Testicular immune cell populations and macrophage polarisation in adult male mice and the influence of altered activin A levels.

Detailed morphological characterization of testicular leukocytes in the adult CXCR transgenic mouse identified two distinct CXCR mononuclear phagocyte (macrophage and dendritic cell) populations: stellate/dendriform cells opposed to the seminiferous tubules (peritubular), and polygonal cells associated with Leydig cells (interstitial). Using confocal microscopy combined with stereological enumeration of CXCR cells established that there were twice as many interstitial cells (68%) as peritubular cells (32%). Flow cytometric analyses of interstitial cells from mechanically-dissociated testes identified multiple mononuclear phagocyte subsets based on surface marker expression (CXCR, F4/80, CD11c). These cells comprised 80% of total intratesticular leukocytes, as identified by CD45 expression. The remaining leukocytes were CD3 (T lymphocytes) and NK1.1 (natural killer cells). Functional phenotype assessment using CD206 (an anti-inflammatory/M2 marker) and MHC class II (an activation marker) identified a potentially tolerogenic CD206MHCII sub-population (12% of total CD45 cells). Rare testicular subsets of CXCRCD11cF4/80 (4.3%) mononuclear phagocytes and CD3NK1.1 (3.1%) lymphocytes were also identified for the first time. In order to examine the potential for the immunoregulatory cytokine, activin A to modulate testicular immune cell populations, testes from adult mice with reduced activin A (Inhba) or elevated activin A (Inha) were assessed using flow cytometry. Although the proportion of F4/80CD11b leukocytes (macrophages) was not affected, the frequency of CD206MHCIIcells was significantly lower and CD206MHCII correspondingly higher in Inha testes. This shift in expression of MHCII in CD206 macrophages indicates that changes in circulating and/or local activin A influence resident macrophage activation and phenotype and, therefore, the immunological environment of the testis.