Region-specific transcriptomic and functional signatures of mononuclear phagocytes in the epididymis

Abstract

In the epididymis, prevention of autoimmune responses against spermatozoa and simultaneous protection against pathogens is important for male fertility. We have previously shown that mononuclear phagocytes (MPs) are located either in the epididymal interstitium or in close proximity to the epithelium. In the initial segments (IS), these ‘intraepithelial’ MPs extend slender luminal-reaching projections between epithelial cells. In this study, we performed an in-depth characterisation of MPs isolated from IS, caput–corpus and cauda epididymis of CX3CR1EGFP+/− mice that express EGFP in these cells. Flow cytometry analysis revealed region-specific subsets of MPs that express combinations of markers traditionally described in ‘dendritic cells’ or ‘macrophages’. RNA sequencing identified distinct transcriptomic signatures in MPs from each region and revealed specific genes involved in inflammatory and anti-inflammatory responses, phagosomal activity and antigen processing and presentation. Functional fluorescent in vivo labelling assays showed that higher percentages of CX3CR1+ MPs that captured and processed antigens were detected in the IS compared to other regions. Confocal microscopy showed that in the IS, caput and corpus, circulatory antigens were internalised and processed by interstitial and intraepithelial MPs. However, in the cauda only interstitial MPs internalised and processed antigens, while intraepithelial MPs did not take up antigens, indicating that all antigens have been captured before they reached the epithelial lining. Cauda MPs may thus confer a stronger protection against blood-borne pathogens compared to proximal regions. By identifying immunoregulatory mechanisms in the epididymis, our study may lead to new therapies for male infertility and epididymitis and identify potential targets for immunocontraception.

The Involvement of the Chemokine RANTES in Regulating Luminal Acidification in Rat Epididymis

“…In the epididymis, macrophages are widely distributed in different segments, exhibiting unique phenotypes and function to establish and maintain an appropriate environment for sperm maturation and storage (18,38,39). Epididymal macrophages can be divided into two subsets according to their distinguished appearances.…”

“…For example, in the small intestinal mucosal system (14,15), macrophages can stretch out their long protuberances to the intestinal lumen to monitor the luminal composition changes so as to regulate the absorption of nutrients and secretion of goblet cells by interacting with intestinal epithelial cells (16,17). Similar to the intestinal tract, macrophages in the initial segment of epididymis also extend long slender projections to the epididymal lumen to sample the fluid components in the lumen (18,19). Besides, there still exists another type of macrophages whose morphology is distinct from those with long projections, presenting basal round-like distribution in the distal segments of the epididymis (4).…”

Differential Immune Response to Infection and Acute Inflammation Along the Epididymis

“…Emerging evidence on cellular and molecular levels has resulted in the hypothesis that the epididymis is “a series of organs side-by-side” ( 9 ). This hypothesis is evidenced by particular region-specific characteristics in regards to (a) the composition of the epithelium ( 4 , 5 ), (b) the distribution and phenotype of resident immune cells subpopulations ( 10 – 13 ), and (c) differential gene expression profiles ( 1 , 2 , 14 , 15 ). In line with that, septae segregate different segments and have been demonstrated to function as diffusion barriers, possibly creating distinct interstitial microenvironments ( 16 , 17 ).…”

“…Different immune-cell populations, including heterogenous subsets of the mononuclear phagocyte (MP) system, T and B lymphocytes reside within the rodent epididymis ( 4 , 10 , 11 , 13 , 18 , 20 – 23 ). Two different T-cell populations [CD4 - CD8 - (DN) and γδ T cells] have been identified recently: DN T cells are more abundant within the caput while γδ T cells are evenly distributed throughout the entire epithelium and interstitium ( 11 ).…”

Pathomechanisms of Autoimmune Based Testicular Inflammation

“…Similar to the observed differential immune responsiveness in a model of acute bacterial epididymitis (85,86), the distally located cauda epididymidis and vas deferens show a severe immune reaction in EAO mice characterized by an upregulated expression of cytokines and immunomodulatory factors (Tgfb1, Ccl2, Il1b, Il10, Tnf, Foxp3, Ido1), immune cell infiltration, fibrosis and epithelial damage resulting in a loss of tissue integrity and subsequent aggregation of displaced spermatozoa within the interstitium (84). The proximal regions (initial segment and caput), in contrast, do not reveal histopathological alterations or an upregulated expression of cytokines, although these regions are more densely vascularized and harbor a high number of resident immune cells (87,88). It needs to be noted though that data on epididymal reactions in EAO models are very scarce and thus the underlying molecular pathomechanisms remain unknown.…”