We've had a lot to say recently about the brain-derived neurotrophic factor -- BDNF. According to Merriam-Webster, a "factor" is a substance that "functions in or promotes the function of a particular physiological process or bodily system." Are there other factors that might function in a bodily system in a negative way? How about one that cancels the good things that BDNF is doing for us?
Enter eosinophil chemotactic protein, or CCL11. [Ominous music]
About a year ago we discussed an emerging picture of covid infections disturbing memory function. We said that, in the brain, a covid infection can prompt a strong inflammatory response characterized by a "cytokine storm." We said that cytokines are proteins that coordinate the body's immune response and promote inflammation. Inflammation is a two-edged sword -- it helps with fighting infection (among other things) but also does its own damage. Inflammation in the brain may be a part of the body's response to infection, but it's also part of the Alzheimer's disease process. CCL11 is a particular cytokine that emerges when someone undergoes chemotherapy for cancer (think "chemo brain") and also during a covid infection.
According to research recently published in the journal Cell, the CCL11 cytokine is doing the opposite of what the BDNF does -- suppressing the generation of new neurons from stem cells in the hippocampus. Logically, it's responsible for both chemo-brain and the brain fog that has been reported in covid cases. (This suggests to me that it could aggravate Alzheimer's disease.) So we see similar brain fog in chemotherapy patients and people infected with covid.
Here's an easier reading article from Wired magazine. Note that the research is, again, based on work with mice. Mice are not people, and results with mice can be misleading. Nevertheless the research appears to explain covid brain fog.
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