Dados do Trabalho

Title

Alloimmune abortion and the immunopathological mechanisms through a literature review.

Objective

Perform a literature review on what alloimmune abortion is and what specific characteristics can cause alloimmune abortion.

Methods

For this review, searches were conducted using Pubmed, Google Scholar, and Scielo, using the keywords: 'alloimmune abortion,' 'in vitro fertilization,' and 'assisted reproduction.' The research criteria included selecting articles in both English and Portuguese, published between the years 2004 and 2022.

Results

Abortion is a public health problem and one of the leading causes of maternal morbidity and mortality (MARIUTTI, 2009). Abortions are considered cases occurring before 20 weeks of gestation, with the fetus measuring less than 16 centimeters and weighing less than 500 grams (MINISTRY OF HEALTH, 2005). There are different types of abortions, such as chemical abortions resulting from abortive medications, and spontaneous abortions resulting from organic disorders that occur in the second or third month of pregnancy (MARIUTTI, 2009). Alloimmune abortion falls under spontaneous abortions, characterized by recurrent cases, involving three or more consecutive spontaneous losses and representing approximately 40% to 60% of spontaneous abortion cases (CAETANO, 2006).
There is a difference between autoimmune factors and alloimmune factors. Autoimmune factors are correlated with the action of autoantibodies in the presence of the embryo, influenced by autoimmune factors such as anti-thyroglobulin (TGO) and anti-nuclear factor (FAN). On the other hand, alloimmune factors are correlated with maternal rejection due to the presence of paternal genetic material from the embryo, with Natural Killer cells (NK) being involved as alloimmune factors. Alloimmune abortion is a result of blastocyst implantation, leading to a highly complex and specialized immune response involving both the embryo and the endometrium (THIENGO). The blastocyst is covered by the trophoblast, a cellular layer responsible for the formation of the embryonic placenta (MOORE and PERSAUD, 2008). The trophoblast acts as a semi-allograft, as a part of the genetic material comes from the father, which is unknown to the maternal immune system, increasing the chances of rejection. Some of the immune mediators involved are cytokines, and the maternal endometrium expresses cytokines essential for blastocyst implantation. Trophoblastic cells express human leukocyte antigens (HLA), ensuring maternal-fetal immunotolerance by interacting with NK cells. HLA-G plays a vital role in preventing cell lysis induced by NK cells by interacting with inhibitory death receptors (KIRs), preventing NK cell activation (THIENGO). Recent studies have indicated a correlation between Natural Killer cells (NK) and alloimmune abortion (NIEKERK, 2013). Some studies associate a high concentration of NK cells in the endometrium and peripheral blood with a higher risk of recurrent abortion, while other results suggest that patients undergoing in vitro fertilization (IVF) with a history of recurrent abortion should be investigated for the presence of factors associated with loss. IVF could reduce recurrent abortion cases by up to 29% (BILIBIO, 2020).

Conclusion

Alloimmune abortion is one of the main causes of spontaneous abortion, but it still requires further study as its causes are not yet fully understood. The most probable cause is the presence of NK cells that cause cell lysis, contributing to the failure of blastocyst implantation. IVF is a method that needs further improvement to ensure better results in blastocyst implantation, as one of the reasons for IVF failure is the maternal immune response's deficiency, affecting processes from blastocyst nidation to placental formation, thus preventing the progression of pregnancy. This indicates that it is essential to study the mechanisms of immune-modulatory tolerance that occur in natural gestation to replicate them in assisted reproduction.

Keywords

alloimmune abortion; in vitro fertilization; assisted reproductive