Sequencing each subject’s risk genes revealed that a small mutation in PTPN2 was present in 78.6 percent of people with RA and 60 percent of people without. Additionally, a mutation specific to PTPN22 was detected in 28.6 percent of RA samples compared with 6.45 percent of healthy controls.
“We believe that individuals born with this genetic mutation and who are later exposed to MAP through consuming contaminated milk or meat from infected cattle are at a higher risk of developing rheumatoid arthritis,” Naser said in a statement.
Another telling finding came about by exposing T-cells (a type of lymphocyte that act like the body’s bouncers to identify and remove threats) within the blood samples to a purified MAP protein. Cells from subjects with multiple mutations responded with a frenzy of activity compared to the T-cells from subjects who had RA but did not carry abnormal PTPN2/22 genes. Moreover, the genetically abnormal subjects' immune cells stayed in overdrive even when the MAP protein was no longer present. In a healthy immune system, cells are supposed to relax from high alert when the perceived threat is neutralized, but those with autoimmune diseases are unable to do so.
“We don’t know the cause of rheumatoid arthritis, so we’re excited that we have found this association,” said co-author and rheumatologist Dr Shazia Bég. “But there is still a long way to go. We need to find out why MAP is more predominant in these patients – whether it’s present because they have RA, or whether it caused RA in these patients. If we find that out, then we can target treatment toward the MAP bacteria.”