This 2014 research studied both humans and rodents to provide further evidence on the physiology of defeat. The researchers demonstrated that with mice:

“Bone marrow transplants of stem cells that produce leucocytes lacking IL-6 (the cytokine interleukin 6) or when injected with antibodies that block IL-6 prior to stress exposure, the development of social avoidance was reduced.”

The researchers also showed in humans that standard antidepressants didn’t act to lower IL-6.

So, what were we to make of this finding?

“Preexisting differences in the sensitivity of a key part of each individual’s immune system to stress confer a greater risk of developing stress-related depression or anxiety.”

• Was it sufficient for the researchers and the news articles covering the research to treat “preexisting differences” as a black box that nobody could enter to find causes for the effects of “developing stress-related depression or anxiety?”
• Did things happen in each individual’s history to cause the “preexisting differences” or was each individual born that way?
• Why was the research directed at symptoms with no mention of any underlying causal factors?

It wasn’t sufficient for the researchers to carry on their experiments with assumptions that there weren’t early-life causes for the above symptoms. Such a pretense leads to the follow-on pretense that later-life consequences weren’t effects of causes, but were instead, mysteries due to “preexisting individual differences.”

http://www.pnas.org/content/111/45/16136.full “Individual differences in the peripheral immune system promote resilience versus susceptibility to social stress”