Pregnancy has historically been viewed as a conflict between mother and the fetus for survival. This traditional view is based on the fact that as 50% of the genetic information of the fetus is from the father, the maternal immune system sees the pregnancy as foreign and mounts an immune response to reject it. According to this outdated view, miscarriage and implantation failure after IVF result from an excessive immune response by the mother which leads to pregnancy failure.
However, there is NO evidence to support the concept of rejection, which from an evolutionary point of view makes no sense.
Instead, the contemporary view of reproductive immunology is that pregnancy far from being a battle between mother and fetus for survival is a co-operative venture between the two. The latest research indicates that miscarriage is due to a loss of ‘tolerance’ by the mother rather than an excessive immune response leading to rejection.
Natural Killer cells
Two types of Natural Killer (NK) cells have been of interest to those studying Infertility and Recurrent Miscarriage. Natural Killer cells in the blood and those in the endometrium (lining of the uterus). There are fundamental differences between Natural Killer cells found in the blood and those found in the endometrium. Blood Natural Killer cells are part of the ‘innate’ immune system. They play an key role in killing viruses and tumour cells. Uterine Natural Killer cells do NOT kill. Instead they produce chemical messengers which are important in implantation of the embryo and in establishment of a blood supply to the fetus.
Women with recurrent miscarriages and those with infertility and / or IVF failure are being offered NK cell testing and immune treatment based on the results of these tests. Is this justified? A recent systematic analysis of 22 studies reports that whilst blood NK cells numbers and activity are elevated in both women with miscarriages and those with infertility and IVF failure, there is NO relationship with pregnancy outcome. It concludes that NK cell analysis and immune therapy should be offered only in the context of clinical research.
A recent review (May 2015) co-authored by one of the first scientists to identify NK cells in the uterus again emphasises the lack of scientific evidence that suppressing uterine NK cells improves pregnancy outcome and cautions that both professionals and patients should very carefully evaluate the practice of immunomodulation to enhance pregnancy outcome.
Pingback: natural killer cells | Raj Rai - Consultant Obstetrician and Gynaecologist