Incidence of testicular mononuclear cell infiltrates in normal human males and in patients with germ cell neoplasia

New Insight into Molecular and Hormonal Connection in Andrology

Hormones and cytokines are known to regulate cellular functions in the testes. These biomolecules induce a broad spectrum of effects on various level of spermatogenesis, and among them is the modulation of cell junction restructuring between Sertoli cells and germ cells in the seminiferous epithelium. Cytokines and androgens are closely related, and both correct testicular development and the maintenance of spermatogenesis depend on their function. Cytokines also play a crucial role in the immune testicular system, activating and directing leucocytes across the endothelial barrier to the inflammatory site, as well as in increasing their adhesion to the vascular wall. The purpose of this review is to revise the most recent findings on molecular mechanisms that play a key role in male sexual function, focusing on three specific molecular patterns, namely, cytokines, miRNAs, and endothelial progenitor cells. Numerous reports on the interactions between the immune and endocrine systems can be found in the literature. However, there is not yet a multi-approach review of the literature underlying the role between molecular patterns and testicular and sexual function.

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.

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.

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

Experimental autoimmune epididymo-orchitis (EAEO) is a model of chronic inflammation, induced by immunisation with testicular antigens, which reproduces the pathology of some types of human infertility. Activins A and B regulate spermatogenesis and steroidogenesis, but are also pro-inflammatory, pro-fibrotic cytokines. Expression of the activins and their endogenous antagonists, inhibin and follistatin, was examined in murine EAEO. Adult untreated and adjuvant-treated control mice showed no pathology. All mice immunised with testis antigens developed EAEO by 50 days, characterised by loss of germ cells, immune cell infiltration and fibrosis in the testis, similar to biopsies from human inflamed testis. An increase of total CD45+ leukocytes, comprising CD3+ T cells, CD4 + CD8− and CD4 + CD25+ T cells, and a novel population of CD4 + CD8+ double positive T cells was also detected in EAEO testes. This was accompanied by increased expression of TNF, MCP-1 and IL-10. Activin A and B and follistatin protein levels were elevated in EAEO testes, with peak activin expression during the active phase of the disease, whereas mRNA expression of the inhibin B subunits (Inha and Inhbb) and activin receptor subunits (Acvr1b and Acvr2b) were downregulated. These data suggest that activin–follistatin regulation may play a role during the development of EAEO.

Dual role of immune cells in the testis: Protective or pathogenic for germ cells?

The purpose of this review is to describe how the immune cells present in the testis interact with the germinal epithelium contributing to survival or apoptosis of germ cells (GCs). Physiologically, the immunosuppressor testicular microenvironment protects GCs from immune attack, whereas in inflammatory conditions, tolerance is disrupted and immune cells and their mediators respond to GC self antigens, inducing damage of the germinal epithelium. Considering that experimental models of autoimmune orchitis have clarified the local immune mechanisms by which protection of the testis is compromised, we described the following topics in the testis of normal and orchitic rats: (1) cell adhesion molecule expression of seminiferous tubule specialized junctions and modulation of blood-testis barrier permeability by cytokines (2) phenotypic and functional characteristics of testicular dendritic cells, macrophages, effector and regulatory T cells and mast cells and (3) effects of pro-inflammatory cytokines (TNF-α, IL-6 and FasL) and the nitric oxide-nitric oxide synthase system on GC apoptosis.

Embryonic Stem Cell-Like Features of Testicular Carcinoma Revealed by Genome-Wide Gene Expression Profiling

Carcinoma in situ (CIS) is the common precursor of histologically heterogeneous testicular germ cell tumors (TGCTs), which in recent decades have markedly increased and now are the most common malignancy of young men. Using genome-wide gene expression profiling, we identified >200 genes highly expressed in testicular CIS, including many never reported in testicular neoplasms. Expression was further verified by semiquantitative reverse transcription-PCR and in situ hybridization. Among the highest expressed genes were NANOG and POU5F1, and reverse transcription-PCR revealed possible changes in their stoichiometry on progression into embryonic carcinoma. We compared the CIS expression profile with patterns reported in embryonic stem cells (ESCs), which revealed a substantial overlap that may be as high as 50%. We also demonstrated an over-representation of expressed genes in regions of 17q and 12, reported as unstable in cultured ESCs. The close similarity between CIS and ESCs explains the pluripotency of CIS. Moreover, the findings are consistent with an early prenatal origin of TGCTs and thus suggest that etiologic factors operating in utero are of primary importance for the incidence trends of TGCTs. Finally, some of the highly expressed genes identified in this study are promising candidates for new diagnostic markers for CIS and/or TGCTs.

