Making themselves scarce: immune cells in the ovary

RESEARCH QUESTION: In human and animal reproduction, the majority of the ovary's reproductive potential is lost before puberty. In order to survive, oocytes must interact with stromal cells. However, the specific distribution and role of ovarian immune cells compared to lymphatic organs is still indistinct. DESIGN: Immune cell composition in the ovary, spleen, and lymph nodes was analyzed in six-week-old female C57BL/6 mice using flow cytometry. The following populations were examined: macrophages, dendritic cells, natural killer cells, NKT cells, B cells, T cells, CD4 + T cells and CD8 + T cells. RESULTS: Only 3% of the cells that make up the ovary are immune cells. Ovarian immune cells consisted of natural killer cells (24%), T cells including CD4+- and CD8 + T cells (21%), macrophages (17%), dendritic cells (7%), NKT- and B cells (each 11%). In contrast, spleen and lymph nodes were dominated by B and T cells (spleen: 56% and 32%; lymph nodes: 33% and 62%). CONCLUSIONS: Ovarian immune cells are scarce in healthy young mice. Apart from a relatively large T-cell population, the ovarian immune compartment is dominated by innate immune cells, particularly macrophages and natural killer cells, which is in line with the multifarious role of macrophages in multiple aspects of ovarian physiology. In contrast, adaptive immune cells such as B and T lymphocytes are primarily enriched in secondary lymphoid organs, including the spleen and lymph nodes.