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

The human breast and ovine mammary gland undergo striking levels of postnatal development, leading to formation of terminal duct lobular units (TDLUs). Here we interrogate aspects of sheep TDLU growth as a model of breast development and to increase understanding of ovine mammogenesis. The distributions of epithelial nuclear Ki67 positivity differ significantly between younger and older lambs. Ki67 expression is polarised to the leading edge of the developing TDLUs. Intraepithelial ductal macrophages exhibit periodicity and considerably increased density in lambs approaching puberty. Stromal macrophages are more abundant centrally than peripherally. Intraepithelial T lymphocytes are more numerous in older lambs. Stromal hotspots of Ki67 expression colocalize with immune cell aggregates that exhibit distinct organisation consistent with tertiary lymphoid structures. The lamb mammary gland thus exhibits a dynamic mucosal and stromal immune microenvironment and constitutes a valuable model system that provides new insights into postnatal breast development. Nagy et al. describe the histomorphogenesis of ovine mammary development in pre- and peri-pubertal sheep as a candidate model for human breast development. They investigate the locale and abundance of several immune cell types at different ages, highlighting this as a valuable model system that can provide new insights into postnatal breast development.

Automated summary

The research focuses on the growth of sheep TDLUs as a model for breast development, revealing differences in epithelial nuclear Ki67 positivity between younger and older lambs. The study also highlights a dynamic immune microenvironment in the sheep mammary gland, indicating its value as a model system for understanding postnatal breast development.