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29 April 2005
A Little Stress Benefits Immune System 
A brief bout of stress can give the immune system a beneficial boost but only under certain conditions, say researchers at Ohio State University. Their experiments, reported in Proceedings of the National Academy of Sciences, showed that short periods of stress mobilized all major types of immune cells, or leukocytes, to potential infection sites around the body. The researchers say this stress-induced boost in the number of immune cells may be advantageous for fighting infections and other diseases. "Acute stress could help increase immune protection. An increase in leukocyte activity and availability may enhance the immune system's ability to protect the body during surgery, vaccination or during an infection," said Firdaus Dhabhar, the study's lead author. There is a downside however, ushering an increased number of immune cells to sites of potential immune reaction could worsen pre-existing inflammatory illnesses such as cardiovascular disease, gingivitis and autoimmune disorders such as arthritis, multiple sclerosis or psoriasis. But Dhabhar believes further research could help tame inappropriate immune responses. "Understanding mechanisms that mobilize leukocytes to potential battle stations during stress could help us figure out ways to boost the immune response when it could be most helpful to do so, such as during surgery, vaccination or infection," Dhabhar said. "And it could also help us tone down the immune response during inflammatory diseases." Leukocytes are always present in the body but remain dormant until an immune response is activated by wounding or infection, or until the brain identifies a stressful situation. When that happens, the brain releases hormones that set leukocytes into motion. "Just one session of acute stress caused a significant increase in the numbers of leukocytes," Dhabhar said. In fact, the amount of certain types of immune cells had increased by 200 to 300 percent in the stressed mice. "Most immune challenges or wounds involve on the skin or other epithelial linings of the body. If nothing happens immunologically following stress - the skin isn't cut or wounded in some other way - activated leukocytes usually return to their resting position in a few hours," Dhabar said.
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