The effect of normal and rheumatic pregnancy sera on intracellular cathepsin B activity in human monocytes.

In a prospective study of pregnant patients with rheumatic disease and healthy pregnant women, the effect of pregnancy serum on human blood monocytes was investigated. Intracellular activity of the collagen degrading enzyme cathepsin B was found to be significantly depressed in monocyte cultures exposed to pregnancy and cord sera, independent of the presence or absence of an inflammatory state in the pregnant woman. Enzyme inhibition developed in a dose-dependent fashion over 3 days in culture. In contrast to cord and pregnancy sera, non-pregnant serum and serum from oral contraceptive users displayed enzyme stimulating activity. The response of monocytes to the stimulating agent carrageenan was unaffected by inhibitory sera. The nature of possible inhibitory factors in pregnancy and cord serum is discussed.