial and antiviral peptides, classified into α-defensins, β-defensins and θ-defensins. Humans only have α-defensins and β-defensins. Apart from their direct antimicrobial functions, defensins have an immunomodulatory function and are involved in many physiological processes. Studies have shown that defensins are widely distributed in the female reproductive tract (FRT) and male reproductive tract (MRT), playing a dual role of host defence and fertility protection. However, to our knowledge, the distribution, regulation and function of defensins in the reproductive tract and their relation to reproduction have not been reviewed.

OBJECTIVE AND RATIONALE

This review summarizes the expression, distribution and regulation of defensins in the reproductive tracts to reveal the updated research on the dual role of defensins in host defence and the protection of fertility.

SEARCH METHODS

A systematic search was conducted in PubMed using the related keywords through April 2022. Related data from original researches and reviews were integrated to comprehensively review the current findings and understanding of defensins in the human reproductive system. Meanwhile, female and male transcriptome data in the GEO database were screened to analyze defensins in the human reproductive tracts.

OUTCOMES

Two transcriptome databases from the GEO database (GSE7307 and GSE150852) combined with existing researches reveal the expression levels and role of the defensins in the reproductive tracts. In the FRT, a high expression level of α-defensin is found, and the expression levels of defensins in the vulva and vagina are higher than those in other organs. The expression of defensins in the endometrium varies with menstrual cycle stages and with microbial invasion. Defensins also participate in the local immune response to regulate the risk of spontaneous preterm birth. In the MRT, a high expression level of β-defensins is also found. It is mainly highly expressed in the epididymal caput and corpus, indicating that defensins play an important role in sperm maturation. The expression of defensins in the MRT varies with androgen levels, age and the status of microbial invasion. They protect the male reproductive system from bacterial infections by neutralizing lipopolysaccharide and downregulating pro-inflammatory cytokines. In addition, animal and clinical studies have shown that defensins play an important role in sperm maturation, motility and fertilization.

WIDER IMPLICATIONS

As a broad-spectrum antimicrobial peptide without drug resistance, defensin has great potential for developing new natural antimicrobial treatments for reproductive tract infections. However, increasing evidence has shown that defensins can not only inhibit microbial invasion but can also promote the invasion and adhesion of some microorganisms in certain biological environments, such as human immunodeficiency virus. Therefore, the safety of defensins as reproductive tract anti-infective drugs needs more in-depth research. In addition, the modulatory role of defensins in fertility requires more in-depth research since the current conclusions are based on small-size samples. At present, scientists have made many attempts at the clinical transformation of defensins. However, defensins have problems such as poor stability, low bioavailability and difficulties in their synthesis. Therefore, the production of safe, effective and low-cost drugs remains a challenge.

Antimicrobial peptide MPX attenuates LPS-induced inflammatory response and blood-testis barrier dysfunction in Sertoli cells

Orchitis accounts for a high proportion of male animal reproductive disorders. Hence, it is urgent to identify drugs for the prevention and treatment of orchitis. Antimicrobial peptides (AMPs) are currently recognized as one of the most promising alternatives to antibiotics. However, the protective effects of AMPs on lipopolysaccharide (LPS)-induced orchitis have not been reported. In this study, we developed an LPS-induced orchitis model in which primary bovine Sertoli cells were used as model cells. MPX was indicated to effectively reduce the inflammatory response of Sertoli cells. MPX attenuated the gene expression of the proinflammatory cytokines TNF-α, IL-6 and IL-1β by suppressing the MAPK pathway, especially the phosphorylation of p38 and ERK. MPX also decreased the oxidative stress response caused by LPS and upregulated Occludin and Claudin-1 expression, thereby maintaining the integrity of the blood-testis barrier. Moreover, we found that MPX inhibited apoptosis in Sertoli cells. In a mouse model, we found that MPX significantly inhibited the disruptive effects of LPS, reducing seminiferous epithelium damage, vacuolations, hyperplasia, and apoptosis in spermatogenic cells and rescuing spermatogenesis. In addition, the expression of inflammatory factors such as IL-1β, IL-18, IL-6 and TNF-α was decreased after MPX treatment in the mouse testes. MPX had no effect on other organs in mice, indicating its safety. This study was undertaken to investigate how MPX regulates the inflammatory response in Sertoli cells and provide a reference for the clinical prevention and treatment of male animal orchitis.

