Association of monocytes and neutrophils with early events of blastocyst implantation in mice.

The distribution and activation of monocytes and neutrophils in the mouse uterus were examined early in the process of blastocyst implantation. Implantation regions, detected by increased capillary permeability at sites of blastocyst apposition to the uterine luminal epithelium, could be distinguished at about 21:00 h on day 4 of pregnancy (day 1 = day of vaginal plug), and were also examined at 01:00, 05:00 and 09:00 h on day 5. Serial sections containing the implanting blastocyst (implantation sites), and random sections of inter-implantation regions were examined by immunohistochemistry using interleukin-1 beta as a marker for monocytes-macrophages and lactoferrin as a marker for neutrophils in the uterine stroma. At implantation sites, interleukin-1 beta-positive cells were transiently abundant within endometrial capillaries. In interimplantation regions only a few interleukin-1 beta-positive cells were dispersed at the myometrial-stromal junction. Northern blot hybridization to RNAs from implantation and interimplantation regions showed that the abundance of interleukin-1 beta and interleukin-1 alpha mRNAs was much lower than that found in the uterus during acute inflammation. However, these cytokine mRNAs were more abundant in implantation regions. On the evening of day 4 and the early morning of day 5, lactoferrin-positive neutrophils were detected juxtaposed to the basolateral surface of the antimesometrial epithelial cells surrounding the implanting blastocyst. They were primarily at the myometrial-stromal junction in interimplantation regions. Metallothionein gene expression was examined as a marker for uterine responses to inflammatory reactions.(ABSTRACT TRUNCATED AT 250 WORDS)