Differential activation of inflammatory pathways in testicular macrophages provides a rationale for their subdued inflammatory capacity.
Spermatogenic cells express cell-specific molecules with the potential to be seen as "foreign" by the immune system. Owing to the time difference between their appearance in puberty and the editing of the lymphocyte repertoire around birth, local adaptations of the immune system coined immune privilege are required to confer protection from autoattack. Testicular macrophages (TM) play an important role in maintaining testicular immune privilege and display reduced proinflammatory capacity compared with other macrophages. However, the molecular mechanism underlying this macrophage phenotype remained elusive. We demonstrate that TM have a lower constitutive expression of TLR pathway-specific genes compared with peritoneal macrophages. Moreover, in TM stimulated with LPS, the NF-κB signaling pathway is blocked due to lack of IκBα ubiquitination and, hence, degradation. Instead, challenge of TM with LPS or polyinosinic-polycytidylic acid induces MAPK, AP-1, and CREB signaling pathways, which leads to production of proinflammatory cytokines such as TNF-α, although at much lower levels than in peritoneal macrophages. Pretreatment of TM with inhibitors for MAPKs p38 and ERK1/2 suppresses activation of AP-1 and CREB signaling pathways and attenuates LPS-induced TNF-α and IL-10 secretion. High levels of IL-10 production and activation of STAT3 by LPS stimulation in TM indicate a regulatory macrophage phenotype. Our results suggest that TM maintain testicular immune privilege by inhibiting NF-κB signaling through impairment of IκBα ubiquitination and a general reduction of TLR cascade gene expression. However, TM do maintain some capacity for innate immune responses through AP-1 and CREB signaling pathways.
Department of Anatomy and Cell Biology, Justus Liebig University Giessen, 35392 Giessen, Germany; and.
Sudhanshu
S
Bhushan
Department of Medical Microbiology, Justus Liebig University Giessen, 35392 Giessen, Germany.
Svetlin
S
Tchatalbachev
Department of Anatomy and Cell Biology, Justus Liebig University Giessen, 35392 Giessen, Germany; and.
Yongning
Y
Lu
Department of Anatomy and Cell Biology, Justus Liebig University Giessen, 35392 Giessen, Germany; and.
Suada
S
Fröhlich
Department of Anatomy and Cell Biology, Justus Liebig University Giessen, 35392 Giessen, Germany; and.
Monika
M
Fijak
Department of Anatomy and Cell Biology, Justus Liebig University Giessen, 35392 Giessen, Germany; and.
Vijith
V
Vijayan
Department of Medical Microbiology, Justus Liebig University Giessen, 35392 Giessen, Germany.
Trinad
T
Chakraborty
Department of Anatomy and Cell Biology, Justus Liebig University Giessen, 35392 Giessen, Germany; and Andreas.Meinhardt@anatomie.med.uni-giessen.de.
Andreas
A
Meinhardt
D000818:Animals; D002478:Cells, Cultured; D017362:Cyclic AMP Response Element-Binding Protein / Q000037:antagonists & inhibitors / Q000096:biosynthesis / Q000378:metabolism; D048049:Extracellular Signal-Regulated MAP Kinases / Q000037:antagonists & inhibitors; D020672:I-kappa B Proteins / Q000378:metabolism*; D007108:Immune Tolerance / Q000276:immunology; D007113:Immunity, Innate / Q000276:immunology; D007249:Inflammation / Q000276:immunology*; D016753:Interleukin-10 / Q000096:biosynthesis / Q000378:metabolism; D008070:Lipopolysaccharides; D020935:MAP Kinase Signaling System / Q000276:immunology; D008264:Macrophages / Q000276:immunology*; D008297:Male; D000072000:NF-KappaB Inhibitor alpha; D016328:NF-kappa B / Q000037:antagonists & inhibitors*; D011070:Poly I-C; D051381:Rats; D017208:Rats, Wistar; D050796:STAT3 Transcription Factor / Q000378:metabolism; D013737:Testis / Q000166:cytology / Q000276:immunology*; D051193:Toll-Like Receptors / Q000276:immunology; D018808:Transcription Factor AP-1 / Q000037:antagonists & inhibitors / Q000096:biosynthesis; D014409:Tumor Necrosis Factor-alpha / Q000096:biosynthesis / Q000378:metabolism; D054875:Ubiquitination; D048051:p38 Mitogen-Activated Protein Kinases / Q000037:antagonists & inhibitors
D017362:Cyclic AMP Response Element-Binding Protein; D020672:I-kappa B Proteins; D008070:Lipopolysaccharides; D016328:NF-kappa B; C000606206:Nfkbia protein, rat; D050796:STAT3 Transcription Factor; C494088:Stat3 protein, rat; D051193:Toll-Like Receptors; D018808:Transcription Factor AP-1; D014409:Tumor Necrosis Factor-alpha; D016753:Interleukin-10; D000072000:NF-KappaB Inhibitor alpha; D048049:Extracellular Signal-Regulated MAP Kinases; D048051:p38 Mitogen-Activated Protein Kinases; D011070:Poly I-C