Fetal development immunity

The use of weedkillers has also been on the increase over the last 20 to 30 years. Although it is difficult to prove specifically which chemicals may be carcinogenic, there are increased levels of herbicidal residues in drinking water and concerns over many of the synthetic substances being used. Every year, governments in various countries withdraw from use chemicals that have previously been used on our food supply when proof of their toxicity is established. The classic example is DDT, which was used as an insecticide from 1939. Over a period of 50 years almost five billion pounds of it have been used across the world. It became prohibited in the US in the 1970s and in the UK in 1984 because of links to deaths, cancer, allergies, infertility, problems in fetal development and major diseases of the immune system. 

Developmental effects discussed in this section are restricted mainly to effects on fetal development, birth weight and weight gain in early life, and teratogenicity. Information regarding effects on the thyroid, immune system, and reproduction in offspring following perinatal exposure to PCBs is presented in Sections 3.2.3, 3.2.4, and 3.2.5, respectively. 

Makori N,Tarantal AF, Lii EX, Ronrke T, Mathas ML, McChesney MB, Hendrickx AG, Miller CJ. Functional and morphological development of lymphoid tissues and immune regulatory and effector fnnction in Rhesus monkeys cytokine-secreting cells, immunoglobulin-secreting cells, and CD5+ B-1 cells appear early in fetal development. Clin Diag Lab Immnnol 2003 10 140-153. 

Dental amalgam, consisting of mercury alloyed with another element, is still approved for use in most countries, but conflicting views have been expressed over the use of mercury as filling material. Some dentists are still recommending the use of dental amalgam with mercury because of its durability, ease of use, and low cost compared to resin composites (for which concerns have been raised due to the presence of plastic chemicals such as Bisphenol A, well known for its endocrine disruptor effects) and dental porcelain. However, it is believed that leaching of mercury into the mouth and consequential health effects related to mercury toxicity (such as risk of impairment in the central nervous system function, kidney function, immune system, and fetal development) are associated with mercury exposure. 

Recently, it has been possible to grow cells of the human immune system in special mice. These mice carry a genetic defect called severe combined immunodeficiency (SCID), which leaves them with crippled immune systems, much like those in AIDS patients. Because SCID mice lack functional cellular immunity, it is possible to implant them with human cells without tissue rejection taking place. Researchers have recently developed techniques to implant human fetal tissues containing stem cells for the blood into SCID mice. It is then possible to reconstitute these mice with functional human immune system cells, including T lymphocytes and B lymphocytes. They have also found that if these SCID mice are infected by HIV, the virus will establish infection in the human tissue and destroy the T helper lymphocytes, just as it does in humans. Thus, it may be possible to study some of the mechanisms by which HIV attacks the immune system in these mice. In addition, they may be very useful for testing potential antiviral drugs. 

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