The regional distribution of resident immune cells shapes distinct immunological environments along the murine epididymis

Abstract

The epididymis functions as transition zone for post-testicular sperm maturation and storage and faces contrasting immunological challenges, i.e. tolerance towards spermatozoa vs. reactivity against pathogens. Thus, normal organ function and integrity relies heavily on a tightly controlled immune balance. Previous studies described inflammation-associated tissue damage solely in the distal regions (corpus, cauda), but not in the proximal regions (initial segment, caput). To understand the observed region-specific immunity along the epididymal duct, we have used an acute bacterial epididymitis mouse model and analyzed the disease progression. Whole transcriptome analysis using RNAseq 10 days post infection showed a pro-inflammatory environment within the cauda, while the caput exhibited only minor transcriptional changes. High-dimensional flow cytometry analyses revealed drastic changes in the immune cell composition upon infection with uropathogenic Escherichia coli. A massive influx of neutrophils and monocytes was observed exclusively in distal regions and was associated with bacterial appearance and tissue alterations. In order to clarify the reasons for the region-specific differences in the intensity of immune responses, we investigated the heterogeneity of resident immune cell populations under physiological conditions by scRNASeq analysis of extravascular CD45+ cells. Twelve distinct immune cell subsets were identified, displaying substantial differences in distribution along the epididymis as further assessed by flow cytometry and immunofluorescence staining. Macrophages constituted the majority of resident immune cells and were further separated in distinct subgroups based on their transcriptional profile, tissue location and monocyte-dependence. Crucially, the proximal and distal regions showed striking differences in their immunological landscapes. These findings indicate that resident immune cells are strategically positioned along the epididymal duct, potentially providing different immunological environments required for addressing the contrasting immunological challenges and thus, preserving tissue integrity and organ function.

Regulatory T cells play a crucial role in maintaining sperm tolerance and male fertility

“…However, the autoimmune inflammatory responses considerably aggravated 2 wk after Treg depletion, inducing severe autoimmune epididymitis and orchitis with a massive influx of F4/80 + and MHCII + MPs. These first immune defenders present high phagocytic and antigen-presenting activities and release cytotoxic mediators that amplify the immune responses ( 66 , 67 ). The role of MPs in the reproductive organs has been extensively studied by our group ( 11 , 12 , 68 ) and others ( 53 , 54 , 66 ) and represent one of the most abundant immune cell populations at a steady state in the epididymis ( 12 , 66 , 68 – 72 ).…”

“…These first immune defenders present high phagocytic and antigen-presenting activities and release cytotoxic mediators that amplify the immune responses ( 66 , 67 ). The role of MPs in the reproductive organs has been extensively studied by our group ( 11 , 12 , 68 ) and others ( 53 , 54 , 66 ) and represent one of the most abundant immune cell populations at a steady state in the epididymis ( 12 , 66 , 68 – 72 ). MPs are essential contributors to the pro-inflammatory responses after immunological tolerance ablation in other organs ( 73 – 75 ).…”

Segmental differentiation of the murine epididymis: identification of segment-specific, GM1-enriched vesicles and regulation by luminal fluid factors

“…Gene expression in these segments is tightly regulated, with differential expression between segments being greater than the difference between some distinct organs, such as the liver and kidney [13]. For example, significant differences exist among segments in terms of their immunological environments and responses [20][21][22][23]. In addition to being androgen dependent, epididymal development and segmental differentiation have also been shown to depend on other factors produced by the testes that are released into the luminal fluid.…”

Immunoregulatory mechanisms between epithelial clear cells and mononuclear phagocytes in the epididymis

“…The epididymis is a single convoluted duct that presents a high level of functional complexity. [1][2][3][4][5][6][7][8][9] It is organized into several segments with distinct key functions: the initial segments (IS), the caput, the corpus, and the cauda. Each segment possesses distinct gene expression profiles as well as discrete morphological features.…”

“…10,11,[15][16][17][18] This barrier is a critical structure for male fertility. 8,[19][20][21][22][23][24][25][26][27][28][29][30] The epididymis depends on a delicate and carefully regulated interaction between the endocrine and immune systems. What is unique and fascinating about this reproductive organ is its ability to produce and nurture spermatozoa that appear long after the establishment of self-tolerance without invoking a damaging immune response.…”