Arthritis Triggers: Tracking the Arthritis Trigger

Those painful arthritis aches -- all too familiar to many a baby boomer -- may be caused by bacterial infections like salmonella, Johns Hopkins researchers say. Arthritis can result when the immune system cells that fight bacteria attack normal cells carrying a protein resembling bacteria, the researchers say in the journal Nature Medicine.

"We've found evidence that the immune system can be fooled, and it suggests subtle changes that could underlie many autoimmune diseases" including arthritis, said Mark Soloski, the Hopkins researcher who led the study.

As many as 10 percent of those who get salmonella, which causes food poisoning, develop a "reactive" type of arthritis lasting a few weeks. But a "significant number" suffer a severe, debilitating and long-lasting arthritis, Soloski said.

The study, based on experiments with mice, showed cells infected with salmonella displayed "flags" or pieces of protein from the bacteria almost identical to a protein found in all living organisms. These flags prompt the immune system cells to attack the healthy proteins as well.

The "flag" molecules appear in other bacteria as well, including E. coli and the bacteria that cause typhoid and stomach cancer. Now scientists hope to find out why and how this immune response translates into arthritis.

Arthritis, which afflicts some 40 million Americans (up from 35 million in 1985), is no small concern to ThirdAgers. As boomers grow older, the number of Americans with arthritis will surge to nearly 60 million, or 1 in 5 people, by 2020, says the Arthritis Foundation, which helped finance the study.

That, in turn, is expected to increase the number of physician visits (now at 39 million a year), hospitalizations (now over 500,000) and costs to the U.S. economy (now some $65 billion). More than half those affected are under 65, and the foundation says: "Baby boomers are now at prime risk."