TreatmentUpdate57, Vol. 7, No. 3 - March 1995
Sean Hosein

Researchers studying pregnancy have found a relationship between the mother's immune system and the placenta (the 'organ' that develops around the fetus). The placenta is rich in blood vessels from the mother and fetus so that the fetus can received oxygen and nutrients from the mother. In order for the fetus to survive, it must be protected from the mother's immune system. It appears that the placenta produces chemicals that alter the mother's immune system.

* CYTOKINES FOR SURVIVAL

Research on pregnant mice and humans suggests that the immune system of the female parent undergoes a complicated change during pregnancy. One arm of the immune system called CMI (cell-mediated immunity) seems to become weaker during pregnancy. The body needs CMI to fight off certain microbes that tend to 'hide' inside cells. Examples of these microbes include CMV and SV, the bacteria that cause TB and related infections and, the parasite that causes the brain infection 'toxo' (toxoplasmosis). To help fight off these microbes the immune system releases chemicals such as IL-2 and interferon-gamma. Interestingly, large doses of these two chemicals can kill the fetus.

The other arm of the immune system is called humoral immunity. Chemicals that strengthen this response include IL-4, -6 and -10. Antibody-producing B cells are an important part of this arm. In experiments on pregnant mice who are not likely to carry the fetus for the full length of pregnancy, injections of IL-3 and GM-CSF (granulocyte macrophage-colony stimulating factor) help correct this problem. Researchers in Alberta and India found that the placentas from women prone to abortion tend to release IL-2, interferon-gamma and TNF (tumour necrosis factor).

* HELPING THE MOTHER

It appears that pregnancy seems to strengthen humoral immunity and weaken CMI. This change seems to help the fetus survive pregnancy. Another issue is the survival of the mother. To strengthen humoral immunity may mean that pregnant women may not be able to maintain a strong defence (CMI) against HIV and other microbes. Thus pregnancy may further weaken the immune systems of HIV-infected women. Researchers need to find out more about the immune systems of women in general and women with HIV/AIDS in particular.

REFERENCES:

1. Wegmann TG, Lin H, Guilbert and Mossman TR. Bidirectional cytokine interactions in the maternal-fetal relationship: is successful pregnancy a TH2 phenomenon? Immunology Today 1993;14(7):353-356.

2. Clarke AG and Kendall MD. The thymus in pregnancy: the interplay of neural, endocrine and immune influences. Immunology Today 1994;15(11):545-551.

3. Moncayo HE, Solder E, Abfalter E and Moncayo R. Cytokines and the maternal-fetal interface. Immunology Today 1994;15(6):295.

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