The key to the puzzle of Gulf War Syndrome may be the synergistic effect of chemicals. It's been hypothesized that GWS could have been caused by the devastating combination of vaccines and pesticides to which the soldiers were exposed. The vaccines suppressed the part of the immune system, Th1, which combats viruses and cancers, while the Th2 part of the immune system, which ordinarily reacts mildly to pollen or housedust mites, was made hypersensitive to outside irritants. This caused the soldiers to become vulnerable to common diseases and to experience highly allergic reactions to what are normally harmless substances.
This was then exacerbated by the heavy exposure to insecticides, which inhibit the functions of Interleukin 2, which plays a pivotal role in Th1 lymphocytes (Lancet, 1997; 349: 1831-3).Researchers at Duke University, studying three chemicals to which US soldiers were exposed during the Gulf War, found that none by themselves caused nerve damage but together, the chemicals caused severe nerve damage (J Tox and Environmental Health, 1996; 48: 35-56).