Natural killer cells in normal pregnancy: analysis using monoclonal antibodies and single-cell cytotoxicity assays.

Peripheral blood lymphocytes (nylon wool non-adherent) from healthy pregnant women and normal non-pregnant females were tested for natural killer (NK) cell-mediated cytotoxicity against K562 target cells both by 51Cr-release assay and single-cell cytotoxicity assay in agarose. The results indicated depression of NK cytotoxicity in pregnancy due to a decrease in the proportion of target-binding lymphocytes as well as a reduction in the lytic capacity of target-bound cells. The ability of active pregnancy-associated NK lymphocytes to recycle appeared to be unimpaired. Analysis of lymphocyte populations with monoclonal antibodies recognizing NK cell-associated antigens showed that the number of Leu-11+ lymphocytes was reduced in pregnancy. Enumeration of Leu-7+ cells and correlation of NK cell subpopulation data with cytotoxicity assay data suggest that pregnancy is associated with a reduction in the number of mature NK cells and probably also an inhibition of post-binding lytic activity.