A relationship between depression and resistance to infection?
A very interesting study which came to my attention from The Atlantic, describing work done by researchers at Emory University and the University of Arizona and published in the journal Molecular Psychiatry. Suicide has been recognized as one of the leading causes of death in the United States, killing more people than auto accidents, and students at YCP this term may have noticed posters pointing out that suicide is the second highest cause (among ALL causes) of death in York County. Although people may have a variety of reasons for choosing to take their life, there is a significant association between suicide and diagnosed depression or other mood-altering disorder. Scientists have identified a number of genes associated with chronic depression, and are currently investigating how those genes contribute to depression. This leads to the question that if depression leads to suicide and death of the individual, how would depression as a phenotype be maintained in a population? This current report makes an attempt to answer this.
The neuropeptide-Y (NPY) gene is one gene that has been implicated in modulating depression, and mutated versions of this neurotransmitter are correlated with the development of depression-associated behaviors. Interestingly, the same mutated versions of NPY are also correlated with the initiation of the inflammatory response, which is a critical process in our body’s innate response to an infectious agent. Therefore, the same mutant form of the protein can have a positive effect on the promotion of our immune response to an outside threat, and at the same time promote altered behavior. The authors then make the argument that, in contrast to the current perception that depression-associated behaviors are detrimental, in the case of combating an infectious agent, these same behaviors might actually be beneficial. Consider: when an individual comes down with an infectious disease, introverted and withdrawn behavior would actually prevent the spread of that agent throughout the population, and additionally might allow the infected individual to ensure that all of their energy is devoted to fighting off their infection.
The current outbreak of Major-Depressive Disorders (MDD) may then to some extent be an evolutionary relic of our innate defenses against infectious disease. Prior to the advent of antibiotics, death due to infectious disease was the most significant cause of death in human populations. The authors of the article in Molecular Psychiatry, cite a research study where they examined the anti-depressive effects of a new drug called infliximab, which works by disrupting cellular communication in the inflammatory pathway. While infliximab did not have significant effects on improving depression symptoms in the group as a whole, it did have positive effects in a subset of the test subjects who had elevated inflammation levels to begin with. This result does appear promising and illuminates the link between depression and inflammation, but does strongly indicate that the mechanisms behind depression-associated disorders are complex.
Posted on October 16, 2012, in Strange but True and tagged Inflammation, Major depressive disorder, Neuropeptide Y. Bookmark the permalink. Comments Off on A relationship between depression and resistance to infection?.