Macrophages in human uteroplacental tissues: a review.

Macrophages are major cellular components of the uterus, the placenta, and the extra-placental membranes throughout pregnancy. Many macrophages in normal uteroplacental tissues are in an activated state as evidenced by their expression of class II major histocompatibility antigens. Activated macrophages are capable of synthesizing and releasing an impressive array of potent "monokines" and other molecules with dramatic effects on receptive cells. Macrophage activation levels can be further enhanced by exposure to either endotoxin from gram-negative organisms or to interferon-gamma from stimulated lymphocytes. Since prostaglandin E2 is one of the products of activated macrophages and can stimulate contraction of smooth muscle, macrophages may be responsible in part for the induction of preterm labor in cases of infection. Thus, understanding the conditions of uncomplicated pregnancy as well as the consequences of local infections requires exploration of the temporal, spatial, and functional characteristics of macrophages residing in uteroplacental tissues.