Natural killer cells in the nonpregnant murine uterus

Recent studies on the origin and function of the large granular cells that accumulate at implantation sites in the rodent uterus during pregnancy have shown that these cells are highly differentiated natural killer (NK) cells. These findings raise questions about the presence and regulation of NK cells in the normal, nonpregnant uterus. For example, do NK cells comprise a major or minor population of leukocytes in the uterus? Are these uterine NK cells (uNK) similar in phenotype and function to NK cells in other organs? Is the population of uNK cells maintained by local proliferation and/or by influx via the blood stream from the bone marrow? This brief review will examine our current understanding of those questions based on the experimental literature on rodents and our own recent studies.