Differences in number and activity of peripheral natural killer cells in primary versus secondary recurrent miscarriage

To compare peripheral natural-killer (NK) cell numbers and activity in women with primary recurrent miscarriage, secondary recurrent miscarriage and controls. Observational study. Academic medical center. Thirty-eight women with primary recurrent miscarriage, 29 women with secondary recurrent miscarriage, and 25 control women. None. [1] The proportion of NK cells in the total lymphocyte population, [2] the concentration of NK cells per microliter of blood, and [3] NK activity (NKA), using both standard and whole-blood assays. Primary aborters had the highest proportion and concentration of NK cells and had the highest activity using the standard assay. Secondary aborters had an intermediate level of these NK cell indices, whereas the control patients had the lowest levels. Using the whole-blood NKA assay, the differences between primary and secondary aborters were most apparent: primary aborters had significantly higher NKA than did either secondary aborters or control women (72, 40, and 35 lytic units, respectively). Approximately 50% of the variability in NKA could be attributed to differences in concentrations of NK cell per microliter of blood. The higher NKA evident in primary recurrent miscarriage and the reported higher efficacy of immunotherapy in primary aborters support the involvement of NK cells in the etiology of primary recurrent miscarriage.