Increased NK activity is responsible for higher cytotoxicity to HEF cells by lymphocytes of women with threatened preterm delivery.

Recently we have shown that lymphocytes of pregnant women with threatened preterm delivery (risk group) exerted significantly higher cytotoxic activity to human embryonic fibroblast (HEF) cells than those of healthy pregnant women. The purpose of this study was to get information on the mechanism of this cytotoxicity. The possibility of prior sensitization to embryonic antigen was excluded, since no difference could be demonstrated between cytotoxic activity of lymphocytes obtained from women with two or more previous pregnancies and that of lymphocytes from never-pregnant women. For determining the effector cell type responsible for cytotoxicity, lymphocytes of 50 healthy pregnant women and those of 50 risk patients were tested in different cytotoxicity tests using HEF and K-562 target cells. The proportion of NK cells among lymphocytes was determined by counting large granular lymphocytes (LGL), IgG Fc receptor bearing cells, and cells positively stained by NK specific monoclonal antibody. Though no difference in the proportion of NK cells between the two groups was found, risk patients' lymphocytes were significantly more cytotoxic to K-562 target cells than those of healthy pregnant women. Investigations at the single-cell level made it obvious that this higher cytotoxic activity originated from increased target cell lysing ability of their lymphocytes, while their conjugating capacity did not differ significantly from that of lymphocytes obtained from healthy pregnant women.(ABSTRACT TRUNCATED AT 250 WORDS)