Testicular Immunity and Its Connection with the Microbiota. Physiological and Clinical Implications in the Light of Personalized Medicine

Reproduction is a complex process, which is based on the cooperation between the endocrine-immune system and the microbiota. Testicular immunity is characterized by the so-called immune privilege, a mechanism that avoids autoimmune attacks against proteins expressed by spermatozoa. Testicular microbiota is connected with the gut microbiota, the most prevalent site of commensals inthe body. Both microbiotas take part inthe development of the immune system and protection againstpathogen invasion. Dysbiosis is caused by concurrent pathologies, such as obesity, diabetes, infections and trauma. The substitution of beneficial bacteria with pathogens may lead to destruction of spermatozoa directly or indirectly and, ultimately, to male infertility. Novel therapeutic interventions, i.e., nutritional interventions and supplementation of natural products, such as, probiotics, prebiotics, antioxidants and polyphenols, may lead to the restoration of the otherwise-impaired male reproductive potential, even if experimental and clinical results are not always concordant. In this review, the structure and immune function of the testis will be described with special reference to the blood-testisbarrier. The regulatory role of both the gut and testicular microbiota will be illustrated in health and disease, also emphasizing therapeutic attempts with natural products for the correction of male infertility, in the era of personalized medicine.

A comparison of different O-antigen serogroups of Escherichia coli in semen samples of fertile and infertile men

Objective

Male genital tract infections have been associated with infertility, and Escherichia coli has drawn increasing attention as an important bacterium in this context. This investigation aimed to characterize and compare the distributions of O-antigen serogroups of E. coli in the semen samples of fertile and infertile men.

Methods

In this case-control study, semen samples were collected from 618 fertile and 1,535 infertile men. The E. coli-positive samples were evaluated in terms of concentration, morphology, viability, and motility parameters according to the World Health Organization 2010 guidelines. Finally, different serogroups of E. coli were identified by multiplex polymerase chain reaction targeting the O-antigen variations of the bacterium.

Results

The prevalence of E. coli among fertile men was significantly higher than among infertile men (p<0.001). The sperm morphology, viability, and motility in the E. coli-positive fertile group were significantly higher than in the E. coli-positive infertile group (p<0.001). E. coli O6 was the most prevalent serogroup found in both groups. However, there was no significant difference in the frequency of different serogroups of E. coil between the two groups (p=0.55).

Conclusion

Despite the higher prevalence of E. coli among fertile men, E. coli had more detrimental effects on semen parameters in infertile men. There was no significant difference in E. coli serogroups between the fertile and infertile groups.

Using the PCR and Blood Agar in Diagnosis of Semen Bacterial Contamination of Fertile and Infertile Men

BACKGROUND

One of the causes of male infertility is Genital tract infections (GTI). Considering the importance of GTI, widespread recognition of them seems necessary. we aimed to characterize and compare semen microbial populations in fertile and infertile men who referred to an infertility clinic in Yazd, Iran.

METHODS

Semen samples were collected from two groups of fertile (268) and infertile (210) men. Sperm analysis (concentration, morphology, viability and motility parameters) were performed according to the World Health Organization (WHO) 2010 guidelines laboratory manual. Bacterial isolation was performed in Sheep Blood Agar and Eosin Methylene Blue (EMB) agar plates. For PCR, samples were analyzed with genus specific primers.

RESULTS

All semen characteristics were poor in the infertile group compared to those in the fertile men (p-value< 0.05). Enterococcus spp. (18.7%, 17.1%; p= 0.814), E. coli (7.9%, 11.4%; p= 0.486), Staphylococcus aureus (6.4%, 2.9%; p= 0.398) and Proteus mirabilis (0%, 2.9%; p= 0.002) were the most common agents, respectively. Also, the results obtained from PCR were confirmed using culture-base method.

CONCLUSION

Proteus mirabilis contamination was identified in the infertile group. While no significant association was observed between male infertility and semen microbial populations, p. mirabilis may be the leading cause of reproduction impairment in men.

