Immune tolerance in pregnancy

Source: Wikipedia, the free encyclopedia.

Immune tolerance in pregnancy or maternal immune tolerance is the

spontaneous abortion.[1][2] It is studied within the field of reproductive immunology
.

Mechanisms

Placental mechanisms

The placenta functions as an immunological barrier between the mother and the fetus.

The placenta functions as an immunological barrier between the mother and the fetus, creating an immunologically privileged site. For this purpose, it uses several mechanisms:

  • It secretes
    parasitic nematodes to avoid detection by the immune system of their host.[3]
  • Also, there is the presence of small lymphocytic suppressor cells in the fetus that inhibit maternal cytotoxic T cells by inhibiting the response to interleukin 2.[2]
  • The placental
    natural killer cells, which otherwise destroy cells that do not express any MHC class I.[4] However, trophoblast cells do express the rather typical HLA-C.[4]
  • It forms a
    immunoevasive action was the initial normal behavior of the viral protein, in order to avail for the virus to spread to other cells by simply merging them with the infected one. It is believed that the ancestors of modern viviparous mammals evolved after an infection by this virus, enabling the fetus to better resist the immune system of the mother.[6]

Still, the placenta does allow maternal

immunoglobulin M type,[7] and therefore usually do not cross the placenta. Still, rarely, ABO incompatibility can give rise to IgG antibodies that cross the placenta, and are caused by sensitization of mothers (usually of blood type O) to antigens in foods or bacteria that are homologous to A and B antigens.[8]

Other mechanisms

Still, the placental barrier is not the sole means to evade the immune system, as foreign fetal cells also persist in the maternal circulation, on the other side of the placental barrier.[9]

The placenta does not block maternal IgG antibodies, which thereby may pass through the human placenta, providing immune protection to the fetus against infectious diseases.

One model for the induction of tolerance during the very early stages of pregnancy is the

CA125, and glycodelin-A
(also known as placental protein 14).

Regulatory T cells also likely play a role.[11]

Also, a shift from cell-mediated immunity toward humoral immunity is believed to occur.[12]

Insufficient tolerance

Many cases of

spontaneous abortion may be described in the same way as maternal transplant rejection,[2] and a chronic insufficient tolerance may cause infertility. Other examples of insufficient immune tolerance in pregnancy are Rh disease and pre-eclampsia
:

Pregnancies resulting from

placental pathology.[15] The local and systemic immunologic changes are also more pronounced than in normal pregnancies, so it has been suggested that the higher frequency of some conditions in egg donation may be caused by reduced immune tolerance from the mother.[15]

Infertility and miscarriage

Immunological responses could be the cause in many cases of infertility and

antinuclear antibodies
.

Antiphospholipid antibodies are targeted toward the

blood flow to the uterus.[16]

Antinuclear antibodies cause an inflammation in the uterus that does not allow it to be a suitable host for implantation of the embryo. Natural killer cells misinterpret the fetal cells as cancer cells and attack them. An individual that presents with reproductive autoimmune failure syndrome has unexplained infertility, endometriosis, and repetitive miscarriages due to elevated levels of antinuclear antibodies circulating.[16] Both the presence of antiphospholipids antibodies and antinuclear antibodies have toxic effects on the implantation of embryos. This does not apply to anti-thyroid antibodies. Elevated levels do not have a toxic effect, but they are indicative of a risk of miscarriage. Elevated anti-thyroid antibodies act as a marker for females who have T-lymphocyte dysfunction because these levels indicate T cells that are secreting high levels of cytokines that induce inflammation in the uterine wall.[16]

Still, there is currently no drug that has evidence of preventing miscarriage by inhibition of maternal immune responses; aspirin has no effect in this case.[17]

Increased infectious susceptibility

The increased immune tolerance is believed to be a major contributing factor to an increased susceptibility and severity of infections in pregnancy.

varicella.[18] Pregnancy does not appear to alter the protective effects of vaccination.[18]

Interspecific pregnancy

If the mechanisms of rejection-immunity of the fetus could be understood, it might lead to

References

  1. .
  2. ^ .
  3. ^ "Placenta 'fools body's defences'". BBC News. 2007-11-10.
  4. ^ Published: September 2003
  5. .
  6. ^ Luis P. Villarreal (Sep 2004). "Can Viruses Make Us Human?" (PDF). Proceedings of the American Philosophical Society. 148 (3): 314. Archived from the original (PDF) on 2005-03-02.
  7. ^ Magnetic immunodiagnostic method for the demonstration of antibody/antigen complexes especially of blood groups Archived 2012-02-29 at the Wayback Machine Yves Barbreau, Olivier Boulet, Arnaud Boulet, Alexis Delanoe, Laurence Fauconnier, Fabien Herbert, Jean-Marc Pelosin, Laurent Soufflet. October 2009
  8. ^ MSD manuals > Perinatal Anemia Last full review/revision Oct 2020
  9. PMID 18384774
    .
  10. ^ .
  11. .
  12. ^ Jamieson DJ, Theiler RN, Rasmussen SA. Emerging infections and pregnancy. Emerg Infect Dis. 2006 Nov. Available from https://www.cdc.gov/ncidod/EID/vol12no11/06-0152.htm
  13. ^ Robertson, Sarah. "Research Goals --> Role of seminal fluid signalling in the female reproductive tract". Archived from the original on 2012-03-29.
  14. PMID 12896827
    .
  15. ^ .
  16. ^
  17. .
  18. ^ .
  19. ^ Darwin's children LeVay, Simon. (1997, October 14). from The Free Library. (1997). Retrieved March 06, 2009