Popular myths in reproductive immunology.

According to Mark Twain, "It ain't what you don't know that gets you into trouble. It's what you know for sure that just ain't so." Four items believed by reproductive immunologists are analyzed. (1) In a semiallogeneic (outbred) mating, maternofetal tolerance is required to prevent immune rejection manifesting as infertility, recurrent pregnancy loss, preeclampsia and fetal growth restriction. (2) Regulation of natural killer (NK) cells at the fetomaternal interface by interaction with fetal trophoblast paternal class I MHC is obligatory for pregnancy success. (3) Failure of angiogenesis triggered by complement activation is a key mechanism in pregnancy pathology. (4) Randomized controlled (double-blind) clinical trials and systematic reviews exemplified by the Cochrane database provide reliable evidence on which to base treatment and promulgate guidelines. Those who heed not the lessons of history are doomed to repeat the same mistakes in the future. History shows that we do this and expect a different outcome.