Uropathogenic Escherichia coli in India-an Overview on Recent Research Advancements and Trends

Urinary tract infection (UTI), a prevalent disease in India, also ranks among the most common infections in developing countries. The rapid emergence of antibiotic-resistant uropathogenic Escherichia coli (UPECs), the leading etiologic agent of UTI, in the last few years, led to an upsurge in the health care cost. This caused a considerable economic burden, especially in low-middle income country, India. This review aimed to provide an explicit overview of the recent advancements in E. coli-mediated UTI in India by incorporation of valuable information from the works published in PubMed and Google Scholar in the last six years (2015 to August, 2020). The literature survey demonstrated UPECs as the most predominant uropathogen in India, especially among females, causing both asymptomatic bacteriuria (ABU) and symptomatic UTI. An overall increasing national trend in resistance to penicillins, cephalosporins, aminoglycosides, fluoroquinolones, and sulfonamides was perceived irrespective of ABU and symptomatic UPECs during the aforementioned study period. High incidences of multidrug resistance, extended-spectrum β-lactamases, metallo β-lactamases, and AmpCs in UPECs were reported. Notable information on the pathogenic profiles, phylogroups, pathogenicity islands, and evidence of pathoadaptive FimH mutations was described. Alternative therapeutics and potential drug targets against UPECs were also reconnoitered. Therefore, the nationwide widespread occurrences of highly virulent MDR UPEC together with the limited availability of therapeutics highlighted the urgent need for promotion and invention of alternative therapeutics, search for which had already been started. Moreover, investigation of several mechanisms of UPEC infection and the search for potential drug targets might help to design newer therapeutics.

The truncated human beta-defensin 118 can modulate lipopolysaccharide mediated inflammatory response in RAW264.7 macrophages

The family of human β-defensins consists of small cysteine-rich peptides, which are receiving significant attention due to their antimicrobial activity. The N-terminal cysteine motif of β-defensin is considered to contribute to its biological activity. Human β-defensin 118 (DEFB 118) is a particular anion β-defensin expressed predominantly in the male reproductive tract, but its physiological activity has not yet been revealed. In order to verify the potential role of the N-terminal domain of DEFB118 peptide in the regulation of infection, the truncated β-defensin core region of DEFB118 peptide was expressed with IMPACT-pTWIN1 system in Escherichia coli. Herein, the purified homogeneous DEFB118 peptide was identified by mass spectrometry and circular dichroism spectroscopy. The in vitro experiments revealed that DEFB118 peptide exhibited prominent LPS-binding potency (K_D: 2.94 nM). Moreover, the DEFB118 core peptide significantly inhibited the mRNA level of LPS-induced inflammatory cytokines including IL-α, IL-1β, IL-6 and TNF-α in RAW264.7 cells, and correspondingly decreased secretion of IL-6 and TNF-α. We concluded that strong binding of DEFB118 to LPS might prevent LPS from binding to its receptor, and hence inhibited cytokines secretion. The results of this study may be a benefit to elucidate the immune protection of DEFB118 in the male reproductive tract.

The Immune Characteristics of the Epididymis and the Immune Pathway of the Epididymitis Caused by Different Pathogens

The epididymis is an important male accessory sex organ where sperm motility and fertilization ability develop. When spermatozoa carrying foreign antigens enter the epididymis, the epididymis shows "immune privilege" to tolerate them. It is well-known that a tolerogenic environment exists in the caput epididymis, while pro-inflammatory circumstances prefer the cauda epididymis. This meticulously regulated immune environment not only protects spermatozoa from autoimmunity but also defends spermatozoa against pathogenic damage. Epididymitis is one of the common causes of male infertility. Up to 40% of patients suffer from permanent oligospermia or azoospermia. This is related to the immune characteristics of the epididymis itself. Moreover, epididymitis induced by different pathogenic microbial infections has different characteristics. This article elaborates on the distribution and immune response characteristics of epididymis immune cells, the role of epididymis epithelial cells (EECs), and the epididymis defense against different pathogenic infections (such as uropathogenic Escherichia coli, Chlamydia trachomatis, and viruses to provide therapeutic approaches for epididymitis and its subsequent fertility problems.

