Time-course analyses addressing the acquisition of DBA lectin reactivity in mouse lymphoid organs and uterus during the first week of pregnancy.

Terminal differentiation of uterine natural killer (uNK) cells is induced in humans and mice at the time of endometrial decidualization. In mice, commitment to this lineage is first recognized at gestation day (gd)5.5 when small, non-granulated lymphocytes in the mesometrial decidua basalis become histochemically reactive with the lectin Dolichlos biflorus agglutinin (DBA). Transplantation experiments in mice have shown that the self-renewing progenitors of uNK cells are present in peripheral rather than uterine tissues. While lymphoid tissues of virgin mice lack DBA lectin reactive putative uNK cell precursors or progenitors, peripheral organs have not been systematically examined in female mice during early pregnancy while the uNK cell population is becoming established. Here we report such a study in gd0.5-7.5 random bred mice. Only mesenteric lymph nodes showed a transient gain in DBA lectin reactive lymphocytes between gd0.5 and 4.5. These cells had cytoplasmic but almost no surface DBA lectin reactivity. This study indicates that the decidual environment is unique and locally promotes DBA lectin surface expression in terminally differentiating uNK cells.