Biology of Reproduction, Vol 12, 498-503, Copyright © 1975 by Society for the Study of Reproduction

Mouse Uterine Antigens in the Implantation Period of Pregnancy

¹ Institute for Cancer Research, Fox Chase, Philadelphia, Pennsylvania 19111

Mouse uterus was analyzed for immunologically specific proteins in the early implantation period (Day 3 of pregnancy in the BALB/c strain). Antiserum was produced in rabbits, absorbed with plasma and other tissues, and subjected to Ouchterlony double diffusion precipitin tests against 16 non-uterine tissues and against uterus from other stages of pregnancy. At least 10-11 soluble antigens were detectable in homogenates of Day 3 pregnant mouse uterus by these methods. Most of the antigens are shared by plasma or are found in non-reproductive tissues, but two uterine antigens are shared only with duodenum. One of the two (designated Band I) may be a uterus-specific product as it is serologically related to, but not identical with, the corresponding duodenal antigen; it shows greatest intensity on Days 3 and 4 of pregnancy. The other (Band II) seems identical in both tissues and decreases as pregnancy progresses. These results are considered in light of our previous observations that the mouse uterus secretes a proteolytic enzyme with peak activity on Day 3 of pregnancy and with an apparent role as an implantation-initiating factor (IIF) causing blastocyst attachment to the uterine wall. The antigens demonstrated in Bands I and II may thus be proteolytic components in uterus and duodenum. The data are consistent with the possibility that the uterus-specific antigen represented by Band I may be the proteolytic IIF and may have a partial relatedness to a proteinase found in the intestine.