Dexamethasone improves therapeutic outcomes in a preclinical bacterial epididymitis mouse model

STUDY QUESTION

Can dexamethasone improve infertility-related cauda epididymidal tissue damage caused by bacterial epididymitis?

SUMMARY ANSWER

Dexamethasone in addition to anti-microbial treatment effectively reduces long-term deleterious epididymal tissue damage by dampening the host's adaptive immune response.

WHAT IS KNOWN ALREADY

Despite effective anti-microbial treatment, ~40% of patients with epididymitis experience subsequent sub- or infertility. An epididymitis mouse model has shown that the host immune response is mainly responsible for the magnitude of epididymal tissue damage that is fundamentally causative of the subsequent fertility issues.

STUDY DESIGN, SIZE, DURATION

Bacterial epididymitis was induced in male mice by using uropathogenic Escherichia coli (UPEC). From Day 3 after infection onwards, mice were treated with daily doses of levofloxacin (20 mg/kg, total n = 12 mice), dexamethasone (0.5 mg/kg, total n = 9) or both in combination (total n = 11) for seven consecutive days. Control animals were left untreated, i.e. given no interventional treatment following UPEC infection (total n = 11). Half of the animals from each group were killed either at 10 or 31 days post-infection.

PARTICIPANTS/MATERIALS, SETTING, METHODS

A mouse model of induced bacterial epididymitis was applied to adult male C57BL/6J mice. At the respective endpoints (10 or 31 days post-infection), epididymides were collected. Effectiveness of antibiotic treatment was assessed by plating of epididymal homogenates onto lysogeny broth agar plates. Overall tissue morphology and the degree and nature of tissue damage were assessed histologically. Quantitative RT-PCR was used to assess local cytokine transcript levels. Blood was drawn and serum analysed for systemic IgG and IgM levels by ELISA. In addition, correlation analyses of clinical data and serum-analyses of IgG and IgM levels in patients with epididymitis were performed.

MAIN RESULTS AND THE ROLE OF CHANCE

The addition of dexamethasone to the standard anti-microbial treatment did not further worsen epididymal tissue integrity. In fact, an obviously dampened immune response and reduced tissue reaction/damage was observed at both 10 and 31 days post-infection following combined treatment. More specifically, epididymal duct continuity was preserved, enabling sperm transit. In contrast, in untreated or antibiotic-treated animals, damage of the epididymal duct and duct constrictions were observed, associated with a lack of cauda spermatozoa. In line with the bacteriostatic/bactericidal effect of levofloxacin (alone as well as in combination), local cytokine transcript levels were significantly and similarly reduced in animals treated with levofloxacin alone (P < 0.01) or in combination with dexamethasone (P < 0.05) compared to UPEC-infected untreated animals. Interestingly, the addition of dexamethasone to the anti-microbial treatment induced a unique dampening effect on adaptive immunity, since systemic IgG and IgM levels as well as the pan-T cell marker CD3 were reduced at both 10 and 31 days post-infection.

LIMITATIONS, REASONS FOR CAUTION

Breeding studies to address the fertility-protecting effect of the combined treatment were not possible in the experimental animals because the vas deferens was ligated (model specific).

WIDER IMPLICATIONS OF THE FINDINGS

Whereas innate immunity is necessary and involved in acute bacterial clearance, adaptive immunity seems to be responsible for long-term, subclinical immunological activities that may negatively affect the pathogenesis of bacterial epididymitis even after effective bacterial eradication. These effects can be reduced in mice by the additional treatment with dexamethasone. This immunological characteristic of bacterial epididymitis shows similarities to the Jarisch-Herxheimer reaction known from other types of bacterial infection.

STUDY FUNDING/COMPETING INTEREST(S)

The study was supported by grants from the Deutsche Forschungsgemeinschaft, Monash University and the Medical Faculty of Justus-Liebig University to the International Research Training Group on 'Molecular pathogenesis of male reproductive disorders' (GRK 1871). R.W., K.L.L. and M.P.H. were supported by grants from the National Health and Medical Research Council of Australia (ID1079646, ID1081987, ID1020269 and ID1063843) and by the Victorian Government's Operational Infrastructure Support Program. The authors have no conflicts of interest to declare.