Local regulation of T cell numbers and lymphocyte-inhibiting activity in the interstitial tissue of the adult rat testis

The testis is an immunologically privileged site, and transplantation data suggest that this privilege may be enhanced in cryptorchidism. Although alphabetaT cells, which mediate and promote the immune response, have access to the normal testis, relatively little is known about these cells in the abdominally located testis. An increase in testicular lymphocyte-inhibiting cytokines has also been implicated in enhanced graft survival following the experimental induction of cryptorchidism. Consequently, T cell traffic and lymphocyte-inhibiting activity in testes of cryptorchid adult rats were examined in the following study. Numbers of alphabetaT cells and the cytotoxic CD8(+) T cell subset in the testis were unaffected following 1 month of cryptorchidism. In contrast, subcutaneous testosterone implants, which inhibit Leydig cell function through suppression of gonadotrophin secretion, reduced these parameters in both scrotal and abdominal testes. Testicular T cell numbers were positively correlated with the number of testicular resident macrophages, which also were reduced by subcutaneous testosterone implants. The concentration of lymphocyte-inhibiting activity in the testicular interstitial fluid was reduced by 80% in short-term (1 month) and longer-term (3 months) cryptorchidism. These data indicate that the T cell population, and in particular the CD8(+) T cell subset, in the rat testis is functionally related to the resident macrophages or Leydig cells. On the other hand, testicular lymphocyte-inhibiting activity does not appear to be a determinant of the number of testicular T cells, and may not be a major factor in the prolonged survival of certain grafts in the abdominal testis.

Experimental testicular teratoma promotes formation of humoral immune responses in the host testis

The testis is an immunologically privileged site. Very little is known about the factors regulating formation of immune responses elicited by a neoplasm in the testis. We have studied the immune response of the host testis against experimental testicular teratoma in mouse by localizing adhesion molecules (CD106, CD54, CD49d/CD29, CD44, CD18, CD8 and CD4), cytokines (IL-2, IL-4, IL-6, IL-10 and IL-12), T-cell costimulators (CD80, CD86) and the lipid antigen presenting molecule CD1d in the testis of 129/SvJ mice with and without experimental testicular teratoma. The testicular teratomas were induced by grafting male gonadal ridges from 12-day-old 129/SvJ mouse fetuses into testes of adult mice from the same strain. The tumors cultured intratesticularly for 2, 3, 4 and 8 weeks (three animals per time point) were used for immunocytochemistry. CD1d was detected in Sertoli cells and in some degenerated tubules of the host testis surrounding the graft. In the tumor, CD1d was detected in glandular epithelia, smooth muscle and in thin fibers of neural origin. IL-2 was observed in some blood vessels of the host testis and of the tumor and in occasional cell infiltrates around these vessels. Some tubular structures of the tumor were also positive for IL-2. IL-6 was detected in Sertoli cells of the normal testis and in Sertoli cells and in solitaryinterstitial cells as well as in the walls of some blood vessels of the host testis. The reaction for IL-6 was more prominent in the tubules apparently damaged by the growing tumor. In the tumor IL-6 was detected in epithelial structures, muscle cells, in thin fibers of neural origin and in some blood vessels. IL-10 was detected in individual cells in the interstitium and in degenerating tubules of the host testis. In the tumor the epithelial structures were positive for IL-10. The interstitium of the host testis was positive for CD106 and the embryonic testicular cords in the graft were also positive, but the tumor was negative. CD44 and CD18 were observed in some blood vessels and in degenerated tubules of the host testis. In the tumor CD44 and CD18 were occasionally observed in cartilage and in epithelial structures. The results of the present study suggest that cytokine microenvironment in the testis containing neoplastic tissue promotes activation of humoral immune responses. In addition, as the damaged seminiferous tubules expressed increased amounts of two cytokines promoting humoral immune responses, IL-6 and IL-10, it is possible that also in other conditions with damage to the tubules, humoral immune responses predominate.