The Lymphatic System in Endometriosis: a Pilot Study of Endometrial-Like Cells and Immune Cell Populations in Lymph Nodes Associated with Deep Infiltrating Bowel Lesions

In endometriosis, the lymphatic and immune systems are implicated in disease establishment and progression. The objective of this pilot study was to examine endometrial-like, and for the first time, immune cell populations in lymph nodes associated with deep infiltrating endometriosis (DIE) bowel lesions. Premenopausal women undergoing excision of endometriosis and/or hysterectomy were included. DIE bowel lesion-associated (n = 10) and other pelvic (n = 15) lymph nodes were studied. Samples were immunohistochemically stained for endometrial-like cells (CD10), T cells (CD3, CD4, CD8, and FoxP3), dendritic cells (DC; DC-Lamp and DC-Sign), B cells (CD20, CD79 and plasma), macrophages (CD68), and natural killer cells (NK; CD57). Cell abundance (percentage positive area) and antigen expression (optical density; OD) were quantified. Endometrial-like cells and each immune cell population were present in all studied nodes. The DIE bowel lesion-associated nodes showed features of immune activation, with T cell proliferation (CD3+ area p = 0.007, CD4+ area p = 0.015 compared with other pelvic nodes); and a mixture of helper and regulatory T cells, B cells, DCs, macrophages, and plasma cells present in the paracortex. In DIE bowel lesion-associated compared with other pelvic nodes, CD10+ endometrial-like cells were reduced (percentage positive area p < 0.001, OD p = 0.004). This study provides new insight into lymphatic and immune system involvement in advanced endometriosis. In particular, we have shown evidence of immune activation in DIE lesion-associated nodes. This was despite lower endometrial-like cell numbers compared with other pelvic nodes. The observations contribute to a developing understanding of the local immune response to advanced disease.