Type I Interferons and Their Role in Maternal Recognition of Pregnancy and Fecundity in Domestic Ruminant Species
Recently it has become evident that molecules that were originally identified as being involved in the growth and differentiation of leukocytes are also implicated in several facets of the reproductive process. For example, colony-stimulating factor-1 (CSF-1), granulocyte-macrophage colony-stimulating factor (GM-CSF), and the related leukemia inhibitory factor (LIF) and interleukin-6 (IL-6) are all produced by uterine epithelial cells during early pregnancy of the mouse in response to steroid hormones (1-4). Of these, CSF-1 is particularly abundant (5), and its absence, e.g., in the osteopetrotic op/op mouse, leads to early pregnancy failure (6). Similarly, blastocysts fail to implant in mice lacking the LIF gene unless the cytokine is provided by injection (7). It is also clear that the conceptus itself, even before it implants, evokes what resembles an inflammatory response in the neighboring uterine endometrium (8), yet evades all attempts at rejection by the maternal immune system. How this escape occurs is unclear, but presumably it involves the release of substances, including 216cytokines, that modulate in a selective manner immune cells in the immediate locality of the implantation site.