Murine peripheral NK-cell populations originate from site-specific immature NK cells more than from BM-derived NK cells

Murine NK cells can be divided by the expression of two cell surface markers, CD27 and Mac-1 (a.k.a. CD11b), into four separate subsets. These subsets suggest a linear development model: CD27^- Mac-1^- → CD27⁺ Mac-1^- → CD27⁺ Mac-1⁺ → CD27^- Mac-1⁺. Here, we used a combination of BrdU labeling experiments and mathematical modeling to gain insights regarding NK-cell development in mouse bone marrow (BM), spleen and liver. The modeling results that best fit the experimental data show that the majority of NK cells already express CD27 upon entering the NK-cell developmental pathway. Additionally, only a small fraction of NK cells exit the BM to other sites, suggesting that peripheral NK-cell populations originate from site-specific immature NK cells more than from BM-derived mature NK cells.