The Truth About Your Immune System: What you need to know

You can't feel it or see it. You can't take its pulse or its temperature. But out of sight and out of mind, your immune system is quietly and constantly patrolling your body to detect and destroy infectious microbes. It is your most powerful protector, working tirelessly around the clock to keep you safe.

Despite its low-key profile, the immune system is the subject of great attention both in the laboratories of prominent scientists and on the shelves of retail stores carrying countless products that purport to boost or support immunity. While researchers are still trying to understand how the immune system works, product manufacturers have rushed to market everything from herbal teas to vitamin supplements that they claim will improve your immune response, with little evidence to support those claims.

To be sure, your immune system is a precious asset. It protects you from the ceaseless assaults of bacteria, viruses, fungi, and parasites. The danger is very real. In 2004, 61,472 people in the United States died of influenza or pneumonia, making those diseases together the eighth leading cause of death. And each year, around 215,000 people in the United States die from a severe bacterial infection known as sepsis, which is more than the number who die from breast, colorectal, pancreatic, and prostate cancers combined. Worldwide, measles killed about 450,000 people in 2004, most of them children. Tuberculosis, once considered under control, was responsible for 1.7 million deaths the same year. At the same time, infectious diseases are emerging around the globe in such forms as bird flu and severe acute respiratory syndrome (SARS). Although the confirmed number of deaths from bird flu is small, experts fear a bird flu pandemic could take a vast toll on human life.

In response to such threats and many that have come before, the human body has developed a coordinated immune response that is both a marvel of elegant simplicity and an amazingly complex set of biochemical interactions. And the harnessing of this process with vaccinations is arguably the greatest public health accomplishment since the beginning of the 20th century.

Usually, your immune system is quite effective in warding off disease. But sometimes things go wrong. A bacterium, virus, or other pathogen might make it past your immune defenses and make you sick. In addition, more than 1 in every 500 U.S. citizens is born with an immune system defect. Even allergies are an example of an immune response gone awry.

This report takes you on a tour through your immune system and includes practical steps you can take to assist your immune system in its mission.