Maturation of human ovarian follicles is accompanied by a decrease in the CD56+CD16+ natural killer cell population.

ABSTRACT

OBJECTIVE: To investigate whether "proangiogenic" CD56+CD16- natural killer (NK) cells, which accumulate in follicular fluid (FF) of patients with a good response to ovarian stimulation, are also present in earlier stages of follicular development. DESIGN: Observational study. SETTING: Academic in vitro fertilization (IVF) unit. PATIENT(S) Patients of similar age and ovarian reserve, undergoing in vitro maturation (IVM; n=10) or IVF (n=22) cycles. INTERVENTION(S) None. MAIN OUTCOME MEASURE(S) FF was collected from the first follicle aspirated in each ovary, and flow cytometry was used to define CD56+CD16- "proangiogenic" or CD56+CD16+ "cytotoxic" NK cells. RESULT(S) FF derived from antral follicles of patients undergoing IVM (maximum diameter 10 mm) showed a slightly higher abundance of "proangiogenic" NK cells compared with FF from preovulatory mature follicles (>18 mm) of patients undergoing IVF (5.4±1.3% vs. 3.0±1.1% of CD45+CD3- cells). Importantly, antral FF contained a significantly higher concentration of "cytotoxic" NK cells (11.4±2.3% vs. 3.7±0.9% of CD45+CD3- cells) compared with FF from mature follicles. CONCLUSION(S) "Proangiogenic" NK cells accumulate in ovarian follicles from as early as the antral follicular stage. Maturation of follicles is accompanied by a decrease in the population of "cytotoxic" NK cells that may have deleterious effects on follicular maturation.