Immunologic Implantation Dysfunction (IID)
Definition - What does Immunologic Implantation Dysfunction (IID) mean?
Immunologic implantation dysfunction is the failure of a transferred embryo to implant into the uterus due to an immunological cause. It represents a form of immunological infertility. The phenomenon is now being recognized and studied by the medical experts.
FertilitySmarts explains Immunologic Implantation Dysfunction (IID)
As soon as the process of implantation begins, the cells of the inner uterine lining, now referred to as the decidua, can interact with other cell types and modify the immune system. This decidual immune system has a potential to decide whether to accept the embryo or reject it via an immune attack. The process of acceptance of the embryo is referred to as alloimmune recognition whereas that of rejection is known as alloimmune implantation dysfunction or rejection.
Various factors may be responsible for this immune-based implantation failure.
- Uterine natural killer cells (aka uNK cells): These cells are different from the NK cells present in the blood that normally kill abnormal cells. However, uNK cells that populate the uterine lining at implantation are not efficient killers. Thus their name has wrongly driven the myth that uNK can kill the embryo and account for the reproductive failure in women with recurrent miscarriages and failed IVF cycles. With that said, because uNK cells do play a role in building up a healthy placenta, a defective placentation can increase the risk of miscarriage.
- An impaired function of the major histocompatibility complex (or MHC) genes may also contribute to implantation failure. Within 12 to 24 hours of the acceptance of a genetically competent embryo by the decidual immune system, the outer layer of the embryo known as trophoblast starts invading into the decidua. The trophoblast expresses specialized genes called MHC genes. These genes protect the placenta against NK cells, and thus, they may be essential for successful implantation.
- Similarly, autoantibodies, which are antibodies that develop against body’s own tissues, may also play a role in implantation dysfunction in IVF-embryo transfer. This process is referred to as autoimmune implantation dysfunction.