PureInsight | April 27, 2008
[Aside from deflecting rising food prices, being sure your food is
grown properly, and the sheer joy of watching living things grow, there
may be another reason depression is unusual among gardeners. Sometimes
getting a little dirty might be good for you. â€“ PureInsight Science
Research on infectious diseases, lung cancer, unstressed mice, the immune system, and Mycobacterium vaccae (M. vaccae) has led to the connection of the immune system with depression.
M. vaccae is a harmless bacterium found in the soil that may take the place of Prozac.
Oncologist Dr. Mary O'Brien tried out an experimental vaccine made from killed M. vaccae
on lung cancer patients at the Royal Marsden Hospital in London. They
improved in every way, from fewer cancer symptoms to better emotional
and cognitive function.
Intrigued by Dr. O'Brien's results, Dr. Christopher Lowry of Bristol University put forth the hypothesis that perhaps M. vaccae
would alleviate depression by causing the production of serotonin, the
antidepressant messenger of nerve cells in the brain. Since the
blood-brain barrier protects us from bacteria, how can this be?
The immune system has two kinds of activated Th cells: Th1 (T helper 1)
and Th2 (T helper 2). Th1 cells attack pathogens within the cell, while
Th2 cells attack pathogens outside the cells. Sometimes Th2 lymphocytes
get out of hand, causing an exaggerated immune response or allergic
reactions to harmless substances. They also interfere with the
infection-fighting abilities of Th1.
Enter M. vaccae, which has a
two-pronged effect. First, it stimulates T cells that immediately get
to work restoring the balance between Th1 and Th2, diminishing
allergic, tubercular, and cancer symptoms. Second, and this is where
Dr. Christopher Lowry and his colleagues of Bristol University enter,
it stimulates the dendritic cells of organs such as the lungs and heart
to secrete cytokines. Dr. Lowry traced the action of the cytokines to
the organs' sensory nerves, which sent messages to the raphe nucleus in
the brain, which releases serotonin into the limbic or emotion center.
Dr. Lowry injected mice with M. vaccae.
To find their stress levels, he put them in water. Stressed mice will
not swim. The injected ones swam happily. Later their brains were
examined to trace the path of serotonin.
There was a saying: "You have to eat a peck of dirt before you die."
Did it mean that you had to eat dirt in order to have a healthy and
happy life? Some people would say so.
This isn't the first study that implicates our super-hygienic lives,
especially as toddlers, with difficulties later on. "These studies help
us understand how the body communicates with the brain and why a
healthy immune system is important for maintaining mental health. They
also leave us wondering if we shouldn't all be spending more time
playing in the dirt," according to Dr. Lowry.