TRIAL REGISTRATION NUMBER

No clinical trial involved.

Differential tissue-specific damage caused by bacterial epididymo-orchitis in the mouse

Ascending bacterial urinary tract infections can cause epididymo-orchitis. In the cauda epididymidis, this frequently leads to persistent tissue damage. Less coherent data is available concerning the functional consequences of epididymo-orchitis on testis and caput epididymidis. This in vivo study addresses the functional and spatial differences in responsiveness of murine epididymis and testis to infection with uropathogenic Escherichia coli (UPEC). Whole transcriptome analysis (WTA) was performed on testis, caput, corpus and cauda epididymidis of adult C57BL/6 J wildtype mice. Following UPEC-induced epididymo-orchitis in these mice, epididymal and testicular tissue damage was evaluated histologically and semi-quantitatively at 10 days and 31 days post-inoculation. Expression of inflammatory markers and candidate antimicrobial genes were analysed by RT-qPCR. WTA revealed distinct differences in gene signatures between caput and cauda epididymidis, particularly amonst immunity-related genes. Cellular and molecular signs of testicular inflammation and disruption of spermatogenesis were noticed at day 10, but recovery was observed by day 31. In contrast to the cauda, the caput epididymidis did not reveal any signs of gross morphological damage or presence of pro-inflammatory processes despite confirmed infection. In contrast to beta-defensins, known UPEC-associated antimicrobial peptides (AMP), like Lcn2, Camp and Lypd8, were inherently highly expressed or upregulated in the caput following infection, potentially allowing an early luminal protection from UPEC. At the time points investigated, the caput epididymidis was protected from any obvious infection/inflammation-derived tissue damage. Studies addressing earlier time-points will conclude whether in the caput epididymidis a pro-inflammatory response is indeed not essential for effective protection from UPEC.

Tlr1-13, Nod1/2 and antimicrobial gene expression in the epididymis and testis of rats with alloxan-induced diabetes

Pattern recognition receptors (PRRs) such as toll-like receptors (TLRs) and nuclear oligomerization domain (NOD) receptors along with antimicrobial proteins and peptides (AMPs) are crucial for innate immunity. The pathology of insulin-dependent diabetes mellitus is associated with the disrupted expression of TLRs, NODs and AMPs in the kidney, lungs and other organs. However, such a relation in the male reproductive tract is not yet investigated. In this study, we analysed the expression pattern of Tlr1-13, Nod1/2 receptors and AMPs (β-defensins and defensin-like proteins of the Sperm-Associated Antigen 11 (Spag11) family) in the male reproductive tissues (caput, cauda and testis) obtained from diabetic or insulin-treated diabetic or untreated control rats. Alterations in the expression pattern of Tlr1-13, Nod 1/ 2, Defb1, 2, 21, 24, 27, 30 and Spag11a/ c/ t were observed under diabetic conditions. Administration of insulin to diabetic rats could modulate the expression pattern of only some these genes. Results of our study indicate perturbed gene expression profile of Tlrs, Nod1/2, Defbs and Spag11 isoforms in the epididymis and testis of diabetic rats, and this could be one of the important reasons for the increased risk of infections in the male genital tract.

Uroplakin expression in the male reproductive tract of rat

Uroplakins (UPKs) play an important role in the normal and pathophysiology of the urothelium. They protect the urothelium and play a crucial role during urothelial infections by Uropathogenic E. coli. However, their functions beyond this organ system remain unexplored. A wide variety of proteins secreted in the male reproductive tract tissues contribute to spermatogenesis, sperm maturation, fertilization and innate immunity. However, the presence of UPKs and their possible contribution to the male reproductive tract physiology is not yet reported. Hence, in this study, we characterized UPKs in the male reproductive tract of rats. To the best of our knowledge, for the first time, we report the expression of UPKs in the male reproductive system. Upk1a, Upk1b, Upk2 and Upk3b mRNA and their corresponding proteins were abundantly expressed in the caput, cauda, testis, seminal vesicles and the prostate. Their expression was not developmentally regulated. UPK protein expression was also localized on the spermatozoa, suggesting a role for these proteins in sperm function. To study the role of UPKs in innate immunity, Upk mRNA expression in response to endotoxin challenge was evaluated in vitro and in vivo. In the rat testicular and epididymal cell lines, Upk mRNA levels increased in response to lipopolysaccharide challenge. However, in the caput, cauda, testes, seminal vesicle and prostate obtained from LPS treated rats, Upk mRNA expression was significantly reduced. Results of this study indicate a role for UPKs in male reproductive physiology and innate immune responses.

