Functional and phenotypic characteristics of testicular macrophages in experimental autoimmune orchitis

Breakdown of immune homeostasis in the testis of mice lacking Tyro3, Axl and Mer receptor tyrosine kinases

Tyro3, Axl and Mer (TAM) receptor tyrosine kinases triple knockout (TAM(-/-)) mice are male infertile due to impaired spermatogenesis. However, the mechanism by which TAM receptors regulate spermatogenesis remains unclear. In this study, we demonstrate that the testicular immune homeostasis was impaired in TAM(-/-) mice. As development after the onset of sexual maturity, germ cells were progressively degenerated. Macrophages and lymphocytes infiltrated into the testis as TAM(-/-) mice aged. Moreover, the integrity of blood-testis barrier was impaired, and the autoantibodies against germ cell antigens were produced. Major inflammatory cytokines, including tumor necrosis factor-α, interleukin-6 and monocyte chemotactic protein 1 were upregulated in the testis of TAM(-/-) mice, and predominantly located in Sertoli cells (SCs). In vitro assays showed that TAM(-/-) SCs secrete significantly high levels of inflammatory cytokines compared with wild-type SCs after coculture with apoptotic germ cells. These results suggest that TAM receptors are important in the maintenance of the immune homeostasis in the testis.

Damaged spermatogenic cells induce inflammatory gene expression in mouse Sertoli cells through the activation of Toll-like receptors 2 and 4

Testicular inflammation, including noninfectious inflammatory responses in the testis, may impair male fertility. Mechanisms underlying the initiation of noninfectious testicular inflammation are poorly understood. In the current study, we demonstrate that damaged spermatogenic cell products (DSCPs) induce expression of various inflammatory mediators, including TNF-α, IL-1β, IL-6, and macrophage chemotactic protein 1 (MCP-1), in Sertoli cells. Notably, the DSCP-induced inflammatory gene expression was significantly reduced by knockout Toll-like receptor (TLR)2 or TLR4, and abolished by double knockout TLR2 and TLR4 (TLR2(-/-)TLR4(-/-)). MCP-1 secreted by Sertoli cells after stimulation with DSCPs promotes macrophage migration. We also provide evidence that busulfan-induced spermatogenic cell damages in vivo upregulate TNF-α and MCP-1 expression in Sertoli cells, and facilitate macrophage infiltration into the testis in wild-type mice. These phenomena were not observed in TLR2(-/-)TLR4(-/-) mice. Data indicate that DSCPs induce inflammatory gene expression in Sertoli cells via the activation of TLR2 and TLR4, which may initiate noninfectious inflammatory responses in the testis. The results provide novel insights into the mechanisms underlying damaged spermatogenic cell-induced testicular inflammation.

Loss of occludin expression and impairment of blood-testis barrier permeability in rats with autoimmune orchitis: effect of interleukin 6 on Sertoli cell tight junctions

Inflammation of the male reproductive tract is accepted as being an important etiological factor of infertility. Experimental autoimmune orchitis (EAO) is characterized by interstitial lymphomononuclear cell infiltration and severe damage of seminiferous tubules with germ cells that undergo apoptosis and sloughing. Because the blood-testis barrier (BTB) is relevant for the protection of haploid germ cells against immune attack, the aim of this study was to analyze BTB permeability and the expression of tight junction proteins (occludin, claudin 11, and tight junction protein 1 [TJP1]) in rats during development of autoimmune orchitis. The role of IL6 as modulator of tight junction dynamics was also evaluated because intratesticular content of this cytokine is increased in EAO rats. Orchitis was induced in Sprague-Dawley adult rats by active immunization with testicular homogenate and adjuvants. Control rats (C) were injected with saline solution and adjuvants. Untreated (N) rats were also studied. Concomitant with early signs of germ cell sloughing, a reduced expression of occludin and delocalization of claudin 11 and TJP1 were detected in the testes of rats with EAO compared to C and N groups. The use of tracers showed increased BTB permeability in EAO rats. Intratesticular injection of IL6 induced focal testicular inflammation, which is associated with damaged seminiferous tubules. Rat Sertoli cells cultured in the presence of IL6 exhibited a redistribution of tight junction proteins and reduced transepithelial electrical resistance. These data indicate the possibility that IL6 might be involved in the downregulation of occludin expression and in the modulation of BTB permeability that occur in rats undergoing autoimmune orchitis.

