What is NK?
NK cells, also known as natural killer cells, are lymphocytes that originate in the bone marrow. NK cells play an important role in the immune response to virus-infected cells, resistance to tumor formation, as well as play an important role in embryo implantation.
Regarding infertility in general and ventricular reimplantation in IVF and consecutive miscarriages in particular, there are two types of NK cells: peripheral NK and uterine NK
NK and recurrent IVF failure
The embryo's genes are different from the mother's genes, it only receives a quarter of the genetic capital from the mother. The embryo is therefore a hemi-allograft. As a result, immunologically, the embryo is a graft that is not compatible with the mother's immune system, and the embryo faces rejection. In other words, for the embryo to successfully implant, it is necessary and sufficient that it initiates an immunosuppressive process, to prevent the mother's body from rejecting the semi-heterozygous piece (embryo).
NK cells are the main immune cells found in the uterus. The number of NK cells will increase during the embryo transfer into the uterus for implantation. NK stimulates angiogenic factors and regulates embryonic invasion into the uterus. The number of NK cells begins to decrease at the 20th week of pregnancy and is at rest during the last stages of pregnancy.
Elevated numbers and activities of NK cells lead to increased secretion of toxicity, unregulated local immunity, embryo rejection, and endometrial degeneration.
In contrast, deficiency of NK cells, immunosuppressive cells, failure to secrete angiogenic cytokines leads to non-reception and adhesion of embryos to the uterus.
- NK testing includes peripheral blood tests and uterine biopsy to assess the number and activity of NK cells. Peripheral blood testing may be done along with a uterine biopsy.
- A biopsy of the uterus is performed by inserting a flexible catheter into the uterus, gently sucking on the uterine wall to remove a small amount of sample and send it to the laboratory. Uterine biopsies are performed in the luteal phase, on days 21 to 28 of the menstrual cycle.
(Ledee et al., 2017)
1, Quenby S, Farquharson R, Young M, Vince G. Successful pregnancy outcome following 19 consecutive miscarriages: case report. Hum Reprod. 2003;18(12):2562-
2, Tang AW, Alfirevic Z, Turner MA, Drury JA, Small R, Quenby S. A feasibility trial of screening women with idiopathic recurrent miscarriage for high uterine natural killer cell density and randomizing to prednisolone or placebo when pregnant. Hum Reprod. 2013;28(7):1743-52.
3, Othman MASSATNKSMAKJSA. P-249 Prednisolone improves implantation in ICSI patients with high peripheral CD69 + NK Cells2011.
Peripheral blood test: