The mice that had been stressed prior to receiving the influenza infection had a stronger immune reaction to it, with markedly higher numbers of two types of T cells specific for influenza. When exposed to the influenza virus a second time, these cells would allow the body to fight off the virus faster and more successfully.

The Ohio State University scientists who conducted the study, graduate student Jacqueline Wiesehan and Dr. John Sheridan of the College of Dentistry, believe their finding has broad implications for more effective vaccination strategies.

Chronic Stress Weakens Immune System

A growing body of literature demonstrates that immune system responsiveness to influenza infection and vaccination is heavily influenced by the nervous system. In fact, previous research at the Ohio State University showed that persons caring for a spouse with Alzheimer's disease did not gain the same level of protection from an influenza vaccination as did their counterparts without the same chronic stress.

The mice in Wiesehan's and Dr. Sheridan's study experienced a very different type of stress, however: short-term, episodic, and severe.

Short-Term Stress Caused Stronger Immune Reaction

The mice lived in a colony with a well established hierarchy of mice, so having a higher-ranked, more aggressive mouse placed in their cage for two hours was definitely disruptive and upsetting. This stressful episode was repeated on six consecutive days, after which both stressed and non-stressed mice were given a low-dose influenza infection.

All mice quickly recovered from the mild infection and within four weeks had developed stable immunological memory to the virus, parallel to what happens after a flu shot.

But delayed hypersensitivity tests and fluorescently labeled antibody screening revealed that the mice that had been stressed prior to receiving the influenza infection had a stronger immune reaction to it, with markedly higher numbers of two types of T cells specific for influenza. When exposed to the influenza virus a second time, these memory helper T cells (CD4) and cytotoxic T cells (CD8) would allow the body to fight off the virus faster and more successfully.

Strategies for Vaccination

Understanding stress as an additional factor that can positively impact immunity to influenza has broad implications for vaccine development, says Dr. Sheridan.

If the mechanisms through which this stressor enhances the immune response can be characterized, it would aid in the development of more effective strategies for vaccination against influenza and possibly other diseases.

Ms. Wiesehan is a graduate student working on a joint DDS/PhD degree in the in the Ohio State University College of Dentistry. In addition to his appointment in the College of Dentistry's Section of Oral Biology, Dr. Sheridan is also a member of the Department of Molecular Virology, Immunology and Medical Genetics in the College of Medicine and of the Institute for Behavioral Medicine.