A subset of CD56+ large granular lymphocytes in first-trimester human decidua are proliferating cells

Objective: To determine whether the unusually high number of CD56+ large granular lymphocytes (LGL) in the decidua of early human pregnancy arises from selective migration or in situ proliferation. Design: Controlled clinical study. Setting: Academic research environment. Patient(s): Thirty healthy women undergoing therapeutic abortion of an intact pregnancy at 5–11 weeks' gestation. Intervention(s): Decidua was obtained by suction curettage; tissue and isolated cells were subjected to immunohistochemical and flow cytometric investigation. Main Outcome Measure(s): Proliferation rate of LGL. Result(s): The proportion of CD56+ cells positive for the proliferation-associated Ki-67 antigen was found to be 7%–23.5% by three different methods of investigation. These findings are consistent with those of flow cytometric analysis of the nuclear phase, which revealed 6%–22% of the LGL nuclei to be in the phases S+G 2 +M. Conclusion(s): The various methods of investigation revealed marked proliferative activity in the LGL of early pregnancy decidua. This finding suggests that in situ proliferation may be responsible for the high density of these cells in the decidua.