The study, conducted by researchers at Yale and Stanford, found that patients whose immune systems responded to the stress of surgery by mobilizing large numbers of pathogen-fighting cells and redistributing them to skin and other tissues recovered more quickly and completely than those patients whose immune system showed little or no reaction. The researchers also found that men were more likely than women to mount the beneficial stress response and recover more fully.
The results suggest that simple blood tests performed while patients are on the operating table could predict how well patients will have recovered months after they leave the hospital. Eventually, doctors might also be able to develop medical interventions to improve that recovery.
The researchers recruited 57 patients who were scheduled for surgery to repair damaged cartilage in their knee joints. Three to 10 days before the surgery, patients gave blood samples to establish a baseline count of immune cells in their blood. Then, on the morning of surgery, the researchers took another blood sample just before administration of anesthesia, looking for an increase in immune cells in the bloodstream. The idea, authors said, was that patients would be somewhat anxious about the impending surgery, triggering the short-term immune response.
About a half-hour after surgery, the patients gave a final sample while in the recovery room. At that point, the researchers reasoned, many blood-borne immune cells should have exited the circulation and entered tissues, including the site of surgery.
Using the data, the team calculated total "redistribution" numbers for three major types of immune cells — lymphocytes, monocytes and neutrophils. These numbers quantified the initial increase and subsequent decline in immune cells in the blood.
The researchers then determined the median redistribution number for the group. Those with redistribution numbers higher than the median were categorized as "high responders." Those whose immune-cell redistribution numbers were smaller than the median or unchanged were grouped as "low responders."
They then followed up with patients for one year, checking knee inflammation and using the Lysholm scale, a well-respected questionnaire, to rank knee function, pain and mobility on a scale of 1 to 100, with scores above 90 representing maximal recovery.
Patients who showed the positive stress response during surgery showed increased recovery as early as one week post-surgery compared to low responders, an effect that carried all the way through the study period. One year later, high immune responders had average Lysholm scores of more than 90. Low responders had scores around 80 and never recovered as fully as their stress-adaptive counterparts.
The study's authors say the next step is to investigate the biological links between the stress-induced immune activation and recovery, and to test the immune measurements in other types of surgery. Researchers can't yet be sure how many people exhibit strong stress-induced immune cell activation and how many don't. But once the mechanisms of response are better understood, doctors could monitor immune cell movements during and after surgery to predict patients' recovery — and design treatments to bring low responders up to speed.
Citation: Patricia H. Rosenberger, Jeannette R. Ickovics, Elissa Epel, Eric Nadler, Peter Jokl, John P. Fulkerson, Jean M. Tillie, and Firdaus S. Dhabhar, 'Surgical Stress-Induced Immune Cell Redistribution Profiles Predict Short-Term and Long-Term Postsurgical Recovery. A Prospective Study', J Bone Joint Surg, 2009