What Does the Environment Have to Do with Diseases That Affect the Immune System?

The rise in recent decades of diseases such as inflammatory bowel disease and rheumatoid arthritis suggests that factors in the environment are contributing.

In 1932, New York gastroenterologist Burrill Crohn described an unusual disease in 14 adults. The patients had bouts of abdominal pain, bloody diarrhea, and lesions and scars on the bowel wall. Doctors in other parts of North America and Europe were seeing it in their patients, too. They called the rare condition Crohn’s disease. After World War II, the number of new people getting inflammatory bowel disease (Crohn’s disease and a related condition called ulcerative colitis) skyrocketed across the West in countries such as the U.S., Canada and the UK. In the last three decades, IBD has begun to crop up in newly industrialized parts of the world like Hong Kong and China’s big cities.

Lindsey Konkel

Other conditions, such as type 1 diabetes, rheumatoid arthritis and multiple sclerosis, are becoming more common, too. These diseases affect different parts of the body, but they all have one thing in common — they’re marked by a malfunctioning immune system. Doctors call these illnesses immune-mediated diseases. (Autoimmune dis eases are a subset of these, though the terms often are used interchangeably in the popular press.) More than 100 conditions fall into this category.

For the most part, these diseases are chronic and cause long-lasting disability. Most were rare or completely unknown until recently, but now constitute what some experts call an epidemic. In Hong Kong for instance, the incidence of IBD spiked 30-fold between 1985 and 2014. “If you look at the past 100 years, you see a huge explosion of diseases that haven’t been seen at any other time in human history,” says Gil Kaplan, a gastroenterologist at the University of Calgary. No one knows for sure what’s behind the increase in immune-mediated disease. However, Kaplan and others are now discovering that human-wrought environmental changes may play a major role...