Male reproductive tract antimicrobial expression in the extremes of ages of rats

Alterations in the global gene expression profile are considered to contribute to the various physiological and pathological changes during the course of ageing. Genes that code for the molecular components of the innate system are alter markedly as ageing occurs; and this may define the susceptibility of very young and very old individuals to reproductive tract infections. The expression pattern of genes that code for beta-defensins (effectors of innate immune response) in male reproductive tract tissues of different stages of ageing is not yet reported. Further, the induction of beta-defensins during endotoxin challenge and whether epigenetic modulators can influence the expression of these genes in different stages of ageing are not reported. We analyzed the basal mRNA levels of beta-defensins and defensin-like proteins (Sperm Associated Antigen 11 (SPAG11) family members), their induction during endotoxin challenge and modulation by epigenetic modifiers (Trichostatin A and Azacytidine) in the caput, cauda, testis, prostate and seminal vesicle of rats that represent early stage to late stages of life (20 day to 730 day old). We observed differential basal gene expression pattern in the male reproductive tract tissues and the induction by LPS was not consistent neither among the age groups not the tissues analyzed. Trichostatin A and Azacytidine also influenced antimicrobial gene expression and the pattern was not consistent in different tissues obtained from different age groups. Results of this study demonstrate that antimicrobial gene expression varies to a great extent during ageing and is strongly influenced by endotoxins and epigenetic modulators.

DICER1 regulates antibacterial function of epididymis by modulating transcription of β-defensins

DICER1 is a key enzyme responsible for the maturation of microRNAs. Recent evidences suggested that DICER1 and microRNAs expressed in epididymis were involved in the control of male fertility. However, the exact mechanism remains to be elucidated. Here, we created a mouse line by targeted disruption of Dicer1 gene in the principal cells of distal caput epididymis. Our data indicated that a set of β-defensin genes were downregulated by DICER1 rather than by microRNAs. Moreover, DICER1 was significantly enriched in the promoter of β-defensin gene and controlled transcription. Besides, the antibacterial ability of the adult epididymis significantly declined upon Dicer1 deletion both in vitro and in vivo. And a higher incidence of reproductive defect was observed in middle-aged Dicer1-/- males. These results suggest that DICER1 plays an important role in transcription of β-defensin genes, which are associated with the natural antibacterial properties in a microRNA-independent manner, and further impacts the male fertility.

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.

Epididymitis: revelations at the convergence of clinical and basic sciences

Acute epididymitis represents a common medical condition in the urological outpatient clinic. Mostly, epididymitis is caused by bacterial ascent through the urogenital tract, with pathogens originating either from sexually transmitted diseases or urinary tract infections. Although conservative antimicrobial therapy is possible in the majority of patients and is usually sufficient to eradicate the pathogen, studies have shown persistent oligozoospermia and azoospermia in up to 40% of these patients. Animal models of epididymitis are created to delineate the underlying reasons for this observation and the additional impairment of sperm function that is often associated with the disease. Accumulated data provide evidence of a differential expression of immune cells, immunoregulatory genes and pathogen-sensing molecules along the length of the epididymal duct. The evidence suggests that a tolerogenic environment exists in the caput epididymidis, but that inflammatory responses are most intense toward the cauda epididymidis. This is consistent with the need to provide protection for the neo-antigens of spermatozoa emerging from the testis, without compromising the ability to respond to ascending infections. However, severe inflammatory responses, particularly in the cauda, may lead to collateral damage to the structure and function of the epididymis. Convergence of the clinical observations with appropriate animal studies should lead to better understanding of the immunological environment throughout the epididymis, the parameters underlying susceptibility to epididymitis, and to therapeutic approaches that can mitigate epididymal damage and subsequent fertility problems.