Developing mammary terminal duct lobular units have a dynamic mucosal and stromal immune microenvironment

Abstract

The human breast and ovine mammary gland undergo a striking degree of postnatal development, leading to formation of terminal duct lobular units (TDLUs). In this study we interrogated aspects of sheep TDLU growth to increase understanding of ovine mammogenesis and as a model for the study of breast development. Mammary epithelial proliferation is significantly higher in lambs less than two months old than in peri-pubertal animals. Ki67 expression is polarized to the leading edge of the developing TDLUs. Intraepithelial ductal macrophages exhibit striking periodicity and significantly increased density in lambs approaching puberty. Stromal macrophages are more abundant centrally than peripherally. The developing ovine mammary gland is infiltrated by intraepithelial and stromal T lymphocytes that are significantly more numerous in older lambs. In the stroma, hotspots of Ki67 expression colocalize with large aggregates of lymphocytes and macrophages. Multifocally these aggregates exhibit distinct organization consistent with tertiary lymphoid structures. The lamb mammary gland thus exhibits a dynamic mucosal and stromal immune microenvironment and, as such, constitutes a valuable model system that provides new insights into postnatal breast development.

Development and Pathology of the Equine Mammary Gland

“…De-paraffinisation and antigen retrieval were performed using Agilent Envision Flex Target Antigen Retrieval Solution High pH (Agilent Technologies LDA UK Limited, Life Sciences and Chemical Analysis Group, Lakeside, Cheadle Royal Business Park, Stockport, Cheshire) in an Agilent PT link pre-treatment module (Agilent Technologies LDA UK Limited) for 20 min at 90°C. Standard protocols for immunofluorescence were followed [151].…”

In the murine and bovine maternal mammary gland signal transducer and activator of transcription 3 is activated in clusters of epithelial cells around the day of birth

“…The mammary gland exhibits extensive postnatal development [1][2][3]. Signal Transducers and Activators of Transcription (STATs) are classically activated by phosphorylation, and play key roles in regulating this development [4].…”

“…We have previously utilised spatial statistical analyses (Getis-Ord GI*) to demonstrate mammary congregation of positive immunohistochemical events [2]. In this study we performed a similar spatial analysis, adopting a local colocation quotient metric (LCQ) and further refining the image analysis by removal of the spaces created by the mammary ductular and alveolar lumina, where positive events cannot occur.…”