Involvement of soluble Fas Ligand in germ cell apoptosis in testis of rats undergoing autoimmune orchitis

Experimental autoimmune orchitis (EAO) is a model of chronic inflammation and infertility useful for studying immune and germ cell (GC) interactions. EAO is characterized by severe damage of seminiferous tubules (STs) with GCs that undergo apoptosis and sloughing. Based on previous results showing that Fas-Fas Ligand (L) system is one of the main mediators of apoptosis in EAO, in the present work we studied the involvement of Fas and the soluble form of FasL (sFasL) in GC death induction. EAO was induced in rats by immunization with testis homogenate and adjuvants; control (C) rats were injected with adjuvants; a group of non-immunized normal (N) rats was also studied. Activation of Fas employing an anti-Fas antibody decreased viability (trypan blue exclusion test) and induced apoptosis (TUNEL) of GCs from STs of N and EAO rats, an effect more pronounced on GCs from EAO STs. By Western blot we detected an increase in sFasL content in the testicular fluid of rats with severe EAO compared to N and C rats. By intratesticular injection of FasL conjugated to Strep-Tag molecule (FasL-Strep, BioTAGnology) and its immunofluorescent localization, we demonstrated that sFasL is able to enter the adluminal compartment of the STs. Moreover, FasL-Strep induced GC apoptosis in testicular fragments of N rats. By flow cytometry, we detected an increase in the number of membrane FasL-expressing CD4+ and CD8+ T cells in testis during EAO development but no expression of FasL by macrophages. Our results demonstrate that sFasL is locally produced in the chronically inflamed testis and that this molecule is able to enter the adluminal compartment of STs and induce apoptosis of Fas-bearing GCs.

Structural, cellular and molecular aspects of immune privilege in the testis

The testis presents a special immunological environment, considering its property of immune privilege that tolerates allo- and auto-antigens. Testicular immune privilege was once believed to be mainly based on the sequestration of antigens from the immune system by the blood–testis barrier in the seminiferous epithelium. Substantial evidence supports the view that the combination of physical structure, testicular cells, and cytokines controls immune responses in the testis to preserve the structural and functional integrity of testicular immune privilege. Both systemic immune tolerance and local immunosuppression help maintain the immune privilege status. Constitutive expression of anti-inflammatory factors in testicular cells is critical for local immunosuppression. However, the testis locally generates an efficient innate immune system against pathogens. Disruption of these mechanisms may lead to orchitis and impair fertility. This review article highlights the current understanding of structural, cellular, and molecular mechanisms underlying the unique immune environment of the testis, particularly its immune privilege status.

Up regulation of nitric oxide synthase-nitric oxide system in the testis of rats undergoing autoimmune orchitis

BACKGROUND

Male reproductive tract infection and inflammation are important aetiological factors of infertility. Experimental Autoimmune Orchitis (EAO) is a model of chronic inflammation useful to study mechanisms of inflammatory reactions leading to testicular impairment. EAO is characterised by interstitial cell infiltrate of lymphomonocytes, producers of pro-inflammatory cytokines involved in germ cell apoptosis. Nitric oxide (NO), a free radical promoting immune cell activation and apoptosis, is synthesised by conversion of l-arginine to l-citrulline catalysed by NO synthase (NOS). The NOS isoforms are: constitutively endothelial (e) and neuronal (n) NOS and inducible (i) NOS.

OBJECTIVES

Although the NO-NOS system was found to be up-regulated by pro-inflammatory mediators in immune and non immune testicular cells, data on its regulation in chronic inflammatory states is lacking.

METHODS AND RESULTS

EAO was induced in rats by active immunisation with spermatic antigens and adjuvants; control (C) rats were injected with adjuvants. Untreated normal (N) rats were also studied. We demonstrated that iNOS, eNOS and nNOS was mainly expressed by interstitial cells in N and C rats and that in EAO NOS was up-regulated and also expressed by tubular cells. Constitutive and inducible NOS content (Western blot) as well as NO production and activity increased in the testis of rats with EAO. iNOS content and activity were selectively up-regulated in the testis of rats with orchitis. Flow cytometric analysis of NOS isoforms in testicular macrophages (M) showed that the percentage of ED1(+)ED2(-) and ED1(+)ED2(+) M subsets, expressing constitutive and iNOS isoforms was significantly higher in EAO, but no change in the percentage of ED1(-)ED2(+) resident M was observed compared to C rats. M from EAO rats also released more NO than C and N rats.

CONCLUSIONS

In testis of rats with EAO, NO-NOS system was up-regulated and both testicular M and cells from seminiferous tubules contributed to NO increase. NO over production in orchitis was generated mainly by increased iNOS content and activity.

Expression of cell adhesion molecules, chemokines and chemokine receptors involved in leukocyte traffic in rats undergoing autoimmune orchitis

The testis is considered an immunologically privileged site where germ cell antigens are protected from autoimmune attack. Yet in response to infections, inflammatory diseases, or trauma, there is an influx of leukocytes to testicular interstitium. Interactions between endothelial cells (EC) and circulating leukocytes are implicated in the initiation and evolution of inflammatory processes. Chemokines are a family of chemoattractant cytokines characterized by their ability to both recruit and activate cells. Thus, we investigated the expression of CCL3, its receptors, and adhesion molecules CD31 and CD106 in an in vivo model of experimental autoimmune orchitis (EAO). In EAO, the highest content of CCL3 in testicular fluid coincides with onset of the disease. However, CCL3 released in vitro by testicular macrophages is higher during the immunization period. The specific chemokine receptors, CCR1 and CCR5, were expressed by testicular monocytes/macrophages and an increased number of CCR5+ cells was associated with the degree of testicular lesion. EC also play an essential role by facilitating leukocyte recruitment via their ability to express cell surface adhesion molecules that mediate interactions with leukocytes in the bloodstream. Rats with EAO showed a significant increase in the percentage of CD31+ EC that upregulate the expression of CD106. The percentage of leukocytes isolated from peripheral blood and lymph nodes expressing CD49d (CD106 ligand) also increases during orchitis. These data suggest that cell adhesion molecules, in conjunction with chemokines, contribute to the formation of a chemotactic gradient within the testis, causing the leukocyte infiltration characteristic of EAO histopathology.

Diphenyl diselenide-modulation of macrophage activation: down-regulation of classical and alternative activation markers

Diphenyl diselenide (PhSe)(2), a simple organoselenium compound, possesses interesting pharmacological properties that are under extensive research. As macrophages respond to microenvironmental stimuli and can display activities engaged in the initiation and the resolution of inflammation, in the present report we describe the ability of (PhSe)(2) to modulate the macrophage activation. Our data indicate that (PhSe)(2) could inhibit the NO production in a dose-dependent fashion in peritoneal macrophages activated by LPS or treated with vehicle alone. We could demonstrate that this effect correlated with a reduction in the expression of the inducible NO synthase in (PhSe)(2)-treated cells. Furthermore, (PhSe)(2) suppressed the production of reactive oxygen species, diminished the activity of the arginase enzyme, and the accumulation of nitrotyrosine modified proteins in LPS-stimulated macrophages. This compound also diminished the antigen presentation capacity of classically activated macrophages, as it reduced MHCII and CD86 expression. In addition, (PhSe)(2) modulated the alternative activation phenotype of macrophages. Dexamethasone-activated macrophages presented higher production of IL-10 and CD206, which were both down-regulated by the addition of (PhSe)(2). These results suggest that (PhSe)(2) possesses antioxidant and anti-inflammatory activities in classically-activated macrophages. We could demonstrate that (PhSe)(2) can be also utilized to modulate the alternative activation phenotype of macrophages.

