Poster Presentation ESA-SRB 2023 in conjunction with ENSA

Quantification of mononuclear phagocyte populations in the mouse epididymis: regulation by activin and effects of sexual maturation (#385)

Rama Ravinthiran 1 , Rosemary Genovese 1 , Rukmali Wijayarathna 1 , Kate L Loveland 1 , Andreas Meinhardt 2 , Mark P Hedger 1
  1. Hudson Institute of Medical Research, Clayton, VIC, Australia
  2. Institute of Anatomy and Cell Biology, Justus-Liebig University Giessen, Giessen, Germany

The immunological environment of the epididymis constitutes a functional gradient from the caput through to the cauda, which correlates with regional differences in macrophage populations. The caput is dominated by resident macrophages with primarily immunoregulatory/anti-inflammatory properties that express the chemokine receptor CX3CR1 and the pan-macrophage antigen F4/80. In the cauda, macrophages lacking CX3CR1, with a pro-inflammatory phenotype, are more prominent. Since production of the immunoregulatory cytokine activin A is highest in the caput and lowest in the cauda, the relationship between activin and macrophage gradients was examined. Mice expressing a fluorescent transgene (Gfp) at the Cx3cr1 locus were crossed with mice heterologous for activin A (Inhba+/-) to produce transgenic littermates with either normal or low levels of activin A. Macrophage subsets were quantified by established stereological methods in adult and immature (56 and 25 day-old) mice by expression of CX3CR1-GFP and immunolocalisation of F4/80. Double-positive CX3CR1highF4/80+ macrophages were the largest epididymal subset. In the adult, their volume density and number was highest within the duct epithelium and interstitium of the caput (30-40,000 cells/mm3), and was significantly lower (15-20,000 cells/mm3) in the corpus and cauda. This subset was not substantially altered in activin-deficient mice. CX3CR1nullF4/80+ macrophages were predominantly localised to the interstitium, with higher volume density in the corpus and cauda (10-15,000 cells/mm3) than in the caput (4-5000 cells/mm3). In mice with reduced activin, the number of these cells increased approximately 2-fold within the interstitium in all regions. In the immature epididymis, however, the volume density of both macrophage subsets was evenly distributed across all regions. These data indicate that the differential macrophage gradient becomes established after sexual maturation and appearance of mature sperm. Activin suppresses the development or maintenance of the CX3CR1null pro-inflammatory population throughout the epididymis, but has no apparent effect on the number of CX3CR1+ immunoregulatory/anti-inflammatory macrophages.