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A strong immune system helps us combat dangerous infections. Unfortunately, it can also trigger autoimmune diseases such as lupus, multiple sclerosis, rheumatoid arthritis, Sjögren's syndrome, and type 1 diabetes.
“There are so many autoimmune diseases affecting all sorts of tissues,” offered Andrea Graham, an evolutionary biologist at Princeton University, at the annual meeting of the International Society for Evolution, Medicine and Public Health in July 2016. What could explain the existence of autoimmune disease? “One potential answer is that vulnerability to immune-mediated disease is simply the price we must pay for potent and rapid defense against infection.”
People Who Have Strong Immune Systems Live Longer, But Not Always Better
Dr. Graham and her colleagues analyzed data from a long-term study of elderly people in Taiwan. This research endeavor has collected blood samples from and secured medical records of more than 1000 people born between 1892 and 1953, and followed their health for 27 years. The study collected data on the participants' physical, emotional, and psychological health, and persuaded them to participate in overnight hospital stays so the researchers could take 12-hour urine samples and fasting blood specimens. Researchers measured everything that would be measured at a doctor's office, and did DNA testing to identify single nucleotide polymorphisms (mutations), telomere length (a measure of how many more times a cell can divide), and the presence, absence, and activation of 164 genes. The oldest participants in the study 27 years ago are, of course, now deceased, but the research team was able to get measurements from 639 of the volunteers in 2000 and 2006.
One of the many laboratory measurements in the study was the level of "self-reactive" antibodies. These are antibodies that are capable of attacking not just a germ, but also the body's own tissue. The researchers found that participants with the highest levels of self-reactive antibodies were 33 percent less likely to live in any given year. However, they were also much more likely to develop chronic autoimmune diseases, especially lupus.
How Can a Super-Healthy Immune System Cause Disease?
One of the puzzles of immunology is that people whose immune systems fight off infections well often live long enough to develop autoimmune diseases. This observation contradicts the widely held view that when it comes to immunity, more is better.
Dr. Graham explains that optimal immunity requires not just the right type of response but also the right amount of response. Excessive immune responses not only can destroy healthy tissues, they can also deplete the body's resources for ordinary maintenance and repair. Sometimes the most effective response to an infection isn't to activate the immune system to kill it, but instead to "starve" it out by depriving the disease organism of the level of nutrients it needs without depriving the body of level of nutrients it needs.
And sometimes the immune system's defense against one infection makes another infection worse. This is what happens in people who have both malaria and intestinal parasites. The parasite-killing cytokines that defeat malaria protect intestinal parasites, and vice versa. When it comes to immunity, more isn't always better.