Impaired expression and distribution of adherens and gap junction proteins in the seminiferous tubules of rats undergoing autoimmune orchitis

Experimental autoimmune orchitis (EAO) is characterized by an interstitial lymphomononuclear cell infiltration and a severe lesion of seminiferous tubules (ST) with germ cells that undergo apoptosis and sloughing. The aim of this study was to analyse the expression and localization of adherens junction (AJ) proteins: N-cadherin, α-, β- and p120 catenins and gap junction protein, connexin 43 (Cx43), to explore some aspects of germ-cell sloughing during the development of orchitis. EAO was induced in Sprague-Dawley adult rats by active immunization with testicular homogenate and adjuvants. Control rats (C) were injected with saline solution and adjuvants. Concomitant with early signs of germ-cell sloughing, we observed by immunofluorescence and Western blot, a delocalization and a significant increase in N-cadherin and α-catenin expression in the ST of EAO compared with C rats. In spite of this increased AJ protein expression, a severe germ-cell sloughing occurred. This is probably due to the impairment of the AJ complex function, as shown by the loss of N-cadherin/β-catenin colocalization (confocal microscopy) and increased pY654 β-catenin expression, suggesting lower affinity of these two proteins and increased pERK1/2 expression in the testis of EAO rats. The significant decrease in Cx43 expression detected in EAO rats suggests a gap junction function impairment also contributing to germ-cell sloughing.

Micro-encapsulated secretory leukocyte protease inhibitor decreases cell-mediated immune response in autoimmune orchitis

AIMS

We previously reported that recombinant human Secretory Leukocyte Protease Inhibitor (SLPI) inhibits mitogen-induced proliferation of human peripheral blood mononuclear cells. To determine the relevance of this effect in vivo, we investigated the immuno-regulatory role of SLPI in an experimental autoimmune orchitis (EAO) model.

MAIN METHODS

In order to increase SLPI half life, poly-ε-caprolactone microspheres containing SLPI were prepared and used for in vitro and in vivo experiments. Multifocal orchitis was induced in Sprague-Dawley adult rats by active immunization with testis homogenate and adjuvants. Microspheres containing SLPI (SLPI group) or vehicle (control group) were administered s.c. to rats during or after the immunization period.

KEY FINDINGS

In vitro SLPI-release microspheres inhibited rat lymphocyte proliferation and retained trypsin inhibitory activity. A significant decrease in EAO incidence was observed in the SLPI group (37.5%) versus the control group (93%). Also, SLPI treatment significantly reduced severity of the disease (mean EAO score: control, 6.33±0.81; SLPI, 2.72±1.05). In vivo delayed-type hypersensitivity and ex vivo proliferative response to testicular antigens were reduced by SLPI treatment compared to control group (p<0.05).

SIGNIFICANCE

Our results highlight the in vivo immunosuppressive effect of released SLPI from microspheres which suggests its feasible therapeutic use.

Testosterone replacement effectively inhibits the development of experimental autoimmune orchitis in rats: evidence for a direct role of testosterone on regulatory T cell expansion

Despite the immune-privileged status of the male genital tract, infection and inflammation of the male genital tract are important etiological factors in male infertility. A common observation in clinical and experimental orchitis as well as in systemic infection and inflammation are decreased levels of testosterone. Emerging data point to an immunosuppressive role of testosterone. In our study, we substituted testosterone levels in experimental autoimmune orchitis (EAO) in rat by s.c. testosterone implants. EAO development was reduced to 17% when animals were treated with low-dose testosterone implants (3 cm long, EAO+T3) and to 33% when rats were supplied with high-dose testosterone implants (24 cm, EAO+T24) compared with 80% of animals developing disease in the EAO control group. In the testis, testosterone replacement in EAO animals prevented the accumulation of macrophages and significantly reduced the number of CD4(+) T cells with a strong concomitant increase in the number of regulatory T cells (CD4(+)CD25(+)Foxp3(+)) compared with EAO control. In vitro testosterone treatment of naive T cells led to an expansion of the regulatory T cell subset with suppressive activity and ameliorated MCP-1-stimulated chemotaxis of T lymphocytes in a Transwell assay. Moreover, expression of proinflammatory mediators such as MCP-1, TNF-α, and IL-6 in the testis and secretion of Th1 cytokines such as IFN-γ and IL-2 by mononuclear cells isolated from testicular draining lymph nodes were decreased in the EAO+T3 and EAO+T24 groups. Thus, our study shows an immunomodulatory and protective effect of testosterone substitution in the pathogenesis of EAO and suggests androgens as a new factor in the differentiation of regulatory T cells.

