Development of conventional, but not tissue resident NK cells requires pH-controlling vacuolar a2v-ATPase

Abstract

Abstract Innate lymphoid cells are abundant in uterine endometrium and their number dramatically increases during pregnancy. In addition to conventional NK (cNK) cells, unique uterine-specific NK cells populate the uterus. These, tissue-resident NK (trNK) cells are characterized by CD49a expression. A2v-ATPase is a proton pump molecule that acidifies intracellular vesicles and is critical in processing of Notch receptors. A knockout of a2v- ATPase in VAV-1 expressing cells (cells of hematopoietic origin) leads to dramatic reduction of NK cells in blood and spleen of the genetically modified animal (a2vKO mouse). Uterine tissues of a2VKO mice were analyzed for NK cell presence based on their reactivity with the lectin DBA. DBA-reactive cells were readily observed in uterine stroma of pregnant a2vKO mice. Although the number of DBA+ cells in a2vKO mice was lower than in wild type (WT) controls, the difference was not statistically significant. Flow cytometry analysis of uterine tissues from virgin a2vKO mice revealed a dramatic decrease of cNK cells (NK1.1+NKp46+CD11b−/lowDx5+CD49a−). However, the frequency of trNK cells, that possess phenotype NK1.1+NKp46+CD11b−Dx5−/+CD49a+, was comparable with what was found in WT. Similar findings were observed in pregnant a2vKO mice. Despite the absence of cNK cells that compose a significant proportion of lymphocytes in pregnant uterine tissue, mice fertility was not critically affected and this suggested a role for trNK cells in supporting pregnancy. In conclusion, the development of NK cells that takes place in endometrium appears to be different from NK cells originated in bone marrow, namely it is not dependent on a2vATPase; this can explain uniqueness of trNK cells.