From initial segment to cauda: a regional characterization of mouse epididymal CD11c+ mononuclear phagocytes based on immune phenotype and function

Abstract

Successful sperm maturation and storage rely on a unique immunological balance that protects the male reproductive organs from invading pathogens and spermatozoa from a destructive autoimmune response. We previously characterized one subset of mononuclear phagocytes (MPs) in the murine epididymis, CX3CR1+ cells, emphasizing their different functional properties. This population partially overlaps with another subset of understudied heterogeneous MPs, the CD11c+ cells. In the present study, we analyzed the CD11c+ MPs for their immune phenotype, morphology, and antigen capturing and presenting abilities. Epididymides from CD11c-EYFP mice, which express enhanced yellow fluorescent protein (EYFP) in CD11c+ MPs, were divided into initial segment (IS), caput/corpus, and cauda regions. Flow cytometry analysis showed that CD11c+ MPs with a macrophage phenotype (CD64+ and F4/80+) were the most abundant in the IS, whereas those with a dendritic cell signature [CD64− major histocompatibility complex class II (MHCII)+] were more frequent in the cauda. Immunofluorescence revealed morphological and phenotypic differences between CD11c+ MPs in the regions examined. To assess the ability of CD11c+ cells to take up antigens, CD11c-EYFP mice were injected intravenously with ovalbumin. In the IS, MPs expressing macrophage markers were most active in taking up the antigens. A functional antigen-presenting coculture study was performed, whereby CD4+ T cells were activated after ovalbumin presentation by CD11c+ epididymal MPs. The results demonstrated that CD11c+ MPs in all regions were capable of capturing and presenting antigens. Together, this study defines a marked regional variation in epididymal antigen-presenting cells that could help us understand fertility and contraception but also has larger implications in inflammation and disease pathology.