"The core sign of AIDS, the reduction of cell-mediated immunity, is one of the typical vegetative signs of depression."
Biomarkers for depression are ridiculous in the first place.
1) We see something we don't understand.
2) We create a criteria to help define patients with this thing.
3) We vote on calling it 'depression'. With a few ammendments to the criteria, it passes. Congrats!
4) We find biomarkers in such patients.
5) These biomarkers are only related to depression as we have defined it, and cannot mean anything but what we have previously decided by committee.
...I think really there's nothing intrinsically wrong with 1-4. Physicians and scientists create categories in order to better understand things, and while this sometimes gets in the way of logical thinking, I understand why we do this as a culture.
At #5 we have a real logical misstep, and I'm not sure that many researchers even realize they have to mind the gap.
Specifically....a reduction in cell-mediated immunity is a sign of a LOT of things. Because it is true of depression as we have chosen to define depression doesn't mean much.
-J