ENDOTOXIN-INDUCED ABORTION IN MICE IS MEDIATED BY ACTIVATED FETAL MACROPHAGES

Leukocyte numbers and function were assessed in uterus, placenta, and fetus during endotoxin-induced abortion, Tissues initially contained h igh numbers of macrophages hut no granulocytes or lymphocytes. Endotox in treatment resulted in rapid, transient neutrophil accumulation in u terus and placenta, Moderate increases in macrophage numbers occurred in tile uterus but there were no changes in tissue distribution., Myom etrial, endothelial, and epithelial cells were unaffected by endotoxin but proliferating, differentiated fibroblasts that made up the primar y decidua disappeared, As abortion progressed, the proportional repres entation of macrophages in placenta and embryo increased until, during the late stages of fetal resorption, they constituted nearly all viab le fetal cells. At the same time, overall expression of class II major histocompatibility complex gene products increased in maternal and fe tal tissue, Leukocyte distribution and macrophage activation data sugg ested that endotoxin-induced fetal failure is mediated hg products of activated maternal and fetal macrophages acting in concert to destroy actively proliferating maternal and fetal cells.