Elevated Serum Levels in Humanpregnancy of a Molecule Immunochemically Similar to Eosinophil

In 1956 Gansler (1) observed infiltration of the rat uterus by eosinophils coincident with the estrus cycle . This observation was confirmed and extended by the work of Bassett (2) and Ross and Klebanoff (3) . Since then, various investigations have shown (a) that injection of estrogen into castrated or immature rodents leads to immediate uterine eosinophilia (4-10), (b) that the uterine eosinophil is marrow derived (11), (c) that the uterine eosinophil number varies >100-fold during the normal estrus cycle (12), (d) that uterine content of eosinophil peroxidase varies directly with the estrus cycle (13, 14), (e) that eosinophils possess a unique cell surface estrogen receptor (4-9), and (f) that estrogen-induced uterine eosinophilia apparently has no dependence upon uterine mast cell activity (15-18). In contrast, there are few observations relating eosinophils to human reproductive physiology . Cyclic eosinopenia correlating with ovulation has been reported (19-21) and cyclic variations in endometrial eosinophils and their uptake of tritiated estradiol have also been observed (22) . However, no role for the eosinophil in normal human reproduction is presently recognized . During the course of studies of hypersensitivity diseases in pregnancy we found that serum levels of a molecule immunochemically similar to the eosinophil granule major basic protein (MBP)' were elevated in all pregnant women, increasing during pregnancy and decreasing to normal levels after parturition . Because eosinophilia is not a feature of normal pregnancy, and serum levels of other eosinophil proteins are not elevated, the results of this study suggest that the immunoreactive MBP in pregnancy serum is derived from a source other than the eosinophil .