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Characterization of the Micro-Environment of the Testis that Shapes the Phenotype and Function of Testicular
Ming Wang1, Monika Fijak1, Hamid Hossain2
1Institute of Anatomy and Cell Biology, Justus-Liebig-University of Giessen, Giessen 35392, Germany.
Abstract:
Macrophages are important in the activation of innate immune responses and in a tissue-specific manner in the maintenance of organ homeostasis. Testicular macrophages (TM), which reside in the testicular interstitial space, comprise the largest leukocyte population in the testes and are assumed to play a relevant function in maintaining testicular immune privilege. Numerous studies have indicated that the interstitial fluid (IF) surrounding the TM has immunosuppressive properties, which may influence the phenotype of TM. However, the identity of the immunosuppressive molecules present in the IF is poorly characterized. We show that the rat testicular IF shifted GM-CSF-induced M1 toward the M2 macrophage phenotype. IF-polarized M2 macrophages mimic the properties of TM, such as increased expression of CD163, high secretion of IL-10, and low secretion of TNF-α. In addition, IF-polarized macrophages display immunoregulatory functions by inducing expansion of immunosuppressive regulatory T cells. We further found that corticosterone was the principal immunosuppressive molecule present in the IF and that the glucocorticoid receptor is needed for induction of the testis-specific phenotype of TM. In addition, TM locally produce small amounts of corticosterone, which suppresses the basal expression of inflammatory genes as a means to render TM refractory to inflammatory stimuli. Taken together, these results suggest that the corticosterone present in the testicular environment shapes the immunosuppressive function and phenotype of TM and that this steroid may play an important role in the establishment and sustenance of the immune privilege of the testis.
Insights
Testicular macrophages (TM) are crucial for immune privilege. Corticosterone in testicular fluid drives TM to an immunosuppressive M2 phenotype, maintaining testicular homeostasis and immune privilege.
Area of Science:
- Immunology
- Reproductive Biology
- Endocrinology
Background:
- Macrophages are key to innate immunity and organ homeostasis.
- Testicular macrophages (TM) are the primary leukocyte population in testes, vital for immune privilege.
- Testicular interstitial fluid (IF) has immunosuppressive properties, but active molecules are unknown.
Purpose of the Study:
- To identify immunosuppressive molecules in testicular IF.
- To understand how IF influences TM phenotype and function.
- To elucidate the role of corticosterone in testicular immune privilege.
Main Methods:
- Macrophage polarization assays using rat testicular IF.
- Analysis of macrophage phenotype markers (CD163, IL-10, TNF-α).
- Assessment of regulatory T cell induction.
- Identification of immunosuppressive molecules via chemical analysis.
- Glucocorticoid receptor antagonist studies.
Main Results:
- Testicular IF shifted M1 macrophages to an M2 phenotype, mimicking TM characteristics (CD163+, IL-10 high, TNF-α low).
- IF-polarized M2 macrophages induced regulatory T cell expansion.
- Corticosterone was identified as the primary immunosuppressive molecule in IF.
- Glucocorticoid receptor signaling is essential for TM phenotype induction.
- TM locally produce corticosterone, suppressing inflammatory gene expression.
Conclusions:
- Corticosterone in testicular IF shapes TM immunosuppressive phenotype and function.
- This steroid hormone is critical for establishing and maintaining testicular immune privilege.
- TM contribute to their own immunosuppressive environment through local corticosterone production.
