Why A Woman Would Not Reject Her Foetus Biology Essay

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Rejection of foetus by the mother is a common disorder characterised by imbalances in pregnancy hormones or mainly problems with the mother's immune system that occurs three out of every ten pregnancies. Survival of species relies on a crucial factor which is: elimination of microbial pathogens while at the same time, guarding foetuses from immune rejection of mother. Recently, researchers have shown an increased interest in the Complement system and T lymphocytes cells that play a key role in immune system. The complement system consists of 20 different protein molecules that are flooding in blood in inactive form which, secure the body against pathogen and any other form of foreign cells. With an infection complement system activated, leading to Membrane Attack Complex (MAC) that helps to eliminate the infection. T lymphocytes cells (T cells) are a branch of white blood cells that contains a specific receptor on their cell surface. T-cells also destroy the infectious in body. There are different types of T-cells that are fighting with infectious in different ways. This paper begins by addressing the autoimmune disease that can affect foetus rejection, it will then go on to the mechanisms that have been suggested which how foetus evade from the mother's immune system.

The term Systemic Lupus Erythematosus (SLE) is generally understood to mean as a chronic systemic autoimmune disease that can affect any part of body's cell, resulting in tissue damage. It is hard to predict SLE during pregnancy but it can worsen after postpartum. Complications can be restriction in foetal growth and congenital heart block due to maternal antibodies that cross the placenta.

It is becoming increasingly difficult to ignore the Lupus as systemic diseases that result from an autoimmune mechanism that have influence on foetus rejection. Individuals with lupus produce antibodies to their own body tissues. Lupus has been identified one of contributing factors for the miscarriage while many patients with this disease have successful pregnancies. ''It has been discovered that women with lupus disease, have a substance in their blood that affects the test that can use for measuring the ability of the blood to clot by prolonged certain type of coagulation test. Patients who had this substance in their blood when tested, they behaved as if they were taking anti-coagulate ''.[5] Scientists have suggested that women who have autoimmune disorder, the blood clots form under the placenta and affect the growth and development of pregnancy. It has also been found that the mother's immune armament during pregnancy shifts to Th2-type responses (i.e. those geared towards antibody-mediated immune reactions) rather than Th1-type responses (those geared towards cell-mediated immunity) that is why systemic lupus during pregnancy becoming worse. Investigations have shown that creating Th1-type cytokine environment, led to foetal los in pregnant mice while Th2-type environment had positive effect on the foetus's well-being.

Immune system cells have been differentiated to protect body against foreign pathogens. Immune system achieve this task by distinguish body's own antigens as self and other antigens as non-self. Autoimmune reaction is the failure of an organism to recognise its own cells as self that leads immune system to response against its own cells. Theoretically the mother's immune system should detect foetus as non-self and reject that because half of the genetic makeup is from father and is foreign to the mother's immune system. However there are limits to how far the concept of immunity's pregnant pause can be taken but to date various suggestions have been developed and introduced to explain the ability of foetus to evade the mother's immune system. ''First, the mother's generally immune-suppressed state during pregnancy may help cushion the foetus from any serious immunological response. Second, the immune cells of the mother may undergo tolerance to foetal antigens in a similar manner to that in which they acquire tolerance to self antigens. Third, an anatomic barrier around the foetus may be present that prevents the maternal immune cells from reaching foetal tissues and afflicting harm. Fourth, foetal cells might somehow be able to suppress the expression and presentation of their own antigens, preventing the immune system from detecting the foetus. The fifth possible mechanism involves the creation of a local area of immune suppression around the foetus.''

A relationship exists between trophoblasts and the mother's immune system. Trophoblast is the separating layer between mother and foetus.[4] It has been found that murine trophoblast cells resist lysis by CD8+ T cells whereas foetal fibroblasts do not. That is the cause of some support for the existence of trophoblast. One other possibility for foetus to evade from the mother's immune system is down- regulate its antigens to avoid immune detection by mother.[3] It has been shown that trophoblast cells in contact with the maternal circulation do not express either Major Histocompatibility Complex (MHC) class I or MHC class II molecules.

It has been observed that foetal tissue transplanted to the mother is rejected as quickly as organ allograft. As foetal cells stimulate immune system responses, in the absence of placenta the mother's immune system is able to recognise and react to foetal antigens. ''Renal tissue removed from foetal rats at 15 days gestation and transplanted into major histocompatibility complex (MHC) disparate adults undergoes delayed rejection compared to foetal hepatic or cutaneous (skin) tissue from the same gestational age''.

Maternal T lymphocytes cells are capable to recognise and react to foetal antigens throughout pregnancy even in presence of placenta, however there is no reliable evidence that can support the effect of recognition and how it is controlled. [2]Previous studies have reported that peripheral blood cytotoxic CD8+ T cells are decreased in the first trimester of human pregnancy andCD4+ t cells are decreased in the third trimester, whereas both population increase 4 months postpartum. [1]Further studies suggested that T cells population in the spleen and para-aortic lymph nodes of mice are decreased during the first trimester of pregnancy.

This study has shown that the mother's immune system play a crucial role in survival of the species. These findings suggest in general that acceptation or rejection of foetus occurs by the mother's immune system. The second major finding was that in absence of placenta, the mother's immune system is capable to recognize the foetus and react with that. We are still unclear how the placenta can cope with the immune system and help the foetus to evade the mother's immune system. It has been suggested that there are five main mechanism that foetus can evade from the mother's immune system. While various degrees of evidence exist in support of each of these arguments, no single explanation has emerged to fully account for this phenomenon.


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