The researchers think the body's own antibodies are to blame in at least a proportion of people with CFS. Relief started four to six months after the first dose of rituximab, approximately the time it would take for existing antibodies to be cleared from the body. Participants relapsed after about a year - roughly how long B-cells take to regrow and start making new antibodies.
"We think the pattern of responses and relapses involves some mechanism with these antibodies," says Fluge.
An infection may trigger the body to produce antibodies that then turn against a person's own tissues, he says. His team suspect that these antibodies may stop blood from circulating properly, preventing people from getting enough oxygen, explaining their extreme fatigue.
The researchers caution that their theory is just speculation for now, but they do have some very preliminary evidence. "We think the antibodies target the blood vessel system, because patients have very low anaerobic pressure, and produce waste lactate earlier, which stops muscles working," says Mella.
If this theory turns out to be true, it would explain why people with CFS suffer muscle fatigue but show no signs of muscular abnormalities.