Intratesticular expression of mRNAs of both interferon γ and tumor necrosis factor α is significantly increased in experimental autoimmune orchitis in mice

Experimental autoimmune orchitis (EAO) is one of the models of immunological male infertility. Murine EAO is CD4+T cell-dependent and classically induced by immunization with a testicular homogenate and adjuvants. We previously established that immunization with viable syngeneic testicular germ cells (TGC) can also induce murine EAO with no use of any adjuvant. Analyses of this EAO model have already revealed that cultured spleen cells of immunized mice secreted interferon (IFN)-γ and that treatment of the immunized mice with anti-IFN-γ monoclonal antibodies significantly suppressed the EAO. It is known that both IFN-γ and tumor necrosis factor (TNF)-α are representative cytokines of Th1 cells and exhibit local toxicity toward the seminiferous epithelium in vivo. However, changes in these two cytokines in EAO-affected testes have not yet been investigated. Therefore, in the present study, we investigated the expression of intratesticular IFN-γ and TNF- α mRNAs in TGC-induced EAO using real-time RT-PCR. The results demonstrated that the intratesticular mRNAs for both IFN-γ and TNF-α significantly increased, while other cytokines such as IL-1α, IL-1β, IL-6 and TGF-β did not show dramatic changes in the immunized mice. These results suggest that secretion of significant amounts of IFN-γ and TNF-α in situ contributes to the spermatogenic disturbance in EAO.

CD4+ and CD8+ T cells producing Th1 and Th17 cytokines are involved in the pathogenesis of autoimmune orchitis

Experimental autoimmune orchitis (EAO) is a useful model to study chronic testicular inflammation and infertility. EAO is characterized by severe damage of seminiferous tubules with germ cells that undergo apoptosis and sloughing. We previously reported an increase in CD4+ and CD8+ effector T cells in the testes of rats with EAO. Since cytokine patterns determine T cell effector functions, in the present work we analyzed the cytokines expressed by these cells during disease development. By flow cytometry, we detected an increase in the number of tumor necrosis factor-α (TNF) and interferon -γ (IFNG)-producing CD4+ T cells in the testis at EAO onset. As the severity of the disease progressed, these cells declined while CD8+ T cells producing TNF and IFNG increased, with the predominance of IFNG expression. As a novel finding, we identified by immunofluorescence CD4+ interleukin 17 (IL17)+ and CD8+ IL17+ cells in the testes of EAO rats, with CD4+ and CD8+ T cells predominating at the onset and in the chronic phase of EAO respectively. Moreover, IL17 (western blot) and IL23 content (ELISA) increased in EAO, with maximum levels in the chronic phase. These results suggest the involvement of CD4+ T helper (Th) 1 and Th17 subsets as co-effector cells governing EAO onset, as well as the central contribution of CD8+ T cells producing Th1 and Th17 cytokines in the maintenance of chronic inflammation. The expression of T-bet and RORγt (western blot) in the testis over the course of disease also supports the presence of Th1 and Th17 cells in the testes of EAO rats.

Immunoprivileged sites: the testis

The testis is an immunological privileged tissue as evidenced by its ability to support grafts with minimal rejection. Immune privilege is essential for the tolerance of neo-antigens from developing germ cells that appear after the constitution of self-tolerance, but imposes the paradoxical task of also providing efficient protection against pathogens and tumor cells. It is becoming increasingly clear that immune privilege cannot be attributed to a single factor such as the sequestration of neo-antigens from the immune system behind the blood-testis barrier, but is based on a complex multifaceted interplay between cells and factors that are essential for the reproductive function of the testis and the testicular immune system. This review summarizes the evidence that has accumulated regarding the role of Sertoli cells, androgens, and selected population of leukocytes in the maintenance of immune privilege and its perturbation in testicular inflammatory sub- and infertility.

