Our immune system is the only thing standing between us and a sea of microbial predators that could send us to an early and ugly death. Equipped with genetic, chemical and cellular weapons, it evicts unwelcome microrganisms that find the human body a delightful place to live, carefully admitting only the few microbes that our bodies need to help us digest food and process vitamins. When the system works successfully, the vast majority of disease-causing microbes - bacteria, viruses, molds and a few parasites - are kept at bay. But the immune system isn't perfect. The same system that could save us in the event of a bioterrorist attack, prevents us from accepting potentially life-saving organ transplants. It overreacts at times, turning too much force against foreign invaders, causing serious - occasionally lethal - collateral damage to our tissues and organs. Worse yet, our immune systems may decide we ourselves are foreign and begin snipping away at otherwise healthy tissues, resulting in autoimmune disease. And the system itself is the target of one of the most deadly viruses humans have ever known: HIV, the agent of AIDS.In In Defense of Self, William Clark invites you on a whirlwind tour of your immune system. Along the way, he introduces some of most important medical advances and challenges of the past hundred years, from the development of vaccines and the treatment of allergies, autoimmunity and cancer, to prolonging organ transplants and combating AIDS. William Clark not only explains how a vital part of our bodies works to ''serve and protect,'' he also provides background for the exciting research themes of today that will produce the medical breakthroughs of tomorrow.