The 'killer cell story' in recurrent miscarriage: Association between activated peripheral lymphocytes and uterine natural killer cells

Peripheral and uterine NK cells (pNK, uNK) can be distinguished according to their receptor expression. Recent studies indicate an association of elevated pNK and uNK with recurrent miscarriage (RM). This study aimed to analyze pNK and uNK in patients with RM and healthy controls. Out of n=590 RM patients screened according to a standard diagnostic protocol, n=268 couples with ≥3 consecutive RM were identified. Subgroups consisted of n=151 primary RM (pRM), n=85 secondary RM (sRM), n=32 tertiary RM (tRM) and n=42 healthy controls. Finally, n=147 idiopathic RM (iRM) and n=121 non-iRM patients were identified. Peripheral blood levels of CD45+CD3-CD56+CD16+ NK cells were determined in non-pregnant patients and controls in the mid-luteal phase by FACS. In n=129 RM patients a uterine biopsy was taken to evaluate CD56+ NK cells by immunohistochemistry. PRM showed higher absolute pNK than sRM (median/μl (Q1;Q3): 234 (147;306) vs 176 (128;245), p=0.02). Further a trend towards higher pNK percentages in pRM was detected. UNK numbers did not differ between RM subgroups and did not correlate with pNK. However, the rate of highly elevated uNK was increased in iRM compared to non-iRM patients (p=0.04). Further, higher numbers of CD45+CD3-DR+ (p