Cytokines and chemokines in testicular inflammation: A brief review

A wide spectrum of data in the literature shows the relevance of cytokines as paracrine regulators of spermatogenesis and steroidogenesis in the normal testis. In this brief review, we highlight the relevance of cytokines in the testis during inflammation. This phenomenon involves complex and multiple interactions among immune and germ cells generally resulting in the alteration of spermatogenesis. The complexity of these cell interactions is multiplied because Sertoli and Leydig cells are also producers of pro- and anti-inflammatory cytokines and chemokines. Also, cytokines are pleiotropic and they exert opposite and/or redundant effects in different conditions. However, in spite of this bidirectional immunoregulatory function of cytokines, the mass of the data, reported from experiments of acute testicular inflammation, shows upregulation of interleukin (IL)-1beta, IL-1alpha, IL-6, and tumor necrosis factor alpha (TNF-alpha), which induce adverse effects on germ cells. In autoimmune orchitis, a chronic testicular inflammation, chemokines such as CCL2, CCL3, and CCL4 induce attraction and extravasation of immune cells within the testicular interstitium. These cells alter the normal immunosuppressor microenvironment principally through the secretion of proinflammatory cytokines, interferon-gamma initially, and IL-6 and TNF-alpha thereafter. Germ cells expressing TNFR1, IL-6R, and Fas increase in number and undergo apoptosis, through the TNF-alpha/TNFR1, IL-6/IL-6R, and Fas/Fas L systems. The knowledge of immune-germ and somatic testicular cell interactions will contribute to the understanding of the mechanisms by which chronic inflammatory conditions of the testis can disrupt the process of spermatogenesis.

Surfactin inhibits immunostimulatory function of macrophages through blocking NK-kappaB, MAPK and Akt pathway

Surfactin is one of the most powerful biosurfactants, and is known to have antibiotic, anti-tumor and anti-inflammatory functions. In this study, we investigated the effect of surfactin on antigen-presenting property of macrophages. Thioglycollate-elicited mouse peritoneal macrophages were tested for surface molecule expression, cytokine production, phagocytosis, capacity to induce T cell activation by mixed lymphocyte reaction, and underlying signaling pathways. Surfactin significantly suppressed lipopolysaccharide-induced expression of CD40, CD54, CD80, and MHC-II, but not of CD86 and MHC-I. Surfactin-treated macrophages also exhibited impaired phagocytosis and reduced IL-12 expression. And surfactin markedly inhibited the activation of CD4+ T cells. Impaired translocation and activation of NF-kappaB p65 were founded on macrophages exposed to surfactin. In addition, surfactin inhibited the phosphorylation and degradation of IkappaB-alpha, and suppressed the activation of IKK, Akt, JNK and p38 kinase. These results suggest that surfactin impair the antigen-presenting function of macrophages by inhibiting the expression of MHC-II and costimulatory molecules via suppression of NF-kappaB, p38, JNK and Akt. These novel findings provide new insight into the immunopharmacological role of surfactin in autoimmune disease and transplantation.

Tumour necrosis factor-alpha released by testicular macrophages induces apoptosis of germ cells in autoimmune orchitis

BACKGROUND

Experimental autoimmune orchitis (EAO) is a model of chronic inflammation and infertility useful for studying testicular immune and germ cell (GC) interactions. In this model, EAO was induced in rats by immunization with testicular homogenate and adjuvants; Control (C) rats were injected with adjuvants. EAO was characterized by an interstitial infiltrate of lymphomonocytes and seminiferous tubule damage, moderate 50 days (focal orchitis) and severe 80 days after the first immunization (severe orchitis). Based on the previous results showing that the number of macrophages and apoptotic GC expressing tumour necrosis factor (TNF) receptor 1 increased in EAO, we studied the role of macrophages and TNF-alpha in GC apoptosis.

METHODS AND RESULTS

Conditioned media of testicular macrophages (CMTM) obtained from rats killed on Days 50 and 80 decreased the viability (MTS, P < 0.01) and induced apoptosis (terminal deoxynucleotidyl transferase (TdT)-mediated dUTP nick end labelling, TUNEL) of GC obtained from EAO but not from non-immunized, N rats (P < 0.001). TNF-alpha content (enzyme-linked immunosorbent assay) was significantly higher in the CMTM from EAO versus C rats on Day 80 (P < 0.05). The apoptotic effect of CMTM from Day 80 rats was abrogated by a selective TNF-alpha blocker (Etanercept). Moreover, TNF-alpha in vitro induced GC apoptosis. TNF-alpha expression (by immunofluorescence) was observed in testicular (ED2(+)) and non-resident (ED1(+)) macrophages, the percentage of TNF-alpha(+) macrophages being similar in focal and severe orchitis.

CONCLUSIONS

Results demonstrated that soluble factors released from testicular EAO macrophages induce apoptosis of GC, biased by the local inflammatory environment, and that TNF-alpha is a relevant cytokine involved in testicular damage during severe orchitis.