The cytokine network during embryo implantation.

Embryo implantation is an essential step in mammalian pregnancy. The molecular events of embryonic attachment to the endometrial epithelium and the subsequent invasion of the stroma have long been of interest. The process involves both the scientific interest of reproductive biologists and clinical interest of physicians that care for infertility couples. Understanding the molecular factors involved in each phase of the implantation process is critical to comprehending the mechanisms that control reproduction, especially as part of a human in vitro fertilization program. This review will focus on the role during early embryonic development and implantation of two distinct cytokines, the interleukin-1 (IL-1) system and interleukin-18 (IL-18) system; it will also examine the role of the matrix metalloproteinases (MMP) and their inhibitors as well as vascular endothelial growth factor (VEGF) system. The possible influence of the cytokines on other systems involved in embryonic implantation, including the embryonic-endometrial dialogue, the subsequent invasion and neoangiogenesis will be discussed. These suggest a role for the two cytokine families in early embryonic development.